Download Fertilization in Sugarcane – Lecturer Madhanzi Tendai

SUGAR CANE NOTES
AGRO 401/NRM306
Compiled by Madanzi Tendai (MSc Crop Sci. UZ)
(Sources: Zimbabwe Sugarcane Production Manual, 1998 and University of Florida,
Institute of Food and Agricultural Sciences (UF/IFAS))
Figure 1. The sugarcane plant
MAIN PARTS OF THE PLANT
The main parts of the sugarcane plant are the stalk, leaf, and root system. Figure 1 shows
these parts, and others, which are examined in more detail below.
The Stalk
The stalk consists of segments called joints. Each joint is made up of a node and an
internode ( Figure 1 and Figure 2 ). The node is where the leaf attaches to the stalk and
where the buds and root primordia are found. A leaf scar can be found at the node when
the leaf drops off the plant. The length and diameter of the joints vary widely with
different varieties and growing conditions. In general, however, the joints at the base are
short and internodal length gradually increases.
Figure 2. Parts of the stalk (stripped of leaves).
The buds, located in the root band of the node, are embryonic shoots consisting of a
miniature stalk with small leaves ( Figure 2 ). The outer small leaves are in the form of
scales. The outermost bud scale has the form of a hood. Normally, one bud is present on
each node and they alternate between one side of the stalk to the other. Variations in size,
shape and other characteristics of the bud provide a means of distinguishing between
varieties. The root band also contains loosely defined rows of root primordia. Each
primordium exhibits a dark center, which is a root cap, and a light coloured "halo."
When seed-cane is planted, each bud may form a primary shoot. From this shoot,
secondary shoots called "tillers" may form from the underground buds on the primary
shoot. In turn, additional tillers may form from the underground secondary shoot buds.
The colours of the stalk seen at the internodes depend on the cane variety and
environmental conditions. For example, exposure of the internodes to the sun may result
in a complete change of colour. The same variety grown in different climates may exhibit
different colours. All colours of the stalk derive from two basic pigments: the red color of
anthocyanin and the green of chlorophyll. The ratio of the concentration of these two
pigments produce colours from green to purple-red to red to almost black. Yellow stalks
indicate a relative lack of these pigments.
The surface of the internode, with the exception of the growth ring, is more or less
covered by wax. The amount of wax is variety dependent. Where the internode is
exposed to the elements, a black mold usually develops on the waxy surface.
The top of the stalk is relatively low in sucrose and therefore is of little value to the mill
early in the harvest season. Later in the harvest season, the top 1/3 of the stalk may have
higher sucrose than the middle and/or bottom 1/3 of the stalk. The top 1/3 contains,
however, many buds and a good supply of nutrients which makes it valuable as seed cane
for planting.
A cross section of an internode shows, from the outside to the center, the following
tissues: epidermis, cortex or rind, and ground tissue with embedded vascular bundles.
The epidermis is a single superficial layer of cells that exhibit different patterns which are
variety dependent. Generally, the patterns are formed by two cell types, the so-called long
cells and short cells, that alternate with one another.
The cortex or rind consists of several layers of cells just inside the epidermis. The cells of
the rind are thick-walled and lignified. These cells help strengthen the stalk.
More toward the center, the ground tissue contains the vascular bundles with the xylem
and phloem. Xylem tissue conducts water and its dissolved minerals upward from the
roots, and phloem conductive tissue transports plant- manufactured nutrients and
products, for the most part, downward toward the roots. The vascular bundles are much
smaller and more prevalent toward the periphery of the stalk.
Two types of cracks are sometimes found on the surface of the stalk; harmless, small
corky cracks which are restricted to the epidermis, and growth cracks which may be deep
and run the whole length of the internode. Growth cracks are harmful since they allow
increased water loss and expose the stalk to disease organisms and insects. Growth cracks
are dependent on variety and growing conditions.
The Leaf
The leaf of the sugarcane plant is divided into two parts: sheath and blade, separated by a
blade joint.The sheath, as its name implies, completely sheaths the stalk, extending over
at least one complete internode. The leaves are usually attached alternately to the nodes,
thus forming two ranks on opposite sides. The mature sugarcane plant has an average
total upper leaf surface of about 0.5 square meter and the number of green leaves per
stalk is around ten, depending on variety and growing conditions.
A cross-section through the leaf blade would show three principal tissues: (a) epidermis,
(b) mesophyll, and (c) veins or fibrovascular bundles. The epidermal cells protect the
underlying tissues from injury and drying. The epidermis contains stomata for controlling
the exchange of gases. The mesophyll, or middle leaf tissue, contains the cells that
perform most of the photosynthesis. The fibrovascular bundles contain the xylem and
phloem elements which conduct water and nutrients to and from the leaves. In addition to
the above, there can be found other fibrous tissue for aiding in shaping and mechanically
strengthening the leaves.
The blade joint is where two wedge shaped areas called "dewlaps" are found. The color,
size, and shape of the dewlaps on a mature plant are more or less characteristic of a
variety. The "top visible dewlap" leaf is a diagnostic tissue that is frequently used in
nutritional studies.
The leaf sheath is similar in structure and function to the leaf blade. It is slightly simpler,
however, in that it lacks some of the more specialized cells of the leaf blade.
The ligule is a membranous appendage inside of the sheath which separates the sheath
from the leaf blade. It is a slightly asymmetric organ whose color, size, and shape are age
and variety dependent.
