Growing Organic Vegetables in Iowa - Transition to Organic Partnership Program

Organic production and consumption has increased over the past 20 years. Learn how to raise organic vegetables – including strategies for composting, pest management, and disease management.
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2012

Growing Organic Vegetables
In Iowa

PM 2086 Revised February 2012

Introduction

Many growers have already raised crops “organically” at
one time or another—simply by growing plants without
the use of synthetic fertilizers or pesticides. Before the
invention of synthetic agricultural chemicals around World
War II, all crops relied on inherent soil fertility, augmented
by manure, kitchen scraps, or nitrogen-fixing leguminous
crops, such as alfalfa. Sir Albert Howard (1873-1947) was a
pioneer in organic farming techniques that were based on
an integration of soil life, plants, animals, and people. He
championed the use of crop rotations (alternating crops
every year within a given section of land) and compost
applications to provide organic matter and replace nitrogen and minerals lost through cropping practices. Others,
including J.I. and Robert Rodale, continued Howard’s work
in promoting organic methods.

Organic production and consumption has increased in the
last 20 years. In 2010, the organic industry grew to over
$28.6 billion. More than 4.1 million acres are in organic
production in the U.S. as the industry continues at 10
percent annual growth rate. Consumers purchase organic
foods for several reasons, including reduced pesticide
residues (organic prohibits the use of synthetic pesticides)
and perceived benefits from organic fertilization in terms of
nutritional content. Many chefs throughout the world select
organic foods for their menus because of the perceived
superior taste. In addition, organic consumers strive to
support local farmers who rely on environmentally-friendly
methods of production that help protect groundwater.

Certified Organic Designation

Organic farming is based on the ecological principles
of nutrient cycling, biotic regulation of pests, and biodiversity. Inputs used in organic farming are derived from
renewable resources in order to preserve our limited
supply of non-renewable petroleum, which is the basis for
most chemicals used in conventional agriculture. Organic
growers rely on materials produced through sunlight, such
as plants/plant parts, and manures produced through an
animal’s consumption of plants. Recycling of wastes that
are potential pollutants, such as animal manure, is a critical
component of organic farming.

“Organic” is a term defined by law (Organic Food Production Act, 1990; U.S. Department of Agriculture-National
Organic Program, 2004). As of October 2002, anyone selling
products labeled as “organic” must be inspected by a
third party to ensure compliance with federal USDA rules
(see Fundamentals of Organic Agriculture, PM 1880).
To sell a product as “organic,” the crop must have been
raised on land where synthetic chemicals (any synthetic
fertilizers, herbicides, insecticides or fungicides) have not
been applied for at least three years prior to harvest. In addition, no genetically-modified organisms (GMOs) or GMO
crops are allowed in organic production (e.g., RoundupReady® soybeans and Bt-sweet corn®). Other practices
specifically disallowed for organic production include use
of “biosolids” (sewage sludge) due to concerns with bacterial and heavy metal contamination. Irradiated products
also are prohibited. Organic producers who gross less than
$5,000 per year and wish to sell their produce as “organic”
are exempt from certification fees but must follow organic
standards and register with the Iowa Department of Agriculture and Land Stewardship (see References).

For commercial organic producers, a third-party certifier
inspects annually to assure that no synthetic materials
have been used in production. This “audit trail” is verified
through farm records, a system that many farmers already
embrace, by tracking planting dates, farm sections (crop
rotations), and input application rates. Thus, the transition
from organic farming to certified organic production
should be relatively easy for anyone wishing to market
crops as “organic.”

Soil Health and Nutrient Cycling
All organic systems are based on the principle of nutrient
cycling. Nutrients in the farm system are in a constant
state of cycling. As plants and animals are raised together,
their residues are recycled into the soil as fertilizers for the
next crop, which may then be used to feed animals and
plants in the system. Because livestock are considered part
of the organic farm system, many organic producers raise
chickens, rabbits, and other small livestock in fenced areas
or in movable, pasture-based chicken tractors.
Iowa is an ideal location for livestock operations; growers
without livestock should be able to locate manure from
nearby farms or livestock operations.

Organic vegetable crops can be planted using
mechanical transplanters to aid efficiency.

Making or purchasing compost for your soil fertility
needs will include assuring that all ingredients meet
organic standards (see table 1).

