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A pest is any organism detrimental to humans; agricultural
pests "interfere with the production and utilization
of crops and livestock used for food and fiber. They include
insects, mites, nematodes, plant pathogens, weeds, and
vertebrates. If pests are not managed, crop yield and
quality drop.
Approximately 600 species of insects, 1,800 weed species,
and numerous species of fungi and nematodes are considered
serious pests in agriculture. From an economic viewpoint,
an agricultural pest is an animal or plant whose population
density exceeds some unacceptable threshold level, resulting
in economic damage. Weeds are by far the most pervasive
pests in U.S. agriculture in terms of the share of pesticide
treatments used to control them. Pest
Management in U.S. Agriculture shows that in 1996:
- The share of all pesticide acre-treatments (number
of acres treated times the number of pesticide treatments)
aimed at controlling weeds was nearly 100 percent for
soybeans, 90 percent for wheat, and 83 percent for corn.
- Among major crops, other pest classes surpass weeds
in control efforts only for fall potatoes and cotton.
Pathogens account for 56 percent of all potato pesticide
acre-treatments, while insects account for 45 percent
of all cotton pesticide acre-treatments.
Contents
Methods for Managing Agricultural Pests
Pest management involves a set of techniques to reduce
pest populations or prevent their detrimental effect both
at and beyond the farm. Underlying pest management is
the philosophy that “pests should be managed, not
eradicated” and that pests are inevitable components
of an agricultural system.
Different pest classes may dominate across different crops
and regions, calling for different pest management techniques
to control them. For example, insects are a major pest
class in cotton production, while minimal for soybeans.
Thus, adoption of insect management techniques is more
widespread among cotton producers than among soybean producers.
Also, insect management has a wider variety of (nonchemical)
control measures than does weed control.
There are four broad categories of pest management tools:
chemical management, cultural management, biological management,
and bioengineered crops.
Chemical management uses any of a large number
of chemical pesticide products to repel, debilitate, or
kill pests. Thousands of formulations (commercial forms
in which the pesticide is sold) are used, with different
mixtures of active ingredients and inert materials. Hundreds
of chemical products are used as active ingredients, and
each has a different spectrum of pest control, a different
potency, and a different impact on human health and the
environment.
Scouting and economic thresholds are techniques to improve
the efficiency of chemical pesticides and to replace routine,
calendar-based chemical applications.
- Scouting involves regular and systematic sampling of fields
to determine the presence and severity of pest infestation
levels, and to determine when an economic threshold
is reached. Scouting may also involve monitoring beneficial
organisms, which help control pests without harming
the crops. The scout may use several techniques, including
visual rating of pest severity and the use of traps
or collecting devices to concentrate pest samples.
- An economic threshold refers to the pest population
density above which economic damage to the crop would
occur without chemical application. When the threshold
is reached or exceeded, control measures must be taken
to prevent pests from reaching the "economic injury
level," defined as the lowest pest population
density that will cause net economic losses.
Cultural management includes mechanical cultivation,
adjusting planting/harvesting dates, and crop rotations,
all designed to make the environment less favorable for
pests. These practices are used fairly extensively on
all field crops. Cultural management also considers plant
density, timing of harvest, water management, the use
of trap crops, field sanitation to destroy or use crop
refuse, mulching, and pest-free seeds and seeding methods.
Biological management accommodates predators (such
as wasps, lacewings, and lady beetles), parasites, pathogens
(including bacteria, fungi, and virus), competitors, and
antagonistic microorganisms, all believed to pose little
health or environmental threat. Another biological technique
is the use of biopesticides, the most successful of which
is the soil bacterium Bacillus thuringensis (Bt).
Bioengineered crops are genetically
engineered with traits for pest management. Their
use has risen dramatically since commercial introduction
in the mid-1990's. Compared with traditional plant selection
and breeding methods, genetic engineering reduces the
time to identify desirable traits and allows a more precise
alteration of a plant's traits. Seed developers are able
to target a single plant trait without the unintended
characteristics that may occur with traditional breeding
methods. The most widely used pest management traits are
herbicide tolerance and insect resistance. Crops having
herbicide-tolerant traits permit farmers to use herbicides
that offer more effective weed control. Insect-resistant
crops containing a gene derived from the soil bacterium
Bt produce their own toxin to protect the entire plant
from certain insects.