The auricles, as their name implies, are ear-shaped appendages located at the upper part
of the sheath margin. Not all sheath margins have auricles.
Leaf pubescence, or the covering of the various leaf parts with short hairs, is also variety
and age dependent. Pubescence is not found on the leaf blade of commercial varieties, but
does exist in sugarcane germplasm. Sheath pubescence can be used to identify plants.
The Root System
The function of the root system is twofold: first, it enables the intake of water and
nutrients from the soil; and second, it serves to anchor the plant. Two kinds of roots will
develop from a planted seed piece. The set roots, which arise from the root band, are thin
and highly branched; the shoot roots, originating from the lower root bands of the shoots,
are thick, fleshy and less branched ( Figure 4 ).
Figure 4. Set and shoot roots.
Before shoots form, the germinating seed piece must depend entirely on the set roots for
water and nutrients. The set roots, however, are only temporary and their function will
eventually be taken over by the shoot roots as they develop. The life of the shoot root is
also limited. Each new tiller (shoot) will develop its own roots that eventually take over
the function of the original shoot roots. This rejuvenation, governed by the periodicity of
tillering, is important because it allows the plant to adjust to changing environmental
conditions.
A longitudinal section of a root tip consists mainly of four parts: the root cap, the
growing point, the region of elongation, and the region of root hairs. The root cap
protects the tender tissues of the growing point as the root pushes through the soil. The
growing point consists mainly of an apical meristem, where cell division takes place. In
the region of elongation, the cells increase in size and diameter until they reach their
ultimate size. The region of root hairs is characterized by epidermal cells forming
outgrowths (hairs) which dramatically increase the root absorbing surface.
The Inflorescence
When a sugarcane plant has reached a relatively mature stage of development, its
growing point may, under certain photoperiod and soil moisture conditions, change from
the vegetative to reproductive stage. This means the growing point ceases forming leaf
primordia and starts the production of an inflorescence. The inflorescence, or tassle, of
sugarcane is an open-branched panicle. Each tassle consists of several thousand tiny
flowers, each capable of producing one seed. The seeds are extremely small and weigh
approximately 250 per gram or 113,500 per pound.
For commercial sugarcane production, inflorescence development is of little economic
importance in Florida. Generally, a day length close to 12.5 hours and night temperatures
between 68 and 77 degrees F will induce floral initiation. Temperatures that are too low
and/or water stress inhibit inflorescence development.
GERMINATION
Commercial sugarcane is propagated by cuttings of the stalk (seed cane) containing
usually two or more nodes with buds. The bud, a miniature stalk with its growing point
and root and leaf primordia, forms the new shoot. In addition, a seed piece contains root
primordia within its root band, which develop into set roots which function until the
young shoot develops its own roots.
The transition from the dormant into the active stage constitutes a complex phenomenon
characterized by changes in the activity of enzymes and growth regulating substances
(hormones, auxins). Maximum germination and shoot vigor will result when both internal
and external factors are optimal. Fortunately, these factors can be regulated to a
considerable degree by cultural methods.
TILLERING
Tillering, or development of secondary shoots, is a beneficial characteristic of a variety
because it provides the plants with the appropriate number of stalks for a good yield.
Also, tillering increases the rate of canopy closure which aids in weed control. Varieties
differ greatly in their tillering capability and the ultimate number of tillers present at
harvest.
Besides variety differences, numerous other factors influence tillering. Ultimately,
tillering is related to the phenomenon of "apical dominance" and therefore plant
hormones are involved in the process of tillering. The most important external factors
influencing tillering are light, temperature, nutrition, moisture and the spacing of the
plantings. Of these factors, experiments have shown that light is the most significant.
Increasing light intensity and duration, in general, greatly increases tillering.
In young cane fields the period of profuse initial tillering is followed by a wave of
mortality as soon as the rows close in. More than 50% of the number of the initial stalks
may die. Much of the mortality is due to light competition.
GROWTH
The growth of the cane plant does not proceed at a uniform rate. Development starts
slowly in the germinating bud and it increases gradually until a maximum is reached
which is followed by a gradual decrease. The time period in which the plant is growing
rapidly is called the "grand growth period."
Cane growth is governed by a complex of internal and external factors. Not surprisingly,
the more important external factors affecting growth are moisture, temperature, light, soil
condition and nutrition. It is beyond the scope of this fact sheet to deal with all these
individual factors. Please see more specific sugarcane fact sheets for further information.
NUTRITION
The "essential elements" for a healthy sugarcane crop include carbon, hydrogen, oxygen,
nitrogen, phosphorus, potassium, calcium, magnesium, boron, chlorine, copper, iron,
manganese, molybdenum, sulfur and zinc. Silicon, although not strictly needed for the
sugarcane plant to complete its life cycle, may enhance sugarcane production
significantly. An over-abundance of one element may cause a deficiency or toxicity of
another. Hence, there is a need for a good nutritional balance to produce the healthiest
plants. Since relatively large quantities of N,P,K,S,Mg, and Ca are needed by the plants,
these are referred to as "macronutrients." The remainder of the elements are usually
called "micronutrients."
Although nitrogen constitutes only a fraction of one per cent of the total dry matter of a
mature sugarcane plant, it plays a role as important as C,H and O, which together, form
more than 90 per cent of the dry matter. Nitrogen deficiency is common in sandy soils
and it is uncommon in organic soils.
