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Agricultural Methods and Pest Management
The Development of Agriculture
 Development of agriculture involved manipulating
the natural environment to produce food desired by
humans.
 This allowed an increase in the size of the human
population.
The Development of Agriculture
 Shifting agriculture involves cutting down and
burning the trees and other vegetation in a small
area of the forest.
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Burning releases nutrients bound up in biomass.
The cleared soil is useful for 2-3 years.
Forest eventually recolonizes the area.
Particularly useful on thin tropical soils.
Not suitable for large, densely populated areas.
Requires a long recovery time between cycles.
The Development of Agriculture
 Shifting agriculture often employs polyculture, or
the planting of a mixture of plants.
 Labor-intensive agriculture is practiced in much of
the world.
• Three situations favor this type of agriculture:
– The growing site does not allow mechanization.
– The crop does not allow mechanization.
– The economic condition does not allow purchase of
mechanized equipment.
The Development of Agriculture
 The primary reason for the use of labor-intensive
agriculture is economic.
• Many densely populated countries have numerous small
farms that can be effectively managed with human labor.
The Development of Agriculture
 Mechanized agriculture is typical of industrialized
countries.
• Fossil fuel replaces human muscle power.
• This method requires large amounts of energy and flat
land.
• Monocultures promote more efficient planting,
cultivating, and harvesting.
• Farmers often rely on hybrids to provide uniform
monocultures.
The Development of Agriculture
 Problems with mechanized agriculture include:
• Large tracts of bare land increases soil erosion.
• Little genetic differentiation often leads to increased
pesticide use.
• No crop rotation depletes soil nutrients, increasing
fertilizer use.
• Fossil fuel energy use has replaced human muscle
power.
The Development of Agriculture
 The Green Revolution has greatly increased
worldwide food production.
• Introduction of new plant varieties and farming methods
has increased food production per hectare.
• Drawbacks:
– Modern varieties of plants require fertilizer and pesticides
that traditional varieties did not need.
– Requires larger amounts of water and irrigation.
The Development of Agriculture
 Increased production has not solved the world’s
food problem because population continues to
increase.
 Global answers are needed for difficult
problems.
• Governments protect farmers with subsidies and
trade barriers. Farming is hindered in poorer nations.
• High fuel costs increase food costs.
• High energy prices divert crops to alternative fuel
crops.
• Higher demand for quality food and meat.
The Development of Agriculture
Increased yields resulting
from modern technology and
the total amount of land
available for cultivation.
Fossil Fuel Versus Muscle Power
 Labor reduction in the United States:
• 1913: 135 hours of labor required to produce 2,500 kg of
corn.
• 1980: 15 hours of labor required to produce 2,500 kg of
corn.
 It takes 5 metric tons of fossil fuel to produce 1
metric ton of fertilizer.
• The developed world is dependent on oil to produce
energy to manufacture pesticides and fertilizer and to
run machines.
• The price of oil has wide ramifications on the world’s
ability to feed itself.
The Impact of Fertilizer
 Approximately 25% of the world’s agriculture crop
is directly attributed to chemical fertilizer use.
• Fertilizers replace soil nutrients extracted by plants.
• The price and availability of chemical fertilizers are
strongly influenced by world’s energy prices.
 The three primary soil nutrients (macronutrients)
are nitrogen, phosphorus, and potassium.
 Micronutrients (e.g., boron, zinc, and
manganese) are needed in smaller amounts.
The Impact of Fertilizer
Increasing fertilizer use
The Impact of Fertilizer
 Chemical fertilizers do not replace soil organic
matter, which is important for soil structure.
 Total dependency on chemical fertilizers usually
reduces the amount of organic matter and can
change the physical, chemical, and biological
properties of the soil.
Agricultural Chemical Use
 A pesticide is any chemical used to kill or control
populations of unwanted fungi, plants, or animals
(pests).
 Pesticides can be subdivided into several categories
based on the organisms they control.
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Insecticides control insect populations.
Fungicides control fungal pests.
Rodenticides control mice and rats.
Herbicides control plant pests.
Biocides kill a large variety of organisms.
Agricultural Chemical Use
 Pests are often referred to as target organisms.
 Many pesticides kill non-target organisms as an
unwanted side effect.
 Persistent pesticides remain active for long
periods.
 Nonpersistent pesticides break down quickly.
Agricultural Chemical Use
 Insecticides are used to control insect populations.
 3,000 years ago, Homer noted the use of sulfur to
control insects.
 It has been known for centuries that certain plant
products produce repellant chemicals.
• Nicotine (tobacco)
• Rotenone (tropical legumes)
• Pyrethrum (chrysanthemums)
Agricultural Chemical Use
 The discovery of chemicals that could kill insects
was celebrated as a major advance in the
control of disease and the protection of crops.
• Mosquitoes are known to carry over 30 diseases
harmful to humans.