By testing your soil, you can estimate the quantity
of nitrogen your cover crop provides (shown: hairy
vetch and rye).

Raw manure can be used from animals that have
not been raised organically but all manure must be
incorporated in the soil 4 months before harvest or
composted (see Composting section on page 4). Composting at the proper oxygen level, temperature, and humidity
should break down all synthetic materials in manure, but
if you are concerned about the persistence of antibiotics,
hormones, or other synthetic substances fed to animals
that have not been raised on organic farms, you may wish
to use manure only from organic farms or from a certified
organic supplier.

A crop rotation plan is helpful in protecting against pest
problems and maintaining soil health. Horticultural crops
should be rotated with a leguminous cover crop at least
once every five years. No more than four out of six years
should be in row crops, and the same row crop cannot be
grown in consecutive years on the same land. Legumes
(alfalfa, red clover, berseem clover, hairy vetch) alone, or
in combination with small grains (rye, wheat, oats, barley),
should be rotated with row crops (corn, soybeans, amaranth, vegetables) to ensure a healthy system.
An example of a seven-year rotation in Iowa would be a
(1) hairy vetch/rye cover crop, (2) tomatoes, (3) onions, (4)
salad greens, (5) garlic, (6) Austrian winter pea/triticale cover crop, (7) strawberries. The highest nitrogen-demanding
crops are followed by crops with lower demands, followed
by nitrogen-supplying crops of legumes and small grains.
Plants of the Solonaceae family (tomatoes, potatoes,
eggplant, pepper) should be separated by a minimum of
three years to avoid nematode or disease problems from
previous Solonaceae crops.

Always ask for a list of ingredients in purchased manure
or compost. You may not wish to use a product on your
farm if prohibited, synthetic substancs have been used in
processing or pelletizing it.
Non-manure-based composts also are available, but are
generally lower in nitrogen (N) than manure-based compost because they use mostly plant-based ingredients,
such as wood chips or straw (see table 1).
Beneficial microorganisms also are critical for recycling
nutrients, and are supplied through manure, compost, and
cover crops. Compost application rates range from 100 to
150 pounds of nitrogen per acre, depending on crop needs,
existing soil fertility, and nitrogen from other sources
(cover crops). Because most composts in Iowa range from
1 to 3 percent nitrogen, rates of 6,000 to 12,000 pounds of
compost per acre are commonly applied.

Soil Quality and Crop Rotations
Soil quality includes all the physical, biological, and chemical (as in mineral elements, such as nitrogen) components
necessary for soil health. Only naturally-occurring materials
are allowed in organic production and processing and
all applied materials must be recorded in farm records if
any produce is sold as “organic.”

Hairy vetch should be plowed down or rolled when
10 to 20 percent of plants are blooming.

temperature of 140°F for at least three days during the
composting process to adequately decompose organic
materials and kill plant pathogens and weed seeds.

Table 1. Composition of typical feedstocks in compost operations.
Material

P2O5

K2O

C/N

Dairy manure

0.6-2.1

0.7-1.1

2.4-3.6

Horse manure

1.7-3.0

0.7-1.2

1.2-2.2

Poultry manure

2.0-4.5

4.5-6.0

1.2-2.4

6-16

Sheep manure

3.0-4.0

1.2-1.6

3.0-4.0

Swine manure

3.0-4.0

0.4-0.6

0.5-1.0

Fish meal

10.0

6.0

–

3.6

Alfalfa hay

2.45

0.50

2.10

Adequate moisture and temperature are required for
proper composting (strive for 45 to 50 percent moisture).
If compost piles reach ideal temperatures and moisture
conditions, and are routinely turned when temperatures
reach 140°F, a finished compost (with the look and smell of
soil) can be obtained in 6 to 8 weeks.

Wheat straw

0.50

0.15

0.60

127

Apple fruit

0.05

0.02

0.10

401

Apple leaves

1.00

0.15

0.35

542

Banana peels

3.25

41.76

Other composting systems include vermicomposting
(using earthworms in “beds” or “towers” to decompose
manure and other wastes), in-vessel digesters, and
anaerobic systems.

Other Soil Amendments and Foliar Treatments

193

Soil testing is essential to determine which, if any,
amendments are needed and in what amounts. Iowa State
University and private labs in the Midwest can analyze
your soils.

