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TAMILNADU AGRICULTURAL UNIVERSITY
SAC CO1 - IMPACT ASSESSMENT OF AROCHEMICALS
IN ECOSYSTEMS (2+1)
Course teacher
Dr.D.VASANTHI,
Associate Professor(SS&AC)
Department Of Soil Science & Agricultural Chemistry,
TNAU, Coimbatore.
2006
1
SAC.C01
IMPACT
ASSESSMENT
OF
AGROCHEMICALS
IN
ECOSYSTEMS (2+1) Cafteria course
Course Teacher : Dr.D. Vasanthi, Associate Professor(SS&AC)
THEORY
Agrochemicals Introduction Usage in India Production techniques and
chemistry of insecticides, fungicides, herbicides and other agrochemicals
registered in India - New classes of agrochemicals - Chemistry of formulationsMultinationalcompanies - Registration requirements of different agrochemicals
Methodology for conducting bio efficacy studies Toxicology studies
Assessment of residues in soil, water and plant Impact assessment of agro
chemicals in different ecosystems Acceptable daily intake (ADI) and Maximum
(permissible) residue limit (MRL) - Occupational exposure of agrochemicals Safety precautions in sampling and storage - Contamination and disposal of
agrochemicals - Plant extracts for ecofriendly pest control - Allelopathy and
weed control - Quality control of agrochemicals - Techniques in residue
analysis - GLP practices.
PRACTICAL
Analysis of pesticides - Physical tests - Acidity/alkalinity - Estimation of
active ingredients in agrochemicals - Extraction and clean up procedures for
determining residues from soil, water and plant samples- Determination of
residues through bioassay and instrumentation techniques - Visit to pesticide
formulation unit and pesticide testing laboratory.
LECTURE SCHEDULE
1. Agrochemicals, definition, synonyms and historical background.
2
2. Chemistry and production techniques of OP compounds.
3. Chemistry and production techniques of carbamates.
4. Chemistry and production techniques of synthetic pyrethroids.
5. Chemistry and production techniques of novel insecticides and
household pesticides.
6.
Chemistry and production techniques of preventive and eradicant
fungicides (available in market only).
7. Chemistry and production techniques of systemic fungicides (only new
classes).
8.
Chemistry and production techniques of systemic fungicides (only new
classes) continued.
9.
Chemistry and production techniques of herbicides (only registered)
10.
Agrochemical combinations and their significance.
11.
Compatibility of different agrochemicals.
12
Chemistry of agrochemical formulations.
13.
Materials required and preparation techniques for agrochemicals.
14.
Functioning of multinational companies.
15.
Registration requirements of different agrochemical formulations.
16.
Methodology for evaluation of bio efficacy of agrochemicals.
17.
Mid Semester Examination .
18.
Toxicological properties of agrochemicals.
19.
Assessment of residues in soil, water and plant.
20.
ADI and MRL of agrochemicals.
21.
Fate of agrochemicals in soil and water.
22.
Fate and metabolism of agrochemicals in plant.
23.
Impact assessment of agrochemicals in environment.
24.
Evaluation procedures for occupational exposure of agrochemicals.
25.
Safety precautions in handling and storage of agrochemicals.
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26.
Contamination and disposal of agrochemicals.
27.
Chemistry of plant extracts.
28.
Allelopathy and weed control.
29.
Insecticides act and it s implications.
30.
Good Laboratory Practices (GLP).
31.
Quality control of agrochemicals.
32.
Bio assay techniques for residue determination.
33.
Instrumentation techniques for residue determination.
34.
Recent advances in residue determination.
REFERENCES
Bochech, K.H. 1983. Chemistry of Pesticides. John Wiley and Sons, New York.
Cremlin, R.J 1992. Agrochemicals Preparation and mode of action, Wily
publications, New Delhi.
Edwards, C.A., G.I. Veeresh and K. Kruger. 1980. Pesticide Residues in the
environment in India. University of Agrl. Sciences, Bangalore, India.
Graniti et al., 1989. Phytotoxins and plant pathogens. Springer Verlog, Berling.
Jayakumar, R and R. Jagannathan 2003.Weed Science Principles, Kalyani
Publishers, Ludhiana.
Muirhead - Thompson, R.C. 1973. Pesticides and Fresh water Fauna. Academic
Press. London.
O' Brien and Yanamoto 1983. Biochemical toxicology of insecticides.
Academic Press Inc. New York.
Handa, S.K. 1999. Principles of pesticide chemistry. Agrobios, Jodhpur.
Roy,
N.K.2002.
Chemistry
of
distributors,NEWDELHI.
4
pesticides.
CBS
Publishers
&
AGROCHEMICALS
DEFINITION
SYNONYMS
AND
HISTORICAL BACKGROUND.
INTRODUCTION
Pesticides are chemicals designed to combat the attacks of various pests
on agricultural and horticultural crops.
The term agrochemicals are broader and include chemicals, which
enhance growth and yield of crop, but exclude large-scale inorganic
fertilizers.
They fall into three major classes: insecticides, fungicides and
herbicides.There are also rodenticides (for the control of vertebrate
pests), nematicides (to kill microscopic eel worms), molluscicides (to
kill slugs and snails) and acaricides (to kill mites). If the chemicals are
applied to inhibit feeding, or to prevent the pest species from attacking
its hosts or induces sterility are referred as antifeedant, repellent and
chemosterilant respectively.
SYNONYMS
Algicide, Anocide, Antibiotics, Antiseptics, Aphicides
Carcinogen, Disinfectant, Limacide, Ovicide, Pheromone, Slimicides.
HISTORY
Prophet Amos
(760
Mentioned blast which is the same
BC)
cereal
rust
that
is
responsible
for
enormous losses.
Theophrastus(Father of (300
Described many plant diseases such as
Botany)
Scorch, rot, scab and rust.
BC)
Old Testament
Before
Several references on locust
100BC
Sulphur was known to avert
5
diseases
and insects
Homer Pliny
(79 AD) Arsenic as insecticide
17th century
Nicotine from extracts of tobacco leaves
was used to control lace bug
Hamberg
(1705)
Mercuric chloride as wood preservative
Prevost
(1805)
Inhibition of smut spores by copper
Sulphate
Michael Faraday
1825
First
prepared
BHC
insecticidalproperties
although
were
its
not
recognized until 1942
1850
Rotenone from the roots of derris plant
and pyrethrum from the flower heads of
chrysanthemum
1867
Paris green for Colorado beetle
1882
Bordeaux mixture against vine mildew
1892
Lead arsenate for gipsy moth.
Bonnet(France)
Schultz
(Germany) 1896
Copper sulphate for weed control
Bulley (USA)
1897
Formaldehyde as fumigant
1900
Paris green (Copper arsenite) was
extensively used as an insecticide in
USA
1900
Irish potato famine – potato late blight–
death of million people (12per cent
Population)– starvation and immigration
6
1.5 million
W.C. Pirer (USA)
1912
Developed
calcium
replacement
of
arsenate
Paris
as
green
a
for
controlling boll weevil in cotton
1913
Organo mercurials were first used as
seed dressing against cereal smut and
bunt Diseases
Woods and Barlet
1919
Sulphuric acid for weed control
1930
Beginning of modern era of synthetic
organic pesticides (alkyl thio cyanate
insecticides)
1931
Salicylanilides
(Shirlan)
(The
first
organic fungicide)
1933
Dinoseb herbicide
1934
Dithiocarbamate
fungicides
for
the
control of scabs and roots of fruit and
potato blight.
Dr. Paul Muller
1939
Discovered insecticidal properties of
DDT
1945
MCPA (UK), 2,4-D (USA) Several
Chlorinated hydrocarbons, cylclodiene
compounds were introduced
Dr. Gerhard Schrader
Dr. Elliot &
Team
Developed OP compound parathion
1950
Malathion
1961
Menazon – selective aphicide
1973
Synthetic pyrethroids
1988
Bipyridillium compounds and triazin
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PESTICIDE USAGE-WORLD SCENARIO
There are about 1250 pesticides registered throughout the
world out of which about 25 per cent have been phased out or banned
due to their hazards to environment (Tomar and Parmar, 1993). The rate
of increase in the usage of pesticides in developing countries is
considerably higher than that of the developed countries.
The introduction of newer molecules into the market has been
reduced in recent years because of the stringent regulations and high cost
of production. The cost of production of individual compound has
increased substantially and at present it is US$ 85 million compared to $
20 million during 1984. It takes almost 8-9 years to develop a pesticide
(Marrone, 1999). However, the production of a biopesticide seems to be
relatively cheaper as compared to chemical pesticide and time required for
the development is also less.
Seventy per cent of world market is controlled by 10 multinational
corporations (MNCs) and 20 MNEs control 93 per cent (Dudani, 1999).
The estimated sale of various top 19 agrochemical companies is given in
Table 1. Novartis records maximum sales of US $ 4425 million followed
by other companies (Iyengar, 1999).
Table 1. Estimated sales of 19 Agrochemical companies
Top Seven Companies
2001 Sales
(in billions of US$)
Change
since 2000
Syngenta (Swiss)
$5.385
-8.5%
Aventis CropScience (Fr.)
$3.842
+5.0%
Monsanto (U.S.)
$3.755
-3.3%
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BASF (Ger.)
$3.105
+39.4%
Dow AgroSciences (U.S.)
$2.612
+11.3%
Bayer (Ger.)
$2.418
+7.4%
DuPont (U.S.)
$1.917
-4.6%
Sources: Agrow: World Crop Protection News, March 1, 2002, March 15, 2002 and
March 29, 2002.
The global pesticide market is in the increasing trend. The current
market of generic pesticides (A generic pesticide is a pesticide produced
by any company in addition to the original patent holder, whose patent has
expired completely or has expired in most - countries) in US$ 17.50
billion which is likely to increase to US$ 27 billion by 2005 (Dave, 1999)
with a growth of 54 per cent. However, the total agrochemical market was
estimated to be US$ 33.5 billion. The organophosphates accounts for US$
3100 millions followed by pyrethroids ($ 2100 million) and carbamates ($
1800 million).
Pesticide usage in India
India is the third largest consumer of pesticides in the world and the
highest among the South Asian Countries. During the last four decades,
the consumption of pesticides in India has increased several folds from
154 MT in 1953-54 to 80000 MT in 1994-95. However there after the
consumption of pesticides steadily declined to the present level of 54135
MT (based on 1999-2000 demand) The decline was primarily because of
ban or restriction on the use of organo chlorine pesticides such as HCH,
DDT, and aldrin etc., which have high application rates and the
introduction of IPM programme. India is also the largest producer of
pesticides in South Asia with the production of 88751 MT in 1998-99. It is
the second largest manufacturer of basic pesticide chemicals in Asia
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next to China, and number twelve globally. The total installed capacity is
about 124000 MT for the manufacture of 62 technical grade pesticides,
which meet 93 per cent of the total need of the country. The imports were
in the order of 5569 MT in 1997-98. The total current investment is about
Rs. 1500 crore with a turn over of Rs. 4000 crore.
In India pesticide consumption is 570 grams per hectare as against
17 kg in Taiwan and 12 kg in Japan, which reveals the limited use of
pesticides in our country. Predominant classes of pesticides used in
India are insecticides, which accounted for about 57 per cent of total
pesticide consumption followed by fungicides (29%) and herbicides,
which constituted about 14 per cent.
There are great regional variations in the consumption of
pesticides in India. The highest pesticide consumption is in Andhra
Pradesh followed by Uttar Pradesh, Tamil Nadu and Punjab. The
pesticide consumption per hectare of gross sown area is the highest in
Tamil Nadu (1.125 kg ha-1) followed by Andhra Pradesh (1.055 kg ha -1)
and Haryana (0.9 kg ha-1), but still much lower as compared to other
developed countries (Sharma and Sharma, 1999).
There is considerable growth in the production and consumption)
of pesticides over the years which has helped in increasing the
productivity. The production has increased from 60,247 MT in 198384 to 96.688 MT in 1995-96. The production of herbicides registered
highest-compound rate (15.97%), followed by fungicides (5.55%) and
lowest in case of insecticides (3.77%) during the period 1981-95.
The pesticide use in India has increased from 2353 MT in 1950-51 to
90,586 MT in 1995-96.The use of pesticides has increased after the
introduction of high yielding varieties during 1966-67.
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Consumption of different groups of pesticides in India.
Group of pesticide
Per cent
Increase/Decreas
e 1988-97
A.
Insecticide
57.00
i.
Organophosphate
50.00
ii.
Synthetic
19.00
-3.88
pyrethroid
iii.
Organochlorines
18.00
iv.
Carbamates
4.00
v.
Biopesticides
1.00
B.
Fungicides
28.70
+2.31
C.
Herbicides
14.00
+13.70
(Source: Sharma and Sharma,1999)
Consumption of pesticides by various crops.
Consumption (%)
Crop
India
World
1.
Cotton
40.00
24.00
2.
Rice
19.20
17.00
3.
Fruits and vegetables
11.00
27.00
4.
Maize
-
7.00
5.
Wheat
5.00
-
6.
Tea
6.00
-
19.00
25.00
and
other
plantations
7.
Others
(Source: Desai and Namboodri, 1996 and Dhaliwal and Arora, 1998).
11
Among the different crops, cotton, consumes 44.5 per cent of the pesticide
worth of Rs.2462.13 millions even though it occupies only 5 per cent of
the cropped area Cotton is followed by rice (22.00% of pesticides) and
other crops.
There are also changes in the usage of different groups of
pesticides. The usage of insecticide was highest during 1988 contributing
to 76 per cent. In 1997 it has declined to 52 per cent. However, there is
increasing trend in the usage of fungicides and herbicides. If we consider
the usage in world as a whole, herbicide constitutes 47 per cent followed
by insecticides (29%) and fungicides (19%).
CHEMISTRY AND PRODUCTION TECHNIQUES OF OP COMPOUNDS
Organo phosphorus insecticides
Organo phosphorus insecticides form an important class of pesticides and about 100
insecticides are registered for use on various crops in the world.
Advantages
Used as insecticides, acaricides, fungicides and herbicides
Broad spectrum activity against number of insect pests
Break down into nontoxic metabolites –no pollution
Most of them have systemic properties
Due to high pesticideal toxicity these are very econimic and used in smaller dosages.
Low chronic toxicity
Disadvantages
Some of the compounds have bad odours
High acute toxicity
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Require special training for application.
OP compouynds can be classified as derivatives of
Phosphoric acid, Thio phosphoric acid, Di thiophosphoric acid,Phosphonic acid, Ester
amides of phosphoric and phosphorothioic acid,Cylic phosphates and
phosphorothiolates,Pyrophosphoric acid and Cylic phosphates.
Reactions involved in the preparation of op compounds
Michaelis-Arbuzov reaction
This reaction is used for the preparation of phosphonate esters. Phosphonates are
formed by the reaction of alkyl phosphates and alkyl halides.The intermediate is a
quasiphosphonium salt which stabilizes by loss of alkyl halide and formation of
phosphonate.
Perkow Reaction
In this trialkyl phosphities are treated with alpha halocarbonyl compounds ,vinyl
phosphates are formed.
A) PHORATE (THIMET)
(0, 0-diethyl-S-2-ethylthiomethyl phosphoro dithioate)
Derivative of Dithiophosphoric acid.
Phorate is produced by reacting dimethyl dithiophosphoric acid with formaldehyde
and ethyl mercaptan at room temperature.
The second method is by condensation of chloromethyl sulphide with sodium
dithiophosphoric acid.
Phorate is a clear liquid. B.P. 100°C, highly soluble in most organic solvents.
It is unstable to hydrolysis. In acid medium it is more stable. It is easily oxidized to
the corresponding sulphoxide which is resistant to hydrolysis and hence persists on
plants for long time providing insecticidal action.
13
Phorate has both systemic and contact insecticidal action and is a very toxic
compound.
Phorate is absorbed and translocated in plants.
It is oxidatively
metabolized. Phorate is employed for control of aphids, carrot fly, fruit fly and wire
worm in potatoes.
b) Phosalone (Zolone)
(0,
0-diethy-S-(6-chloro-2,
3-dihydro-2
oxobenzoxazol-3-yl)
methyl
phosphorodithioate).
