VEGETABLE
RESEARCH AND
INFORMATION
CENTER
Organic
Vegetable
Production in
California
Series
Small Farm
Program
University of California • Division of Agriculture and Natural Resources
Publication 7251
Before planting a crop, an organic vegetable grower
needs to understand the pests and beneficial organisms
that usually occur in that crop and anticipate the pest
problems that are likely to occur. Experienced growers
act before problems reach devastating levels because
they know that pests are more effectively controlled
when their numbers are low. The major emphasis of
insect pest management in organic vegetable produc-
tion systems should be placed on the use of cultural
and biological control methods.
By paying attention to crop rotations and crop
residue incorporation, the grower can help prevent
population buildup in many pest species. The practice
of growing the same crop continuously, season after
season, on the same piece of ground is an invitation to
insect pests and diseases. In some locations, pest prob-
lems are so severe that it is not economically possible to
grow certain crops organically using current technolo-
gy. In areas of the San Joaquin Valley, for example,
where lygus bugs migrate into fresh market bean fields,
it is not possible to stop crop losses by using any of the
available materials approved for organic vegetable
growers. For the organic grower, the best solution to
pest problems often will only come out of a thorough
understanding of local conditions and a knowledge of
what varieties or crops to grow and when to plant them
in order to avoid the most severe problems. Good
record keeping on pest problems—when they occur
and what control strategies are effective—will help
build a foundation for next year’s pest control strategy.
MONITORING FOR PESTS AND BENEFICIALS
The correct identification of the pests and beneficials
present in a crop is very important. Identification of the
immature life stages such as eggs, nymphs, and larvae
will greatly aid the grower’s efforts to prevent econom-
ic damage to the crop. Many of the key pests in veg-
etable crops are described in pest management manuals
and literature available from the University of
California’s Division of Agriculture and Natural
Resources (see Resources). An experienced pest control
advisor can alert a grower to potential problems before
any crop losses occur.
If pheromone traps are available for key pest species,
they can help determine the timing of population cycles
and predict local increases in pest activity. In some situ-
ations, pheromones can be used to confuse males and
prevent them from mating, thus reducing next-genera-
tion pest populations and the feeding damage they
would cause. Be careful, though, to recognize when
biological control factors are beginning to influence the
pest population. Often, growers are unaware that bene-
ficial insects and microorganisms are working to con-
trol pests, and they end up treating crops when they do
not need to. By understanding the life cycle and biology
of both pests and beneficials, you can make the most of
the insect community that lives in the crop field.
To follow the activity of pests and beneficials in the
crop, it is important that the grower make regular
weekly checks in the field with a hand lens, inspecting
the underside of foliage for the first signs of insect activ-
ity. Many pest species are very small and so often go
unnoticed until they have caused considerable damage.
More frequent checks may be necessary during periods
of rapid increase for pests such as spider mites. Using a
sweep net in cover crops, field edges, and adjacent
crops, you can check for insect activity and help deter-
mine which beneficials or pests may be developing
nearby with the potential to move into the crop.
The grower must identify tolerable levels or action
thresholds for the particular pest species and crop. If it
Specific information on organic vegetable production practices in California is scarce, and growers need sound information
to guide their management decisions. The Organic Vegetable Production in California Series is made up of publications
written by Farm Advisors and Specialists from the University of California’s Division of Agriculture and Natural
Resources. Each publication addresses a key aspect of organic production practices applicable to all vegetable crops.
INSECT PEST MANAGEMENT
FOR ORGANIC CROPS
CALVIN FOUCHE, UC Cooperative Extension Farm Advisor,
San Joaquin County; MARK GASKELL, UCCE Farm Advisor,
Santa Barbara and San Luis Obispo Counties; STEVEN T. KOIKE,
UCCE Farm Advisor, Monterey and Santa Cruz Counties;
JEFF MITCHELL, UCCE Vegetable Crops Specialist,
Kearney Agricultural Center, Parlier; and RICHARD SMITH,
UCCE Farm Advisor, Monterey and Santa Cruz Counties
www.sfc.ucdavis.edu vric.ucdavis.edu
http://anrcatalog.ucdavis.edu/
http://www.sfc.ucdavis.edu/
http://www.sfc.ucdavis.edu/
http://vric.ucdavis.edu/
http://vric.ucdavis.edu/
is a pest that feeds on the fruit or on a part of the veg-
etable that is sold, the tolerance for damage is generally
lower. Pests feeding on portions of the plant that will
not be sold, such as the leaves of a tomato plant, can
often be tolerated at much higher levels.