Beans (pods)

0.25

0.08

0.30

Coffee grounds

2.08

0.32

0.28

Eggshells

1.19

0.38

0.14

Fish scrapes

6.50

3.75

–

Potato peels

5.18

27.50

Wood ashes

1.50

7.00

Sawdust

0.24

440

Includes all fruit wastes (average)
2
Includes all leaf wastes (average)
3
Includes all vegetable wastes (average)

Although compost contains the majority of necessary
nutrients, many other soil amendments are available to
add nitrogen (N), phosphorus (P), potassium (K), calcium
(Ca), sulfur (S), and other nutrients to soil and plants. For
example, lime (calcium carbonate) is a common amendment to raise soil pH to the preferred neutral status of 6.5
to 7. Gypsum adds both calcium and sulfur. Rock
phosphate can be used to add phosphorus.

Composting
Composting is the preferred method of fertilization in
organic fruit and vegetable production. Composting stabilizes nutrients from manure and raw organic materials
(e,g., crop residues, kitchen scraps) and reduces odors and
high ammonia levels. Because all operations in compost
making must be recorded for the certifying agency, most
growers opt to go under the “raw manure” rule and apply
their compost 4 months before harvest.

Several foliar nutritional treatments are available for
organic farmers, including Earth Juice™ and many fish
emulsion products. These products can be used alone or
in combination with soil amendments. Compost tea is
another foliar spray that provides some nutrition and also
has been used for powdery mildew and other diseases.

Composting is a controlled process where nitrogen-containing materials (manure, yard/kitchen waste) are mixed
with a carbon-containing source (corn stalks/cobs, straw,
wood chips) to produce a substance preferably in a carbonto-nitrogen ratio (C:N) of 25–30 to 1 (see table 1 for examples). A general rule of thumb in making compost is to
use 4 parts carbon-containing materials to 1 part nitrogencontaining materials, Oxygen is supplied to the beneficial
microorganisms through turning of the compost pile.

Pest Management Strategies
Preventative practices are the cornerstone of organic pest
management. Prevention starts with planting the most
insect- and disease-resistant varieties. Other cultural,
physical, and biological controls include using fabric row
covers, trapping or hand-picking beetles, attracting natural
enemies, or using organic-compliant insecticides. Pesticides
are applied only in emergencies and must be justified to
your certification agency.

Many methods of composting are available—from simple
piles to bins, barrels, or drums, to expensive machines,
such as hydraulic windrow-turners. All systems operate on
the same principle of providing sufficient heat to kill harmful microorganisms and weed seeds, but retaining beneficial organisms that help convert ammonia to the preferred
form of nitrate-nitrogen.
A minimal size of 3 ft. x 3 ft. x 3 ft. is required to obtain
adequate heating. The compost mixture must reach a

Insect pests are less prone to colonize healthy plants that
contain the proper balance of nitrogen, phosphorus, and
potassium than plants in a stressed situation. Thus, soil
health is critical in helping prevent pest problems because
many leaf-feeding insects prefer plants with high concentrations of free amino acids that may be present in plant
tissues containing high amounts of nitrogen.

bugs). Organic-compliant insecticides are most effective
on soft-bodied insects. Because beetles are hard-bodied
insects, effective management often requires multiple applications of organic-complaint insecticides.

Companion Planting
Many farming books encourage the planting of
certain plants with others in order to increase
yields or prevent pest attack. The majority of
these plans are based on grower-experience
and are often site-specific. Some growers have
experienced reduced infestations of squash
pests when squash is planted with corn, for
example. This system is referred to as the “Three
Sisters” (corn, beans, and squash) planted
by Native Americans. The theory behind this
strategy is that the presence of the other plants
“masks” the squash from squash pest species.
Other tactics include planting mint around
brassicas (broccoli and cabbage family) to repel
the cabbage butterfly and reduce egg-laying.
Marigolds, which exude a nematode-repelling
chemical called thiopene, often are planted with
tomatoes to help manage root-knot nematode.

