Organic Vegetable Production - Purdue Extension

ID-316

Organic Vegetable
Production

The authors wish to thank Bruce Bordelon, Rick Foster and
Karen Rane for critical comments and Brenda Nowaskie
for manuscript preparation.

The information given herein is supplied with the understanding
that no discrimination is intended and no endorsement by the
Purdue University Cooperative Extension Service is implied.

Organic Vegetable Production
Gerald Brust, former Purdue Extension Entomologist, presently Director of Research at Glades Crop
Care, 949 Turner Quay, Jupiter, FL 33458; Daniel S. Egel, Extension Plant Pathologist, Department
of Botany and Plant Pathology, Southwest Purdue Agricultural Program, Vincennes, IN 47591;
Elizabeth T. Maynard, Regional Horticulture Specialist, Northwest Commercial Horticulture Program,
Department of Horticulture and Landscape Architecture, Purdue University, 1401 South U.S. Highway
421, Westville, IN 46391

disease, and weed management. Information on other aspects
TABLE OF CONTENTS: of vegetable production may be found in other sources listed
at the end of this publication.
“Organic” usually refers to a crop management sys-
Introduction .......................................................3 tem that promotes biodiversity, biological cycles, and soil
biological activity. Organic production concentrates on
Soil Fertility ......................................................3 natural processes and how to manage them. Other materials
and products are additions to, not replacements for, manage-
ment. It is a total approach. One cannot convert to organic
Seeds and Transplants .......................................6 production by substituting an “organic” insecticide or adding
manure. The system will fail if this approach is taken.
An organic system takes time to develop. It may be
Safety ................................................................6 achieved in stages, for example by starting with organic soil
amendments and other soil improving procedures. Then, try
Insect Management ...........................................7 biological control of pests, some companion plants, etc. Even-
tually, the entire system will be changed. It will take YEARS
to convert to a healthy organic system.
Disease Management ......................................10
The Legal Definition of “Organic” - Federal as well as
state regulations govern the use of the term “organic” in the
Weed Management ..........................................11 marketplace. Vegetables sold as “organic” must be grown and
handled in accordance with these regulations. Operations with
more than $5,000 gross annual income from sales of organic
Organic Insect Management (Table 3) ............13 products must have their production and handling methods
certified by an officially recognized organic certification
Organic Disease Management (Table 4) .........17 agency. See Additional Sources on page 18.

Production and Markets - Organic produce is usually
Additional Sources of Information .................18 marketed separately from conventionally grown produce
in order to be profitably sold. Because of the amount of
management and time invested in developing the system,
Purdue University Extension organic produce should bring a premium price compared
Publications .....................................................19 with non-organic vegetables. In the Midwest, most organic
growers usually cannot compete with the volume produced
by non-organic growers. Niche or specialty markets, which
Organic Web sites ...........................................19 require lower volumes, will often pay a premium for organic
produce. These markets include CSAʼs (Community and Sup-
Soil Fertility Publications ...............................19 ported Agriculture), restaurants, roadside stands, and farmers
markets. It is ESSENTIAL to thoroughly investigate markets
and develop a marketing plan BEFORE you decide what or
how much to grow.

Introduction
Soil Fertility
Organic production is a systems approach. Although
many aspects of vegetable production remain the same in Organic production relies on fertile, biologically active
both “organic” and “non-organic” or “conventional” systems, soil. Fertile soil has a combination of organic matter, accept-
there are differences. The purpose of this bulletin is to able pH, and a balance of plant nutrients suitable for healthy
discuss the major components of production which differ plant growth. Organic matter is maintained and biological
between the two systems. These components include activity is promoted by regular additions of organic material
transplant production, soil fertility management, and insect, to the soil. Examples of organic material include compost,