Derivative of Dithiophosphoric acid
Phosalone is a systemic insecticide and acaricide used in citrus and orchard
fruits. It is also used to control aphids in cereals, oilseed, rape and brassicas. It is also
used for testing seeds to protect the seedling from insect damage. LD50: 135 mg/kg.
Phosalone
is
produced
by
condensation
of
sodium
or
ammonium
diethyldithiophosphoate with 6-chloro-3 chloromethyl benzoxazolone.
It is practically insoluble in water. It is a white crystalline substance, m.p. 4517°C. It is relatively stable in acid medium but in alkaline medium it is rapidly
hydrolyzed to the 6-chloro-benzenehexazolone diethyl thiophosphoric acid and
formaldehyde.
c) Dimethoate (Rogor, phosphamide, cygon)
(0, 0-dimethyl-S-methyl carbamoylmethyl phosphoro dithioate).
Derivative of Dithiophosphoric acid
Dimethoate is a systemic and contact insecticides and acaricide, produced by
reacting salts of dimethyldithiophosphoric acid with N-methylchloroacetamide in
aqueous medium in the presence of some organic solvents.
It is also produced by reacting dithiophosphate with aqueous methylamine at
low temperature.
Pure dimethoate is a white crysatalline substance with camphor like odour. The
technical material is a yellowish brown (amber) coloured oily liquid with sulphurous
14
acid smell. It is highly soluble in water and most organic solvents. Dimethoate is
thermally unstable and on heating it decomposes.
d) Quinalphos (Ekalux) or (Bayrusil)
Derivative of Thiophosphoric acid.
Quinalphos (0, 0diethyl-0- (2-quinoxalinyl) phosphorothioate) is obtained by
condensation of 0-phenylenediamine with the hemi-acetal of glyoxylate.
The compound is highly active against biting and sucking insects and has an
LD50: 70 mg/kg rat (oral).
Quinalphos developed by Bayer AG (1969) is prepared by reaction of 0phenylenediamine, chloroacetic acid and 0, 0-diethyl phosphorochloride thioate.
Quinalphos is a broad-spectrum contact and systemic insecticides, applied as
spray to control pests in cereals, brassicas and other vegetables. The mammalian
toxicity is quite high (LD50: 70 mg/kg) but the compound is degraded in plants within
a few days of application.
a) Monocrotophos (Azodrin)
Derivative of phosphoric acid
Monocrotophos (Dimethyl-1 methyl-2-methyl carbamoyl-venyl phosphate)
H3CO
O
P
H3CO
O
C
CH-CO-NH-CH3
(Monocrotophos)
CH3
LD50: 21 mg/g
b) Phosphamidon (Dimecron)
(2-chloro-2diethyl carbamyl-1-methylvinyl dimethyl phosphate)
15
1. Derivative of Phosphoric Acid
Phosphamidon is produced by reacting equimolecular quantities of trimethyl
phosphite with boiling solution of diethylamide of dichloroacetic acid in
chlorobenzene.
O CH3
|
|
(CH3O)3P+CH3CO C Cl2 CON(C2H5)2(CH3O)2-P-O-C=CCl-CON-(C2H2)2+CH3Cl
Phosphamidon is very similar to mevinphos in toxicity has a broad spectrum of
activity against biting and sucking pests and spider mites.
H3CO
O
P
H3CO
O
C
CH3
C-CO-N(C2H5)2
Cl
LD50: 10 mg
Pure phosphamidon is colourless. Commercial product is bright violet due to
the presence of a dye. B.P. 70°C, with a faint pleasant odour.
Highly soluble in water, alcohol, acetone, slightly soluble in saturated
bydrocarbons like hexane and insoluble in kerosene. Does not clogg the nozzles and
hence suited to ultra low volume and low volume sprays.
 Phosphamidon is stable in neutral and weak acidic aqueous solutions.
 It is rapidly hydrolysed in alkaline medium.
 Stable for 2 years when stored in closed containers.
 It is compatible with most pesticides except alkaline ones.
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 When mixed with captan it is synergistic. Toxicity is reduced when mixed
with copper oxychloride.
 When insects feed on this, the choline esterase is inhibited and the insect
gets killed.
 Used as a systemic to control sucking pests in cotton.
c) Malathion
(0, 0-dimethyl S-(1, 2, dicarbethoxy) ethyl phosphorus dithioate)
Derivatives of Dithiophosphoric acid
Dithiophosphoric acid + Maleic acid  Malathion
Malathion is obtained by addition of dimethyl dithiophosphoric acid to maleic
acid ester in the presence of basic catalyts.
Malathion was introduced in 1950 by the American Cyanamid company. It is
an important and widely used contact insecticide and acaricide for the control of
aphids, red spidermites, leafhoppers and thrips on a wide range of vegetable and other
crops. It was important in the history of development of OP insecticides since it was
the first member with a broad spectrum of contact insecticidal activity combined with
the remarkably low mammalian toxicity (LD50: 1300 mg/kg rats). Malathion is also
valuable to control insect vectors eg. Mosquitoes and can be used as a substitute for
organochlorine insecticides.
Pure malathion is a colourless liquid boiling at 120°C. It is sparingly soluble in
water but highly soluble in most of the organic solvents except in saturated
bydrocarbons.
Malathion on prolonged heating at 150°C is isomerised and goes over to thiolo
isomers.
d) Chlorpyriphos (Dursban)
(0, 0-diethyl 0-(3, 5, 6 trichlorophyridine-2 yl phosphorothioate)
17
Derivative of Thiophosphoric acid
Chlorpyrifos is used for mosquito control but may also be employed against
ectoparasites on domestic animals.
LD50: 135-163 mg/kg rat oral.
Metallic ions in soils often interact with organophosphorus insecticides; the
cupric ion is a very effective calalyst for the degradation of some organophosphorus
esters, such as diazinon and chlorpyrifos.
Chlorpyrifos has low acute mammalian toxicity in the 2000-5000 mg/kg range.
 Many organophosphorus insecticides contain heterocyclic moieties with
nitrogen heterocycles.
 The only important pyridine derivatives are chlorpyrifos and chlorpyrifos
methyl.
 Chlorpyrifos is a very valuable contact insecticide some 3500 tonnes were used
in USA in 1982.
 It has a wide spectrum of activity, by contact, ingestion and vapour action. It is
moderately persistant and retains its activity in soil for 2-4 months and is
valuable against mosquito and fly larvae, cabbage root fly, aphids and codling
and winter moths on fruit trees.
 Chlorpyrifos has become one of the most widely applied insecticides in homes
and restaurants against cockroaches, and other domestic pests.
 It is a comparatively safe insecticide. Chlorpyrifos methyl (R=CH 3) is quite
volatile and is used to control insects in grain stores.
Mode of action of organophosphates and carbamates.
 Acetyl choline esterase is an essential components of nervous systems of both
insects and mammals and plays an important role in the transmission of nerve
impulses.
 Acetyl choline esterase catylses the hydrolysis of acetyl choline to choline and
acetic acid.
18
 The OP and carbamate owe their insecticidal properties because they
phosphorylate or carbomylate the enzyme acetyl cholinesterase.
 In the abscence of acetylcholine esterase ,there is an accumulation of
acetylcholine which violates the function of the nervous system.
 This results in giving rise to typical cholinergic symptoms associated in insects
with poisoning hyperactivity, tremors, convulsions, paralysis and death.
 The active centers of the enzyme acetylcholine esterase contain two main active
sites , an anionic site which is negatively charged and binds into the cationic
part of the substrate(acetylcholine) and the esteratic site containing the primary
alcoholic group of the aminoacid serine which attacks the carbonyl atom of the
substrate.
CHEMISTRY AND PRODUCTION TECHNIQUES OF C RBAMATES.
Carbamates
Carbamates are an important group of insecticides since 1958 and
the usage increased with time. The advantages are
 Rapid action
 A reasonable rate of biodegradation
 Selective toxicity towards target organism
 Metabolized in plants which prevents the accumulation of
potentially harmful residues.
Carbamates are derivatives (esters) of carbamic acid.(HO-CO-NH2)
Several
carbamates are systemic, transported in the xylem. It is possible to control pests on
shoots and roots which are otherwise difficult to reach. Hence, they are used as soil
insecticides and nematicides (aldicarb, carbofuran, oxamyl etc.). Commercial products
available are grouped into three groups.
19
1. N, N-dimethyl carbamates of enols and hydroxy heterocycles
2. Phenyl carbamates
3. Oximecarbamates
Mechanism of action
 The mechanism of action of the insecticidal carbamates is identical to that of the
organophosphates, viz., inhibition of the enzyme cholinesterase.
 The carbamate insecticides are strong inhibitors of cholinesterase
and may have direct effect on acetyl chlorine receptors because of
their structural resemblance to acetyl chlorine.
 The poisoned insects exhibit violent convulsions and neuro
muscular disturbances.
 The metabolism of carbamates in plants and animalsis dominated
by hydrolysis to phenol, oxime and other hydroxyl compound
together with methyl carbamic acid which decomposes to
ammonia and CO2.
 The phenols and other hydroxyl compounds from water soluble
conjugates with sugars and sulphates which in mammals are
excreted in urine.
 Inhibition of acetylchlinesterase (ACHE) leads to a buildup of acelylcholine in
the post synaptic membrane and hence to a permanent nerve stimulation with
lethal results.
This stimulation of insects manifests itself in uncountrolled
movements and paralysis.
A) Carbaryl (Sevin, Hexavin, Ravyon)
(Naphthyl carbamate, 1-Naphthyl-N-methyl carbamate)
20
LD50: 850 mg.
 Broad spectrum contact insecticide, non-systemic used in cotton, fruits,
vegetables, forage crops etc. Also to control of earth worms.
 Carbaryl, introduced by American Union Carbide Company in 1956 was the
first successful commercial carbamate. Carbaryl is produced by any of the
general methods of preparation of carbamates, like reacting 1-naphthol with
methyl carbamoyl chloride at room temperature.
 The rate of reaction is increased by removing the HCl that is formed with a
strem of air or nitrogen.
 Pure compound of carbaryl is obtained by reacting 1-naphthol with methyl
isocyanate.
 Carbaryl is also synthesized by reacting 1-naphthylchlorocarbonate with
methylamine in the presence of HCl acceptors.
 Carbaryl is a white crystalline compound with M.P. 142° C. it is highly soluble
in organic solvents; resistant to the action of water at room temperature and also
to light and oxygen of air.
 In alkaline medium, it is rapidly hydrolysed and so it is not compatible with
compounds of alkaline nature like Brodeaux Mixture.
B) Carbofuran (Furadan)
 (2, 3, dihydro 2, 2 dimethyl 7, benzofuranol)
 Broad spectrum insecticide, nematicide and miticide.
 LD50: 8-14 mg/kg rat.
 It is prepared by treating 2,3-dihydro-2,2-dimethyl-7-benzofuranol with methyl
isocyanate.
 It can be incorporated in soil at 6-10 kg/ha for control of soil insects and
nematodes.
 It has high mammalian toxicity but is rapidly metabolized to non-toxic products
in plants and animals.
21
 It is a systemic carbamate, broad spectrum insecticide. It is stable in acid and
neutral media but unstable in alkaline medium. Sparingly soluble in water; but
soluble in organic solvents.
 It is compatible with non-alkaline pesticides and fertilizers. It is not phytotoxic
to rice.
 Carbofuran when applied to soil is absorbed by plant roots and distributed to
stems and leaves and metabolized to non-toxic compounds in 30 days.
Carbofuran present in soil is degraded by hydrolysis depending on soil pH and
clay content. Toxic residues do not remain in the soil for long.
C) Carbosulfan
 Carbosulfan, a sulphanylated derivative of carbofuran acts as a contact and
systemic insecticide. It can be applied to the foliage or soil as a nematicide. It
has a lower mammalian toxicity.
 LD50: 209 mg
 The
carbomates,
carbofuran,
carbosulfan
and
aidicarb
are
valuable
nematicidesss. Carbosulfan formulated as granules is used in vegetables. eg.
brassicas, carrots and turnips.
D) Aldicarb (Temik)
2-Methyl-2-(methylthio) propanol 0-Methylamino carbonyl oxime)
 Systemic insecticide, acaricide, nematicide for soil use; only available as
granules to reduce handling hazards.
 LD50: 0.93 mg/kg rat.
 It is prepared by reacting 2-Methyl-2-(methylthio) propionaldoxime with
methyl isocyanate.
 Used for cotton, sugarbeet and ornamentals. Aldicarb is extremely toxic and is
absorbed through skin. It is therefore marketed as a granular formulation.
22
 White crystalline substance m.p. 100°C. Sparingly soluble in water prepared by
reacting corresponding oxime with methyl isocyanate.
 Aldicarb is a carbamate of carbamoyl oxime group. It is effective for control of
aphids, nematodes, flies beetles, leaf miners, thrips and white flies on a wide range
of crops.
 Aldicarb is readily translocated in plants after soil applicatikon where it is
metabolized to the sulphoxide and the sulphore which are also active.
CHEMISTRY AND PRODUCTION TECHNIQUES OF SYNTHETIC
PYRETHROIDS.
Synthetic pyrethriods
Pyrethrum is derived from the dried flowers of the plant Chrysanthemum
cineariaefolium. The name given to the active insecticidal components of the dried
flowers is known as pyrethrins. Chemically pyrethrins are organic esters formed by
the combination of two carboxylic acids and three keto alcohols.
The synthesis of chrysanthemic acids and of cyclopentenolones
opened up the possibility of obtaining synthetic pyrethroids, a
remarkable class of insecticides.
The outstanding properties of pyrethrins are
 Rapid action
 Low mammalian toxicity
 Broad spectrum activity
 Lack of persistence
 Repellency
Allethrin is the first of its kind prepared by esterification of
synthetic chrysanthemic acid with the alcohol allethrolone.
23
Allethrin had strong insecticidal activity (0.1 µg / insect) and
removal of keto group gave another synthetic pyrethroid known as
bioallethrin (0.02 µg / insect).
Bioresmethrin is an extremely active insecticide (0.005 µg /
insect). This is photosensitive and consequently was not persistent.
However when the isobutenyl group of bioresmethrin was replaced by
the dichlorovinyl group, the resultant compound is NRDC134 which
was more toxic to house flies and mustard beetles than the most known
insecticides.
Permethrin was active against houseflies and mustard beetles and
showed much greater photostability and consequently was a moderately
persistent insecticide. It was the first synthetic pyrethroid effective as a
seed treatment against wheat bulb fly.
Decamethrin was prepared by replacement of chlorine atoms by
bromine and the introduction of  cyano group from permethrin. This
was discovered in 1974 is a potent insecticide known. (0.0003 µg /
insect) 50 times more active than Pyrethrin I. This has reasonable
photostability and very low mammalian toxicity.
The corresponding chloro derivative as the cis – trans mixture is
known as cypermethrin which is a broad spectrum insecticide (dose
20-80 g /ha) with good residual activity on plants.
A survey of the esters of furylmethanol led to the discovery of
insecticidal activity in a group of phenyl acetic acid esters and Japanese
chemists at Sumitoma company introduced fenvalerate in 1974.
Fenvalerate is a mixture of 4 isomers and is used at 20-150 g ai/ha
against a wide range of pests and relatively stable in light.
24
American Cynamid introduced another phenyl acetic acid esters
viz., flucythrinate and fluvalinate.
Bromination
of
the
double
bonds
on
decamethrin
and
cypermethrin gave tralomethrin and tralocythrin. Both are highly active
– activity may be due to the in vivo conversion in to parent compounds.
Lambda Cyhalothrin has a comparatively high mammalian
toxicity (LD 50 (Oral) 60 mg /kg). It is effective at very low doses (530 g ai/ha) against major insect pests in many crops. Little hazard to
honey bees and this represents an important advantage over OP
insecticides which are highly toxic to honey bees. At normal rates
cyhalothrin shows low toxicity to birds with no accumulation in eggs or
tissues and no effect on earthworms. The half life in soil is 3-12 weeks;
in aerobic soils it undergoes extensive mineralization to CO 2. In flooded
soil degradation was slower and only hydrolysis products were
detected. No phytotoxicity towards major crops and controls a wide
spectrum of lepidopteran pests. This is valuable for the control of plant
virus vectors.