Organic insecticides that are derived from plants are called
botanical insecticides. Other approved insecticides are derived from mineral sources and operate on the principles
of repellency and irritation.
Biological insecticides include microorganisms that are
harmful or competitive with pests, for example, Bacillus
thuringiensis or Bt. This naturally-occurring bacterium
is found in soil. For commercial production, bacteria are
multiplied in vats, with harvested spores dried to a powder that can be applied to crop plants. This bacterial toxin
is not harmful to humans but is a stomach poison when
consumed by lepidopteran larvae (caterpillars). Many Bt
formulations are available but certified organic growers
must read the label carefully; any Bt with petroleum carriers or other synthetic materials would be disallowed in
organic production. A Bt that is effective against Colorado
potato beetle larvae (immature stage) is called Bacillus
thuringiensis tenebionis or Btt. A new biological control,
Bacillus subtilis, is a bacterial preparation that has been
used against bacterial blight disease in tomatoes and for
soybean rust in Florida. This bacteria competes with fungi
that causes the disease and in certain cases, disease has
been reduced.

Biological control is a predominant factor in all
organic farms. Nearly every insect pest in Iowa has a
“natural enemy” or beneficial organism (predator, parasite, or pathogen) that helps manage that particular pest.
Farmers rely on beneficial insects (ladybeetles and spiders,
for example) to prey on pests such as aphids and caterpillars, or they employ physical, preventive measures, such
as fabric row covers. Because our extended winter weather
kills many insects, most organic farmers in the Midwest
have not needed insecticides for managing pests. Damaged plant parts can be removed prior to selling or eating
produce, as many organic farmers expect to “donate”
some of their leaves or fruit to the insects and diseases
that are part of the ecosystem.

Most of these materials may require multiple applications,
and even then, will not result in the “100% knockdown”
obtained with synthetic chemicals. Most insecticides are
repellent in nature (insects decrease feeding or avoid colonization through chemical or visual cues). Some, such as
neem, also are insect growth-limiting, Some insecticides
available for organic growers are listed in table 2.

Even when organic-compliant insecticides are sprayed on
the farm, beneficial organisms also may be harmed, so the
first rule of pest management is to prevent insect pests
through the following methods:
• Plant resistant or tolerant crop varieties, such as the VFN
series (Verticillium, Fusarium and Nematode resistant
cultivars);
• Plant under proper conditions (when the soil is
adequately warmed and all danger of frost has passed);
• Harvest in a timely manner; and
• Practice good sanitation by collecting and destroying
infected plants.
Insect pests are either soft-bodied (easily crushed) insects,
such as aphids, mites, and lepidopteran larvae (caterpillars), or hard-bodied (hard, exterior wings protect insect
body) insects, such as beetles or true bugs (e.g., squash

Organic strawberries should be grown on
straw-mulched beds to help prevent disease
and keep produce clean.

Materials that can accumulate in the soil and may lead
to toxic levels, such as copper fungicides, are considered
restricted materials in organic production. The use of all insecticides or fungicides should be justified through monitoring for insect/plant pathogen numbers and determining
economic damage thresholds. If there are low populations
of insect pests or disease, the use of pesticides will not be
warranted.

Table 2. Insecticides used in organic production in the Midwest.1
Common Name

Use2

Neem
Scientific Name:
Azadiracta indica

Botanical
insecticide
(seeds
primarily, but
also leaves,
pods, and
other parts)

Soft-bodied and some
hard-bodied insects;
neem oil used for
downy and powdery
mildew control; do not
apply when bees are
active in the area

Pyrethrum

Botanical
insecticide:
flower petals

Soft-bodied and
somehard-bodied
insects

Sadadilla

Botanical
insecticide
from roots

Leafhoppers,
caterpillars, and thrips;
do not apply when bees
are active in the area

Ryania

Botanical
insecticide
from roots

Codling moth, thrips,
and European corn
borer

Rotenone

Botanical
insecticide
roots

Restricted insecticide
(reports of human
illness associated with
use)

Natural
bacteria
Bacillus
thuringiensis

Caterpillars (Bt
kurstaki), Colorado
potato beetle (Bt
tenebrionis), and black
flies (Bt israeliensis)

Granulosis virus

Naturally
occurring
microbial
insecticide

Codling moth

Soaps

Fatty acids
derived from
plant sources

Mites, aphids, and
mealybugs; check if
organic-compliant—no
synthetic oils

Vegetable oils

Insecticide
derived from
several seed
oils

Scale insects, aphids,
and mites

Surround™

Naturally
Soft-bodied and hardmined mineral bodied insects
(kaolin clay)

Sulfur

Naturally
Mites; disease control
mined mineral for mildew and other
diseases; use caution
when applying (may be
phytotoxic and cause
respiratory problems)

Lime sulfur

Mixture of
naturally
mined
minerals

Type

Read all pesticide labels carefully for instructions. The
label is considered a legal document and violation of label
directions can result in damage to plants, people, and the
environment. Consult with your certification agency or the
Organic Materials Review Institute (OMRI) before applying
any materials to assure organic approval if you sell your
product as organic. Applying prohibited materials can result in a one- to three-year loss of certification, depending
upon the material applied and the extent of spread.