Purdue University • Cooperative Extension Service • Knowledge to Go

or to land from which harvest of edible crops will not take
place within 4 to 6 months, and only when the soil is warm
enough for biological activity to break down the manure.
Many certification programs have a list of approved, restricted,
and prohibited materials. These lists should be carefully
consulted before applying any material to a field which is
to be certified organic. Just because a fertilizer product is
advertised or labeled as “organic” or “natural” does not
mean it will conform to standards set by the National
Organic Program.
How much of a supplemental nutrient to apply should be
determined based on prior experience of the farmer, obser-
vation of plant growth, knowledge of soil characteristics
such as organic matter, cation exchange capacity, phosphorus
and potassium supplying ability, and base saturation, knowl-
edge of crop needs and field history, and understanding of
the nutrient supplying power of the material to be used. An
example of nutrient application rates is provided in Table 2.
Overapplication can cause problems in crop production as
well as in the environment. When excess nitrogen or phos-
phorus is applied there is potential for pollution of surface
and groundwaters. Heavy applications of manure can easily
result in overapplication of these nutrients. A regular soil
testing program aids the farmer in understanding soil charac-
teristics and monitoring changes over the years. For further
information on soil testing, soil characteristics, crop needs,
and use of compost and manure as nutrient sources, see the
publications listed at the end of this bulletin.

Nitrogen (N) - In organic production, nitrogen is
supplied by soil organic matter and additions of high-
nitrogen organic materials to the soil. Soil organic matter
can supply roughly 20 lb. nitrogen annually for each 1% soil
organic matter. High-nitrogen organic materials such as
composted manure, legume green manure crops, and soybean
meal release additional nitrogen as they decompose in the
soil over a period of months to years.
The release of nitrogen from organic matter of any type
requires moisture and warmth, because it depends on
microbial activity. If it is too dry or too cold for microbes to
be active, then little nitrogen is released. In early spring, the

manure and cover crops. Proper pH is maintained by
applying agricultural lime when necessary based on soil test
recommendations. A balance of nutrients in adequate supply
is maintained by applying nutrient-rich natural materials to
supplement nutrients supplied by soil minerals and organic
matter. Some organic fertilizer materials are purchased as
processed inputs (i.e. fish emulsions); while others may
be produced on-farm (for example a legume green manure
crop). Examples of materials used in organic production for
supplying nutrients are listed in Table 1. The first column
lists the material, and the next three columns describe the
nutrient content of the material in terms of a standard
N-P2O5-K2O fertilizer analysis.
Some natural materials are not acceptable in organic
production or are restricted for use in particular ways. For
example, the original national rule states that mined muriate of
potash (also known as potassium chloride) may be used only
in ways that do not lead to a buildup of chloride in the soil.
The use of raw (uncomposted) or aged manure is allowed
only when the manure is handled in a way to minimize the
risks of contaminating food crops with pathogenic organisms
and polluting the environment with nitrogen. Typically this
means that raw manure may only be applied to a cover crop