Extent of Adoption of
Pest Management Tools
Chemical management—Scouting was used extensively
by most field crop farmers in 2000:
- 57 to 90 percent of the major field crop acreage
was scouted for diseases, with winter wheat the lowest
and durum wheat the highest
- 71 to 97 percent of the major field crop acreage was
scouted for weeds, with winter wheat the lowest and
durum wheat the highest
- 62 to 91 percent of the major field crop acreage was
scouted for insects, with winter wheat the lowest and
cotton the highest.
Biological management—Across
all of the surveyed field crops in the 1996, the pest
management practice of considering beneficial insects
when selecting pesticides was more broadly used than any
of the other biological practices, particularly for cotton,
with 52 percent of the planted acres, and fall potatoes,
with 29 percent of the planted acres. Cotton growers were
also the major users of most other biological practices:
they used pheromone lures to control pests on 7 percent
of their planted acres, foliar Bt on 4 percent of their
insecticide-treated acres, and Bt varieties on 15 percent
of the planted acres. However, soybean farmers were the
largest users of herbicide-tolerant varieties.
Cultural management—Crop rotations
were used on at least 82 percent of the 1996 planted acres
for major field crops except for cotton and winter wheat,
where only 33 and 58 percent of the planted acres were
in rotation, respectively.
Cotton growers used mechanical cultivation and adjusted
planting or harvesting dates on 89 and 25 percent of the
acres, respectively.
Bioengineered crops—U.S. farmers
have rapidly adopted genetically engineered (GE) crops
since their introduction in 1996, notwithstanding conflicting
claims about consumer acceptance and economic/environmental
impacts. Soybeans and cotton with herbicide-tolerant traits
have been the most widely and rapidly adopted GE crops
in the U.S., followed by insect-resistant cotton and corn.
Herbicide-tolerant (HT) crops, developed to survive application
of specific herbicides that previously would have destroyed
the crop along with the targeted weeds, provide farmers
with a broader variety of options for effective weed control.
In 2002, plantings of HT soybeans reached 75 percent of
soybean acreage and HT cotton expanded to 58 of cotton
acreage.
Insect-resistant crops containing the gene from the soil
bacterium Bt (Bacillus thuringiensis) have also been available
for corn and cotton since 1996. These bacteria produce
a protein that is toxic to certain lepidopteran insects
(insects that go through a caterpillar stage), protecting
the plant over its entire life. In 2002, plantings of
Bt corn reached 24 percent of the corn acreage and Bt
cotton expanded to 35 percent of the cotton acreage. The
above figures include "stacked" varieties of
cotton and corn, which have both HT and Bt traits.
Pest management tools used by fruit and vegetable
producers—A common pest management practice among
growers of fruits and vegetables was alternating pesticides
to reduce pest resistance. Its use ranged from 36 percent
for grape acreage to 75 percent for apples in 1993-95.
- Scouting for pests ranged from 68 percent of the
grape-planted acreage to 98 percent for strawberries,
with an overall average of about 80 percent.
- Pheromones for control were more often used on fruit
and vegetable acreage relative to field crops.
- Pest-resistant varieties were also used at relatively
high rates for
tomatoes (37 percent), strawberries (37 percent), and
peaches
(44 percent).
- Growers considered beneficial insects in selecting
pesticides on 80
percent of the apple acres, and smaller amounts in other
fruits
and vegetables.
Pesticide Use
Trends in the United States
Synthetic pesticides were initially developed
for commercial agricultural use in the late 1940s and
1950s and were widely adopted by the mid-1970s. Pesticide
use on major field crops, fruits, and vegetables more
than doubled from 215 million pounds in 1964 to 511 million
pounds in 2001. The crops included in USDA's pesticide
surveys—corn, cotton, soybeans, wheat, fall potatoes,
other vegetables, citrus, apples, and other fruit—account
for about 76 percent of current cropland used for crops.
Pesticide use first peaked in 1982 when cropland used
for crops was record-high. This peak can be attributed
to increased planted acreage, a greater proportion of
acres treated with pesticides, and higher application
rates. Herbicides accounted for most of the increase.
Total pesticides declined between 1982 and 1990 as commodity
prices fell and large amounts of land were taken out of
production by Federal programs.
Since 1990, pesticides have edged above the 1982 peak,
largely due to expanded use of soil fumigants, defoliants,
and fungicides on potatoes, fruits, and vegetables. Total
herbicides and insecticides remained relatively unchanged
despite more intensive insecticide treatments on cotton
and potatoes and an increased share of wheat acres treated
with herbicides.