Tefluthrin is the first pyrethroid effective as a soil insecticide at
doses of 12-150 g ai/ha. It is formulated as granules and may also be
applied as foliar spray or seed dressing. Tefluthrin kills insects that are
resistant to OP and carbamate insecticides. Low mam. toxicity LD 50
=1500mg/kg.Little hazard to earthworms and birds but highly toxic to
fish. Half life in soil is 4-12 weeks and there is no danger of residue
accumulation.
Mode of action of pyrethroids
25
 The symptoms of insects poisoned by pyrethroids clearly show
that the chemical attacks the insect’s nervous systems.
 Pyrethroids cause hyper excitation followed by convulsions and
death in arthropods.
 The rate and mechanism of metabolism has a major influence on
the toxicology of a compound.
 In (rats) mammals pyrethroids are very rapidly metabolized by
ester cleavage, oxidation hydroxylation.
 The synthetic pyrethriods are very expensive to prepare on a tonnage basis.
 The high insecticidal activity and low mammalian toxicity of pyrethroids are
especially significant now that compounds stable to light and oxygen are
potentially available.
 Their toxicity to fish is high. They are rapidly degraded in soil and have no
detectable illeffects on soil microflora and microfauna. They are not active
against mites.
 The major symptoms of pyrethroid poisoning in insects may be accounted by
effects on the kinetics of nerve membrane sodium channels.
 The mean open times of these channels are prolonged with consequent
hyperactivity of nerves.
 The synthetic pyrethroids have been found to be useful as early season sprays to
control the variety of insects that occur on cotton including boll worms, leaf
worms, jassids, thrips and whitefly. They are used in combination with an
organo phosphorus insecticide as an ultra-low volume spray.
26
 They are non toxic to humans and animals. LD50 to rats is around 8000 mg/kg.
They are used at only 50 g/ha. The cost/of treatment per hectare is low.
CHEMISTRY
AND
INSECTICIDES AND
PRODUCTION
TECHNIQUES
OF
NOVEL
HOUSEHOLD PESTICIDES.
Many organisms are known to excrete chemicals which induce a specific
behavioural response from other members of the same or different species some
distance away from their point of release. Such signalling chemicals
(semiochemicals) are usually divided into those acting between the same species
(pheromones) or different species (allelochemicals). As potential insect control
agents, the most valuable are the insect sex pheromones or attractants. These are
volatile chemicals, generally released by the female, which facilitate mating, either
by attracting a male insect or by inducing courtship ritual)
Considerable work has been carried out on the sex pheromones of certain moths
e.g. gypsy moth and others which are the adults of economically important
caterpillar pests such as cotton leafworm and tobacco budworm.
REPELLENTS
Repellents are chemicals which cause insects to make oriented movements
away from its source. The first chemical repellent was discovered soon after
man became acquainted with fire. When he found that fire was a fairly
efficient method of repelling insects. Plant extracts of citronella, which is
extracted from Andropogm nardus (L.), which contains gerniol, cintronellol,
cintronellal, borneol, and terpenes are considered to be the principal
mosquito repellents. Now more effective, synthetic repellents are in use.
Dimethyl Phthalate
Dimethylphthalate is used as effective mosquito repellent. The disadvantage of
this repellent is that it causes irritation to the eyes and mucous membranes. Its
27
LD50 value is 8200 mg/kg.
N,N-Diethyl-m-toluamide (Deet)
Deet is used as repellent for various insects particularly to mosquitoes. Its
LD50 value is 200 mg/ kg.
Benzyl Benzoate
Benzyl benzoate is used as repellent for clothing treatment against chiggers and
mites. Its LD50 value is 7900 mg/kg.
Butoxypolyproplene Glycol
Butoxy polyproplene glycol is used as repellent for flies against cattle.
1,5a, 6,9,9a,9b-hexahydro-4a (4H) dibenzofuran-carboxaldehyde (MGK,
Repellent 11)
MGK repellent used as repellent for cockroaches and for biting flies on cattle.
Its LD50 value is 2500 mg/kg.
2-Ethyl-1,3-hexanediol (Rutgers 612)
CH3CH2 CH2 CH-CH-CH20H
I
I
OH C2H5
Ruters 612 is used as repellent against flies and mosquitoes.
Butyl 3,4-dihydro-2,2-dimethyl-4-oxo-2H-pyran-6-carboxylate (Indalone)
Indalone is used as repellent against mosquitoes and bitting insects. Its LD50
value is 7800 mg/kg.
Di-n-propyI2,5-pyridine dicarboxylate (MGK 326)
MGK 326 is used as repellent against housefly.
ATTRACTANTS AND PHEROMONES ___ _
Attractants are chemical substances whose vapours attract insects. They are
mostly divided into food attractants and sexual attractants. Important examples of
food attractants are products of decomposition of food products,proteins,
28
enzymatic and also molasses. Some of the important synthetic attractants are
methyl eugenol (1-allyI 3,4-dimethoxybenzene) attracting estern fly and
trimedlure (l,l-dimethylethyl,
4 (or
5)
chloro-2-
methyl (cyclohexane)
carboxylate, an attarctant for melon fly. There are few examples of synthetic
attractants that are effective for using over fruit flies.Butyl sorbate is an effective for
European cockroaches and methyl linoleate for bark beetle.
PHEROMONES (SEX ATTRACTANTS)
Pheromones are those chemicals that are secreted into the external environment by an
animal and that elict a specific reaction in receiving the individual of the same species.
Sex pheromones are those which are realeased by one sex only and triger behaviour
patterns in other sex that facilitate mating. Sex pheromones are produced by males of
certain insect species. Mostly they serve as short range mating stimulants after the
individuals have come into close proximity.
The identified sex pheromones are
Silk worm-10-cis-12-hexadecadienol
Gypsy moth- Lymantria obfuscate: 10-Acetoxy-cis-7- hexadecadienol
Cabbage looper, Trichloplusia ni (Huubner) - Cis-7- dodecenyl acetate
Honey bee Queen, Aphis mellifera L. 9-keto-trans-2-decenoic acid
CH3-C-(CH2)5 CH=CH-COOH
║
O
Aggregation pheromones, are those pheromones which may be released only by
one sex but cause approach responses by individual of both sexes of the species.
Uses
29
To attract insects to site where they are then destroyed by treatment with insecticides
It enables pests to be controlled specifically. The minute application quantities avoid
contamination of food and fodder as well as environment.
They have great potential usefulness in surveys to determine the presence of abudance
of species in question.
Synergists.
It may be defined as any chemical which itself is not toxic to insects at dosages used ,
but when combined with an insecticide greatly enhances the toxicity of the insecticide
. Synergisms differs from potentitation which occurs when two toxic materials applied
together elict a response greater than that expected from the sum of the individual
toxicants.
Advantages
It reduces the amount of pesticide required for insect kill, much smaller application of
pesticides would be required for field application.
It reduces environmental pollution
It broadens the spectrum of the insecticide.
Most widely used chemicals are methylene dioxyphenyl derivatives. Important
examples are piperonyl butoxide, safrole, sulfoxide, tropitol and thanite.
Autosynerg ism
Autosynergist is a compound which synergises its own toxicity. This would involve
forging a synergophore and toxophore into the same molecule in such a way that the
former does not interfere with the action of the latter. Important example of
autosynergism is 3,4- methylenedioxy phenyl N-methyl carbamate.
Synthetic inhibitors
Inhibitors are organic or inorganic substances of a varied chemical nature and also
30
the products of metabolism of a cell, that cause the partial or complete suppression
of the activity of enzymes or metabolism in a living organism.
Chitin, essentially a polymer of N-acetyl-glucosamine, is a structural feature of the
insect cuticule and fungal cell walls, hence it biosynthesis is an attractive target for
selective fungicide. Importart example of chitin inhibitor is diflubenzuron.
Diflubenzuron is highly active against mosquitoes, livestock fly pests, cabbage
white butterfly caterpillars, moths and other larval fly pests at low dosages. The
biochemical basis of action is considered to be disruption of the moulting process
by inhibition of the normal insect cuticle formation. Diflubenzuron is prepared
by the reaction 2,6 dichlorobenzamide with p- chlorophenyl isocyanate. BPU are
important developing class of chitin inhibitors. They will interfere with chitin
synthesis in immature insects and are highly selective insecticides with low toxicity
to target organisms
CHEMOSTERILANTS
Chemosterilants are chemical substances that sterilize insects to prevent
reproduction. The sterilizing action of a chemical may be due to the fact that
1. It damages the chromosomes and leads to the lethal mutations in the semen
of the males or matures eggs of females.
2. It inactivates the sperm
3.Under the influence of chemosterilants, females lose the ability of laying eggs
.. 4.It causes perishing of the cells in the premeiotic stages or
aspermia
Most chemosterillants relate to highly toxic compounds with a mutagenic,
tetragenic, and carcinogenic action.
Chemosterilants are divided into three groups:
1. Alkylating agents
2. Antimetabolites
3. Miscellaneous.
31
Alkylating agents are compounds in which hydrogen atom of molecule of a
substance is replaced by an alkyl group. They readily enter into the chemical
alkylation reactions with various compounds of a cell, including proteins and
nucleic acids) The most important compounds of this group are' .
ETHYLENE IMINE ___________________________________ _
Tepa
(1,1 " 1 "-Phosphinylidynetrisaziridine)
Apholate
(2,2,4,4,6,6-Hexakis( 1-aziridinyl)-2,2,4,4,6,6-hexahydro-1 ,3,5,2,4,6,
triazatriphosphorine)
Antimetabolites are substances whose structure is very close to that of the
natural metabolites of an organism. When they enter the organism they
displace these metabolites in exchange reactions. Upon entering an insect
organism, these substances violates the synthesis of nucleic acid (DNA and
RNA) in the nuclei of the sexual cells: Among the anti-metabolites of folic
acid, the best examples are methotrexate (N-p-2,4-diamino-6-pteridyl) methyl
methylaminobenzoyl) glutamic acid), aminoprotein (2,4 diaminoptereldyl
glutamic acid) and fluorouracil very close to the structure of folic acid.
CHEMISTRY AND PRODUCTION TECHNIQUES OF PREVENTIVE AND
ERADICANT FUNGICIDES (Available in market only).
Fungicides are chemicals that have the ability to reduce or prevent
the damage caused by fungi in plants and their products. Fungicides are
classified based on mode of action as protective, curative and eradicant
fungicides.
32
Protective fungicides prevent fungal infection by sporicidal activity.
These arrest the germination of spores or kill the fungal hypae as they
penetrate the leaf or prevent their penetration. E.g. Sulphur
Curative fungicides penetrate cuticle and kill young fungal mycelium
growing in the epidermis and this prevents further development of fungal
growth. E.g. Organomercurials.
Eradicant fungicides are agents that make control of fungus even after the
symptoms become visible and that kill both newly developed spores and
the mycelium. E.g. Systemic fungicides.
The early fungicides were inorganic materials like sulphur, lime sulphur,
copper and mercury compounds.
Sulphur compounds
Elemental Sulphur is available in dust, wettable powder and colloidal
forms. The efficiency of S dust increases with fineness of the particle size.
A high proportion should pass through 200 – 300 mesh sieve. Colloidal
sulphur is formulated with kaolin (diluent) with 40 per cent S and a
particle size of < 6 . Sulphur is a contact and protectant fungicide used to
control powdery mildew in fruits, vegetables, flowers and tobacco. It is
also effective against apple scab and rust of field crops. Lime sulphur: It is
aqueous solution of calcium poly sulphides. It is prepared by sulphur
solution in calcium hydroxide suspensions under pressure in the presence
of air. Calcium penta sulphide and calcium tetra sulphide found in the
mixture are the active materials of fungicidal value which on exposure to
air release elemental S.
Mode of action: At first it was observed that S could not be the toxic
agent. Sempio (1932) reported that the action was due to the production of
various S derivatives. Another theory was that the fungal spores reduce S
to H2S which has shown to be toxic to the spores. However in 1953 this
33
theory was disproved as colloidal S was more effective than H2S. Another
hypothesis ascribed to various oxidation products such as SO2, H2SO4 and
thiosulphuric acid. Then no S derivative is responsible and came to
Sempio and finally that S itself is fungi toxic.
Among the heavy metals only Cu and Hg have been widely used as
fungicides although silver is most toxic metal cation. The relative toxicity
is in the order of
Ag > Hg > Cu > Cd > Cr > Ni > Pb > Co > Zn > Fe > Ca
Copper compounds
Copper sulphate has been used since 18th century as seed treatment
against cereal bunt later replaced by organomercurials. Cu ions in solution
are toxic to all plant life. Selective fungicidal action can therefore be
achieved by application of insoluble Cu compound on the foliage.
E.g. COC, Copper carbonate, Copper hydroxide, Bordeaux mixture etc.
Bordeaux mixture
Millardet in 1882 discovered the Bordeaux mixture effective against
powdery mildew. A mixture of copper sulphate and lime was initially applied as a
paste and thus gained wide recognition as “Bovillie Bordelaise” (Bordeaux Mixture).
As the initial mixture continuing 8 kg of blue stone dissolved in 100 litres of water
and 30 litres of lime suspension prepared with 15 kg lime was found to cause foliar
injury. Various combination were tried. Now a 4-4-50 mixture (copper sulphate in 1
b; lime in 1 b; water in gallons), is used but the concentration of the ingredients is
varied depending on the purpose. However, the proportion of copper sulphate to lime
usually remains constant. In India Bordeaux mixture is being made by preparing a
solution of copper sulphate and quick like (or hydrated lime) in finely ground form in
separate containers and then mixing them simultaneously into a third container with
copper sulphate like copper, wooden and earthern vessels. Wide variation in the
composition of the resulting mixture will be observed due to chemical reactions
34
between calcium hydroxide and copper sulphate in solution when the ratio between
the components is changed. Bordeaux mixture named from the locality of its
origin consists of Cu SO4 (4.5 kg) and Ca (OH) 2 (5.5 kg) in 454 litres
of water. It is prepared under a wide range of formulae. Once the
mixture has been prepared it should be sprayed immediately on the crop since
the toxicity decreases on standing. It is rather difficult to apply because the
precipitate tends to block the nozzles. Jaggary or sugar is added to prevent
crystallisation.
Mode of action is complex. The ai is probably not Cu (OH)
2
but rather
basic Cu SO4 approximately to the formula [Cu SO4. 3 Cu (OH) 2].
Bordeaux mixture is almost insoluble in water. So how is Cu mobilized in
plants to kill the fungus? The exudates both from the surface of leaf and
from the fungal spores can dissolve sufficient quantities of Cu from the
dried deposits due to the presence of certain compounds like amino and
hydroxy acids which can form chelates with copper.
B) Copper oxychloride
(Blue copper 50: Fytolan) Cupramar, Blimix 4%, Blitox 50%.
Copper oxychloride is one of the low soluble copper fungicides produced by the
action of air on cupric chloride solution or scrap copper.
4Cu + O2  2Cu2O
Cu2O+2HCl  2CuCl + H2O
2 CuCl + O + 2 HCl  2CuCl2 + H2O
CuCl2 + Cu  2 CuCl
4CuCl2 + 3CaCo3 + 3H2O  3Cu(OH)2 CuCl2 + 3Cl2
It is marketed in the form of wettable powder containing 50 and 90% copper
oxychloride and dusts containing 4 to 12% metallic copper. The 50% formulation
contains a diluent (Kaolin) and a surface active agent.
Burgandy mixture
35
This was introduced by Mason in 1887 by mixing copper sulphate (1 part)
with sodium carbonate crystals (1 part) and is less effective than Bordeaux
mixture.
Cheshnut compound
This is suggested by Bewley in 1921 consists of 2 parts of Cu SO4 and 11
parts of (NH4)2 CO3. The two compounds are well powdered thoroughly
mixed and stored in air tight containers for 24 hours before use.
Chaubattia paste
This was developed at Government Fruit Research Station, Chaubattia,
Almora district, UP. It is prepared by mixing copper carbonate (800 g) and
red lead (800 g) in 1 litre of linolin or raw linseed oil. It is used as wound
dressing agent on pruned parts.
Copper oxy chloride approximately Cu Cl 2. 3 Cu (OH) 2 is marketed as
colloid and wettable powder. It is a protective fungicide used to control
potato blight, several leaf spots and effective against several diseases of
horticultural crops.