 In 1867, the first synthetic inorganic insecticide
was formulated.
 In 1942, DDT became the first synthetic organic
insecticide produced.
 Several new categories of these compounds
have since been developed.
Agricultural Chemical Use
 Chlorinated hydrocarbons are a group of
complex, stable-structure, long-lasting, persistent
pesticides.
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They remain effective for long periods after application.
They tend to accumulate in soil and animal bodies.
They affect many non-target organisms.
They are no longer used in many parts of the world.
– They are still used in many developing countries to protect
crops and public health.
• Because of their persistence and continued use in many
parts of the world, they remain present in the food chain.
Agricultural Chemical Use
 Organophosphates and carbamates are shortlived pesticides that do not persist in the
environment.
 Both work by interfering with the ability of the
nervous system to conduct impulses normally.
 These pesticides affect the nerve cells of humans
and other vertebrates as well.
 Persons who apply such pesticides must use
special equipment and should receive special
training in safe application practices.
Agricultural Chemical Use
 Common organophosphates are malathion,
parathion, and diazinon, which is widely used in
gardens.
 Carbaryl, propoxur, and aldicarb are examples
of carbamates.
• Carbaryl is sold under the brand name Sevin and is
widely used in home gardens.
Agricultural Chemical Use
 Herbicides are used to control unwanted plants.
• About 60% of pesticides used in U.S. are herbicides.
• Weeds compete with crops for soil nutrients.
• Traditional weed control methods are expensive in terms
of time and energy.
Agricultural Chemical Use
 Several major types of herbicides are in current
use.
• Synthetic plant growth regulators mimic natural growth
regulators (auxins).
– 2,4-D; 2,4,5-T
• Photosynthetic disruptors
• Enzyme inhibitors
Agricultural Chemical Use
 Some herbicides are toxic to all plants
(nonselective), and some are selective as to the
plant species they affect.
• Atrazine is often used to control broad-leaf and
grassy weeds.
• Glyphosate (Roundup) is a broad-spectrum,
nonselective, systemic herbicide used to control
annual and perennial plants.
Agricultural Chemical Use
 Fungicides are used to protect agricultural crops
from spoilage, to prevent the spread of disease,
and to protect seeds from rotting in the ground
before they can germinate.
• Methylmercury is extremely toxic to humans.
 In some parts of the world, governments pay a
bounty to people who kill rats because they can
destroy agricultural crops.
• Rodents also carry diseases harmful to humans.
• Rodenticides must be used with great care to prevent
poisoning non-target organisms.
Problems with Pesticide Use
 A perfect pesticide would have the following
characteristics:
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Inexpensive
Only affect target organisms
Short half-life
Break down into harmless materials
 Newer pesticides have fewer drawbacks than early
pesticides, but none are devoid of problems.
Problems with Pesticide Use
 Persistent pesticides become attached to small
soil particles and are easily moved by wind or
water.
• They may be distributed throughout the world from
local applications.
• Persistent pesticides have been discovered in polar
ice and are present in detectable amounts in the
bodies of animals, including humans, throughout the
world.
Problems with Pesticide Use
 Bioaccumulation is the process of accumulating
higher and higher amounts of material within an
organism’s body.
– Many persistent pesticides are fat soluble and build up in
fat tissues.
 Biomagnification is the process of acquiring
increasing levels of a substance in bodies of higher
trophic-level organisms.
– DDT, mercury, and PCBs are all known to accumulate in
ecosystems.
– DDT was banned in the U.S. in the early 1970s.
Problems with Pesticide Use
The biomagnification of DDT
Problems with Pesticide Use
 Pesticide resistance is a problem associated with
the widespread use of pesticides.
• Insecticides only kill susceptible individuals.
• Most surviving individuals have characteristics that
allowed them to tolerate the pesticide.
– Survivors pass on genetic characteristics for tolerance.
– Subsequent pesticide applications become less effective.
Problems with Pesticide Use
 Most pesticides are not species-specific, and kill
beneficial species as well as pest species.
• Many kill predator and parasitic insects that normally
control pest insects.
• Insecticides may change the population structure of the
species present so that a species not previously a
problem may become a serious pest.
Problems with Pesticide Use
 Short-term and long-term health effects to persons
applying pesticides and the public that consumes
pesticide residues in food are also concerns.
 Acute poisoning during application sometimes
occurs when farmers cannot read caution labels on
packaging or do not have access to protective
gear.
 The WHO estimates between 1 million and 5
million acute pesticide poisonings occur annually,
resulting in 20,000 deaths.
Problems with Pesticide Use
 For most people, the most critical health problem
is inadvertent exposure to small quantities.
• Farmers who were occupationally exposed to
pesticides over many years show that they have
higher levels of certain kinds of cancers than the
general public.
 Chronic minute exposures to pesticide residues
in food or through contaminated environments
are also of concern.