In 2001, corn received almost 37 percent of total pesticides
applied to the major crops. Corn accounted for almost
58 percent of all herbicide use and 16 percent of insecticides.
Cotton was the leading user of insecticides, accounting
for around 48 percent. Potatoes and vegetables used the
most fungicides, soil fumigants, desiccants, growth regulators,
and vine killers.
Herbicides—Herbicides are the largest pesticide
class, accounting for 60 percent of total pounds of pesticide
active ingredient in 2001. With a decrease in corn and
soybean acreage, herbicide quantities were down slightly
in 2000 and 2001, about 30 percent less than the levels
applied in 1982.
Insecticides—Insecticides accounted for 12
percent of total pesticides applied in 2001 to the surveyed
crops. Corn and cotton account for the largest shares
of insecticide use. Insecticide use includes both preventative
treatments, which are applied before infestation levels
are known, and intervention treatments, based on monitored
infestation levels and expected crop damages.
While insecticides applied have fluctuated between 60
and 80 million pounds, the amount is down significantly
from the 1960s and early 1970s, primarily due to the replacement
of organochlorine insecticides with insecticides that
can be applied at much lower rates.
Fungicides—Fungicides are applied to fewer
acres than are herbicides or insecticides and account
for the smallest share of total pesticide use. Fungicides
are mostly used on fruits and vegetables to control diseases
that affect the health of the plant or the quality and
appearance of the fruit. The 33 million pounds estimated
in 2001 is down slightly from 2000, in keeping with declines
in potato and vegetable acreages.
Other pesticides—These pesticides include
soil fumigants, growth regulators, desiccants, and harvest
aids, and had the largest increase in use of any of the
pesticide classes. The use of these pesticides, whose
function is not necessarily to destroy a pest organism,
peaked at 119 million pounds in 1999 and declined 9 percent
since then. Other pesticides account for about one-fifth
of the total pounds of all active ingredients applied
to the surveyed crops.
Fumigants, normally applied at high application rates,
are used mostly on potatoes and vegetable root crops susceptible
to damage from soil nematodes and other soil organisms.
Sulfuric acid (often applied at several hundred pounds
per acre to kill potato vines and to aid harvest) and
soil fumigants account for most of the quantity of fumigants,
but they are applied to a small share of the total acreage.
Small changes in the use of these ingredients, when averaged
with other products applied at only a few pounds or less
per acre, can grossly affect the total quantity of pesticide
use in this class.
Growth regulators, desiccants, and harvest aids, normally
applied at low rates, are used to affect the branching
structure of plants, to control the time of maturity or
ripening, to alter other plant functions to improve quality
or yield, and to aid mechanical harvest.
Integrated Pest Management
(IPM) and Factors Influencing its Adoption
Techniques or practices collectively referred
to as Integrated Pest Management (IPM) were designed to
address some of the health and environmental concerns
of pesticide use and to combat pest resistance to pesticides.
IPM practices that would meet production and environmental
goals differ by crop, region, and pest problem. IPM attempts
to capitalize on natural pest mortality factors: pest-predator
relationships, genetic resistance, and the timing and
selection of cultural practices, such as tillage, pruning,
plant density, and residue management. In practice, however,
IPM is often based on:
- Scouting fields to determine pest populations or infestation
levels
- More precise timing and application of pesticides
based on scouting
- Better knowledge of the consequences of various levels
of pest and predator populations
- Rotations
- More precise timing of planting
The USDA, other government agencies, land-grant universities,
agricultural extension services, private consultants,
consumer groups, and environmental organizations have
actively encouraged IPM adoption. A 1999 ERS report, Pest
Management in U.S. Agriculture, notes that because
different pest classes may dominate among different crops
and regions, requiring different pest management techniques
to control them, adoption of pest management practices
varies widely. For example, insects are a major pest class
in cotton production, while minor for soybeans. As insect
management has a wider variety of nonchemical techniques
than weed control, cotton growers are expected to be further
ahead on the IPM continuum than soybean producers. On
the other hand, weed control is very important for soybeans
and corn. As a consequence, and given the large corn and
soybean acreage, future progress in IPM adoption will
depend upon weed management efforts.
A complete, practical, and accepted method to measure
overall IPM adoption is not yet available. (One source
for aggregate information for particular pest management
practices on selected crops is USDA's National Agricultural
Statistics Service (NASS) 1997 and 1998 Fall Area Surveys.)