C o p p e r h y d r o x i d e CU (OH)2 is a new formulation introduced.
Mode of action is the denature of proteins by free copper ions. Since
enzymes are made up of proteins, the Cu inactivates the enzymes. The Cu
kills the fungal spores by combining with the sulphohydril groups of
certain enzymes.
Mercury Fungicides
Mercury compounds are known for their fungicidal and bacterial
properties. They are mainly seed dressers but because their toxicity the
mercurial are banned for use.
Inorganic – Mercuric chloride
Organic – Phenyl mercury acetate
Methyl ethyl mercuric chloride (Emisan)
36
Ethyl mercuric chloride
Mercury like Cu an other heavy metals is known to affect cellular
respiration by poisoning essential respiratory enzymes in fungal cells.
Dithiocarbamates (Organic sulphur compounds)
Investigations of the DuPont Company (USA) showed that some of the
derivatives of dithiocarbamic acid H2N ,CSH had insecticidal and fungicidal
properties. However dithiocarbamic acid itself is not known to exist in the free state.
When the primary and secondary aliphatic and aromatic amines are treated with
carbon-di-sulphide in alcoholic solutions, dithiochrbamates are produced.
The hydrogen attached to S dissociates and may be replaced by a metal or other
radicals producing a variety of derivatives. The group > NCS is considered to be
essential for insecticidal and fungicidal action. By reacting dimethylamine and CS 2
under alkaline conditions, Thiram and salts of Na, Fe and Cd were prepared. Nabam
was produced by reacting ethylene diamine and CS2. Subsequently the heavy metal
complexes of dithiocarbamates like Ziram and Ferbam and complexes of
bisdithiocarbamates like maneb and zineb were developed.
A large number of derivatives of dithiocarbamic acid possess fungicidal
properties. They can be classified as follows.
1. Metalic dithiocarbamates – Ziram and Ferbam
2. Thiuram disulphide (Thiram) –S-Slinkage
3. Bis dithiocarbamates – Manels, Nabam, Zineb
A) Zineb (Dithane-A 78)
Dithane-Z 78 is a white crystalline substance insoluble in water and most organic
solvents; moderately soluble in pyridine. It is unstable in the presence of moister, heat,
light and alkali. Moist compound under unfavourable storage conditions may decompose
to 50% in a year. To reduce the chance of explosive evolution of CS2, Zineb has to be
37
stored in a well ventilated place at low temperatures.
It is compatible with most
insecticides like Ferbam.
It is formulated as wettable powder. Its residual effect depends on weather and
season. Zineb can be of great use on Zn deficient soils.
B) Maneb (Dithane-M 45, Manzate)
It is the manganese salt of ethyulene bisdithiocarbamic acid; is similar to zineb, in
most physical and chemical properties. Decomposes rapidly under high temperature and
moisture. It is a yellow crystalline substance insoluble in water and organic solvents.
Compatibility is similar to Ferbam.
When stored in bulk, Maneb is capable of
spontaneous decomposition with charring which can be avoided by diluting with an inert
material. Other analogues are Dithane C-31, Propineb, Thioneb (carbathene).
Thiram as tetra methyl thiuram disulphide was the first compound to be
applied as a fungicide and is still used, especially against moulds and as a
seed dressing against soil fungi causing damping off. Thiram is prepared
by the interaction of carbon disulphide and dimethylamine in the presence
of NaOH which is subsequently oxidized to thiram.
Later work resulted in the discovery of the fungicidal activity of zinc and
ferric salts of dimethyl dithiocarbamates known as ziram and ferbam
respectively. Disodium ethylene bis dithiocarbamate or nabum is also
fungicidal and is used to control stem rots. Nabum is the insoluble zinc
and manganese salts known as zineb and maneb which are produced by
reaction with an aqueous solution of zinc and manganese sulphate have
largely replaced water soluble. These are used as protectant fungicides and
are applied for the control of wide range of phyto pathogenic fungi such as
downy mildews. They have very low mammalian toxicities (LD
mg kg-1).
38
50
> 7000
Metham-sodium (N- methyl dithiocarbamate) is a valuable soil sterilant
for the control of damping off diseases.
Mancozeb, a coordinated complex of zinc and manganous salts was
introduced in 1962. Maneb and mancozeb are formulated with synthetic
fungicides to reduce development of resistance.
[-SCSNHCH2CH2NHCSSMn-]x (Zn)y
The dithiocarbamates owe their fungicidal activity due to their ability to
chelate with metal cations such as copper. The dithiocarbamates get
metabolized to isothio cyanates which react with vital thiol compounds
with in the fungal cell.
Heterocyclic N compounds
Captan (N-(trichloromethylthio)-4-cyclohexane-1,2-dicarboximide) is a
very effective and persistent foliage fungicide against many soil and seed
borne diseases. Analogues that have been subsequently developed as foliar
fungicides include folpet and difolatan, which are most active against
potato blight. These are some of the safest fungicides (LD
50
> 10000 mg
kg-1).
Captan interacts with cellular thiols to produce thiophosgene which poison
the fungus.
Dichlofluanid, introduced by Bayer is a broad spectrum protective
fungicide which is less sensitive than captan.
39
Phenols
The majority of phenols, especially those containing chlorine, are toxic to
microorganisms, their bacterial action has been known for along time and
many phenols are also fungicidal. However many are phytotoxic.
Shirlan or salicylanilide is used to inhibit the growth of moulds on cotton
and against a number of laef diseases as tomato mould.
Dinocap is a non systemic aphicide and contact fungicide which is
effective for the control of powdery of mildew on many horticultural
crops. Low mammalian toxicity LD 50 > 980 mg kg-1.
Binapacryl is closely related to dinocap and is used for the control of
powdery mildew on apples.
Oxine -hydroxy quinoline is a protectant fungicide, when suitably
formulated, appears to possess limited systemic action. Oxine has a
striking capacity to form chelates with metals (Cu) which is effective
against a range of phytopathogenic fungi.
Chlorobenzenes and related compounds
2,6-dichloro-4-nitro aniline was marketed in 1959 by Boots Ltd.
Especially valuable for the control of Botrytis in tomatoes and against
fungal organisms causing post harvest decay of fruits.
Penta chloro nitro benzene (PCNB) called quintazene is a widely used
soil fungicide for damping off diseases. Chloroneb is used to control soil
borne fungi as seed dressings or by soil application.
Chlorothalonil is a broad spectrum foliar or soil applied fungicide used in
many crops. Sandoz kavach.
CN
Cl
Cl
Cl
CN
Cl
40
Chlorothalonil
Quinones
A number of quinines occur in plants and are also products of fungal
metabolism.
Dichlone is more stable in light has been used as a seed dressing agent
and a foliage spray against powdery mildew.
Dodine (N-dodecyl guanidine acetate) has been known asa bactericide
(1941) and more recently has been shown to have fungicidal activity.
Dodine is a cationic surfactant is generally formulated as wettable powder.
Low mammalian Toxicity (LD 50 > 1500 mg kg-1).
Guazatine is mainly used as seed dressing agent for cereals at 0.6 –0.8 g ai
kg-1 of seed and against post harvest diseases. (LD 50 > 500 mg kg-1).
The fungicidal activity of these compounds probably depend on their
ability to alter the permeability of the fungal cell wall, causing loss of vital
cellular components such as amino acids and P compounds.
Dicarboximides
All members contain the 3,5-dichlorophenyl moiety and the fungicidal
activity depends on the presence of the two chlorine atoms in 3, 5
positions.
Procymidone,
hydantoin,
iporodione
and
vinclozolin
have
been
extensively used for the control of Botrytis and Scelrotinia sp in cereals,
fruits and vegetables but their use is restricted due to the development of
resistance.
More recently metomedan, chlozolinate and myclozoline have been
introduced.
Drazoxolon (ICI,1960) is a valuable seed dressing agent against damping
off diseases.
41
The dicarboximides have low mammalian toxicities (LD 50 > 3500 mg kg-.
SYSTEMIC FUNGICIDES or PLANT CHEMOTHERAPEUTANTS
The idea is earlier but 1960 only commercial systemic fungicides
have come to market. A systemic fungicide is a compound that is taken up
by a plant and is then translocated with in the plant, thus protecting the
plant from attack by pathogenic fungi or limiting an established fungal
infection.
If a candidate chemical is to be an effective systemic fungicide the
following criteria must be satisfied. It must be fungicidal or to be
converted in to an active fungitoxicant with in the host plant.It must
possess very low phytotoxicity. It must be capable of being absorbed by
the roots, seeds or leaves of the plant and then translocated, at least locally,
within the plant.
The earlier protectant fungicides applied as foliar sprays formed dried
deposits on the leaves of the host plant, protecting it from fungal attack.
However the deposits are of course gradually removed by the effects of
weathering and cannot protect new plant growth formed after spraying or
any part of the plant not covered by spraying. These disadvantages can be
overcome by the use of systemic fungicides which since penetrates the
plant cuticle. They also offer the possibility of controlling an established
fungal infection. There fore systemic fungicides should exhibit both
protectant and eradicant activity.
Sulphonamides
Sulphonamides have been used mainly against diseases on cereals, but
comparatively large doses are needed and there is a danger of phytotoxic
damage to the host plant.
42
Antibiotics
Antibiotics are chemicals produced by living organisms that are
selectively toxic to other organisms. The first successful antibiotic against
human diseases was penicillin discovered by Fleming (1929) but it has
never achieved commercial significance as a systemic fungicide.
Glitoxin, an antifungal antibiotic produced by the soil fungus Tricoderma
viride inhibited the growth of Botrytis and Fusarium spores at 2-4 ppm
concentration but the compound was too unstable for use as a soil
fungicide.
Streptomycin and cycloheximide are antibiotics obtained from the culture
filtrates of Streptomyces griseus is used for the control of bacterial
pathogens of plants.
Griseofulvin isolated in 1939 from Penicillium griseofulvum is an
important antifungal antibiotic showing a wide spectrum of activity
especially against Botrytis in lettuce and Alternaria solani on tomato.
Blasticidin,
a
pyrimidine
derivative
isolated
from
Streptomyces
griseochromogenes give excellent control of rice blast and also inhibits
certain bacteria. The antibiotic polyoxin D is another pyrimidine derivative
which is toxic towards several fungi including rice blast. The fungi
toxicity is due to interference with chitin synthesis.
Melanin Biosynthesis Inhibitors (MBI s) act on the pathogen to
prevent it penetrating the plant epidermis; these compounds block melanin
synthesis in a variety of Ascomycetes and fungi imperfecti. They provide
practical control of rice blast and experimental control of some
Colleotricum species. Tricyclozole prevents the rigidity of penetration by
Pyricularia oryzae. Validamycin is an aminoglucoside antibiotic active
mainly against Rhizactonia diseases and has been widely used to control
rice sheath blight. Probenazole related to saccharin is effective by root
43
application against rice blast and bacterial leaf disease Xanthomonas
oryzae. It is not fungi toxic Invitro and probably acts indirectly by
enhancing the resistance response of the host plant.
Benzimidazoles
These represent a new era in fungicide use when they were introduced in
late 1960s.
CONH(CH2)3CH3
H
N
N
NHCO2CH3
NHCO2CH3
N
N
Benomyl
Carbendazim
The most important members of this group are benomyl [methyl –1- (butyl
carbamoyl) benzimidazole-2- carbamates] TN: Benlate and thiobendazole.
Both are wide spectrum systemic fungicides effective against many
pathogenic fungi including powdery mildews and soil borne pathogens.
These fungicides may persist in plants for several months.
Benomyl was introduced in 1967.
It was synthesized from cyanide and
methylchloroformate. Benomyl and thiabendazole are both wide spectrum systemic
fungicides active against many pathogenic fingi including powdery mildews and soilborne pathogens, Verticillium alboatrum on cotton and black spot on roses.
Du-pont; Benlate LD50: > 9590
Foliar fungicide in wine grape fruits, vegetables, citrus, cereal seed dressing.
Benomyl is the more active compound and is widely applied as a foliar spray, seed
dressing or to the soil for control of grey mould (Botrytis cinerea), apple scab (Venturia
inequalis) canker and powdery mildew (Podosphaera leucotricha), leaf spot (Cercospora
beticola), major fungal diseases of soft fruits and some pathogens of tomato and
44
cucumber.In aqueous solution benomyl is rapidly hydrolysed to methyl
benzimidazole – 2 – carbamate and this is probably the active
fungitoxicant carbendazim which is used as a wide spectrum systemic
fungicide formulated as 50 per cent WP.
Metalaxyl
Metalaxyl is included in the phenylamides group of systemic fungicides.
The compounds of this group show protective and systemic activity against
Oomyceles causing foliar, root and crown diseases in wide range of crops eg. downy
mildews and late blight. The first members of this group Metalaxyl and Furalaxyl
were introduction by Ciba-Geigy in 1977 (Metalaxyl = Ridomil).
With
a
high
activity at low rates of foliar or soil application metalaxyl controls diseases caused by
air or soil borne comycetes in crops like potatoes, grapes, tobacco, cereals, hops and
vegetables. A wettable powder formulation with mancozeb, (a complex of Zn and
Mn salts fungicides) is widely used as a foliar spray against hlight on potatoes.
Metalaxyl has the broadest spectrum of fungicidal activity of this group of fungicides;
it is good against downy mildew on vines, lettuce, maize and Pythium diseases and
can be formulated as a seed dressing.
E) Carbendazim (Bavistin, Derosol)
Foliar fungicide in grapes, fruits, vegetables, cereals, cereal seed dressing
LD50: 15.000
Carbenda in methylbenzimidazole-2-carbamate is used as a
wide spectrum systemic fungicide and may be formulated as a 50% w.p. for control of
Botrytis, Gloeosporium rots, powdery mildews and apple scab.
Carbendazim is
absorbed by the roots and foliage of plants and is quicker acting than Benomyl.
The activity of the benzimidazole fungicides (Benomyl, thiabendazole and
carbendazim) is due to the inhibition of nuclear division due to their action on the
microtubule assembly and the resistance developed in fungi is the result of mutant
strains possessing an altered microtubule assembly.
45
Carboxin and related compounds (Oxathiins)
Oxathiins are another group of heterocyclic compounds with interesting
systemic fungicidal properties. Carboxin and the sulphone analogue
known as oxycarboxin are primarily effective against basidomycetes class
of fungi which includes such economically important group of fungal
pathogens rusts, smuts and bunts of cereals and the soil fungus
Rhizactonia solani.
O
S
CH3
CONH
The fungitoxicity is due to inhibition of glucose and acetate oxidative
metabolism and RNA and DNA synthesis.
Carboxin and Oxycarboxin
Oxathins are another group of heterocyclic compounds with systemic fungicidal
properties.
Examples are Carboxin (5, 6 dihydro-2-methyl-1, 4 oxathin-3-
carboxanilisde) (Vitavax) and the sulphone analogue known as Oxycarboxin
(Plantvax).
LD50: 3820
LD50: 2000
Seed dressing: cereals, cotton
Sol and foliar fungicide
smuts & Rests
Rusts
Carboxin is prepared by reaction of -chloroacetoacetanilide and 2-thiothanol
followed by cyclization. Oxycarboxin is obtained by subsequent oxidation of
carboxin with hydrogen peroxide.
Both are fairly water soluble and are not
46
phytotoxic. They are active against Basicdiomycetes class of fungi causing rusts,
smuts and bunts of cereals and soil fungi Rhizoctonia solani.
Carboxin can be
formulated with other fungicides like thiram, copper oxine.
C) Oxycarboxin
Oxycarboxin has systemic action against rusts of cerals, and vegetables and
seed treatment or soil application can be done.
Carboxin
is
absorbed
and
translocated by plant roots. In water, soil and plants; the compound is oxidiseds to
sulphozide but further oxidation to sulphone was not observed. The sulphoxide is
much less fungicidal and so oxidation causes loss of activity.
The primary mode of
action of carboxin and related compounds probably involves the blocking of succinate
oxidation in the mitochondria of sensitive fungi.
Aminopyrimidines
Some 30 years ago there is a series of 2-amino-4-hydroxypyrimidines had
specific systemic activity against powdery mildews. These structure
activity studies led to development of dimethrinol and ethrinol.