CULTURAL CONTROL
You can coordinate the planting and harvesting dates
to avoid certain pests that would otherwise build up in
some crops. Sweet corn grown early in the summer, for
instance, is subject to less danger of earworm damage
than late-season corn. If aphid-transmitted virus dis-
eases are a problem, successive plantings of the same
crop will allow aphid populations to build up and
damage late-season crops unless virus-resistant vari-
eties are available. You may be able to reduce the
spread of disease by planting later crops upwind of ear-
lier-planted fields. In some areas, midsummer and late-
season plantings must be located in isolated fields.
Other pests such as lygus, flea beetles, squash bugs, and
many caterpillar species can build up in early crops and
cause extensive damage in later plantings unless they
are controlled before they can mature and reproduce.
Vegetable growers need to provide optimum grow-
ing conditions for their crops. Many plants are able to
withstand insect feeding if they are actively growing
and are able to compensate for some loss of foliage and
root tissues. Soil type and nutrient content can effect
crop vigor. Poor water management (especially too lit-
tle water) can predispose plants to certain pests such as
spider mites. Cover crops planted prior to the main
cash crop can improve soil fertility and provide a valu-
able source of organic matter. Proper rotation of pest-
susceptible main crops with non-susceptible varieties
and cover crops can keep pest numbers low. The incor-
poration of a grass species into a rotation is often rec-
ommended, as grasses tend to be resistant to most of
the insect and disease pests of common cash crops.
Field borders or strips within the field that are plant-
ed to species and varieties different from the main crop
can provide habitat for beneficial arthropods and can
slow the spread of pest species in the field. Flowering
plants along borders and edges of fields can provide
habitat and food for beneficial insects. Research in Yolo
County has shown that substantial numbers of benefi-
cial insects can move up to 250 feet from hedgerows into
adjacent vegetable fields. Weed management in borders
can be a challenge, and the grower will need to check
the borders to make sure that pest species are not build-
ing up there and migrating out into cropping areas.
Crops such as alfalfa that attract pests away the main
crop have been used in strawberries and cotton, and
have potential for the organic vegetable grower. If the
alternate crop (or trap crop) is maintained in a vigorous
state, the pest may never even leave the trap crop. If the
pest population builds up and begins to leave the trap
crop, the trap crop can be mowed or sprayed to prevent
damage to the main crop. The trap crop can also serve
as an additional reservoir of beneficial predators and
parasites in the event the adjacent crop field has to be
treated.
Many of the true bugs (such as squash bugs, lygus,
and stink bugs) overwinter outside of the field, so
efforts to control them can be directed toward their
winter and early spring sites before they move into the
crops for the growing season. Also check box piles,
lumber, and storage buildings for over-wintering pest
species.
MECHANICAL CONTROL
Soil tillage can destroy insects and expose them to birds
and other predators (see UC ANR Publication 7248, Soil
Management and Soil Quality for Organic Crops). It can
also speed the breakdown of plant residues that harbor
insects and plant pathogens. By either allowing the
organic matter in a field to decompose completely
before you plant the next crop or allowing a fallow peri-
od between crops, you can enhance control of cut-
worms, root maggots, and bulb mites.
Certain soil and nutrient conditions can be associat-
ed with pest problems. High organic matter content, for
instance, can lead to an increase in problems with sym-
phylans, springtails, cutworms, wireworms, and root
maggots. Sandy soils will tend to support higher nema-
tode and wireworm populations. Organic growers
farming on lighter soils have to be more careful with
crops such as tomatoes, cucumbers, and root crops such
as carrots. Longer fallow periods or more frequent
grass rotations are necessary to prevent a buildup of
soil pests. You can help prevent damage by growing
sensitive crops when soil conditions are not favorable to
pests. Fall- and winter-planted vegetables may escape
damage that would be severe for the same crops if they
were planted in spring or summer. Mechanical control
in the form of vacuuming and destroying lygus bugs in
strawberries has proven effective when the program
includes frequent passes through the fields during criti-
cal pest periods.