Nitrogen has the greatest influence on cane ripening (discussed below) of all the nutrient
elements. Sugarcane will store a higher percent of sucrose when nitrogen is limited 6 to 8
weeks prior to harvest.
Sugarcane nutrition is an extensive topic. Refer to Agronomy fact sheet SS-AGR-228
Nutritional Requirements for Florida Sugarcane or notes below for more information.
ENERGY RELATIONS
Photosynthesis
Photosynthesis is the process by which plants transform the radiant energy of the sun into
chemical energy stored in carbohydrates. Photosynthesis involves a fairly long series of
complicated reactions, but can be summed up in the following equation:
6CO 2 + 6H 2 O (+ Sunlight) ----> C 6 H 12 O 6 + 6O 2
Sucrose (C 12 H 22 O 11 ) is the major carbohydrate formed, used and stored by the
sugarcane plant.
Respiration
Respiration is the process in which the stored chemical energy is released to the plant for
its various functions such as growth and moving certain nutrients against concentration
gradients. Chemically, in essence, it is the reverse of photosynthesis:
C 6 H 12 O 6 + 6O 2 ----> 6CO 2 + 6H 2 O (+ Usable Energy)
The balance of the carbohydrates not used for the building of the plant frame or the
production of energy is stored in the stalk mainly in the form of sucrose.
TRANSLOCATION
The rapid translocation of sucrose and other carbohydrates and nutrients takes place
mainly in the phloem. These plant foods move to the tissues utilizing them. Thus, food
can move from the leaves where manufactured, to the stalk, regions of growth, and roots.
The loading and unloading of the phloem elements could be by diffusion in the direction
of a concentration gradient, but is more likely to be a metabolically-mediated, regulated,
and reversible process.
RIPENING
The storage of sucrose in the stalk is known as ripening. Describes the improvement in
quality brought about naturally as a combination of age, season, variety and management
(e.g. drying-off, and use of chemical ripeners).Ripening is a joint to joint process and the
degree of maturity of the individual joints depends on their age. In young plants, the
sucrose content exhibits a distinct maximum which is located approximately at soil level.
The sucrose content in these plants decreases through the stalk toward the top of the stalk.
As the plant matures, a more uniform sucrose content is found throughout the stalk
except for the top few internodes and the below-ground stool.
Certain plant growth regulators can accelerate the accumulation of sucrose in the stalk.
These regulators, or chemical ripeners, can be used to a commercial advantage.
Natural ripening
Zimbabwe experiences good conditions for natural ripening as the cold winters favour
natural ripening. Despite this some varieties are more suited to early ripening e.g ZN 1L
and late ZN 2E. ZN 6 and ZN 7 can be harvested all year round.
Chemical ripening
Cane is actively growing at the beginning of the milling season and sucrose content is
naturally low. Quality can be improved by use of ripeners like ethrel, fusillade super and
round-up. These inhibit apical growth. ETHREL is applied at 1,5l/ha and is effective on
young actively growing cane with a juice purity of about 70 %. It is not suitable in
summer as it might stimulate growth in some varieties.
FUSILADE apply 300 to 400 ml/ha. Cane increase sugar yield by 1.5t/ha. Has similar
response to roundup and has no residue on the crop. Should be applied when juice purity
is about 77 % but not over 85 %.
ROUNDUP 600 ml/ha. Can cause chlorosis and stunting of ratoon regrowth especially if
cane has been stressed or if chemical is over applied.
Application methods include aerial using helicopters. However application of ethrel by
helicopter is not recommended as it damages the plastic bulb. There is the ZSAES
sprayer, which utilises CO2, pressurised spray tank and the Buffalo Range sprayer, which
is a pressure regulated knapsack sprayer operated by 3 people.
EVAPOTRANSPIRATION
Transpiration is defined as the giving off of water vapor by the plant, almost exclusively
from the leaves. Evapotranspiration is the release of water vapor from a unit surface of
land which includes the soil and the plants. The plant controls the inflow and outflow of
water vapor and other gases by way of stomata on the leaf surface. The stomata can be
opened or closed by a pair of guard cells that respond to leaf water status.
Experiments with Florida sugarcane have shown it requires about 220 to 275 lb of water
to produce one lb of dry biomass, and about 520 to 680 lb of water to produce one lb of
sugar.
The sugarcane plant's response to drought is somewhat variety dependent. The main line
of defense may be tight control of stomatal opening and closing. Other mechanisms
include leaf canopy collapse and leaf senescence which can reverse itself once the
drought ends.
Nutrition in Sugar Cane
The most important elements in sugarcane are Nitrogen (N), Potassium (K), Phosphorus
and Sulphur. There are general guidelines to use of these fertilisers but soil and foliar
analyses must be done accurately to determine fertiliser requirements.
Nitrogen
Several experiments done at the Zimbabwe Sugar Association (ZSA) Experiment Station
show that there is no relationship between soil Nitrogen, cane yield and nitrogen
requirements. This is because nitrogen requirements of cane under different conditions
have been satisfactorily determined from cane responses to applied levels of N fertiliser.