4

soil is usually so cold that nitrogen is not released quickly tapped into by growing deep-rooted crops or cover crops.
enough from organic matter for optimal growth of vegetable When soil levels of sulfur are inadequate, potassium mag-
crops. In that situation, using materials which contain nitro- nesium sulfate, potassium sulfate, or magnesium sulfate are
gen in a soluble form will improve crop growth. good sources.
Materials listed in Table 1 as having rapid availability
have some nitrogen in a soluble form. Since these materials Micronutrients - Mineral nutrients required in smaller
are often more expensive than slowly available materials, amounts than those mentioned in preceding paragraphs are
they are often side-dressed – applied close to the crop, in a usually in adequate supply when the soil pH is at the desired
band alongside the row, or around individual plants – instead level. These include manganese, iron, copper, zinc, boron,
of broadcast across the entire field. and molybdenum. If a deficiency is suspected, it is important
to have it accurately diagnosed before taking corrective
Phosphorus (P2O5) - Phosphorus is supplied as phos- measures. Metal chelates or sulfates, borax, and sodium mo-
phate-containing soil minerals and soil organic matter that lybdate are used to correct deficiencies when necessary.
gradually breaks down, releasing phosphorus for plant
uptake. One of the most important factors in determining Cover Crops - Important components of soil fertil-
the availability of phosphorus to plants is the pH of the soil. ity management in organic production are rotations which
In mineral soils, phosphorus is most available when pH is include cover crops and/or sod-forming crops. Cover crops
between 6 and 7. are planted for the primary purpose of improving and main-
Many soils which have received manure or synthetic taining soil fertility. Typically they are in the field for less
applications over a number of years contain relatively high than a year, and often grow during periods when the land
levels of soil phosphorus. In soils which have not been so would otherwise be left fallow. Sod-forming crops, such as
fertilized, phosphorus levels may be low. Rock powders such a legume/grass pasture, may grow for several years or more,
as colloidal phosphate and rock phosphate can be applied and may have uses in addition to the soil-building function.
to build up the phosphorus-supplying power of a soil over Both types of crops add organic matter to the soil, improv-
time. However, these products become available to plants
very slowly, and cannot be relied upon to supply adequate
phosphorus to a crop the year of application when soil levels
of phosphorus are low. They are more efficiently used by
incorporating into a compost-making operation where the
compost process will make them more available to plants.
Organic fertilizer materials and manure also contain
phosphorus, which is made available as the materials de-
compose in the soil. Bone meal has a relatively high concen-
tration of available phosphorus compared to other organic
fertilizers, and poultry manure has a higher concentration of
phosphorus than other manures (see Table 1).
As with nitrogen, when cool temperatures limit de-
composition of organic matter in the early spring, phos-
phorus may not be readily available to vegetable crops. This
problem is compounded because root growth is slow when Cover crops help improve soil fertility and reduce weed
temperatures are low. Even in soils which have high levels growth. In this photo, oilseed rape, bare ground, and winter
of phosphorus, it can be helpful to sidedress with a material rye (l to r) are compared.
high in available phosphorus early in the season.
ing soil fertility. Not only the aboveground portions of the
Potassium (K) - Potassium becomes available to plants crop, but also the entire root mass is new organic matter
by the gradual breakdown of soil minerals and clays. Rock which stimulates microbial activity leading to improved soil
powders such as granite dust and greensand contain 1-7% structure, nutrient-holding capacity, water infiltration, and
potash (K2O) but they break down very slowly and are of water-holding capacity. Planted in the late summer or fall,
little fertilizer value. Potassium magnesium sulfate (lang- they protect the soil from erosion and leaching of nutrients
beinite) and potassium sulfate provide K in a readily-avail- during winter and early spring.
able form. These materials both supply sulfur and the former Legume cover and sod crops, in addition to adding or-
supplies magnesium, both essential plant nutrients. Compost ganic matter, add nitrogen to soil. The nitrogen is absorbed
and manure are other sources of readily-available K. from the air by symbiotic bacteria living in the roots of the
legume crop, and is transformed by the bacteria into forms
Secondary Nutrients - Calcium, magnesium, and sulfur usable by plants. Non-legume cover crops do not add plant
are often in adequate supply in the soil. If the pH is in the nutrients to the soil, but they can help to redistribute them
desired range, calcium levels usually are adequate. The most from deeper soil. Deep-rooted cover or sod crops can take up
common calcium source is agricultural limestone, which also nutrients below the root zone of shallow-rooted cash crops,
raises the soil pH. Magnesium is supplied by break down of and recycle them into the plow layer when the cover or sod
soil minerals. If soil tests or plant response suggest a defi- crop is tilled under. Some cover crops, such as winter rye,
ciency, it can be supplied from sulfate of potash magnesia, contain compounds which suppress weed seed germination
magnesium sulfate (epsom salts), or, if an increase in soil and growth.
pH is desirable, dolomitic lime. Sulfur becomes available as Cover crops may be planted at any time during the year.
organic matter decomposes and as soil minerals break down. A late summer or fall seeding is common for winter cover
Subsoils often contain higher levels of sulfur which can be crops such as winter rye, or winter rye/hairy vetch mixture,