Disease Management Strategies
Planting resistant or tolerant varieties and rotating crops
every year is the first line of defense for plant diseases.
Downy mildew (Pseudoperonospora cubensis) and powdery mildew can be found on cucurbit plants in the Midwest. Symptoms first appear as pale green spots on the
upper leaf surface that become angular lesions. A whitishgray “downy” mildew-looking mass soon covers the lower
surface of the leaves. Stunted growth, reduction in yield,
defoliation, and eventual death of the plant may result.
Products that are available for disease management in
organic vegetable production include Bacillus subtilis (a
biological control agent formulated as Seranade™), a hydrogen peroxide-based product, and baking soda products
(formulated as Armicarb 100™ or FirstStep™). The efficacy
of these products has not been tested in Iowa.
Compost teas also have been reported to help manage
diseases in research at Michigan State University, but
information from Iowa is limited. It is believed that compost
teas contain antagonistic or competitive biological control
agents, such as Bacillus subtilis and Trichoderma sp., which
may decrease harmful microorganisms.
Bacterial wilt is a disease transmitted by the cucumber
beetle. Symptoms include a rapid wilting of the plant and a
slimy exudate from plant stems upon cutting. Bacterial wilt
is controlled by preventing or reducing beetle populations
through row covers or organic-compliant spray treatments.

Mites; disease control
for mildew and other
diseases; use caution
when applying (may be
phytotoxic and cause
respiratory problems)

From University of California-Davis: Pests of the Farm and Small Farm, Pub. No. 3332.

Because registrations and formulations change routinely, check with state and federal
labels before using any insecticides. Your certification agency and OMRI (Organic
Material Review Institute) can provide status for use in organic operations.

EXAMPLE:
Pest Management for Organic
Squash Production

Spotted and striped
cucumber beetles can
spread bacterial wilt in
cucurbits.

General comments: Squash and other cucurbit
crops require more intensive management than most
crops, such as lettuce and kale. Squash is considered
a medium-feeder—it requires more nitrogen than
lettuce and greens but less than tomatoes and sweet
corn. In Iowa State University trials, organic squash
yields were not increased with the addition of
compost in very fertile soils but adding compost to
more sandy soils can increase yields.

Cucumber beetles that bother squash include
the striped cucumber beetle—Acalymma vittatum
(Fabricius) and the immature spotted cucumber
beetle—Diabrotica undecimpunctata howardi Barber
(also known as the Southern corn rootworm that
migrates from the south into Iowa cornfields every
year). Cucumber beetles have two generations; the
first appears in early spring and the second appears
in July and August.

Predominant pests: Squash bug has been the
predominant pest in Iowa State University organic
squash trials. Cucumber beetles and squash vine
borers also can cause problems in certain years.

Scout for yellow-orange eggs at the base of
plants or in soil cracks near the plants. The larvae
(immature form) are tiny, white, grub-like worms
in the soil that feed on plant roots.

Squash bug (Anasa tristis) can be a very
destructive cucurbit pest in Iowa. Adults are
about 5/8 inch long at maturity, grayish-brown or
yellowish-brown, flat-backed, with the edges of the
orange/orange-brown abdomen protruding from
beneath the wings at rest. The nymphs (the immature
forms without wings that are normally seen in the
farm) are primarily all gray and feed in groups. Eggs
are usually seen as bright bronze elliptical-shaped
clusters of 7 to 20 eggs laid under the leaf in the
angles formed by two leaf veins.

Damage: Only in the case of severe infestations
is larval feeding a concern. The most important
consideration for the cucumber beetle
management is the transmission of bacterial wilt
by the beetle. Jack-o-lantern pumpkins and some
squashes are rarely susceptible to this disease.
Hubbard and butternut squash, however, are
susceptible to bacterial wilt. In Iowa State
University organic squash trials, the incidence of
bacterial wilt was very low but can be a concern
in years of heavy beetle numbers.