Pest barriers can be incorporated into high-value
vegetable plantings. Floating row covers and plastic
tunnels effectively reduce access by many pest species.
Reflective mulches have been effective for prevention of
early aphid infestations in row crops such as tomatoes,
squash, and eggplant. Sticky barriers can be useful as
monitoring devices, but they have seldom been effec-
tive in themselves for control of pest species.
Insect Pest Management for Organic Crops • 2
BIOLOGICAL CONTROL
The organic farmer should strive to conserve the many
naturally occurring beneficial organisms that are pre-
sent in the crop. If it were not for the naturally occur-
ring biological control factors, most crops would be
inundated with dozens of pests. If you find it necessary
to treat for a particular pest in order to prevent econom-
ic losses, choose a selective spray material and use only
enough of it to keep damage levels within economically
acceptable limits. Short-residual pesticides will allow
beneficial insects and predator mites to return to the
field and help control remaining or newly introduced
pest species.
An organic farming system offers many opportuni-
ties for enhancing biological control factors. Since most
organic farms apply little or no harsh pesticides, it is
possible to build up large numbers of beneficial para-
sites and predators that help control pests in many
crops. The introduction of biocontrol organisms to a
field may be most cost effective when a grower is mak-
ing the transition from conventional to organic produc-
tion systems. Make sure that the introduced pest is well
adapted to the particular climate or site and that it is the
correct species for the pest that you wish to control.
When purchasing biological control agents, buy from a
reputable supplier. Multiple releases of the biological
control agents may be required in order to bring pest
populations to very low levels. Suppliers will often
assist with suggestions for managing introduced bio-
logical control agents.
When pests such as aphids build to large popula-
tions, they will often be controlled by ladybird beetles,
lacewings, syrphid flies, or wasp parasites. For many
growers this control may come too late to prevent
extensive damage to the crop. If alternate plants are
allowed to support aphids in high numbers early in the
season, the predators and parasites that develop on
those aphids may later move into the crop. If the aphids
are vectors of viral pathogens, it will only take a few of
them to cause extensive losses. In this case, predators
and parasites will not effectively prevent the spread of
disease into or through the field.
Many caterpillar pests infest vegetable crops.
Trichogramma wasps can be highly effective in prevent-
ing caterpillar damage. The wasps parasitize the eggs of
pest species, killing the pests before any feeding injury
can occur. When purchasing Trichogramma wasps, buy
the species that is appropriate for the intended pest and
make frequent releases of enough wasps to control the
pest. In many situations, this will require multiple
weekly releases of millions of wasps. When releasing
live organisms, it often is wise practice to set some of
them aside and check to make sure they are still viable
at the time of release. Heat, cold, time, and diseases all
can affect the viability of biological control agents.
CHEMICAL CONTROL
A number of organically acceptable insecticides are
available, and each may be useful to you in specific cir-
cumstances. For up-to-date information, see the UC
IPM website listed in the Resources section at the end of
this publication. If you do plan to use organically
acceptable pesticides, several factors should be consid-
ered.
Low mammalian toxicity. The materials selected
should not present a health risk to the applicator or the
people who must work in the crop after application.
Although most organically approved pesticides are rel-
atively safe, their use does involve some risks. The
highest level of risk is often present when the materials
are in concentrate form and are being added to the
spray tank. Materials such as sulfur can cause skin and
eye irritation during application and for some time
afterward. Some individuals may develop an allergic
reaction to pesticides or the solvents used in the formu-
lation process.
Minimal effect on beneficial organisms. While many
selective pesticides are directly toxic only to pest
species, their use can cause disruption to nontarget ben-
eficial species by eliminating their insect hosts and thus
starving the beneficial species or prompting them to
migrate out of the field. This indirect reduction of bene-
ficials may allow the remaining pest population to
increase to higher levels if their reproductive potential
exceeds that of the remaining beneficials.