5

or spring oats. Spring or summer-planted annual cover crops
include sudangrass, sorghum sudangrass, and buckwheat.
Buckwheat is particularly useful for areas which are un-
cropped for short periods of time, since it establishes quickly
and can go from seed to seed in less than 8 weeks. Yellow-
blossom sweet clover, a deep-rooting biennial, is often
planted in spring or summer and left to grow until the
following spring. Cover crops may be overseeded or inter-
seeded while a cash crop is still in the ground, if care is taken
to provide a good seed bed and moisture. This is often done
at the final cultivation.
Species mixtures are often recommended over single-
species cover crops or sod crops because the mixtures tend to
use resources more fully and provide a more diverse habitat.
Except in situations where a legume would not establish
well, or where the nitrogen-fixing power of legumes is not
desired, at least one legume and one non-legume are recom-
mended.
Some growers establish a sod-forming crop between
rows of a cash crop, forming a living mulch which provides
soil-improving benefits without taking land totally out of Figure 1. Common Natural Enemies
vegetable production. The sod-crop typically must be
carefully managed to limit competition with the cash crop Purdue Greenhouse Media Analysis Lab
for nutrients and water. For example, the low-growing Dutch 625 Agriculture Mall Dr.
white clover can be seeded between rows of a tomato crop West Lafayette, IN 47907-2010
several weeks after transplanting. Periodic mowing can be
Phone: (765) 494-6619
used to control its growth. This system has worked best when
irrigation is available and the sod crop grows only in a strip E-mail: tk@hort.purdue.edu
between cash crop rows, with an uncropped area between the
Transplants will usually require fertilization after a
sod and the cash crop.
couple of weeks. Observations of plant growth combined
with knowledge of nutrients available in the growing
Seeds and Transplants medium before planting, and nutrients available in applied
materials should be the growersʼ guide to fertilizing trans-
plants. We have had success with weekly applications of fish
Seeds and transplants should be produced using organic
emulsion (analysis 3-2-2) at a rate of 250 to 500 ppm N (2 to
methods. Greenhouse grown transplants are usually grown
4 tablespoons/gallon), applied to the growing medium with
in a peat- or compost-based growing medium. Some growers
the irrigation water. Other practices include using magne-
use commercially available products, while others mix their
sium sulfate or extracts of plant compost or seaweed.
own. Many commercial products contain synthetic fertilizers
Keeping transplants healthy requires attention to the
and/or synthetic wetting agents that are not allowed by
greenhouse physical environment (light, temperature, air
national organic standards; these should be avoided. Growers
quality, and humidity), growing medium (moisture content,
who mix their own growing medium usually experiment with
pH, nutrient status), and sanitation. Refer to Purdue Exten-
different recipes over several years to develop one that works
sion Publication BP-61 for more details.
well for them. A sample recipe is provided below. If compos-
ted materials are used, it is important that they be fully
Potting Mix Recipe
composted, because incompletely composted materials will
1 part peat, 1 part compost, 1 part vermiculite or perlite
continue to compost and may temporarily deplete nitrogen
per 25 gallons finished product, mix in 1.5 cups each of
in the growing medium. Whether the growing medium is
superfine dolomitic, blood meal, bone meal and
purchased or mixed on the farm, it is wise to have it tested
greensand.
for pH, soluble salts content (also called electrical conduc-
tivity), and major nutrients (N, P, K, Ca, Mg) before seeding.
This service is provided by commercial soil testing labs as
well as many companies that produce growing media. The
Safety
Greenhouse Media Analysis Lab of Purdue University also The safety of the applicator is just as important with the
tests greenhouse media (see below). application of organically approved pesticides as it is with
The media samples should be representative of the conventional pesticides. Organic pesticides, although they
crop or problem you wish to analyze. The sample should be may be the result of natural processes, can be health hazards
collected from top to bottom of the growing container so the if used improperly. Research the chemicals you plan to use
entire root zone is included. At least a cup of medium is carefully for possible health hazards. Read the label of each
needed for a proper analysis. The samples should be mailed product carefully and follow the precautions listed there.
in a plastic bag. New media should be wetted to field or Always wear the protective clothing called for in the label.
container capacity before mailing. Contact the Media Double check the calibration to make certain the proper
Analysis Lab for details. amount is applied.