Scout for overwintered adults as soon as
plants emerge and for eggs beginning in midJune. There is one generation per year in Iowa,
with five nymphal stages. Scout for adults and
nymphs on top and under leaves and on the soil
surface around plants.

Squash vine borer (Melittia satyriniformis) adults
are members of the moth and butterfly order of
insects (Lepidoptera) in a sub-category called clear
wing moths which resemble wasps. The moth’s
body is red with black bands, and its hind wings
are transparent and fringed by reddish-brown
hairs. Adults usually fly in the daytime and can be
seen laying eggs at the base of the plant, or on leaf
petioles and stems. Adults emerge when squash
plants are blooming from over-wintering pupae
(resting forms in the soil). This period usually follows
squash bug and cucumber beetle emergence.

Damage: Squash bugs feed by sucking plant
leaf sap and causing a wilting of the plant from
the feeding point forward. Fruit can be damaged
if populations are allowed to increase during
the season. Young plants and plants at the initial
flowering stage are particularly vulnerable.

Ornamental
and edible
hard squashes
and gourds
can be grown
using organic
techniques.

Scout for small disk-shaped, reddish-brown
eggs or sawdust-like frass (fecal pellets and
chewed plant parts) at the base of the plant.
Damage: Once eggs hatch and larvae tunnel
into plant, squash plants will begin to wilt—a
symptom that can be confused with bacterial
blight.

Strategies for handling squash
bug, cucumber beetle, and
squash vine borer

Prevention through the use of pheromone
traps: These traps emit a chemical that disrupts the
mating ability of the adult squash vine borer moth
and leads to lower insect populations. Hanging
squash vine borer pheromone traps around the field
should help in managing SVB pests.

Prevention through use of row covers: Row
covers are used in managing all squash pests: squash
bugs, squash vine borers, and cucumber beetles.

Pheromone
traps can be
used to catch
and monitor
squash vine
borer adult
moths.

In research at Iowa State University, cucumber
beetles and squash bugs were more successfully
managed with floating row covers compared to
the use of a clay-based insecticide (Surround®)
or interplanting squash with an insectary plant
(buckwheat) to attract natural enemies.
Row covers are available in many weaves and sizes.
Pre-cut rolls are best for small farms but commercial
rolls that can be cut to grower’s specific row shape
are more cost-effective for larger operations. Row
covers should be placed over the squash crop as
soon as plants are established (approximately
6 inches in height). If feasible, row covers can be
removed for a few hours each day once flowers are
opening in order to allow pollination to occur. Other
systems have bee boxes at the end of row-covered
tunnels that allow the bees entrance without the
labor of removing and replacing row covers each
day.

Attracting natural enemies: The beneficial insect,
Trichopoda pennipes, is a fly that parasitizes the
squash bug by laying eggs on the bug’s body. The
larvae (maggots) that emerge from the eggs feed
internally on the squash bug’s hemolymph (fluids)
until the bug’s death ensues. Look for the fly’s tiny
white eggs on the squash bug and allow that bug
to remain in the farm. Flies that emerge from the
parasitized squash bug will then continue the cycle
of biotic regulation by attacking other squash bugs
in the field. Adult flies feed on nectar that can be
supplied through flowering plants (also known as
insectary plants), such as buckwheat and sweet
alyssum. Oftentimes, however, the population of
parasitic flies is inadequate to manage squash bugs
below economic damage levels.

Row covers can be placed on wooden or metal
frames over squash beds, or placed as floating
covers directly on squash plants. There may be some
deformation of squash leaves from direct contact,
but yields are not affected. At a certain point (when
fruit set appears complete), row covers can be
removed permanently.

Two beneficial insects, a robber fly and a ground
beetle, are generalist predators that can prey on
squash vine borer (SVB). A parasitic wasp also
attacks SVB eggs and parasitic nematodes can prey
on SVB. Beneficial flies and wasps feed on nectar
that can be supplied through flowering insectary
plants such as buckwheat and sweet alyssum.
Ground beetles prefer mulched areas. Beneficial
nematodes can be purchased for distribution in
the field. There is no guarantee, however, when

White, spun fabric row covers (shown on the groundon the right-lifted off the hoops that keep it off
plants) help protect crops from beetles (cucurbits)
and caterpillars (brassicas) until crops are large
enough to withstand damage from insect pests.