Generally plant cane has a lower N requirement than ratoon crop if harvested at 14
months. Other differences are due to main soil textural classes. Experience and
knowledge of each field should be used to determine the rates to apply. Excessive
application of fertiliser does not always result in increase in yield but may result in
decrease in yield and losses in monetary return. Nitrogen is essential in good growth of
sugarcane.
N can be applied as Ammonium nitrate (AN) or Urea and both are soluble in water and
can be applied with irrigation water i.e. drip or overhead irrigation. General management
decisions one can make when using nitrogen in sugarcane include:
a. Delaying harvesting by 4 weeks if nitrogen is applied later than 14-16 weeks after
cutting.
b. Reducing N application when water is in short supply
c. Increase and split N applications on sandy soils where leaching occurs.
Time of N application
Urea: applied directly to the soil before irrigation (if Urea is left on the soil surfaces it
turns to gaseous form and evaporates).
A.N.: apply before or after irrigation.
Table 1: Shows time of N application after planting
Month cane is planted
April to August (2 splits)
September to October (2 November to December (3
splits)
splits)
1/3 at 4 weeks
1/3 at 4 weeks
1/3 at 4 weeks
2/3 at 8 weeks
2/3 at 8 weeks
1/3 at 8 weeks
1/3 at 10 weeks
Table 2: Shows time of N application after harvesting
Month cane is Harvested
April to May (2 splits)
June to October (2 splits)
1/2 at 4 weeks
1/2 at 8 weeks
1/2 at 4 weeks
1/2 at 8 weeks
November to December (3
splits)
1/3 at 2 weeks
1/3 at 6 weeks
1/3 at 10 weeks
N.B. There need to split N during the rainy season due to leaching.
Table 3: shows N and AN bags applications to plant and ratoon crops
Soil
Class
Sandy
loam
Sandy
clay loam
Basalt
clay
Crop
Plant
Ratoon
Plant
Ratoon
Plant
Ratoon
Application range
N kg/ha AN kg/ha AN *bags/ha
120-160
140-170
110-140
130-160
120-160
140-180
350-465
405-495
320-405
375-465
345-465
405-525
1/3
at
weeks
6-8
8-9½
7-9 ½
8-11
4
Phosphorus
Recommendations for P are based on yield responses and are specific to soil type,
growing conditions and soil analysis. Plant crops planted on virgin soils have a greater
requirement for P than in previously cropped soils. It is important to note that:
a. P can last in the soil for years and amounts can be reduced basing on foliar or soil
analysis. Amounts may be reduced in times of financial hardships.
b. P is essential for good root development and must be applied before planting and
just after harvesting.
Plant cane
P is broadcast, disced or else band applied in the planting furrow.
Ratoon cane
P is banded on both sides of the cane row.
General guidelines for P requirements in sugarcane
Table 4: P requirements in both plant and ratoon crops
Available soil P2O5 Application range of SSP kg/ha (5.4 % P2O5)
(ppm)
Resin extract
P2O5
SSP Kg/ha
*Bags SSP/ha
0-12
100-150
540-810
11-16
13-25
50-100
270-540
5 ½ -11
26-40
20-50
110-270
2-5 ½
More than 40
Nil
Nil
Nil
Potash
Actively growing sugarcane consumes K more than any other nutrient and can consume
it luxuriously if its available. This K will be stored in the plant but will not result in
appreciable gains in either yield or quality. K availability to the crop is complicated by a
number of factors, which include K held in non-exchangeable form, can become
available to the plant (i.e. K not detectable by soil analysis). Secondly most soils in the
lowveld contribute considerable amounts of K which is not measured by the routine soil
sample of 30 cm deep.
Different soil textural classes determine K requirement and the following guidelines must
be used:
a. Additional K is likely to be required when using borehole water high in Mg and
Ca.
b. K persists in the soil longer than N but not longer than 12-18 months.
c. K can be applied with irrigation water as muriate of potash.
d. N 14 can take up more K2O than Nco 376.
e. Plant and ratoon crops must be given one dressing of 60 kg per ha K2O together
with the first Nitrogen application in April to October harvested cane (4 weeks
after planting or ratooning).
f. In November and December harvested cane, apply 2 equal dressings with the first
and third Nitrogen application (2 and 10 weeks after cutting).
Table 5: general recommendations for K as muriate of potash (KCL) based on soil
K content
*Potassium in Soil Type
K2O
Muriate
of **Bags MOP
soil me % K
Kg/ha
Potash Kg/ha
(50 Kg)
Less than 0.2
Loamy Sand
130-260
215-435
4-9
Loamy Sand Clay
200-330
335-550
7-11
Sandy Clays
260-330
435-550
9-11
0.2-0.25
Loamy Sand
70-130
115-215
2-4
Loamy Sand Clay
130-200
215-335
4-7
Sandy Clays
200-260
335-435
7-9
0.25-0.3
Loamy Sand
0-70
0-115
0-2
Loamy Sand Clay
70-130
115-215
2-4
Sandy Clays
130-200
335-435
4-7
0.3-0.35
Loamy Sand
Nil
Nil
Nil
Loamy Sand Clay
0-70
0-115
0-2
Sandy Clays
70-130
115-215
2-4
More than 0.35 Loamy Sand
Nil
Nil
Nil
Loamy Sand Clay
Nil
Nil
Nil
Sandy Clays
0-70
0-115
0-2
Sulphur
S is one of the essential elements in sugarcane production. Cane consumes 25 to 45 kg
S/ha/annum. S deficiency is likely to occur as a result of continued cropping without
sufficient S being applied e.g. us of triple superphosphate instead of single
superphosphate (a source of S). SSP contains 12 % S and is a regular source of the
nutrient. Some compounds also contain S e.g.