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Insect Management sucking insects resulting in mummified prey. A parasitized
aphid will be about two times its normal size and be brownish-
tan. The parasitized aphid will not move. If there is no hole
In organic systems, insect pests are managed preventively in the parasitized aphid, the wasp is still inside. The im-
rather than curatively. The idea is to alter the system so that mature wasp completes its development within the mum-
pests do not find the plants, are controlled by natural enemies,
or their damage is kept to a minimum. Insect management is
also dependent upon having a healthy organic system. This
includes a proper balance of nutrients in the soil and in the Nonparasitized Aphid
plant. Plants that are vigorous have a much better ability to
withstand damage caused by insects and disease. Healthy
soil and plants, therefore, are the best defense. Table 3 (at the
end of this publication) gives information on pests and which
of the following management systems might work best in
their control.
This section describes the general principles of insect pest
management in organic production. For more information
regarding the efficiency of specific practices, refer to Table 3.

Biological Control - In organic systems, much of the
Parasitized
“control” of insect pests is by natural enemies. These natural Aphids
enemies can be broken into two major categories: predators
and parasitoids. Predators catch and eat their prey much like
wolves or other carnivores. There are several predator If mummified aphids are present on a leaf with aphids,
species commonly found in gardens (Figure 1). Lady beetles no action should be taken.
are oval and usually red, orange, or yellow with black spots.
Lady beetle eggs, laid in groups of 5-20, are oblong and mified aphid, until it emerges, leaving a hole in the para-
orangish/yellow. Eggs are almost always laid near some prey, sitized pest. If mummified aphids are present on a leaf that is
so that when the eggs hatch, larvae will have a food source. infested with aphids, no action should be taken.
Larvae are alligator-shaped and are black with yellow or Tachinid flies are another group of common parasitoids.
orange spots. Lacewings are green or brown and have These flies look like large houseflies and lay their white, oval
iridescent eyes of green or gold. Their wings have many eggs on the backs of caterpillars and other pests. The eggs
veins and, as their name implies, appear lacey. Immatures are hatch and the fly larvae enter and kill the caterpillar.
alligator-shaped and have long sickle-like mouthparts that
they use to impale their prey and suck out juices. Lacewing
eggs are laid near prey and on the ends of silk threads.
Another common predator is the syrphid fly (flower fly).
The adult syrphid has two wings and therefore is a fly, but
resembles a bee with its black and gold stripes. The im-
mature is a maggot, which feeds on aphids and other soft-
bodied insects. The adult is called a “flower” or “hover fly”
and it feeds on nectar and pollen. Other less commonly seen
predators are minute pirate bugs, big-eyed bugs, assassin
bugs, certain stinkbugs, spiders, and soldier beetles.
Some predators spend most of their time on the ground,
and climb plants at night to search for prey. The most
common of these are the carabids or ground beetles. These
are dark-colored, sometimes shiny iridescent beetles that
run rapidly along the ground when disturbed. The adults John Obermeyer
eat many types of things, which is a benefit because these The white, oval eggs on the back of this caterpillar are signs
predators will be present even if there are few pests. The of a tachinid fly parasitoid.
immatures of carabid and staphylinid (another group of
predators found in the soil) beetles are predaceous and feed Two other types of natural enemies are birds and bats.
almost exclusively on other insects such as caterpillars. Other Birds will eat a variety of pests and some beneficial insects
predators found in the soil are centipedes, and wolf, garden, too, as will bats. Attracting birds to your farm is possible, but
and jumping spiders. a large scale (larger than just a vegetable field) is usually
The other group of natural enemies is parasitoids (or necessary – see Farmscaping (p. 8). Bats can be encouraged
parasites). These are adult insects that usually do not eat their to roost nearby by putting up bat houses or being sure not to
prey, instead they lay their eggs on or in the host (insect) disturb a nearby colony.
such as a caterpillar, and when the eggs hatch, immatures In the field it should NOT be necessary to purchase
use the host as food. Some parasitoids are very specific in these various biocontrol agents. All of these natural enemies
selection, while others are more general. Many parasitoids are quite common in the Midwest. A grower just needs to
are relatively small wasps that will be seldom seen, but the know how to invite and keep these biocontrol agents in their
results can be detected if one knows what to look for. For system. If they are not present in your field, it could mean
instance, parasitic wasps often attack aphids and other that environmental conditions are not conducive to their
presence and purchasing them would not help, as once they