Squash bug (L) and the natural enemy (R), a
parasitic fly, whose eggs are visible on the back of a
parasitized bug.

Sanitation: Removing debris that may harbor
squash bugs or eggs can help reduce populations.
Insects or eggs can be hand-picked from plants and
crushed (between the board and a hand trowel, for
example) or vacuumed (mini-vacs or commercial
D-Vac® machines work well).

augmenting natural populations of beneficial insects
with purchased natural enemies. Conservation of
natural enemies by providing nesting and flowering
sites is always the best practice.
Planting techniques: Planting squash after June
may help plants escape the arrival of the first squash
bugs although the insects may eventually locate and
colonize later plantings.

Vines should be destroyed as soon as possible
following harvest to prevent further development
of SVB larvae inside squash plants. Tillage and
incorporating through plowing will destroy cocoons
(resting stages of the SVB moth).

Late planting or staggered plantings also are used
to escape SVB populations, or to allow adequate
plant populations in the event of SVB attack of one
planting. Sustaining vigorous plant growth (through
compost applications and irrigation) is essential to
maintaining plants that can tolerate SVB injury.

Economic thresholds and organic-compliant
pesticides: The economic damage threshold for
squash bugs is one egg mass on each monitored
plant. If all previously described methods have been
used and you continue to find extensive egg masses,
consider using organic-compliant insecticides (see
table 2). Although these plant and mineral-based
insecticides are less damaging to natural enemies
than synthetic insecticides, some harmful effects
may occur with extensive use.

Varietal selection also is important—squash bugs
prefer squash and pumpkins over zucchinis. Squash
vine borers prefer winter squash, followed by
summer squash, zucchini, and pumpkins, with
cucumbers and melons the least preferred. Of the
winter squashes, butternut is the most tolerant
cultivar, and the hubbard types are the most
susceptible.

Research at Iowa State University did not perceive
any benefits from the use of clay-based insecticide
for squash bugs because of our inability to cover
plant undersides where squash bugs clustered.
Other botanical insecticides that have been tested
for general insect pest control include neem (from
the plant Azadirachta indica), garlic, and pyrethrum
(from daisy plants). These insecticides are generally
more successfully used against soft-bodied insects,
such as aphids and mites. Detailed information
about these insecticides can be found in the ATTRA
(Appropriate Technology Transfer for Rural Areas,
a USDA-supported organization that serves as a
clearinghouse for organic and sustainable agriculture
information) publication (see References).

Trapping: Squash bugs can be trapped under
boards in the fields where they tend to congregate.
Another option is to plant an early trap crop
of squash or pumpkins where the bugs can be
trapped and then vacuumed or handpicked from
the underside of the boards or managed with an
organic-compliant insecticide before the main crop is
planted.
Planting an early crop of squash or zucchini also may
help manage SVB. When the trap crop is colonized
by SVB larvae, it can be treated with one of the
approved insecticides or plowed under to destroy the
insects.
Physical control: Physically removing the SVB
larvae from the stem of the plant is a labor-intensive
method employed by small-scale growers. Using a
knife or Exacto® blade, growers slit the stem at the
base of the plant and kill the larvae inside the stem.
Many growers cover the injured area with moist soil
to encourage new rooting and re-growth, however,
this method is not always effective.

Weed Management Strategies

Cover crops also are under investigation for their efficacy in
weed management on organic farms. Successful production of organic corn, soybean, tomatoes, pumpkins, and
strawberries has been achieved with rolled cover crops in
Pennsylvania and Michigan. Trials at ISU have shown that
rolled or crushed cover crops can provide a season-long
mulch for organic tomatoes.

Weed management is a critical component of organic
vegetable production for transitioning and certified organic
growers. If vegetable crops are planted in rows of sufficient width, row cultivators (either front-mounted or rearmounted) can be used to kill weeds between rows. Crops,
such as strawberries and tomatoes, should be mulched to
prevent weed infestations. While plastic mulch is allowed
in organic production (provided it is removed after each
season to avoid degradation in the soil), many organic vegetable farmers use alternatives, such as straw and natural
fiber mulches. In trials at ISU, organic squash crops were
cultivated while small, and mulched with alfalfa hay after
vines extended beyond the row.