Adequate coverage essential. Thorough coverage of the
plant is important with almost all organically accept-
able pesticides. For many pests, the young insect or
mite can be found on the underside of the leaf surface
and must have direct contact with the spray material
for control to be achieved. In many cases, high volumes
of water are necessary to get the pesticide to the target.
As much as 100 or 200 gallons of water or more per acre
may be required to achieve thorough coverage of the
leaves of vegetable plants.
Often, the best sprayer nozzle configuration will
direct the spray to the underside and interior of the
plant, with as many as six nozzles for each row. Higher
pressure at the nozzle tips will break the water up into
smaller droplets, and often help the material reach the
interior of the plant. The nozzle size should be matched
to the application pressure to produce the desired
droplet size for optimum coverage.
Many growers are finding that air blast and electro-
static sprayers can provide excellent coverage without
requiring the high volumes of water needed by conven-
Insect Pest Management for Organic Crops • 3
Insect Pest Management for Organic Crops • 4
tional spray equipment. The initial cost for air-blast
equipment is higher than for conventional sprayers, but
the savings in time taken to refill the tank can allow a
grower to treat more crops in a given period of time.
Soil compaction can be reduced if less water is being
carried across the field. Proper timing of the spray to
intercept the pest in a susceptible stage is important no
matter what equipment you use to deliver the product.
Many organically approved pesticides degrade
rapidly in the environment. Control of a continuing
pest problem may require repeated applications.
Because insects can become resistant to pesticides that
are used frequently, those pesticides will become less
effective over time. This is not so common with short-
residual pesticides as with materials that have a long
residual activity. Pests are not likely to develop resis-
tance to materials such as oils and soaps that use physi-
cal actions such as suffocation or physically dislodging
the pest from the crop as their mechanism of control.
Here are some examples of pests that can be con-
trolled by organically approved materials:
• Aphid populations can be reduced with oils, soaps
and pyrethrum/rotenone combinations. If ants are
protecting the aphids from predators and parasites,
the best control is often achieved by controlling the
ants and allowing biological control to resume in the
crop. Ant colonies can be physically destroyed or
treated with boric acid baits.
• Whitefly populations can be suppressed by multiple
applications of soaps and oils. Since the pupal stage
is resistant to control, it is important that you make at
least two applications close enough together to pre-
vent more pupal stages from occurring. Thorough
coverage of the underside of the leaves is important,
as this is where most of the whitefly nymphs will be
feeding.
• Leafminer control may require several applications
within a two-week period. Many of the pupae are in
the soil and will not be controlled with short-residual
materials. Sprays containing azadirachtin, pyrethrins,
and rotenone will kill some of the adults and help to
limit the population. Sprays for leafminers will slow
the build-up of native wasp parasites.
• Leafhopper numbers can be reduced with applica-
tions of pyrethrins and rotenone if the nymphs come
into contact with the materials. Adults and eggs that
are inserted in the plant tissues will not be controlled
very well with chemicals.
• If flea beetle numbers are high when young plants are
in the cotyledon stage, you can reduce damage from
adults by applying soaps and pyrethrin/rotenone
combinations.
• Stinkbugs can be difficult to control, and only the
first two instars are susceptible to soap sprays. If
allowed to build up in the field to high levels, they
cannot be controlled with organically approved
chemical treatments.
• Russet mites can be controlled with sulfur sprays or
dusts. Light mineral, vegetable-based, or neem seed
oils can be effective against pest mites. Some damage
to crop foliage or fruit can occur when you use oils. It
is advisable to treat a test area first before applying
the material to the whole field if you have not
usedthe product before on that crop. Hot weather
and higher oil concentrations can increase the toxic
reaction in the plants.
• Worm pest control can be difficult in many crops.
Bacillus thuringiensis (Bt) formulations are available
that enable the organic grower to limit damage from
worms. Smaller worms are controlled more easily by
this method, and since the Bt must be ingested by the
worm thorough coverage of al leaf surfaces is neces-
sary. For best results, these materials should be
applied early, as control will lag several days behind
the application. Worms must be controlled before
they enter into the fruits or go deep into foliage
where they will not ingest the spray residues.
For each of the abo