7

were released they would leave the area. Purchase of biocon- strating their efficiency. For example, marigolds are sup-
trol agents does however, make good sense in greenhouse posed to have many insect repellent properties, but in our
situations where the beneficial insects can be contained. studies, we found no difference in the number of pests on
Since many adult predators and parasitoids feed on cabbage or tomatoes when marigolds were present vs. when
nectar and pollen, it is essential to have these resources they were not. The key to mixing plants is usually NOT the
nearby. A variety of plants will be more effective than a repelling action per se, but the plants contrasting “desir-
single species. An example would be several types of clover ability” to the pest. In a complex system where plants are
(red, crimson, sweet, white, etc.) along with more traditional mixed, insect pests spend a great deal of time moving from
flowers like marigolds, zinnias, etc. The objective is to have plant to plant looking for the right one instead of eating.
a continuous nectar and pollen source throughout the season. When they are moving, the pests are much more vulnerable
The closer these flowering plants are to the vegetables the to natural enemies and diseases. Companion plantings should
more often the vegetable plants will be searched by the be chosen so they 1) will not interfere with one anotherʼs
parasitoids or predators. In addition to natural enemies, growth and 2) are from different groups so that the pest
flowering plants will attract a wide variety of pollinators cannot utilize both of the plant types present. For example,
such as honeybees, bumble bees, wasps, and butterflies. flea beetles can feed on many members of the solanaceae
family, so peppers or tomatoes would be poor companion
plants. Herbs make good companion plants, as most insects
do not like their taste. Beans (dry or snap) would also work
as a companion plant with eggplant.

Farmscaping - Just as you can mix plants in your
vegetable field you can also plan your entire farm for
positive interactions of plants. For example, to attract birds
to your farm grow a border (or an area of your farm) that has
fruiting trees and shrubs in it. The larger the area the better,
but even a narrow border will help. A portion of the farm
may be left to a natural area of diverse plants that flower at
different times, have different growth patterns, and different
light needs. Another possibility would be to plant native
Midwestern plants (example of some natives: Ascelepias
tuberosa L butterfly milkweed, Echinacea purpurea Mo-
Creating a diverse environment of flowers and vegetables nench. – purple coneflower, Helianthus tuberosus L –
favors parasitoids, predators, and insect diseases over pests. Jerusalem artichoke, etc.) around the farm. When compared
with bedding plants, native plants attract more natural
Organic mulch, such as straw and grass clippings not only enemies and require less care.
acts as a weed barrier, but as it decays, the mulch becomes .
a haven for soil predators such as carabid and staphylinid
beetles, spiders, and centipedes. Therefore, mulching should
be encouraged in the field whenever possible, but not too
early in the year when the soil is cold and damp. This could
lead to additional pest problems. Wait until the soil warms to
approximately 70°F at a 4 inch depth before mulching. With
nectar/pollen sources and mulch available throughout the
growing season, natural enemies should be present in
numbers sufficient to handle most potential pest problems.
Another biocontrol is insect diseases (or microbial
controls). There are fungi, viruses, bacteria, and nematodes
that attack insects and help keep their populations under
control. Moist conditions are usually necessary for most of
these to work, especially fungal pathogens. Insect popu-
lations often need to be at fairly high numbers (numbers too
high to be tolerated in the field) before the diseases spread Organic mulches help control weeds and provide an
efficiently. There are a few commercial products that contain excellent habitat for soil predators.
these microbial organisms. These products will be discussed
in the “organic insecticides” section. In very dry years, the Timing of Plantings - Sometimes pests will cycle,
pathogens will not work as well as they should and there could peaking at certain times of the summer or be present at only
be an explosion of some pests like grasshoppers or hornworms. one time. Knowing when this occurs can allow you to plant
earlier or later to avoid pests. For example, the adult seed
Companion Planting (Intercropping) - In natural corn maggot lays eggs in cool, moist soil, so by delaying
systems (especially old field) there is always a variety of planting until the soil warms you could avoid the problem
plant species. However, in the vegetable garden we abandon entirely. Sweet corn has greater numbers of corn earworms
this companion planting scheme and make our vegetables the later it is planted in the season. Peppers rarely have worm
mini-monocultures. There has been much said and written damage (mostly due to European corn borer) until late in the
about the insect repellent properties of certain plant combi- season (late August or September).
nations, but there is little experimental evidence demon-

