Chapter 22: Pests and Pesticides: Growing Crops
Sustainably
22.1 Chemical Pesticides
Pest control measures have been used for centuries. Earliest techniques included cultural
controls, such as burning fields to kill locusts, and chemical controls, the use of toxic
chemicals to kill insect pests. Early chemicals have been abandoned because they were
toxic, ineffective, or environmentally persistent.
Modern Chemical Pesticides
The first synthetic organic chemical used as a pesticide was a chemical called DDT,
whose discovery ushered in a new era of synthetic chemical pesticides. Chemical
pesticides are either broad-spectrum substances that kill a variety of pest species, or
narrow-spectrum chemicals that are effective against one or a few pests.
Three main types of synthetic organic chemical pesticides have been developed over the
years – chlorinated hydrocarbons, organophosphates, and carbamates. These are all
neurotoxins. Carbamates are less persistent in the environment or body fat of organisms –
and are thus less likely to be biomagnified in the food chain than organochlorines.
Unfortunately, they are much more toxic to people.
Growth in the Use of Chemical Pesticides
The more developed nations, including the United States, are the major consumers of
chemical pesticides. In the United States, the bulk of the pesticides in use are herbicides.
Overuse
Pesticides are often applied far in excess of what’s needed by farmers and especially
homeowners. Homeowners also often fail to take precautions to protect themselves from
exposure.
Biological Impacts of Pesticides
The initial success of DDT led to a rapid increase in pesticide use and in the number of
new chemical pesticides. Problems soon began to emerge, though.
One major impact of pesticides is that they often kill natural pest control agents such as
predatory insects that are more sensitive to pesticides. This unleashes the growth of pest
populations. Pesticides also kill other beneficial insects such as pollinators.
Pesticide use results in the formation of genetically resistant pest species. Higher doses
and new pesticides, used to combat them, only worsen the situation by creating even
more resistant species.
Pesticides poison fish, birds, and other species outright and also biomagnify in the food
chain. Thus, seemingly low concentrations in the environment can result in very high
levels in organisms in the uppermost trophic level, which may impair reproduction.
Pesticides contaminate many foods and have been found in human body tissues even in
remote areas of the world, indicating that pesticides are globally distributed. Chemical
and farm workers are frequently exposed to the highest levels, especially in the less
developed nations. The effects of pesticide exposure range from mild neurological
problems to death, depending on the exposure level and type of chemical.
The Economic Costs of Pesticide Use
Pesticide use is not just a threat to human health and the environment, it causes
considerable economic damage.
Herbicides in Peace and War
Plant auxins are hormones that stimulate plant growth. Two of the most widely studied
herbicides are auxin-like compounds.
Herbicides provide many benefits but do not come without social and environmental
costs. Fortunately, there are many ways to reduce or eliminate herbicide use.
Extensive use of chemical defoliants (Agent Orange) during the Vietnam War has
resulted in substantial environmental and health impacts in soldiers and their offspring.
The health effects are attributed to dioxins that contaminate the herbicide.
The Alar Controversy: Apples, Alar, and Alarmists?
Children may be at higher risk to pesticides than adults, especially pesticides used on
fruit.
22.2 Controlling Pesticide Use
Bans on Pesticide Production and Use
Many environmentally harmful pesticides have been banned in the United States in the
past 30 years. Some of these pesticides, however, continue to be used in other countries,
where they poison wildlife and migratory birds and contaminate crops destined for local
markets as well as markets in the United States and other more developed countries.
Registering Pesticides
The EPA registers newly developed and previously introduced pesticides for general or
restricted use and stipulates what crops they can be used on, a process called registration.
Many improvements are needed in this system to make it more effective, especially more
rigorous education and testing of users.
Establishing Tolerance Levels and Monitoring Produce
The EPA also sets tolerance levels – acceptable levels of pesticides on food – which are
monitored by the U.S. Food and Drug Administration. Unfortunately, inadequate funding
prohibits thorough sampling.
Weakening Protection
22.3 Integrated Pest Management: Protecting Crops Sustainably
Integrated pest management is a set of alternative strategies to control pest populations at
manageable levels. It offers substantial social, economic, and environmental benefits and
is the cornerstone of a sustainable system of agriculture.
Environmental Controls
Environmental controls seek to change both the biotic and abiotic conditions of crops in
ways that reduce the growth of pest populations, while causing little if any damage to the
crop itself.
Planting several different crops on a farm and rotating crops in fields from one year to the
next are very effective means of reducing the growth of insect populations without
pesticides.
Crops can be planted after the emergence of insect pests so that the pests have little to eat
and subsequently perish.
Insects are sensitive to nutrient levels in plants, so raising or lowering soil nutrients – and
thus plant nutrients – can effectively control some species.
Adjacent weeds or crops may harbor beneficial or harmful insects. Controlling what
grows beside a given crop can therefore be a powerful tool in protecting crops, with little
or no pesticide use.
Many natural biological control agents can be used to prevent the outbreak of pest
species.
Genetic Controls
Many insects breed only once, so the introduction of large number of artificially sterilized
males into a pest-infested region will result in an abundance of sterile eggs.
Plants and animals that are resistant to pests and diseases can be developed through
genetic engineering and artificial selection. Bacteria that live on the roots and other parts
of plants can also be genetically engineered to make them lethal to insect pests.
Chemical Controls
Conventional pesticides will remain in use, but they must be screened carefully to avoid
harmful ones. Those that are used must be administered with caution – in amounts and at
a time when they are most effective, to minimize their environmental impact. This
requires better monitoring of crops and infestations.
Scientists and farmers are exploring a whole new group of naturally occurring chemicals
to control insect pests. These could eventually become the cornerstone of pest
management in a sustainable system of agriculture.
Pheromones are natural sex attractants released by insects. They can be used to draw
insects into traps or can be sprayed on fields to confuse males so they cannot find females
with which to mate. These substances are nontoxic and biodegradable.
Two hormones control the life cycles of insects and can be sprayed on crops to alter these
cycles and lead to the death of pests. Unfortunately, to be effective, application must be
precisely timed and these hormones take a fair amount of time to kill off a pest.
Plants have evolved many natural insect repellants that can be commercially produced
and sprayed on crops to help control pests.
Cultural Controls
Insect pests can be controlled by many techniques that do not require the use of
chemicals. These are called cultural controls and include measures such as noisemakers
to frighten birds from crops, manual removal of insects, and quarantines on imported
food.
Educating the World About Alternative Strategies
Educating farmers and others about alternative strategies is imperative if sustainable pest
management is to become widely adopted the world over. Universities, agricultural
agencies, farmers’ groups, and nonprofit organizations are several of the avenues
available for this important task.
Government Actions to Encourage Sustainable Agriculture
Governments can promote sustainable agriculture by providing low-cost crop insurance
for farmers who make the transition to integrated pest management, and by developing
organic certification programs.