Dimethrinol discovered in 1965, showed outstanding systemic activity by
root application against certain powdery mildews in vegetables and some
ornamentals.
Piperazine, pyridine, pyrimidine, imidazole and
triazole fungicides
These fungicides are considered together because they all show a common
biochemical target, namely synthesis of ergosterol; they are methylation
inhibitors.
Triforine is the only piperazine derivative showing systemic activity
against powdery mildews on cereals and vegetables.
47
CCl3C HNHCHO
N
N
CCl3C HNHCHO
Buthiobate and pyrifenox are pyridine fungicides. Buthiobate is used
mainly in Japan against powdery mildews while pyrifenox controls a wide
range of leaf spot pathogens of fruits and vegetables.
Triarimol,
fenarimol
and
nunarimol
are
pyrimidine
derivatives
introduced by Eli Lilly in the late 1960s. Triarimol has been withdrawn
due to its undesirable toxicological properties. Fenarimol, a systemic and
protective fungicide is used as a foliar spray to control a broad spectrum of
powdery mildews, scabs, rusts and leaf spots. Nuarimol is used against
powdery mildews in cereals.
OH
OH
Cl
N
F
C
N
C
N
N
Cl
Cl
Fenarimol
Nunarimol
Imazalil, the first imidazole agricultural fungicide (1960) is now used as
seed dressing in cereals.
(CH2)2CH3
Cl
CONCH2CH2O
N
OCH2CH=CH2
CH
Cl
Cl
Cl
Cl
CH2
N
N
N
Prochloraz
Imazalil
48
Prochloraz (Boots, 1973) is a broad spectrum fungicide with good activity
against ascomycetes and fungi imperfecti but rather less activity against
basidamycetes.
Triflumizole controls a wide range of pathogens Viz., powdery mildews
and scabs.
Triadimefon [(1-(4-chlorophenoxy) 3,3-dimethyl –1-(1,2-triazol –1yl)
butan-1-one)] TN: Bayleton has systemic activity against a broad range of
plant pathogens effective at rates of 0.1 – 2.0 ppm. This discovery led to
the introduction of several 1,2,4- triazole fungicides.
Cl
O
CH COC(CH3)3
N
N
N
Triadimefon
These fungicides owe their fungitoxicity due to their ability to inhibit
ergosterol biosynthesis. Ergosterol is a major sterol in many fungi where it
plays a major role in membrane structure and function.
Morpholine fungicides
Dodemorph (roses) and tridemorph (cereals) are systemic foliar
fungicides effective against powdery mildews at 0.75 litres ha-1.
CH3
N
O
CH3
CH3 (CnH2n)
N
O
CH3
CH3
n = 10, 11, 12 (60 70%) or 13
Dedemorph
Tridemorph
49
Organo phosphorus fungicides
Today more than 100 OP compounds show fungicidal action. However
relatively few compounds are of practical use as fungicides, Many are
phytotoxic and very specific against fungal species.
One of the first Op fungicides was triamiphos claimed to be the first
systemic commercial fungicide. Since then many compounds were
derived. Pyrazophos TN: Afugan is a foliar systemic fungicide effective
against apple powdery mildew.
Triclophos – methyl is effective against Rhizactonia and other soil borne
diseases as a drench in vegetables and against black scarf and canker in
seed potatoes.
Iprofenfos TN: Kitazin P introduced in 1968, is a systemic rice fungicide
applied as granules in paddy water to control rice blast and it inhibits
mycelial growth in tissues.
Edifenphos is also very effective against rice blast.
O
S P S
OCH2CH3
OP fungicides have shown to block the synthesis of phospholipids. The
reduction in phospholipids alters the membrane structure, increasing the
permeability and consequent loss of vital cellular components and
eventually killing the fungus.
Phenyamides and related compounds
 Metaloxyl – broad spectrum
50
 Furalaxyl – soil drenching
 Benalaxyl – potato blight
 Oxadixyl –with mancozeb to control potato blight
Carbamates
 Prothiocarb – ornamentals
 Propamocarb – Fruits and vegetables
 Cymaxanil – Potatoes and vines
Miscellaneous compounds
Isoprothiolane – systemic fungicide against rice blast
Dithiolane
Formaldehyde (Formalin 40 %) is used as seed dressing and soil sterilant
Substituted
azepenes – systemic fungicidal activity against leaf spot, powdery mildew
and rust diseases.
Recent potent fungicides for future use
Chlorooximes
Very effective broad spectrum fungicide. Substitutients in the oxime moiety plays a
key role in the biological activity.
Cyano-oximes : The most active compound in this group is Cymoxanil
which
controls grape vine downy mildew disease. The analogous compound a propargyll
derivative, is equally effective. After isosteric replacement of the acetylenic triple
bond by the cyanide triple bond the resulting compound showed enhanced activity
against downy mildew
Aryl sulfonylallyl trichloromethyl sulfoxides : A series of 2-aryl sulfonylallyl
trichloromethyl sulfoxides , have been found effective as broad spectrum fungicides
with residual activity against grape downy mildew
CH2 0
II
51
ArSO2C - CH2 - S – CCl3
β methoxyacrylates with oxime ether side chain:
Azoxystrobin, is a well known broad spectrum fungicide which facilitates the
control of a wide range of major plant pathogens. If the central pyrimidine ring is
replaced with an oxime ether moiety, it yields a highly effective fungicide.Analogous
compounds containing a heterocyclic moiety instead of phenyl ring were also
prepared to ascertain the fungicidal activity.
Pyrimidine derivatives: A series of novel 2-anilinopyrimidine compounds, based
on lead compound were synthesized and introduced to the market in 1994. The
synthetic compound mepanipyrim, exhibited excellent activity against grey mould of
vine and vegetables, scab of apple and pear and brown rot of peach.
Biofungicides
These comprise of antibiotics and a few microbes such as Pseudomonas cepacia,
Peniophora gigantea and Trichoderma viride which control a number of fungi
associated with major crops
Mode of action of fungicides
Non systemic
The toxic action of sulphur in the cell is still not clear, however, several theories have
been proposed from time to time. The theory accepted at present is that sulphur acts as
hydrogen acceptor in metabolic systems to form H2S, and in doing so disrupts the
normal hydrogenation and dehydrogenation reactions in the cell. But in case of Cufungicides, the Cu ions precipitate or inactivate the proteins (enzymes of sulphydryl
group) and thus kill the spores.
The mercury fungicides also act either as vapour or in ionic form and destroy
sulphydryl group of (.SH) enzymes. Organomercurials are more toxic than the
52
inorganic mercuric ones due to enhanced lipid solubility facilitating diffusion through
the spore membrane to the site of action.
The mode of action of quinone derivatives may be due to binding of the quinone
nucleus to .SH and -NH2 groups in the cell leading to disturbance in the electronic
transport systems. The activity of captan and related analogues may thus involve the
role of CI and S atoms of the molecule leading to inactivation of sulphydryl group of
enzymes.
b) Systemic
The general mode of action of systemic fungicides is associated with a) interference
with the
electron transport chain influencing the energy budget of the cell, b)
reduction in the biosynthesis of new cell material required for growth and
development of the organism, and c) disruption of cell structure and permeability of
cell membrane.
Benomyl and its related compounds interfere with mitosis in cell division in
angiosperms and fungi. Benzimidazoles, thiophanates, oxathins, phenylamides
(metalaxyl derivatives) influence DNA synthesis and are also mitosis inhibitors. The
triazole group of fungicides interfere with the biosynthesis of fungal steroids and
ergosterol which are important constitutents of the cell wall. Pyrimidine derivatives
inhibit purine biosynthesis and several pyridoxal dependent enzymes. The mode of
action of morpho lines is still not well understood but appears to be inhibition of
sterol biosynthesis. The mode of action of organ phosphorus fungicides is different
from insecticides due to the absence of cholinesterase enzyme in fungi. The widely
accepted theory is that it inhibits permeation through cytoplasmic membrane of the
substrates for chitin synthesis.
The thiono compounds appear to be inactive against fungi and this may be due to
fungus being unable to activate the thiono group to the ox on form by oxidation. The
effect of penetration into the fungal hyphae depends on the polarity of the P=O
group and needs to be balanced by a larger liphophilic group such as, the second
53
thiophenyl group in case of edifenphos, cyclohexyl group in case of cerezin, benzyl
mercaptan in case of kitazin or kitazin-P and the phenyl radical in the case of inezin.
Metabolism
The stability of fungicides in soil depends on chemical structure,
nature of soil and
climatic conditions. In general, the fungicides are not as stable as organochlorine
insecticides. The most versatile dithiocarbamate group of compounds, decompose in
acidic soils to give non-toxic amines and carbon disulfide. Metabolism of alkyltin
compounds in liver microsomal monooxygenase system and in mammals leads to the
following sequence of detannylation (carbon-tin cleavage) reaction
The first step reaction product possessed increased toxicity and potency as
inhibitors to mitochondrial respiration whereas in the subsequent steps the reaction
. R4Sn - R3SnX - R2SnX2 - RSnX3 - SnX.
product possesses less potency and has altered nature of biocidal activity.
.
The carboximides such as captan, folpet, captafol are hydrolysed under neutral and
alkaline conditions. Chloroneb degrades to the
R
.
S
n
54
~
phenolic derivative but reconversion to parent molecule is a microbial process and
this might be the probable reason for long term effectiveness of chloroneb in soil.
The metabolic fate of organophosphorus compounds is quite interesting and a
number of metabolites from kitazin-P were identified from rice plant (p). The major
metabolite was O,O-diisopropyl hydrogen phosphorothioate along with several minor
metabolites such as n hydroxy derivative, diisopropyl hydrogen phosphate and
isopropyl dihydrogen phosphate along with sulfides and disulfides. chlorophenyl
methyl carbonate and an unknown product.
Benzimidazole systemic fungicides like benomyl, thiabendazole and thiophanate methyl are
first converted to carbendazim, an active ingredient at the site of action. These are finally
degraded to non toxic compounds such as aniline, phenyl diamine and cyanoaniline. The
breakdown of benomyl into MBC occurs by intramolecular process in slightly acidic or
neutral media. A hydrogen bond is formed between the free electron pair of the N atom of the
benzimidazole ring and hydrogen on the nitrogen of the butylcarbamoyl side chain, forming
an unstable four membered ring which opens up to yield MBC and butylisocyanate. The
cyanate rapidly forms butylcarbamic acid with water which in turn decomposes into CO2 and
butylamine. The major metabolites of dimethirimol are ethirimol and 2-amino derivative.
Benomyl and thiophanate-methyl, in plants decomposes first to MBC which then gives
photoproducts) like carbomethoxyguanidine (i), carbomethoxyurea (ii) and guanidine
(iii)other minor compounds depending on the nature of the solvents used Piperazine, a
metabolite of the fungicide triforine in barley degraded to non toxic products such as
iminodiacetic acid, glycine, and oxalic acid on the surface of the plants by photodecomposition Chlorthalonil, 2,4,5,6-tetrachloroisophthalonitrile, in benzene solvent was photodegraded
to amonophenyl adduct 3,5,6-trichlorobiphenyl-2, 4-dicarbonitrile, (i) as major photoproduct
55
CHEMISTRY AND PRODUCTION TECHNIQUES OF HERBICIDES
(ONLY REGISTERED) HERBICIDES
Herbicides
are classified based on their method of
use, crop to which applied, mode of action and chemical key structure.
The
major
classification
groups
according
of
the
to
their
(
herbicides
chemical
into
structure
proposed by Silk et. al. (I977) is used mostly with a few alterations.
Organic Compounds
Holalkanoic Acids
The haloalkanoic acids are
very
active
against
grasses inhibiting growth and causing chlorosis and necrosis of the
leaves.
Probably the first herbicide to deal specifically with grass
weeds was TCA (sodium trichloroacetate) marketed by Du Pont and
Dow Chemical in 1947. It may be used as pre-emergence together with
appropriate cultivation techniques for the control of couch grass
(Agropyron repens) and for the control of grass weeds in sugarcane
plantations.
In
1953,
Dow
Chemical
produced
dalapon
(2,2,dichloropropionic acid) also for the control of couch and other
grasses. It may be used in established orchards and for the control of
grasses, reeds and sedges in or near water. Chlorfenprop-methyl,
(methyl – 2 - chloro - 3 - [4- chlorophenyl] propionate), an important
post-emergence herbicide, to deal specifically the wild oats (Avena
fatua) weeds in barley, spring oats and wheat was introduced by Bayer
In 1968 as 'Bisidin'.
1
CCl3COONa
CH3CCl2COOH
TCA
Dalapon
Phenoxyalkanoic Acids
It was during the 1939-45 World War II that the foundations were
laid for the massive development of organic herbicides that was to take
place with the coming of peace and which has continued almost
unabated through the present time.
Phenoxyacetics
The development of herbicides in their present form is due to the
discovery of the 'hormone' herbicides. In the 1920s it was shown that
plants produce a hormone, Indole-acetic acid (IAA) which played a
major part in controlling their growth.
It was not however until the
early days of the 1939-45 war that this knowledge was applied to the
killing of weeds.
Slade, Templeman and Sexton in 1945 while
investigating the role of hormones in plant growth, sprayed mixed
stands of oats and charlock (Brassica sinapis) with - naphthalene
acetic acid (NAA) and found that it killed off the latter but left the
cereal unaffected.
They tried out NAA against a great variety of
dicotyledonous weeds, finding that many of them were killed and
against a variety of cereals finding that all of them were unharmed.
They turned their attention to chemicals related in structure to NAA
and with appropriate substitutions, in an attempt to find some that might
be even more potent than NAA. One of these MCPA was a very active
compound and could kill many weeds selectively at low concentrations.
They tried out 2,4-D (2,4-dichlorophenoxy acetic acid) which had
been first mentioned by Pokorny in 1941 in the U.S.A. though not as a
2
weed, killer. It is therefore difficult to establish precedence for the
precise discovery of 2,4-D as a herbicide (Fletcher, 1974).
Cl
OCH2CO2H
CH3
MCPA
OCH2CO2H
Cl
Cl
2,4-D
Both MCPA and 2,4-D were shown to be potent selective
herbicides In the field and were quickly adopted, the former being
almost exclusively preferred in the United Kingdom whereas in the
U.S.A. 2,4-D was the chemical of choice. They are widely used for
selective weed control in turf and cereals. MCPA and 2.4-D are not
active against all dicotyledonous weeds. in 1944 Amchem introduced 2,
4, 5 -T (2.4,5-trichlorophenoxy acetic acid) as ‘Weedone'. It resembles
2.4-D in its herbicidal properties but is much more active against many
woody species. The compounds 2, 4-D, MCPA and 2, 4, 5-T are
formulated as salts with the alkali metals and amines which are water
soluble. They are also formulated as esters which are water insoluble
but are soluble in oils.
Phenoxybutyrics
The first substituted phenoxybutic herbicide MCPB (4-(4-chloroo-tolyloxyl butyric acid) was introduced by May & Baker in 1954 as
'Tropotox’. It may be used on under sown wheat, barley and oats, on
certain varieties of peas when bushes have ceased to make new growth
in apples and pears as a directed spray. 2,4-DB (4-(2,4dichlorophenoxyl
butyric acid) was introduced as 'Embutox’ by the same company in
1957. Both are formulated as alkali metal and amine salts and as esters.
3
O(CH2)3CO2H
Cl
Cl
2, 4 - DB
Aromatic Acids
The first herbicide based on the aromatic acids was 2,3,6-TBA (2,3.6trichlorobenzoic acid) introduced by Du Pont in 1954 as 'Trysben'.
It is mixed with other herbicides such as MCPA for the control of
annual and perennial weeds in cereals.
Chloramben(3-amino-2,5-dichlorobenzoicacid)was introduced by
Amchem in 1958 as ‘Vegiben' for pre-emergence control of weeds in
soybeans, groundnuts, maize, carrots and other crops.
CO2H
CO2H
Cl
Cl
Cl
Cl
2,3,6-TBA
Cl
NH2
Chloramben
Cl
CO2H
OCH3
Cl
Dicamba
Dicamba (3.6-dichloro-o-anisic acid) was Introduced in 1965 as
'Banvel’ and ‘Mediben’ by Velsicol for both pre and post-emergence
weed control in maize, post-emergence weed control in small grains.