8

Trap crops - These crops are used to lure a particular and insect life cycles. Sanitation includes cleaning up,
pest away from a more important crop. The trap crop is tilling under or composting crops that have been harvested
usually considered expendable and is usually destroyed once for the last time to stop insect pests from building their
it is heavily infested. If it does not become heavily infested population. Broccoli or cauliflower should be removed
and retains most of the pests that visit it, then it can be left completely once harvest is over to stop cabbage worms
in the field. An example would be using Hubbard Squash to from using the plants as a nursery. Destroy all potatoes
attract squash vine borer and striped cucumber beetle away and volunteers after harvest to cut down on Colorado potato
from watermelon, pumpkin, or cantaloupe plantings. Corn beetle food sources before they go into hibernation.
(sweet or field) before silking will attract European cornborer When these biological or cultural controls do not work,
from plantings of pepper and earworms (fruitworms) from and at times they wonʼt, then the grower has to make more
tomatoes. immediate management decisions to stop the pest. This is
when organic pesticides may be used.

Organic Pesticides are products usually made from
plants that control insects by killing, repelling, or disrupting
their life cycle. Because of differences in certifying agen-
cies, it is best to check on the status of the following
“organic pesticides” to see if they are allowed, restricted,
or prohibited for use in your organic system. Some organic
products may contain unacceptable additions to them so that
even though the active ingredient is allowed the other
chemicals are not. Check labels and your certifying
agency before using.

Sticky traps, which attract and trap insects, are an example
of mechanical control.
Mechanical Controls - These include barriers and
physical controls. A mechanical barrier is anything that
physically prevents the pest from reaching the crop. The most
common barrier is row cover. The most common row cover is
REMAY®, which is spun-bound polyester; another material
is cheesecloth. The barrier can be laid directly on plants or
supported above plants with wire or other supports. Other
barriers could include plastic or metal cylinders (e.g., metal
soup cans with the top and bottom removed, plastic milk jugs
with bottom cut out) surrounding small plants to protect them There are several types of organic pesticides available to
from cutworm or armyworm feeding. As an example, the first the organic grower.
12 inches of the base of pumpkin or squash plants could be
wrapped with aluminum foil or an old stocking to stop squash Bacillus thuringiensis (Bt) is a soil bacterium that when
vineborers from laying eggs in this area. Copper strips ingested destroys the stomach of certain insects (caterpillars,
around plants (like strawberries) can stop slugs or snails from immature Colorado potato beetles, mosquito larvae, and
crossing over the strip. When slugs touch the copper strip maggots). Insects quickly stop feeding but take a few days to
they receive a small shock which keeps them from moving die. There are several types (subspecies) of Bt – Bt kurstaki,
any further. Traps also are types of barriers that attract insects Bt aizawai (trade names: Agree, Biobit, Design, Foray,
to them and then hold them. Sticky cards, usually yellow, can Dipel, Javelin, Thuricide, Xen Tari), that work well on many
be placed in a row to collect flies or moths. Removal of pests caterpillars, loopers, hornworms, and bagworms. Bt israel-
by picking them off by hand or any other method (e.g., strong ensis (Bactimos, Gnatrol, Vectobac) is effective against fly
water spray) or by removing the entire infested plant from the larvae such as mosquitoes and fungus gnats; Bt tenebrionis
field is one of the oldest and most basic of insect controls. (Novador) is most effective against small Colorado potato
This can work well on a few plants, but it takes time, patience, beetle larvae. Bt products work best on small larvae and
and perseverance, and when there are a lot of plants this ONLY on those that are chewing. Sucking insects such as
method is not cost effective. aphids and plant bugs are NOT affected by Bt. Larvae need
to feed on the plant somewhat to ingest enough Bt to die. Bt
Cultural Controls - These include those already dis- will last only a few days on plant leaves and will need to be
cussed such as trap crops, inter-planting a companion crop, applied 2-3 times over an 8 day period for best control. Bt is
using organic or non-organic mulches, proper fertilization one of the most effective organic insecticides. Most certi-
and watering. By using rotation of crops, following one crop fying agencies will not allow liquid forms of Bt containing
that is not closely related to another (e.g., corn or legumes xylene or petroleum distillates. Bt will not harm predators,
following tomatoes or crucifers) growers can disrupt disease parasitoids, or mammals. We have had very good success
with Bt for certain pests (See Table 3).