However, some progress has been made on IPM research regarding
the factors influencing adoption. Among fruit and vegetable
growers:
- Adopters of IPM are more inclined to risk-taking
than nonadopters
- Operators of large farms are more likely to adopt
IPM than operators of smaller farms
- Availability of both managerial and nonmanagerial
labor are significantly and positively associated
to the adoption of IPM
- Farm ownership is not a factor in IPM adoption because
IPM does not require investments tied to the land
- The physical environment of the farm is also a factor
because it may affect profitability directly through
increased fertility, and indirectly through its influence
on pests
Slowing the rate of IPM adoption may be the difficulty
growers face in quantifying the economic advantage of
IPM. Also, unlike traditional chemical methods that provide
the farmer with precise instructions, IPM is less precise
and its recommendations often conflict with a farmer's
intuition. In addition, IPM is a complex, knowledge- and
information-intensive technology, and many farmers believe
that IPM is complicated and difficult to use.
The evidence from previous studies on the effects of
IPM is sketchy. In many cases, adoption of IPM leads to
a reduction in pesticide use, an improvement in yields,
or both. Most studies also show that farmers increase
their net returns by using IPM. Estimates of the impact
of IPM on pesticide use, yields, and farm income are summarized
in the Agricultural Resources
and Environmental Indicators.
Implications of the
Methyl Bromide Phase-Out
The United States and many other countries are
phasing out production and importation of the fumigant
methyl bromide under the Montreal
Protocol on Substances that Deplete the Ozone Layer.
Methyl bromide has been classified as one of a number
of substances that deplete the stratospheric ozone layer.
Ozone depletion could cause increased skin cancer, sunburn,
eye damage, crop damage, and temperature extremes.
The schedule for reducing methyl bromide production
and importation—from a 1991 baseline—for the
United States and other developed counties is 25 percent
in 1999, 50 percent in 2001, 70 percent in 2003, and 100
percent in 2005. For developing countries, there will
be a freeze in 2002 at a 1995-98 baseline and a reduction
of 20 percent in 2005 and 100 percent in 2015. The Montreal
Protocol also allows preshipment and quarantine uses of
methyl bromide and critical-use exemptions after 2005.
In agriculture, methyl bromide is used as a preplant soil
fumigant to control a wide spectrum of pests (nematodes,
weeds, and pathogens) in fruits, nuts, vegetables, ornamentals,
and agricultural nurseries. It is also used in commodity
storage facilities prior to shipment to protect product
quality from pest damage, and to satisfy government quarantine
requirements in order to prevent the spread of exotic
pests.
Worldwide, over 95 percent of methyl bromide is used
for preplant or postharvest fumigation, while the remainder
is used for structural fumigation. In the United States,
EPA estimates that 38.1 million pounds were used for preplant
fumigation in 1997. Fresh-market tomatoes and strawberries,
primarily in Florida and California, accounted for over
40 percent of the use.
The economic implications
of the phaseout will depend on the cost-effectiveness
of alternatives and when they become available for use.
Many researchers believe that the development of cost-effective
alternatives for many methyl bromide uses will be difficult.
If new alternatives are not as cost-effective as methyl
bromide, the cost of growing some crops-such as tomatoes,
strawberries, nursery transplants, and other fruit and
vegetable crops-could increase. This could dampen U.S.
production and acreage, increase imports, and raise consumer
prices. There could also be higher storage costs and instorage
quality losses for such commodities as dried fruits and
nuts. While quarantine and preshipment uses are exempted,
costs of these treatments could increase as limitations
on methyl bromide supplies become stricter.
To help reduce the impact of the phaseout, USDA, EPA,
State universities, and private firms are working to develop
alternatives and make them available to methyl bromide
users.
Some methyl bromide users in the United States and other
countries have applied for critical use exemptions. To
qualify, methyl bromide alternatives with acceptable health
and environmental effects must be shown to be technically
and economically infeasible and there must be a significant
market disruption without the use of methyl bromide. Additionally,
the country must take steps to develop alternatives and
to minimize the methyl bromide used and emissions. The
parties to the Montreal protocol are scheduled to authorize
exemptions for 2005 in late 2003.