In 1958 Amchem introduced chlorfenac (2,3,6 - trichlorophenyl
acetic acid) as 'Fenac’, a total weed killer for non-crop areas (though it
may also be used as pre-emergence in sugarcane).
4
It has little or no effect on weeds and grasses already grown but It has
the ability to 'fix’ in the soil when weed seeds sprout so that when
developing roots come into contact with the herbicide in the soil these
weeds are killed.
Amides
The members of this group are primarily soil acting especially
against annual grasses.
Many are important seed-germination inhibitors.
Naptalam (N-1-naphthyl phthalic acid) was the first of the group to be
introduced by Uniroyal in 1950 as 'Alanap' for use as pre-emergence on
a number of crops including potatoes and groundnuts controlling annual
weeds and grasses.
CO2H
CONH
Naptalarn
CHCON(CH3)2
Diphenamid
Nitriles
Dichlobenil (2,6-dichlorobenzonitrile) was the first member of
this group to be introduced as 'Casoron' by Philips Duphar in 1960.
It can be used both as pre and post-emergence for control of weeds in
many crops but it is mainly soil acting. It controls germinating annual
weeds and buds of perennial weeds such as Pteridium aquillinum,
Agropyron, Artemisia and Cynodon Spp.
It may be also used for
aquatic weed control.
Chlorthiamid (2,6-dichloro thiobenzamide) is classified here
because it is converted in the soil to dichlobenil. It is toxic to
5
germinating seeds and it is highly effective against a number of hard-tokill weeds such as Tussilago, Aegopodium, Rumex and Equisetum Spp.
It is used for total weed control and for selective control in apples and
gooseberries. It is also used for 'spot' treatment of docks (Rumex Spp.)
and thistles (Cirsium Spp.) and for aquatic weed control in water
courses and dry ditches.
Bromoxynil (3,5 - dibromo - 4 - hydroxybenzonitrile)
‘Buctril’ is used in similar situations as loxynil. Both herbicides show a
high degree of selectivity to graminaceous crops. Both are active within
24 hours of spraying showing necrotic spots on affected leaves. These
spread until the plant dies.
S
C
CN
Cl
Cl
Cl
CN
NH2
Cl
I
I
OH
Dichlobenil
Chlorthiamid
loxynil
Anilides
The type of activity and the range of weed control vary greatly
within this group some being used post-emergence while others are
active through the soil.
Group 1
Propanil (3.4-dichloropropionanflide) was introduced by Rohm
and Haas in 1960 as ‘Stam F-34'. It was formerly manufactured by
Monsanto as 'Rogue'. It is a contact herbicide, used as post-emergence
for the control of annual grasses and broad-leaved weeds in rice and
potatoes.
6
NHCOCH2CH3
Cl
Cl
Propanil
Group 2
In 1965, 1966 and 1969 Monsanto introduced three anilides for
pre-emergence control of annual weeds.
(1)
(-chloro-N-isopropyl acetanilide) as 'Ramrod' which shows a
high degree of specificity for annual grass weeds and certain
broad- leaved weeds in maize, soybeans, sugarcane, peanuts and
certain
vegetables.
(ii)
Alachlor
(-chloro-2'6'-diethyl-
Nimethoxy methyl acetamide) as 'Lasso’ for use in maize,
cotton, soybeans, sugarcane, peanuts and certain vegetable crops
where it shows very good activity against annual grasses,
particularly Echinochloa crus-galli, Setaria Spp. and Digitaria
Spp.
(iii)
Butachlor
(N-[butoxymethyl]-chloro-2',6'-diethyl
acetanilide) as 'Machete' for the control of most annual grasses,
certain broad- leaved species in transplanted rice. In
1974,
Ciba Geigy introduced metolachlor (2-chloro-6'-ethyl-N- [2methoxy-l-methylethyl]
acet-o-toluidide)
as
'Dual',
a
pre-
emergence germination inhibitor, active mainly on grasses for
use in maize, soybeans and groundnut.
7
CH2CH3
COCH2Cl
N
CH2O(CH2)3CH3
CH2CH3
Butachlor
Group 3
In 1969, Shell introduced a herbicide for the post-emergence control
of wild oats namely benzoylprop-ethyl (ethyl N-benzoyl-N-[3,4dichlorophenyl]-DL-alaninate) as 'Suffex’ for use in wheat field and
broad beans and rye grass grown for seed.
Nitroanilines
The first herbicide of this group was trifluralin(ααα-trifluoro-2,6dinitro-N,N-dipropyl-p-toluidine) introduced as 'Treflan' by Eli Lilly in
1960 for the control of annual weeds in cotton, groundnuts and
brassicas.
It is a soil-incorporated pre-emergence herbicide which
prevents the germination of susceptible weed seeds and prevents weed
growth by inhibition of root development.
NO2
F3C
NO2
N(CH2CH2CH3)2
NO2
CH3
CH3
Trifluralin
NHCH(CH2CH3)2
NO2
Pendimethalin
In 1974, American Cyanamid introduced pendimethalin (N-(Iethyl propyl) 2,6-dinitro-3,4-xylidine) as 'Prowl', 'Stomp' and 'Herbadox
for the selective control of annual broad-leaved weeds including some
traditionally difficult species such as Viola Sp., Veronica Sp., and
Gallium
aparine
and
annual
grasses
in
many
agronomic
and
horticultural crops.
8
Nitrophenols
The first organic selective herbicide to be widely used was a
nirtophenol DNOC (4, 6-dinitro-o-cresol).
It was much more efficient as a contact post-emergence selective
herbicide in cereals than sulphuric acid which was widely used till then.
In 1945, Crafts described dinoseb (2-s-butyl-4.6-dinitrophenol), a postemergence herbicide. Introduced by Dow as 'Premerge' for the control
of dicotyledonous annual weeds in peas, Lucerne, cereals, beans and
peas.
OH
O2N
CH3
NO2
ClCH2CH2N+(CH3)3
DNOC
Cl
Dinoseb acetate
Nitrophenyl ethers
Members ofthis group have two benzene rings joined together
through oxygen. They are used as pre-emergence spray to soil surface
to control germinating seeds. They cause shoot inhibition. Nitrofen
(2,4-dichlorophenyl 4-nitrophenyl ether) was introduced by Rohm and
Haas in 1964 as 'Tok E-25' for use in cereals as pre-emergence to the
crop. It is most effective when applied as a thin layer on top soil, as
activity is quickly lost when it is incorporated into soil. It may also be
used on a number of vegetable crops. In
1980,
Rohm
and
Hass
introduced oxyfluorfen (2'-chloro-aaa trifluoro-p-tolyl 3- ethoxy-4nitrophenyl ether) having mainly pre-emergence activity both on grass
and dicotyledons but it can also be used as post-emergence.
It is safe on cotton and soybeans in dry areas. Transplanted onions are
tolerant and wheat, corn and tomatoes are unaffected.
9
OCH2CH3
F3C
O
NO2
Cl
oxyfluorfen
Carbamates
In 1951, Columbia Southern introduced chlorpropham (isopropyl
3- chloro carbanilate) as a pre-emergence herbicide for the control of
many weeds in bulb crops and some vegetables. It may also be used as
a sprout inhibitor in potatoes.
One major problem facing farmers had
long been the control of annual grasses such as wild oats (Avena fatua)
and black grass (Alopecurus myosuroides) in cereals. The introduction
of post-emergence barban (4-chloro but-2ynyl 3-chlorocarbanflate) as
'Carbyne' by Spencer in 1958 was a major step.
Applied when the
majority of the wild oats are in the 2-leaf stage it gives effective control
without harming seedling wheat, barley and a number of other crops
including lucerne, beans and sugar-beet.
NHCO2CH(CH3)2
Cl
Chlorpropham
Thiocarbamates
EPTC (S-ethyl-N.N-dipropylthiocarbamate).'Eptam', was introduced
by Stauffer in 1954. It kills germinating seeds, a number of annuals and
inhibits bud development in the underground organs of perennial weeds
such as couch grass (Agropyron repens) and sedges (Cyperus Sp.). It
may be used soil incorporated 3 weeks before planting potatoes, field
10
beans, sugar beet and others.
'Avadex’
Monsanto
introduced
(S-2,3-dichloroallyl-N,N-di-isopropyl
di-allate
(thiocarbamate)),
as
a
volatile herbicide for pre-plant control of Avena fatua and Alopecurus
myosuroides in brassica and beet crops in 1960; and tri-allate (S[2,3,3’- trichloroallyl]-di-isopropyl (thiocarbamate)) in for the control
of these grasses and others in cereals and peas.
In 1970 thiobencarb (S-4-chlorobenzyl diethyl thiocarbamate)
was introduced It is an important herbicide for the control of weeds in
rice showing very high selectivity between rice and barnyard grass
(Echinochloa crus-galli).
In addition it controls many other grass
cyperaceous and broadleaved weeds.
(CH3CH2)2NCOSCH2
Cl
Thiobencarb
Substituted Ureas
Diuron (3-[3,4-dichlorophenyl]-1,1-dimethylurea) as 'Karmex’,
was introduced by Du Pont in 1954 and Fenuron (I,I-dimethyl-3phenyl urea) as 'Dybar' was introduced in 1957 and is used for the
control of woody plants by basal application.
Fluometuron (1, I –dimethyl-3-[α-trifluoro-m-tolyllurea) as 'Cotoran'.
was introduced by Ciba Geigy and is used for the control of weeds in
cotton.
Another very important herbicide for the control of annual,
grasses including Alopecurus myosuroldes, Avena fatua and Poa annua
and many annual broadleaved weeds in cereals was isoproturon (3-[4isopropyl-phenyl]- 1, I –dimethyl urea) marketed by three companies -
11
Hoechst (as 'Arelon'), Ciba Geigy (as 'Graminon') and Rhone-Poulenc
(as 'Tolkan') in 1972.
NHCON(CH3)2
Cl
(CH3)2CH
Cl
Diuron
NHCON(CH3)2
lsoproturon
Heterocyclic Nitrogen Compounds
Triazines
In general triazines have little effect on germination and they are
taken up by the roots or leaves. Due to an inhibition of the Hill reaction
of photosynthesis, affected plants turn yellow and necrotic symptoms
develop.
With a few exceptions, the symmetrical triazines have got
substituted amino groups at two of the carbon atoms while the third
carbon has a chloro, a thioether or a methoxy function.
The
chloro
compounds (CI) end in azine, the thioethers (-S-) end in tryne (e) and
the methoxy ones (CH30) in ton.
In the list of herbicides which
follows all were introduced by Ciba Geigy unless stated otherwise.
The first commercial triazine, simazine (2 – chloro - 4, 6 - bis
[ethyl -amino] - I,3,5 -triazine) was introduced as 'Gesatop' in 1956 for
the selective residual pre-emergence control of a great many annual
grass and broadleaved weeds in a variety of deep-rooted crops
(including citrus fruits, coffee, tea and cocoa), due to its low solubility
in water (3.5 mg I-1 at 20C). It is also used for the control of most
annual and perennial weeds in non-crop areas.
It is remarkably
selective for use on maize because of the ability of this crop to degrade
it non-enzymically to the non-active hydroxy derivative.
12
Cl
NHCH2CH3
N
N
N
NHCH2CH3
Simazine
The
second
introduction
atrazine
(2-chloro-4-ethylamino-6-
isopropylamino-1,3,5-triazine), introduced as 'Gesaprin’ and 'Primatol
in 1958, is both foliar and soil acting being taken up both by leaves of
emerged weeds and by the roots of weed seedlings emerging after
spraying. In maize, where it is also degraded in, a manner similar to
simazine, it is preferred to the latter especially in dry years. Being more
water soluble (30mg I-1 at 20C) it is more suitable for the dry soils on
which this crop is grown where it will effectively control couch grass
(Agropyron repens) and other perennial grasses. It is also used in roses,
for selective use in coniferous forests and for non- selective use on noncrop land and industrial sites.
Cl
NHCH2CH3
N
N
N
NHCH(CH3)2
Atrazine
Pyridines
In
1957
and
1958
I.C.I.
introduced
two
very
important
bipyridillium quaternary herbicides. Both are broad spectrum, rapidly
acting causing wilt and desiccation, and are translocated to a certain
extent.
Diquat (1, I'-ethylene-2,2'-bipyridillium ion formulated as
dibromide) under various trade names 'Reglone', Weedol', 'Path clear' is
13
used for potato haulm desiccation, for seed crop desiccation and for
aquatic weed control.
'Aquacide’.
The Chapman Chemical markets it as
Paraquat (1,1'-dimethyl-4,4'-bipyridilium ion formulated
as dichloride) as 'Gramoxone' destroys photosynthetic tissues and Is
used for a variety of purposes Including stubble cleaning, inter-row
weed control, desiccation of various crops and killing out of old
pastures which can then be resown without ploughing.
It is very fast acting, the first effects being noticeable after a few hours
and kill is usually completed in 3-4 days. It is quickly absorbed on to
soil (particularly clay) particles so that sowing can follow soon after
application.
+
N
CH3 N+
Diquat
+
N
2 Br
+ N CH3
2 Cl
Paraquat
The Dow chemical has Introduced three foliar-applied, selective,
growth-regulatory herbicides which produce symptoms on susceptible
plants very similar to those produced by the auxin type herbicides,
namely tissue proliferation, epinasty, leaf curling and production of
adventitious roots.
Pyramidines (uracils)
These herbicides are derived from uracil. They are applied to the
soil and are absorbed via the roots but eventually inhibit the 'Hill’
14
reaction of photosynthesis causing chlorosis and death. All the three
have been introduced by Du Pont.
Bromacil (5-bromo-3-s-butyl-6-mcthyluracil) was introduced in
1963 as 'Hyvar X’ a foliar and root-acting residual 'total’ herbicide for
use on non-agricultural land; and as a selective herbicide in citrus and
pineapple plantations. It is active against a wide range of annual and
perennial weeds including established couch (Agropyron repens) and
bent grass (Agrostis Sp.).
CH3
H
H
N
O
CH3
N
N
Br
O
CHCH2CH3
N
Cl
CH3
O
O
C(CH3)3
H
N
O
N
O
Bromacil
Terbacil
Lenacil
Unclassified Heterocyclic Nitrogen Compounds
This group of compounds has a variety of chemical structures and
types of herbicidal activity. Aminotriazole (1,2,4-triazol-3-yl amine) as
'Weedazol’ was introduced by Amchem in 1955. It is a non-selective
herbicide, absorbed by both roots and foliage; it is readily translocated
being active against annual and perennial weeds where it inhibits
regrowth from buds.
15
Organophosphorus Compounds
The organophosphorus compounds include: (1) bensulide (0,0diisopropyl-S-2-phenyl-sulphanylaminoethyl
phosphorodithioate)
which was introduced by Stauffer in 1964 as 'Prefair' for pre-plant preemergence use on cucurbits, brassicas, lettuce and cotton, and as
'Betasan' for pre-emergence control of annual grasses and broad-leaved
weeds
in
lawns.
(2)
Piperophos
(S-2-methylpiperidino-carbonyl
methyl-0,0-dipropyl phosphorodithioate) was introduced by Ciba Geigy
in 1969. It can be used pre-emergence in rice, maize, cotton, soybeans
and groundnuts for the control of many monocotyledonous weeds
including Cyperus Sp., Echinochloa Sp., Trianthema portulacastrum
and Monochoria vaginallis.Glyphosate (N-[phosphonomethyl] glycine)
a derivative of the amino acid, glycine, was introduced by Monsanto as
'roundup' in 1971. It is used post-emergence and is rapidly absorbed by
the leaves and translocated from vegetative parts to underground parts,
rhizomes or stolens of perennial grass and broad-leaved weed species
giving good control of both above-ground and underground organs
Agropyron repens is very sensitive.
Glyphosate is inactivated on
contact with the soil. It provides excellent weed control in pre-tillage of
post-harvest treatments of annual crops or when applied as a direct
spray in woody crops such as vineyards, deciduous fruit, rubber, coffee,
citrus, tea and oil palm.It can also be used in non-agricultural areas and
for bush control in forestry.