Granular
15: 15: 15: + 7 % S
Bulk blend
16: 16: 16: +3.5 % S
Bulk blend
12: 24: 0 + 7.5 % S
Sugar blend
10: 15: 30 + 5 % S
Varieties
Selection programme started in 1976. The objectives being to increase yield, quality, and
disease resistance.
Progress to date
Selecting for high sucrose content, and selection against smut (the most problematic
disease in sugarcane) and leaf scald has produced very tolerant varieties. Varieties like
ZN 7 and ZN 6 are new in the Lowveld and are replacing NCo 376 as the dominant
varieties. They have better tolerance to smut than both N 14 and NCo 376. They also
have higher yield than both N 14 and NCo 376 in trials grown up to the third ratoon crop.
Another advantage is they have a higher estimated recoverable crystal % (ERC %) than
the above two varieties. ERC % is calculated as:
ERC % = (a x Pol %) – (b x Non-Pol %) – (c x Fibre %)
All variables are expressed as % cane. The constants a, b, c, are derived from mill
performance data and vary from year to year and have the following range if produced
under normal conditions: a = 0.97 to 0.98; b = 0.45 to 0.50; c = 0.020 to 0.0230
Pol losses in: a) filter cake, b) molasses and c) bagasse respectively. Pol is the apparent
sucrose content in cane or juice expressed as a percentage by mass.
Current varieties
(Information on the most current varieties can be obtained from the Zimbabwe Sugar
Association Experiment Station)
NCo 376
Has the following characteristics:
High yield cane; low sucrose content in early season; high sugar yield; very good
ratooning (has produced good yield beyond the 10th ratoon) high fibre; high stalk
population; has proved to be reliable under all conditions (soil types, management etc);
canopies early; vigorous growth; very high susceptibility to smut; resistant to leaf scald;
shows slight symptoms of yellow leaf syndrome; lodges and flowers prolifically.
N 14
Best for early to mid-season harvesting and gives better yields than NCo 376 throughout
the year; very high cane yield; similar sucrose content to NCo 376; higher sugar yield
than NCo 376; less fibre than NCo 376; 81 % stalk population of NCO 376; good
ratooning (up to 3rd ratoon crop in trials); canopies very early; vigorous growth; resistant
to smut and leaf scald and; susceptible to ratoon stunting disease; less lodging than NCo
376 and flowers prolifically; showed slight symptoms to yellow leaf syndrome.
Table 6: Performance of N 14 compared to NCo 376
Harvesting
season
Early
Late
All year
% of NCo 376
Cane
107
106
106
ERC %
102
100
101
ERCt
109
107
108
ZN 1L, ZN 2E, ZN 6 and ZN 7
N.B. these characteristics are general in comparison to N 14 and NCo 376.
Have higher sucrose content than NCo 376 especially in the mid to late season. ZN 1L
has blower sucrose content in the early season and might need ripeners; higher yield
compared to NCo 376; has less fibre than NCo 376; has between 80-87 % stalk
population compared to NCo 376; good ratooning up to 3rd season in trials; canopies
early; very vigorous growth; high tolerance to smut and scald; high lodging; very little
flowering.
Table 7: Performance of ZN 1L compared to NCo 376
Harvesting
season
Early
Late
All year
% of NCo 376
Cane
108
103
105
ERC %
94
104
101
ERCt
101
107
105
Table 8: Performance of ZN 2E compared to NCo 376
Harvesting
season
Early
Late
All year
% of NCo 376
Cane
91
92
91
ERC %
114
111
109
ERC t
111
114
112
DISEASES
There are five major diseases of sugarcane in Zimbabwe. These include ratoon stunting
disease (RSD), smut, leaf scald, rust and yellow leaf syndrome.
Ratoon stunting disease
Is caused by a bacteria Clavibacter xyli p.v. xyli. Globally it is the most yield reducing
disease causing losses of between 30 – 40 %. In Zimbabwe yield losses are between 5-10
%. Symptoms include general loss of vigour and stunting in ratoon crop, brown to pink
streaks in the nodes of infected plants. Ratoon stunting disease (RSD) is considered by
many to be the most important disease affecting sugarcane production worldwide. It can
cause a 5 to 15% loss in crop yield worldwide without the grower even knowing his
fields have been infected. The disease is caused by a bacterium. RSD has no easily
recognized external symptoms, only stunting of growth that may not always be apparent
in the field. Furthermore, even when stunting of growth is noticeable, it could be caused
by other factors, including poor cultural practices, inadequate moisture or nutrient
deficiency. During dry weather, the diseased cane will often show signs of drought stress
earlier than healthy cane, but with adequate moisture, visual detection of differences may
be difficult or impossible.
SYMPTOMS
Although there may be no externally conspicuous symptoms of the disease, internally
there is usually an orange-red discoloration of the vascular bundles containing the waterconducting tissues (xylem) at the basal nodes of the stalk ( Figure 1 ). Similar
discoloration is also associated with other sugarcane diseases so it is not a totally reliable
indicator of RSD. The discoloration of RSD, however, does not extend into the
internodes as it does with some other diseases. Usually adjacent nodes in mature stalk
should also show similar discoloration if it is RSD infection.