Implications of
the Current Assessment of the Risks of Organophosphate
Pesticides
Organophosphates are among the first pesticides
to have their food residue tolerances reassessed under
the Food Quality
Protection Act of 1996 (FQPA). A tolerance (or exemption)
is required for residues of a pesticide to be present
in a food; it also defines the maximum legal limit of
the pesticide residue in the food.
The FQPA amended the Federal Insecticide, Fungicide,
and Rodenticide Act (FIFRA) and the Federal Food, Drug,
and Cosmetic Act (FFDCA). It set a consistent safety standard
for risks from pesticide residues in foods: “ensure
that there is a reasonable certainty that no harm will
result to infants and children from aggregate exposure
to the pesticide chemical residue.” Pesticide residues
are no longer subject to the Delaney Clause of FFDCA,
which prohibited processed foods, but not fresh foods,
from containing even trace amounts of carcinogenic chemical
residues. Now, both fresh and processed foods may contain
residues of pesticides classified as carcinogens at tolerance
levels determined to be safe. Benefits of pesticide use
no longer have a role in setting new tolerances, but may
have a limited role in decisions concerning existing tolerances.
FQPA included special provisions to encourage registration
of minor-use and public-health pesticides.
The FQPA requires a reassessment
of all residue tolerances for uses of currently registered
pesticides against the new safety standard. EPA must consider
dietary exposures to a pesticide from all food uses and
from drinking water, as well as nonoccupational exposure,
such as homeowner use of a pesticide. EPA must also consider
increased susceptibility to infants and children or other
sensitive subpopulations and the cumulative effects from
other substances with a “common mechanism of toxicity.”
If risk of a pesticide exceeds the standard, EPA will
reduce residue limits or revoke tolerances for uses of
the pesticide until the standard is met. If a common mechanism
of toxicity is identified for a group of pesticides, the
cumulative risk of the group must meet the standard. EPA
was required to reassess 33 percent of all tolerances
by 1999, 66 percent by 2002, and the remainder by 2006.
EPA must give high priority to reviewing tolerances of
pesticides that appear to pose the greatest risk to public
health. In 1997, EPA gave high priority to organophosphates,
as well as to carbamates and probable human carcinogens.
One reason for organophosphates' high priority is dietary
exposure by children. Of the approximately 1,800 organophosphate
tolerances, over 300 are for foods among the top 20 consumed
by children. EPA also has expressed concern that organophosphates
exhibit a common mechanism of toxicity, which requires
a cumulative assessment of risk.
Organophosphates are a health concern because they affect
acetylcholinesterase, the enzyme that controls the nervous
system. Exposure to these materials can occur through
inhalation, skin absorption, and ingestion. Common symptoms
from overexposure are headaches, nausea, and dizziness,
but more severe exposures can cause sensory and behavior
disturbances, incoordination, and depressed motor function,
and, at high concentrations, respiratory and pulmonary
failure. The long-term effects of these chemicals, especially
when exposure is during early growth and development periods,
is not fully known.
Farmers have used organophosphate pesticides for many
years to reduce pest damages on many crops. Many are insecticides
that kill a broad spectrum of insects and have a longer
persistence than some alternatives. Widely used organophosphate
insecticides include chlorpyrifos, methyl parathion, terbufos,
dimethoate, malathion, phorate, chlorethoxyfos, and acephate.
In 1996, 26.2 million acres were treated with organophosphates.
Field crops—primarily corn, cotton and wheat—accounted
for most of the crop acreage treated, with 52 percent
of cotton acreage treated. And while they represent a
much smaller acreage receiving organophosphates, a high
percentage of land in fruits and vegetables (for example,
94 percent of apple acreage and 67 percent of lettuce)
is treated. Organophosphates were applied to nearly half
the acreage of crops identified as most common in the
diets of infants and children (apples, peaches, pears,
carrots, sweet corn, snap beans, peas, and tomatoes).
If tolerances of any of the organophosphate pesticides
are revoked, the registration to use the pesticide on
the crop must be canceled, forcing growers to find alternative
practices. Depending upon their cost-effectiveness, the
use of alternatives could lower yields or increase costs
per acre. In some cases, one or more organophosphates
will be among the alternative practices for another. For
some crops treated with organophosphates, grower returns
could decline, production and acreage could decrease,
and prices and imports could increase. While they account
for a small portion of total organophosphate use, several
fruit and vegetable crops are particularly vulnerable
to large economic impacts.
Additional information on FQPA
and tolerance assessment is available from EPA.
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