16
S
N COCH2SP(OCH2CH2CH3)2
CH3
O
HO2CCH2NHCH2 P(OH)2
Piperophos
Glyphosate
Sulphonyl ureas
The sulphonylureas are a new class of herbicides introduced by
Du Pont in 1982 and within a comparatively short period they have
made a major impact on weed control technology. They are remarkably
active compounds, selectively controlling many dicotyledonous weeds
in cereals at dose rates of grams rather than kg ha -1.
In the general
structure of sulphonylureas, herbicidal activity is usually restricted to
those derivatives containing a methyl or methoxy group substituted in
the 4-or 6-position of heterocyclic nucleus.
The structures of some
commercially useful sulphonylurea herbicides are illustrated.
Compound
n
X
R
Y
0
CO2CH3
H
OCH3 CH3
DPX-F 6025
0
CO2CH3
H
Cl
DPX-F 5384
1
CO2CH3
H
OCH3 OCH3 CH
Sulfometuron
methyl
W
Z
CH
OCH3 CH
17
Chlorsulfuron
Metsulfuron
methyl
0
Cl
H
CH3
OCH3 N
0
CO2CH3
H
CH3
OCH3 N
H
OCH3 OCH3 N
OCH2
Triasulfuron
0
DPX-15300
0
CO2CH3
CH3
OCH3 CH3
N
0
COCH3
H
OCH3 CH3
N
Bensulfuron
methyl
CH2Cl
The sulphonylureas are prepared from the appropriate aryl
sulphonyl chloride. The sulphonylureas are potent inhibitors of plant
growth; seed germination is not generally affected but subsequent root
and shoot growth is severely inhibited in sensitive seedlings.The death
of susceptible plants is accompanied by chlorosis, necrosis, vein
discolouration and death of terminal buds.
Sulphonylureas are
generally formulated either as wettable powders or water dispersible
granules, and the compounds are readily absorbed by both the roots and
foliage of plants. They are translocated via the xylem and phloem. The
potency of the sulphonylureas is outstanding: conventional herbicides,
e.g. triazines require dose rates of 0.5 to 2.0 kg ha -1 but with
sulphonylureas rates of only 0.002 kg ha-1 are often effective.
CO2CH3
OCH3
N
CH2SO2NHCONH
N
OCH3
Bensulfuron methyl
18
Sulfometuron methyl is broad spectrum selective herbicide against
broad-leaved and some grass weeds in cereals at 4- 10 g ha-1, which can
also be applied as a total herbicide. Chlorsulfuron controls the majority
of broad leaved weeds in cereals at 10-40 g ha-1; it acts as a residual soil
herbicide with a half-life in soil of 1-2 months and is degraded- in soil
by hydrolysis to inactive compounds. The herbicidal activity can be
increased by addition of non-ionic surfactants to chlorsulfuron.
The
other compounds are used as selective herbicides against broad leaved
weeds
in
cereals at
very
low
dose rates (10-20
g
ha-1).The
sulphonylureas have low mammalian toxicities (LD50 oral toxic rates
of approximately 1000 mg kg-1).
Imidazolines
The imidazolines represent a new class of herbicide developed by
American Cyanamid in 1963 for control of mono and dicotyledonous
weeds. The structural formulae for some important herbicides are given
variation in the z-aryl substituent on the imidazoline ring results in
considerable
variation
in
the
spectrum
of
herbicidal
potency.
Imazaquin and imazethapyr are effective as pre and post-emergence
herbicides at doses of 75-250 g ai ha-1 to control grasses and
dicotyledonous weeds in soybeans and other leguminous crops.
The most direct preparative route to the imidazolines is via an 0dicarboxyhc and anhydride and an α-aminocarboxamide. The initial
product is extracted with aqueous sodium hydroxide and the final
cyclisation is affected by heating. The imidazolines have low
mammalian toxicities (LD 50 oral to rats > 5000 mg kg-1).
19
(CH3)2CH CH
3
N
O
N
N
H
CO2H
(CH3)2CH
N
N
CH3CH2
Imazapyr
CH3
O
N
H
CO2H
Imazethpyr
Herbicide Protectants or Antidotes or Safeners
A new development in herbicide usage Is the use of protectants or
antidotes in order to protect the crop plant from possible damage by a
herbicide (Fryer, 1977).
This means that ft may be possible to use
certain herbicides on crops that would normally be affected by the
herbicide.
Safeners fall into four major classes
(a)
Naphthopyranone derivatives, e.g. naphthalic anhydride (NA) and
phthalic anhydride (PH4). For activity, the presence of the dicarboxylic
anhydride group and at least one attached aryl group appear essential.
20
Cl2CHCON(CH2CH=CH2)2
NA
b)
Chloroacetamides, e.g. allidachlor CDAA and dichlormid DCCA.
The presence of the dichloracetamide moiety gave maximum safening
activity against maize.c)
Oxime ether, e.g. cyometrinil, CGA - 133205
and the pyridine aldoxine ethers.d)
2,4-Disubstituted
5-thiazole
carboxylates e.g. the most effective member of this group was the 2chloro-4trifluoromethyl derivative, flurazole.
Naphthalic anhydride or dichlormid protected maize, sorghum and
rice injury by chlorsulfuron. Use of NA also protected the crops from
damage by imidazolines e.g. imazaquin.
formulated as seed dressings; eg.
Several safeners can be
NA protects rice against alachlor,
allowing this herbicide to be used for the selective control of the weeds
in rice; cyometrinil protects sorghum against metolachlor.
Safeners are generally most effective when mixed with the
herbicide and applied to the soil. The protection is more marked with
maize, sorghum and rice.
There has been only limited success in
protecting broad leaved crops. The precise knowledge of the mode of
action of safeners remain incomplete; however the action of NA in
counter
acting
the
phyto-toxicity
of
chloroacetainilide
and
thiocarbamate herbicides to maize demonstrated that the safener
markedly
increased
the
levels
of
glutthione-S-transferase
and
glutathione in treated maize seedlings which are involved in the
detoxification of herbicides.
The mode of action of safeners with
21
sulphonylurea herbicides in wheat and maize also appears to be
associated with enhanced metabolism to herbicidal inactive product
Formulation
A pesticide.formulation can be defined in a broad sense as a physical mixture of one
or more biologically active chemicals with inert ingredients in a definite proportion so
as to make it more effective, safe, economical and easy to use. It is a process through
which a small quantity of an active ingredient (a.i.) is formulated into a final product
to be used by the farmers/consumers to control insect pests and diseases. The prime
purpose of formulation is the dilution of high concentration pesticide down to an
applicable level at which it is toxic to target pests but non toxic to non target species
and environment.Pesticide formulations are generally classified into liquid or dry form
. The conventional liquid formulations can be emulsifiable concentrate, oil
concentrate, oil solution and aqueous concentrate while the dry powder type
formulations include dust, water dispersible powder, granules and water soluble
powder (SP). While these formulations effectively and efficiently Control plants
pathogens, insect pests and weeds, they pose a potential hazard during their storage,
transportation and application. Many liquid formulations are highly inflammable and
being petroleum based products amount to resource depletion. On the other hand, the
dust formulations pollute the air and ground water and endanger the existence of nontarget organisms including man. A considerable amount of these preparations miss the
target and amount to substantial waste. It has been estimated that even with careful
appiication only 10-20% of the dust and 25-50% of the spraysare deposited on the
plant surfaces and rest pollute the environment. This calls for further improvement in
the application technology and developing more ecofriendly formulations. A few new
safe or eco-friendly formulations have been developed recently. Among new solid
formulations, one can mention driftless-dust, dry flowables or dispersible granules,
floating granules, fine granules and encapsulated granules with controlled release. The
new liquid formulations developed include wet flowable (suspension concentrate),
22
aqueous emulsions, microemulsions and suspoemulsions
Liquid formulations
a) Oil concentrates (OC) contain high concentration of active ingredients. They can
be used undiluted for ultra low volume (UL V) applications but can also be diluted
conveniently with hydrocarbon solvents as and when needed.
b) Emulsifiable concentrates (EC) are similar to oil concentrates but in addition
contain a surfactant or emulsifier for quick and easy dilution with water for spra.y
application. The solvent system must be immiscible with water to produce an
uniform emulsion lasting throughout the spraying period. Commonly used
solvents are xylene and solvents of aromatic naphtha type (aromax) or aliphatic
kerosene type. Solvents may be chosen based on flash points so as to reduce
possible risks of fire during transportation and use. This is a most convenient and
popular form of formulation usually available for most of the recommended
pesticides.
c) Aqueous concentrates (AC). Some pesticides readily dissolve in water. Salts of
certain herbicides are soluble in water. They are formulated as AC concentration
and are generally expressed in terms of amount of acid equivalent per unit
volume.
d) Oil solutions (OS) contain pesticides in low concentration usually below 5% by
weight. These formulations are generally used for household or institutional
insect/pest control measures. These are odourless, colourless and contain nonstaining high flash point solvents to minimise the fire hazard.
e) Invert emulsifiable concentrates (IEC). These formulations differ from normal
EC by the fact that their dilution with water provides an emulsion in which the
external or continuous phase of the emulsion is the oil phase whereas the internal
or discontinuous phase of the emulsion is water. The oil soluble herbicidal esters
are in general formulated as lEC. These formulations have several advantages
over normal EC as they require less quantity of water at the time of dilution and
23
also oil which has a low vapour pressure due to which the evaporation of
continuous phase is minimum.
Dry formulations
Conventional dry formulations include dust, granules and wettable powders which are
mixed with water during application.
a) Dust bases or concentrates are dry, free flowing powder containing a high
concentration of active ingredients varying from 25 to 75 per cent. These are
mixed with a suitable inert material before field application.
b) Dust. These are finely powdered pesticides which are formulated to field strength
varying
from I-tO per cent depending upon the potency of the pesticide and the
rate of application.The, particle size is usually less than 30 um diameter. The use of
dust has been limited by their tendency to drift downward and they are mostly used
for seed dressing.
c) Wettable powder (WP). These are similar to dust bases except that they are
formulated for dilution with water into final spray. The qqality is judged by the
rapidity of wetting and stay in suspension when mixed with water for field
application. The proper choice of wetting agents is to enhance the wetting power
and good suspensibility which can be maintained by reducing the particle size.
Surfactants of the dispersant class are added to prevent the agglomeration of the
particles resulting in sedimentation. WP is frequently used for the slurry treatment
of seeds. In general wettable powder formulations are not compatible with other
types of formulations specially with emulsions causing sedimentation.
d) Granules (GR). The granular pesticides are different from powdered pesticides
according to the mesh size. The mesh size starts from 4 mesh (U.S. standard) to 80
mesh. The granular pesticides are generally free flowing and do not cake during
storage and there is no problem of drift during application, hence easy to handle.
Since the activity depends on the release of the a.i., the granules should have fast or
slow disintegration after entering the system. Granules are more effective as
24
prophylactic application when weather conditions are unfavourable for spray
New generation formulations
There are many problems associated with conventional formulations of pesticides. WP
formulations are dusty and not easy to measure. Further, the dust clouds from WP are
not only very fine but also have high concentration of pesticides endangering human
health and contaminating the environment. The organic solvents used in EC
formulations,enhance the percutaneous toxicity of the pesticide by altering the dermal
penetration. Moreover these are inflammable and expensive. Due to these
disadvantages, the ecofriendly new generation formulations have been developed
during the last decade. The most important of these are discussed in the following text.
i) Water-dispersible granules (WG). It is an improvement over wettable powder
preparations. (WP). The product looks like small spheres, flows like a liquid and be
measured by volume. The product may be sometimes called as dry flowable (DF).
Most of the sulfonylurea herbicides are now available in this formulation. For safer
use, these products are now available in water soluble polyvinyl alcohol bags in premeasured quantity to avoid direct contact with the workers
Water emulsifiable gels (GL). It is an improved version of emulsifiable
concentrate (EC). These gel formulations can be packaged in water soluble
polyvinyl alcohol bags in pre-measured quantities to avoid exposure to pesticides.
iii) Floating granules. These formulations are characterised by the release of the
active ingredient from the granules floating on the water surface and functioning
nas an efficient aquatic pest control measure.
iv) Fine granules (ordinary & FG). Both these formulations are prepared with active
material like systemic pesticides which may be absorbed and translocated through
the plant tissue. The ordinary granules have particle size range of 105-297 µm
(150-48 mesh) whereas 90% of the fine granules lie in 62-210 µm (250-65 mesh)
range. These formulations are suitable for use in situation where-drift of the dust
25
needs to be checked. These formulations are very efficient and environmentally
safe, convenient to handle and less hazardous to workers.
v) Dust driftless (DL-dust). This formulation overcomes the drift problems
associated with the conventional dusts. It has mean particle diameter of 20-30 µm
which differentiates it from the conventional dusts having mean diameter of only I
0-12 µm. It has good flowability which enables the coverage of lower side of the
leaf also. It is environmentally safe, floats less during application and has good
coverage of the target. Many organophosphate, carbamate compound. insecticides
are recently being formulated as DL-dust,for-use in Japan.
vi) Controlled release formulations (CR) this formulation is a relatively new
development aimed at providing controlled release of a.i. for specific types of
biological actions. The controlled release may be defined as a method by which an
active agent is released on to an intended target at a slow rate so that the
contamination of environment is minimised. The primary aim of all the CR systems
is the employment of a suitable natural and biodegradable polymer to act as a rate
controlling device, container or membrane, for the a.i. to be released at the desired
rate helped by the moisture or soil microorganisms. The rapid progress in CR
technology has been possible because of the fast advancement in polymer science
which provided materials for preparation of CR. Today a variety of natural and
biodegradable synthetic polymers and elastomers, often suitably modified by copolymerization, cross-linking, degradation and chemical reactions, are being
employed in this technology'. In general. there are two types of CR Chemical type-a
chemical linkage exists between a.i. and polymer and (2) Physical type-where no
chemical linkage exists. These can be further classified as :a) Micro and Macro
capsules, b) Hollow fibres, c) Monolithic matrices, d) Laminated structures
a) Microcapsules [Encapsulated Suspension (CS)] are small particles of solid
or liquiddroplets of the a.i. enclosed in a thin polymeric wall material spherical in
shape (5-50 microns) and normally dispersed in water for use. The capsules bigger
26
in size are known as macrocapsules.
b) Hollow fibres. The utility of pheromones has been realised through the use of
well defined controlled release delivery system. The hollow fibres comprise of fine
capillary tubes sealed at one end which hold the liquid a.i. inside it by capilliary
action. The device is found suitable as insect attractant baits as well as insect
mating disruption aids.
c) Monolithic matrices are made by incorporating a.i. into a polymeric or
elastomeric matrix by extrusion, injection molding or casting. These are used for
the preparation of CR larvicides, herbicides and molluscicides.
d) Laminated structures consist mainly of three layers of laminated plastic
material. The
control layer is a reservoir for the a.i. and is sealed between two
outer plastic layers to control its release. The pheromone is thus released by
diffusion from the reservoir through the membrane. The rate is controlled by the
membrane composition and thick ness.The advantages of these formulations
include increased persistence of biological activity, reduced phytototoxicity, low
mammalian toxicity with reduction in environment contamina. tion. The highly
toxic pesticides formulated as CS are mainly parathion, phorate and aldicarb.
vii) Flowable (Suspension concentrates OF/SC). This involves dispersion of
micronised tech. nical grade solid pesticide in water. Hydrolytically stable, high
melting point, friable crystal compounds having low solubility in water are
formulated in this form. It has several advantages over the EC formulations and
WDP such as non-dustiness, reduced operational hazards, minimum nozzle
blockages, easier ULV application, non-inflammability, easy handling and
transportation, low phytotoxicity and better biocidal activity. It is thus suitable
for both soil and foliage application.
viii) Concentrated emulsions (emulsion concentrate, EW). This formulation is
produced by dispersing or emulsifying the technical grade liquid pesticide in
water or dissolving in minimum quantity of solvent. The advantages of this
27
formulation are minimum use of solvents, reduced operational hazards and
toxicity to mammals, less phytotoxicity and enhanced bioactivity due to fine
droplet size.
ix) Microemulsions. This formulation is transparent liquid forming micelles of
liquid pesticide (technical). It requires. selection of suitable solvent and surfactant
package. Thermodynamically stable microemulsions provide an alternative
approach to conventional kinetically stable, coarse emulsions. These preparations
have low phytotoxiciy, are non-corrosive, do not vaporise at ambient conditions
and have almost no toxicity to mammals, fish and birds.
x) Suspoemulsions (SG). This comprises of suspension of a pesticide emulsified in
water as the dispersing medium. The preparation and stabilisation of this multiple
phase suspension concentrate is rather a difficult task. The oil phase containing
the highest possible content of a.i. (ideally a liquid) having no water solubility
product, exists side by side in a dispersed solid phase whose a.i. is insoluble in
water as well as in the dispersed oil phase.
xi) Ultra-low volume (UL V). An ULV undiluted formulation. is more potent per
unit volume for a large scale aerial spray on forest or river terrain. This
formulation must contain sufficient anti-evaporant to prevent the evaporation of
spray droplets during their free fall to reduce drift and the formulation must be
non-corrosive to aircraft and spray equipment.
xii) Briquitte BR is a solid block formulation and is made by mixing the a.i. with
low density, inert granules and binding agents. It is convenient for the manual
application of pesticides in aquatic environment where spray application is
ineffective.
xiii) Smoke. The pesticide is mixed with an oxidant and combustible material which
generates large amount of hot gas. A special form of smoke generator is the
mosquito coil which is used as a mosquito repellent.