Figure 1. Discoloration of sugarcane vascular bundles caused by ratoon
stunting disease.
In some clones, very young shoots may have a pink discoloration in the immature nodes
near the apical meristem. Again, this symptom is not a reliable indicator of RSD but may
serve as an aid in detection of the disease at an early stage.
In diseased fields where stunting is apparent, the shortening of stalks is not usually
uniform from stool to stool. Such fields may show an "up and down" appearance.
CAUSAL AGENT
The RSD causing organism, Clavibacter xyli subsp. xyli , is a small aerobic bacterium.
There has been a suggestion to reclassify the pathogen to the genus Leifsonia but a
consensus on the new name has not developed. Although it can be isolated from diseased
cane, it is very difficult since it is slow growing and must be grown on specialized culture
media.
Historically, diagnosis of RSD has been difficult because there are no definitive external
symptoms and internal symptoms do not develop adequately in all varieties. Reliable
diagnosis of the disease can be performed using microscopic and/or serological
techniques. Phase contrast microscopic techniques have proven to be rapid but are not as
sensitive as serology for RSD detection. Serological techniques include direct
fluorescent-antibody staining, dot blot immunoassay and the Enzyme-Linked
Immunosorbant Assay (ELISA). Recently a variation of the dot blot immunoassay
technique was developed to diagnose the disease and to assess its severity. The technique
is called the Tissue Blot Immunoassay (TBIA) and can rapidly test large numbers of
sugarcane samples for RSD. This technique has been used to screen clones for RSD
resistance and determine disease incidence of seedfields.
SPREAD OF THE DISEASE
The RSD bacterium is transmitted through seed cane taken from diseased plants. Because
symptoms of the disease are not readily visible, the bacterium may be spread unwittingly
from one area to another. Stalks in potential seedfields can be randomly sampled and
serologically assayed to determine RSD incidence.
RSD can be readily transmitted by knives and mechanical harvesting machines that
become contaminated with pathogen that is contained in juice from diseased stalks.
Transmission by harvesting machinery is very significant.
Cane chewing animals may be capable of transmitting the disease when they gnaw on a
diseased stalk and then a healthy one. Not much is known about this means of
transmission or its significance.
There are new reports that the pathogen survives in the soil after harvest to re-infect
healthy plants. The extent of infection by the pathogen surviving in the soil is not known.
The effects of the disease are usually more severe in ratoon crops than in plant-cane
crops. This is especially true following a drought, or other stressful crop condition, which
usually increases losses due to RSD.
PREVENTION AND CONTROL
Since RSD bacteria are easily transmitted mechanically, sanitation is important in
preventing healthy cane from becoming infected. All cane cutting implements should be
protected from contamination from diseased cane or be disinfected before use on healthy
cane. Disinfection can be achieved by heat or chemicals.
Chemical disinfectants that may be used on cane cutting knives include Lysol, Dettol,
ethanol, Mirrol and Roccal. At least 5 minutes of contact with the cutting surface is
needed to assure disinfection, but a shorter disinfection time will be partially helpful.
Heat treatment of seed cane before planting is used to eliminate bacteria prior to the
establishment of seed cane nurseries. Hot-water treatment [water containing Benlate 50
% WP) (50° C for 2-3 hours)] is the method most commonly used to control RSD. A
serological assay can be used to monitor the effectiveness of the heat therapy. Due to
reinfection, heat therapy has to be repeated to ensure disease-free seed cane.
The use of resistant clones has been shown to control RSD.
Smut
Is caused by fungus Ustilago scitaminea and is the most problematic disease in
Zimbabwe. Yield losses of up to 40 % have been recorded in NCo 376 due to reduction
in millable stalks. An infection of 1 % means a loss of 1500 stalks/ha. Symptoms include
development of long, unbranched, dark brown, whip-like structures from the top of
infected stalks. Infected stools are pale and grassy. Disease can be identified before
emergence of whip. Such cane has small and narrow leaves and slender stalks with
widely spaced nodes. The disease is transimitted by wind-borne spores and infected seed
cane. Control includes integrated disease management IDM including use of resistant
varieties such as N 14, ZN 1L, ZN 2E etc. Use of certified smut-free seed cane treated
with appropriate fungicides such as TILT, BAYLETON, or BAYFIDAN. Rouging of
infected fields on time and ploughing out heavily infected ones is one management
strategy that can be used. Rouged cane should be immediately put in plastic bags and
must be discarded in dumping sites away from the field. Crop rotation reduces the
amount of smut pores in the soil, as Ustilago scitaminea is specific to sugar cane.
Sugarcane Rust Disease
Since 1978, sugarcane production in Florida has been threatened by sugarcane rust
caused by Puccinia melanocephela. This fungal pathogen is now found almost
everywhere sugarcane is grown. The spread of the disease has had considerable economic
impact. Screening for resistance has become an integral part of Florida sugarcane
breeding programs. However, due to genetic variability within the pathogen population,
resistance to the disease has not been stable. An example of this is CP 70-1133, an
important variety grown for years without any sporulating pustules developing on it.
Now, this same cultivar would be classified as moderately susceptible. Other important
commercial clones have also demonstrated increasing susceptibility to sugarcane rust
over time.