Cover crops are planted in the fall, then rolled and killed in
the spring with a goal of having a dense cover crop-mulch
capable of suppressing weeds so that additional weed
control is unnecessary. The roller consists of a large steel
cylinder (10.5 ft wide x 16 in. diameter) front-mounted on
the tractor and filled with water to provide 2,000 pounds
of weight. Steel blades are welded in a chevron pattern to
crimp and mechanically kill the fall-planted cover crops.
Afterwards, vegetable crops are planted into the flattened
cover crop, using no-till drilling of seeds, high-residue
transplanters, or hand-transplanting.

No-till roller research in Iowa
The Rodale Institute (Kutztown, PA) provided
a no-till roller/crimper to ISU and four other
Midwest universities. Two seasons of research
with the no-till roller at the ISU Neely-Kinyon
Farm in Greenfield demonstrated excellent
tomato yields with reduced weed pressure.
Cover crops (rye and hairy vetch or winter wheat
and Austrian winter pea) were planted in
September-October and then killed in late May
when the rye/wheat was headed out and the
vetch/peas were at 20 percent bloom.
Twenty days later, 6–inch ‘Roma’ tomato
seedlings were transplanted into the dried
mulch. Transplants were side-dressed with 0.5
pounds of organic compost per plant at the
time of transplanting.
Harvests began in August and lasted until frost.
Weed pressure was half that of tilled plots
because of the season-long mulch from the
rolled cover crops. Disease pressure also was
reduced because the mulch helps prevent
some splashing of disease spores. Research
will continue on no-till organic production of
corn, soybean, and tomatoes.

The roller/crimper crushes a cover crop planted in
the previous fall. Seeds can be directly planted or
drilled into the flattened mulch.

Row cultivators can be used for weed management
between rows when crops are small and there is
sufficient width between rows.

Marketing and Economic Strategies

References

Organic vegetable production is a management-intensive
system that can pay economic dividends but also requires
continuous monitoring for insects and diseases and a rapid
response when economic threshold levels are met. Crop
rotation provides much protection against insect, weed,
and disease problems but selection of resistant or tolerant
varieties, and timely harvests also are critical.

ATTRA. 2009. Appropriate Technology Transfer to Rural
Areas. Organic Vegetable Production. ATTRA, Fayetteville,
AR. www.attra.org/horticultural.html#Vegetables.
Carr, A (ed.). 1978. The Encyclopedia of Organic Farming,
Rodale Press, Emmaus, PA.
Chase, C. 2006 Iowa Vegetable Production Budgets. Iowa
State University Extension. Ames, IA. www.extension.
iastate.edu/agdm/crops/html/a1-17.html

The most common approach for marketing organic vegetables in Iowa includes farmers’ markets and Community
Supported Agriculture farms. Restaurant and institutional
food service purchasing also has become more popular in
the last five years.

Delate, K. 2003. Fundamentals of Organic Agriculture. PM
1880. Iowa State University Extension, Ames, IA
http://store.extension.iastate.edu/

For detailed marketing information, see Using Organic
Agriculture and Sustainable Crops and Livestock in the
Local Food Systems (PM 1995) at https://store.extension.
iastate.edu/

Iowa Department of Agriculture & Land Stewardship
(IDALS) Organic Certification and Organic Standards, Des
Moines, IA. www.iowaagriculture.gov/AgDiversification/
organicCertification.asp

Knowing the economical outcomes of your operation is
critical for your success. Keeping track of all expenses and
revenue is a tedious but necessary part of determining
which crops are aiding or hurting your bottom line.

Iowa State University Organic Agriculture
http://extension.agron.iastate.edu/organicag/
(See especially “Research and education” for research reports on organic squash, sweet corn, and broccoli production and “Resources” for information on organic seeds and
supplies.)
Sustainable Agriculture Network (SAN). USDA-SARE (Sustainable Ag. Research & Education). Beltsville, MD. www.
sare.org/
This research project was partially funded by the Leopold
Center for Sustainable Agriculture at Iowa State University.
Prepared by Kathleen Delate, extension organic agriculture
specialist, Iowa State University Department of Horticulture.

Farmers’ markets provide an excellent venue for
selling local, organic produce.

Photo credits: K. Delahaut, K. Delate, J. DeWitt

Organic produce is preferred by The Chefs’ Collaborative
that promotes local and organic food.

www.extension.agron.iastate.edu/organicag

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PM 2086 Revised February 2012