Biopesticide formulations
28
The types of formulations applied to microbial agents are quite similar to that of
chemical pesticides. The aim is to produce a stable product that exhibits optimum
effectiveness and economical use for a particular environment and circumstances,
with special reference to shelf stability. There in difficulty is that the hydrophobicity
and particulate nature of microbes effects the wettability, :spersibility and
suspensibility of the preparation. In general the microbials are much more Rsitive to
temperature and their half life is short. The preparation based on B. thuringiensis and
dear polyhederosis virus remain stable only under freezing temperatures. The stability
of the otozoan N. locustoe is extremely poor. Amongst all microbials Bt is most
widely used because of its stability.
The stability of the formulation also depends on field application. Under aerobic conditions,
the liologically active protein may be inactivated by the cleavage of the peptide chain . This
happens due to the formation of OH radicals which react with the biomolecules yield peroxy
radicals and oxyradicals which ultimately decompose to fragments. .
Attempts to block the free radical formation by various means, like encapsulation have
successlly enhanced the microbial persistence. The research on improving the field
persistency of microbial agents is still under investigation.
Formulation of microbials available for general use are, water dispersible granules
DG), wettable powder (WP), granules and dust. Liquid formulations are suspension
concentrates (L:C), ultra Ibw volume (ULV), oil miscible flowable concentrate (OF)
and briquette (BR)
The quality control of formulations can be defined as an effective mechanism of coordinating the maintenance and improvement of quality at different stages of
formulation and production, so that the finished product with assured quality is made
available to the consumer at competitive price.The control has to be effected at every
stage of the manufacturing process starting from the raw! material, processing to
packaging. This can be done by defining the quality of the raw material I and devicing
29
quick analysis methods so that the product can be tested at crucial stages along the
downstream process. In most cases the suppliers of raw materials follow their own
specifications. If the supplier is reliable, the raw materials can usually be accepted on
a warranty basis, from the supplier. But still it is advisable to carry out, on the spot
checks to determine the quality. It is observed that the presence of unknown
contaminants in the raw materials can cause degradation and sometimes enhance
toxicity in the pesticide formulation. Excess acidity, alkalinity or traces of moisture
Quality
might aggravate the problem. Frequent checks should be made on raw materials after
procurement to keep the contaminants within the permissible limits. In case dustiness
arises in the formulation, tl1e screen size of clay granules must be checked. Dust
diluents and granules must also be examined for the presence of foreign matter such
as nails, twine from bagging operations, sticks, stones or any material likely to
interfere with the product application.Some insecticides which are stable in technical
form and in liquid formulations show marked decomposition/degradation if the
commercial mineral carriers are used in dust and water dispersible powder
formulations. The carriers like clay diluents and emulsifiers must be pre-tested before
use in formulations. The shelf life expectancy and satisfactory physical characteristics
of a particular formulation depend on the quality of carriers, diluents and emulsifiers.
It has been observed that traces of metallic ions and metallic oxides, if present on the
surface of carriers may enhance degradation of pesticides after prolonged storage
conditions. Deactivators may be added in these cases in order to counter effect the
situation and with the hope to improve the quality of the product. Specifications of
solvents with reference to water, acidity or alkalinity, colour, specific gravity also
must be examined before use.The assay results of the technical grade pesticides
supplied by the manufacturer must be studied thoroughly before preparing the
formulations. Information on formulation compatabilities and uses should also be
procured from the suppliers.
30
The specifications of packaging material are also important and must be clearly
defined. Since moisture content is important for stability of dusts and water
dispersible powders, there should be a layer of material in the bag wall as moisture
trap. Care must be taken to use polyethylene bottles for packaging to keep away the
air moisture. Sometimes polyethylene bottles and caps may be affected by the solvents
or components of the formulations. These are also to be inspected for chips, cracks or
brakes. Many liquid pesticides of technical grade and formulations are found unstable
when kept in metal container because of interactions. In order to prevent this, a nonreactive resin material is coated inside the metal container before packaging.
Pesticides
requiring
refrigeration
should
be
stored
at
about
0-5°C.
Organophosphorus pesticides during storage under cold conditions show signs of
condensation or precipitation. Such preparations which require refrigeration, must be
allowed to reach room temperature before removing the cap for use. If instrumental
method is used, the analyst must obtain a standard of performance for reference
material for purpos~ of comparison specially retention time, number of peaks and
instrument response if the same quantity of standard is used.The writing and printing
of labels on packages should conform to all government and international rules and
regulations. Instructions for use, precautions for storage and use of specific antidotes
in case of mishandling must be clearly printed on the packages before it goes to the
market.In recent years the problem of cross contamination or accidental mixing of two
pesticides in the formulation has been reported. The presence of a herbicide in an
insecticide formulation for use on an agricultural crop might cause the loss of some or
the entire treated crop in the field. In order to prevent cross contamination it is
necessary to keep the equipment in the plant and operating lines thoroughly clean.
Flushing with steam or hot water before switching ove"r to another formulation may
help to a great extent.
31
Some factors which influence the quality of the formulations are
listed below:
Surfactants. Surfactants reduce the interfacial tension between immiscible liquids
or between liquids and solid surfaces. In pesticide formulation, the characteristics
of the surfactant are easy wetting dispersion and emulsifiability for water
dispersible powders and emulsifiable concentrates. The chemical structure of the
surfactant comprises of two parts, one is oriented towards one phase while the other
faces the second phase. If the system is oil and water, one portion of the molecule
should be soluble in oil and the other i... water. The surfactant molecules are
generally non ionic and anionic types. In formulating pesticides both anionic and
non-ionic surfactants are important. The wetting agents used in water dispersible
powders (WDP) are usually of the. anionic type, Among them, the largest number
are probably sodium salts of alkyl benzene sulfonates.Dispersing agents used in
addition to the wetting agents in WDP to impart some electrical charge to all the.
particles in suspension. The effect is that the individual particles repel each other
and consequently, resist flocculation and agglomeration. Dispersants used in the
WDP may be of lignosulfonates type with cations such as sodium or calcium
sulphonatesof polymeric phenols. Mostly these are dry, powdered solids which
facilitate their incorporation in WDP.
b) Emulsifiers. The selection of proper emulsifiers to maintain the quality of
formulations is very important. In order to select the proper emulsifier, the
manufacturer prefers a paired emulsifier system. The paired emulsifier system
represents a blend of anionic and non ionic emulsifiers with different hydrophilic
and lipophilic characteristics. One part of the pair with lipophilic natu~ emulsifies
easily with the pesticide solvent while the other part favours the emulsification of
the hydrophilic pesticide solvent system.
32
Adjuvants. These are added to pesticide formulations to improve quality,
effectiveness and user safety. A variety of adjuvants are added to perform different
functions. The penetrant additives help the formulation to penetrate through the
protective lipid membrane of the insect pests and enhance the rate of reaction of
the pesticid,e at vital reactive sites.
d) Deactivators. The carriers and diluents of dry formulation such as clays and
minerals have the property of surface acidity which catalyze the deactivation of
pesticidal molecules. Thus deactivators are generally employed organic molecules
such as ethers, ketones, esters, amine and glycol, which contribute a pair of
electrons to the acid sites of the catalytically active substance to reduce
decomposition.
e) Anti-caking agents. Caking sometime occurs during storage of dry formulations
such as dust concentrates, WDP and granules due to coalescence of individual
particles to form solid hard lumps. Diatomaceous earth or fine synthetic silica and
silicates are added as anticaking agents.
f) Dry lubricants. In order to improve the flow of the formulations, dry lubricants
such as
graphite, soapstone, talcs and metal stearates are added.
g) Protective colloids. Protective colloids derived from polymeric materials like
polyvinyl pyrrolidine, sodium carboxymethyl c~llulose and collagen are added to
improve the quality and inhibit the agglomeration and sedimentation of liquid
formulations or aqueous dilution of WDP formulations.
h) Stickers.
These are adjuvants sometimes added to spray tank prior to the
pesticide application
in order to prevent the run off of spray solution when
applied to crops.
i) Anti-dusting agents. WDP and granular formulations contain a.i. in finely
powdered form hazardous to operators to minimize undesirable effects, antidusting
agents such as glycerine are added to prevent the dustiness.
33
j) Anti-foaming agents. To prevent excessive foaming during dilution of the
formulation,antifoaming agents such as liquid silicone or higher homologues of
alcohol are added toreduce froth formation and maintain proper spraying conditions
by the operator
Methods of analysis
The analytical methods to determine the active ingredient (a.i.) content are readily
available with Collaborative International Pesticide Analytical Council (CIP AC) and
World Health Organisation (WHO). The conventional methods of analysis of
formulations
are
volumetric,
potentiometric,
gravimetric,
colorimetric
and
spectnophotometric. These methods are still being used commonly in spite of some
limitations. Alternatively, one can use for thin layer chromatography (TLC) which can
be employed even for chemical identification and cross contamination tests. The
recent analytical tools are gas liquid chromatography (GLC) and high performance
liquid chromatography (HPLC) which are rapid and give reproducible and accurate
data. A number of senstive detectors of GLC and HPLC such as FID, NPD, ECD and
UV can analyse minute quantities of formulated products with great accuracy [6]. The
chiral column (CC) analysis both by GC and HPLC are now becoming popular. The
supercritical fluid extraction (SFE) analysis of environmental samples for various
compounds can also be recommended for extraction of pesticides from solid,
formulations. Another improved extraction procedure known as accelerated solvent
extractor (ASE) can also be employed for analysis of environmental samples which
takes very less time (10-15 min) and energy; This extractor can be employed for
extraction of solid formulations. The most recent one is capillary electrophoresis (CE).
which is extremely suitable for pesticide residue analysis. However, its use on
formulation analysis might create a problem because capillary column can
accomodate only microgram quantity of analyte which means large dilution of the
samples isrequired resulting in an increase in error. Other analytical methods use
infrared spectrophotometer (lR), nuclear magnetic resonance spectrometer (NMR) [2]
34
and atomic absorption spectrophotometer (AAS) which also give dependable accurate
results. The realistic methods of analysis using other properties such as specific
gravity, specific rotation, refractive index, emulsification, apparent density (for dusts
and granules) colour, pH, particle size, dispersibility and acidity or alkalinity are also
recommended by recognised institutions and research and development organisations.
The analytical control laboratory should be headed by a technical officer who
maintains a detailed inventory for each formulated product comprising specifications,
methods of analysis and analytical results.
Shelf life
Crops may be adversely affected if pesticides are applied after the expiry date. Partial
or total damage of the crops may occur because of the presence of toxic degradation
products .formed during storage. The stability of fonnulations depends on weather and
storage conditions, quality of packaging and kind of transport. The inerts added in the
pesticide fonnulations should not have any adverse effect on the active ingredient. The
acid and basic sites, invariably carried by the clay diluents cause decomposition of
pesticides. Hence, t aking proper precautions at the time of fonnulation and production
become imperative for the stability of the pesticide. The minimum shelf life of the
fonnulation should be 1.5-2.0 years. This would effectively contain transportation and
storage loss and facilitate creation of a reasonable stock ensuring off the shelf
availability of the product to the consumer. Hence, before recommending a
fonnulation for mass production, samples should be tested for a.i. content after storing
at 25°C for 18 months, 37°C for 12 months and 45°C for 3 months. The auxilliary
attributes such as emulsification, appearance, suspensibility wetting time and caking
of the fonnulations must be taken as adjuncts.
Safety aspects
Persons engaged in pesticide fonnulation and production plants are often exposed to
relatively high levels of pesticides. This makes them prone to allergic reactions,
35
respiration problems, eye and skin irritation and a variety of other health hazards
including carcinogenic reactions. In order to minimize these risks, the workers should
be encouraged to use protective clothings, gas masks, gloves and other devices. They
should be trained to carefully handle the equipment during production as well as in
packaging. No person should be allowed to work alone in the laboratory/plant. Proper
warning labels should be put on the chemicals which are known carcinogens,
mutagens and teratogens. Drinking and smoking should be strictly prohibited inside
the plant. Proper ventilation to keep inhalation exposure within pennissible limits must
be maintained. Blood analysis of plant workers must be carried out annually. In
addition to mamalian toxicity, protective measures should be taken against explosion.
a) Fire. The plant should have emergency exit plan, prohibition of smoking and
proper marking for fire exit, and location of fire extinguishers. An efficient alann
system and functional
emergency showers are indispensible. .
b) Explosion. Workers must be familiar with explosive nature of the chemicals being
handled and proper explosion shields and eye protectors should be located within easy
reach.
c) Storage. All volatile chemicals must be stored in a covered area preferably in an
under ground enclosure and extra precautions should be taken during the use and
storage of highly inflammable solvents.
d) Disposal. Solvents should be evaporated in fume hoods, and not discarded in drain.
Application
of
modern
tools
In
Agrochemicals formulation [
Computers are being employed very effectively for evaluation and optimization of
pesticide fonnulations. Computer assisted correlation analysis of both physical and
biological properties of any fonnulations and its economic viability based on types and
concentrations of the ingredients can be carried out smoothly and rapidly. Statistical
methods are utilized to measure the degree of correlation between responses and
36
independent variables. The computer programmes can also be designed to operate
equipment used to evaluate pesticide formulations and to carry out complex
theoretical calculations to guide choice of ingredients. Computer aided technique is
used for the evaluation of sedimentation rates/shelf life. Of flowable formulation and
solubility parameter theory to optimize the choice of emulsifiers for EC formulation.
ii) Laser. The laser technique allows the application of basic colloidal theory to the
practical development for pesticide formulation. It has been found that alachlor
microcapsule shows enhanced bioactivity as compared to conventional formulation
technique.
iii) Fluidized bed granulation. In this process granulation and drying occur
concurrently in -the same unit. This eliminates operator exposure, protects dust
explosion and does not contaminate the environment. The process is ideally suited
for the preparation of controlled release formulations. In the granulation process
one can convert a liquid formulation containing a surfactant into a solid
formulation (WG and SG). Besides these a few more equipments such as particle
size analyser (PSA), electronic particle counter (EPC) and rheometer are being
used in pesticide formulations.
Environmental aspects
Escaping gases, obnoxious smell along with solid, powdery and liquid exhausts from
the formulation plants contribute vastly to air, ground water and soil pollution. Plants
manufacturing dust formulations produce noise from jet or hammer mills.
Emulsifiable concentrate formulation plants consume large quantity of solvents like
xylene which are highly inflammable and toxic to human beings. These pollution
problems can be reasonably controlled by employing appropriate engineering
techniques and plant management.All the applied pesticides ultimately reach the soil,
water and air and influence the eco-system. The ever increasing sacrilege uf air we
breathe, water we drink and food we ingest, has become a matter of great concern.
While the use of these chemicals cannot be completely stopped, All these aspects must
37
- ~ be borne in mind at the time of formulation and screening of the product. The
formlation chemists must be involved in the decision making process for roduct
[
development to ensure that the fioal product is ecofriendly. Emphasis should be laid
on data generation, toxicity to non-target organisms and effect on persistence
residues. Perhaps the slow release formulations with effectively targetted kill and easy
biodegradability hold out the promise for ecologically safe pest control measures.
;
38