Yield loss assessment due to rust is difficult, but realistic estimates have been obtained.
During 1988, rust was particularly severe on the variety CP 78-1247 in Florida. A
comparison of CP 78-1247's yield that year with a variety of equal yield potential
revealed yield losses of nearly 40% (averaged over 13 different locations where the
varieties were grown side-by-side). Another yield loss study, conducted by establishing a
near disease-free check using a fungicide as a means for comparison, demonstrated losses
of 20-25% on a moderately susceptible variety, CP 72-1210. This particular variety
dominated the Florida sugarcane industry during the late 1980s, occupying as much as
60% of Florida's sugarcane acreage. Based upon the acreage of CP 72-1210 during the
1987 rust epidemic and using a conservative estimate of 20% yield loss, economic losses
on CP 72-1210 during this single season were estimated as surpassing $40 million.
SYMPTOMS
Sugarcane rust is mainly a disease of the leaf. The earliest symptoms are small, elongated
yellowish spots that are visible on both leaf surfaces. The spots increase in length, turn
brown to orange-brown or red-brown in color, and develop a slight, but definite, chlorotic
halo ( Figure 1 ). Lesions typically range from 2-10 mm in length but occasionally reach
30 mm. They are seldom more than 1-3 mm in width. Infections are usually most
numerous toward the leaf tip, becoming less numerous toward the base. Pustules, which
produce spores, usually develop on the lower leaf surface ( Figure 2 ). Certain cultivars,
however, may have some pustules on the upper surface.
Figure 1. Rust lesions on sugarcane leaf.
Figure 2. Rust pustules on lower leaf surface.
Pustules may remain active over a considerable period of time and spore production is
highly dependent upon climatic conditions. However, eventually lesions darken and the
surrounding leaf tissues become necrotic.
On a highly susceptible variety, considerable numbers of pustules may occur on a leaf,
coalescing to form large, irregular, necrotic areas. High rust severities may result in
premature death of even young leaves. Severe rust has caused reductions in both stalk
mass and stalk numbers, thereby reducing cane tonnage.
CAUSAL AGENT
The fungus Puccinia melanocephela causes sugarcane rust. An obligate parasite, the
pathogen incites new infections only on living host tissue. Changes in varietal
susceptibility to rust have been observed over the years, suggesting the existence of
fungal variants.
SPREAD OF THE DISEASE
Rust spores are very well suited to dissemination by air currents. In fact, rust spores are
so well-adapted for atmospheric transport that it has been hypothesized that the original
source of rust in the Americas came from the continent of Africa via high altitude trans-
Atlantic winds. On a more local scale, rust epidemics have been demonstrated to develop
in the direction of prevailing winds.
Leaf wetness and atmospheric temperature are the environmental factors most influential
for rust development. Several hours of free moisture on the leaf surface at a favorable
temperature is necessary for successful spore germination and infection, and hence,
spread of the disease. While long dew periods and rainfall events both contribute to leaf
wetness, rainfall events are not quite as favorable for rust development. Heavy rains tend
to remove spores from the atmosphere, rendering them infective if they land on the soil.
There are reports that high soil moisture also strongly favors infection. Presumably, high
soil moistures would increase the humidity within the canopy, lengthening the duration of
leaf wetness.
The optimal temperatures for spore germination are between 15° to 30° C (60° to 85° F).
Under favorable moisture conditions, however, infection may occur within the
temperature range of 5° to 34° C (40° to 90° F). In Florida, rust is most severe from
February to May since its development is favored by the cool to moderate temperatures.
Plants that are 3 to 6 months old are also prevalent during this period and the crop
appears to be most susceptible at this stage.
Several soil factors may also significantly influence rust infection levels on sugarcane.
Studies have shown rust levels to be higher on sugarcane grown on low pH soils than on
high pH soils, particularly when high levels of phosphorus and potassium nutrients are
present in the soil.
PREVENTION AND CONTROL
The best means of control for sugarcane rust is to grow resistant varieties. However,
resistance has not been stable or durable on certain varieties, presumably because of rust
variants. For this reason, it is highly recommended that growers diversify their varietal
holdings. In this way, they will not have a predominance of one variety, should a rust
variant develop that is capable of infecting that particular variety. Varietal diversification
may play an important role in holding down the overall area-wide disease pressure,
thereby reducing the natural selection pressure for one particular rust variant. It is
believed that this may assist in preserving the durability of host plant resistance in current
resistant varieties.
Although a number of chemicals are registered for foliar disease control on sugarcane,
including sulfur and the phosphonics, chemical control of sugarcane rust does not offer
enough economic return to be used at present.
Since soil factors have been identified as being associated with rust infection levels on
sugarcane, avoid growing susceptible varieties in areas with low soil pH and/or high
levels of P and K nutrients. Sugarcane grown in fields receiving recent applications of
cachaza or mill mud is typically very prone to rust. If possible, plant these fields with
varieties that have demonstrated, durable rust resistance.
Sugarcane Leaf Scald Disease
Leaf scald was first recognized as a bacterial disease of sugarcane in the 1920s. It is a
vascular disease caused by Xanthomonas albilineans. The disease has been found in at
least 55 countries. Many of these countries are in the most productive sugarcane areas of
the world.