Problems with Pesticide Use
 A variety of factors is likely to make people in
developing countries, especially farmers and
agricultural workers, more vulnerable to the
toxicological effects of pesticides:
• Low literacy and education levels
• Weak or absent legislative and regulatory frameworks
• Climate factors that make the use of protective
clothing during pesticide application uncomfortable
• Inappropriate or faulty spraying technology
• Lower nutritional status (weaker physiological
defenses against toxic substances)
Why Are Pesticides So Widely Used?
 Food Production
• Worldwide, pests destroy 35% of crops.
– This represents an annual loss in U.S. of $18.2 billion.
 Economic Concerns
• Pesticides increase yields and profits.
 Health Reasons
• Insecticides curtail many diseases.
Why Are Pesticides So Widely Used?
Changes in pesticide use
Alternatives to Conventional Agriculture
 Prior to the invention of synthetic fertilizers and
other agrochemicals,
• Animal manure and crop rotation provided soil nutrients.
• A mixture of crops prevented regular pest problems.
• Manual labor killed insects and weeds.
Alternatives to Conventional Agriculture
 With the development of mechanization, many
farmers changed from mixed agriculture to
monocultures.
• This presented greater opportunities for pest
problems to develop.
• Chemical pesticides were used to “solve” the
problem.
Alternatives to Conventional Agriculture
 Alternative agriculture includes all
nontraditional agricultural methods.
 Sustainable agriculture seeks to produce
adequate, safe food supplies in an economically
viable manner while protecting or enhancing
ecosystem health.
 There are many different types of sustainable
pest and weed control practices.
Alternatives to Conventional Agriculture
 They are guided by some general principles that
include:
• Keeping insecticide, herbicide, fungicide, and fertilizer
use to a minimum.
• Biological diversity should be encouraged.
• Healthy, biologically active soils lead to healthier, more
insect- and disease-resistant plants and animals.
• Natural or supplemented populations of beneficial
insects (“good bugs”) will keep pests (“bad bugs”)
below economically damaging levels. Many sustainable
farmers purposely grow plants that will attract beneficial
insects.
Alternatives to Conventional Agriculture
 Organically grown is a legally defined term in the
U.S. that tells you how a food or fiber crop was
grown.
 The U.S. Federal Organic Foods Production Act of
1990 defines national organic standards, which
generally:
• Require organic farms and handlers to be “certified,” or
inspected by a disinterested third party.
• Require that an organic farm be increasing its soil fertility
through sustainable soil-building techniques.
• Prohibit synthetic pesticides and fertilizers.
Alternatives to Conventional Agriculture
 While the cost of organic products can be more
expensive, they may be thought of as less
expensive in the long run.
 The organic market, while growing, is still limited
by low supply, so prices are higher than they
might otherwise be.
 Most organic food is produced by smaller farms
that do not have the economics of large-scale
industrial agribusiness.
Alternatives to Conventional Agriculture
 Changes in agricultural production methods can
help to reduce the problems of soil compaction and
loss of organic matter:
• Reducing the number of trips farm equipment must
make over the land reduces soil compaction.
• Incorporating crop residue into the soil builds organic
matter.
• Reducing fertilizer runoff helps aquatic ecosystems.
• Careful selection, timing, and use of pesticides
decreases the extent to which these materials become
environmental contaminants.
Alternatives to Conventional Agriculture
 Precision agriculture is a new technique that
addresses many of these concerns.
 With modern computer technology and
geographic information systems, it is possible,
based on soil and topography, to automatically
vary the chemicals applied to the crop at
different places within a field.
 Crop rotation is an effective way to enhance soil
fertility, reduce erosion, and control pests.
Alternatives to Conventional Agriculture
 Integrated pest management (IPM) uses a variety
of methods to control pests rather than relying
solely on pesticides.
 It requires information about:
• Crop plant metabolism
• Biological interactions between pests and their predators
and/or parasites
• Climatic conditions favoring pests
• Techniques to encourage beneficial insects
Alternatives to Conventional Agriculture
 Several methods are employed in IPM:
• Disrupting reproduction
– Female pheromones
– Male sterilization
• Natural predators
– Aphids can be controlled with ladybugs
– Bacterial strains
Alternatives to Conventional Agriculture
• Developing resistant crops
– Genetic engineering or biotechnology involves inserting
specific pieces of DNA into the genetic makeup of
organisms.
– Genetically modified organisms can be developed for pest
and herbicide resistance, although some groups are
opposed to the use of genetically modified organisms.
– The European Union will not import genetically modified
grains from the U.S.
Alternatives to Conventional Agriculture
• Modifying farming practices
– Crop rotation tends to prevent the buildup of specific pests
that typically occurs when the same crop is raised in a field
year after year.
• Selective use of pesticides
– Identification of the precise time when pesticide
application will have the greatest effect at the lowest
possible dose is a useful practice.