Leaf scald is a disease with the potential to seriously limit the cultivation of susceptible
varieties. The disease is insidious in that it may have a latent (asymptomatic) period that
lasts for years. Leaf scald is further complicated by the fact that it may be manifested in a
chronic phase or acute phase.
SYMPTOMS
Some leaf scald-infected plants do not have any external symptoms. These plants are
referred to as being latently infected and the mechanism of latent infection is not
understood. There are also cases of apparent recovery in which symptoms subside and do
not become visible until ratoon crop regrowth or after planting infected seed cane.
However, during apparent recovery, the disease is in a period of latent infection in the
affected cane.
The chronic phase is characterized by several external symptoms. The most typical
symptom is a white pencil-line streak about 1 - 2 mm wide on the leaf that extends from
the midrib to the leaf margin running parallel to the veins ( Figure 1 ). A diffuse
yellowish border of varying widths runs parallel to the pencil line streak. The pencil line
may have areas of reddish discoloration along part of its length. As the disease
progresses, necrosis develops from the leaf tip or leaf margin.
Figure 1. Pencil-line mark on sugarcane leaf caused by leaf scald disease.
Leaf scald can also cause partial or complete chlorosis (scalding) of the leaf blade. Close
inspection of these areas may reveal the diagnostic white pencil line or its reddish
necrotic sections.
The disease can also cause shoots to be stunted and wilted. Usually, affected leaves turn a
dull blue-green color before dense browning (a late symptom of the disease). Under stress
conditions the whole stool may die. This has happened in a few fields of CP 80-1743
grown under stressed conditions.
On mature stalks, the spindle leaves become necrotic from the tips and moderate to
profuse side shoots develop. Side shoots first appear at the bottom of the stalk and
progress upward. These side shoots usually show the scalding and/or white pencil lines
(Figure 2). The side shoots often die while quite small (<18 inches).
Figure 2. Sugarcane side shoots infected with leaf scald.
Internally, affected stalks may show bright to dark red streaks caused by necrosis of the
vascular bundles. These streaks are most prominent at the nodes and are nearly always
present at the juncture of side shoots and the stalk.
A sudden wilting and death of mature stalks, often without previous symptom expression,
characterize the acute phase. The onset of this condition generally follows a period of
stress, especially of prolonged drought.
CAUSAL AGENT
The leaf scald bacterium has been found to be restricted to the xylem elements of the
vascular bundles in the white pencil line streaks. It is not found in the surrounding
chlorotic tissues. A phytotoxin has been isolated from chlorosis-inducing strains of X.
albilineans. It has been proposed that this phytotoxin may inhibit chloroplast
development and/or in some way disrupt photosynthesis.
SPREAD OF THE DISEASE
Since scald is a systemic disease, which may be inconspicuous (latent) for lengthy
periods of time, infected seed cane is a major cause of disease spread. Cutting knives,
including those on machinery, are an important source of infection.
The pathogen can also survive in stubble. The organism does not appear to survive for
long periods of time in soil or undecomposed cane trash.
Alternative hosts may offer another means of pathogen survival. X. albilineans naturally
infects several wild grass weeds, such as elephant grass.
Besides transmission by cutting knives, evidence is accumulating to suggest aerial
transmission. This may explain, in part, the recent spread of leaf scald.
The amount of damage caused by leaf scald appears to be influenced by environmental
conditions. Periods of stress such as drought, waterlogging and low temperature are
reported to increase the severity of the disease. The yield of stalks that are dead or have
necrotic tops and leaves with numerous side shoots is decreased to 20 to 30% of that of
symptomless stalks. Fortunately, over the last ten years, only a few fields of CP 80-1743
had over 10% incidence of stalks with these severe symptoms, and these fields were
environmentally stressed.
PREVENTION AND CONTROL
The best control is prevention and the replacement of susceptible varieties with resistant
varieties. Due to the latency of leaf scald, however, growers should be alert for infection
even in those varieties thought to be resistant.
Seedcane can be given a long-hot-water treatment to kill the pathogen. The Australians
use a 24-hour presoak in flowing water, followed by a 3-hour 50° C treatment. The 2hour 50° C treatment used for ratoon stunting disease would give partial control.
To prevent mechanical spread of the pathogen, all cane cutting knives, including those on
mechanical harvesters, should be sterilized when coming from suspect fields.
Disinfection of the knives can be accomplished by cleaning and immersing for several
minutes in a suitable antiseptic solution, such as Lysol, alcohol or a dilute solution of
bleach. Aerial transmission of the pathogen would also influence the length of time
disease-free seedfields would remain disease-free. There are no known chemical or
biological controls for this disease.
Yellow leaf syndrome
Yellow leaf syndrome (YLS) that is common in many sugar producing countries. In
Zimbabwe it is fairly new. It causes yield losses of 40 %. However other factors led to
this loss. Losses in varieties currently grown in Zimbabwe are very small.
Symptoms
YLS consists of a non-specific yellowing
Disorders
Include hail, frost which affects injury on young leaves, buds, and internodes, and
lightening.
Insect pests
Include soil dwelling pests like termites, black maize beetle (BMB), pearly scale. Later
cut cane is more susceptible to termites and BMB (the most problematic pests). Control
include use of dieldrin (removed from the market for environmental reasons), and Regent
200 SC. Other pests include leaf eaters like locusts, army worm, stalk borers like Sesamia
and Eldana. Sap sucking pests include plant hopper, pink mealy bug and aphids.