9

Pyrethrums are found in chrysanthemum flowers. Suffocating oils or horticultural oils are used either
Pyrethrums are essentially nontoxic to mammals and are fast when plants are dormant (dormant oils), or when plants are
acting in insects. As with Rotenone, pyrethrums are highly actively growing (summer oils). They are usually used on
unstable in light, moisture or air and therefore, do not last woody plants for control of aphids, mites, whiteflies, and
very long on plants, (1-2 days). Pyrethrum acts on contact on thrips. Under some circumstances, oils can burn foliage such
a broad spectrum of insects, which includes predators and as on cloudy, humid days. Plant-based oils are best; petro-
parasitoids. In our studies, it had moderate success in leum oils are restricted by most certifying agencies. Be sure
controlling pests (Table 3). to check before using.
There are several plant extracts used to repel insects
Rotenone (Derris, cube, timbo) is derived usually from (such as hot pepper wax, garlic spray, citrus oil, etc.). Our
tropical plants (Derris malaccenis and elliptica), although a studies and others have found they work poorly if at all, and
native weed (devils shoestring – Tephrosia virginiana) also we generally do not recommend them.
contains some rotenone. It is usually sold as a powder, but
there are some liquid formulations. Be careful not to buy any
rotenone that has been adulterated with synthetic chemicals Disease Management
(Piperonyl Butoxide (PBO) is not allowed by most organic
certification agencies). Rotenone acts as a stomach or contact Diseases can be very difficult to control in organic
poison on a broad spectrum of insects, including predators systems. Once a disease is present and the environmental
and parasitoids too. It is very toxic to fish. In our studies, it conditions favor disease, there is little an organic grower can
had moderate success in controlling some pests (See Table do. Therefore it is best to be proactive. The following items
3). As with pyrethrums, rotenone products are relatively are important to understanding Table 4 on plant disease
unstable. management.

Insecticidal Soaps (Ringers, M-pede, Saferʼs Soap) are
potassium salts of fatty acids that work by dehydrating
insects by breaking down the waterproof covering on their
bodies. It works best on soft-bodied insects such as aphids
and mealy bugs, and also mites. In our studies, it had little
overall success in controlling pests in the field, but can work
fairly well if only a few plants are moderately infested with
aphids. However, it does not work well on mites (See Table 3).

Diatomaceous earth is composed of microscopic
organisms (diatoms) that are made of silica (these organisms
are no longer alive). Because they have hard pointy bodies,
diatoms abrade the outer covering of an insectʼs exoskeleton
and cause the insect to dehydrate and die. Diatomaceous
earth works best on soft-bodied insects. It is difficult to get
the material to the pests, as most soft-bodied insects are on The tomato leaves shown are heavily infected with the
the underside of leaves. We have had little success with this disease early blight. Organic growers have limited resources
product under field conditions. to combat heavy infections, therefore preventative steps such
as crop rotation and tillage are critical to prevent severe
Azadirachtin (Margosan-O, Neemix, Azatin) is the disease outbreaks.
active ingredient from the neem tree. It can act as a repellent
(although in our studies, we have seen little evidence of this) Crop Rotation - Many disease-causing microorganisms
and a growth regulator. Small larvae should be targeted. In (pathogens) can survive in plant debris. When one plants a
our studies, neem has worked well when applied for control specific crop year after year in the same soil, the pathogens
of small worms or small sucking insects. For best control, can build up to high levels. Crop rotation allows the plant
applications need to be made every three days. Neem does debris to decay and the associated pathogens to die out. If
not work well on adults or large larvae (large caterpillars). pathogens survive in the soil itself, crop rotations will have
to be longer. Growers should rotate from the crop in question
Entomophagous nematodes (Steinernema riobravis, S. to a crop in another family. For example, after growing
carpocapsae) (Biovector) are soil nematodes that attack and tomatoes, one should avoid tomatoes, potatoes, peppers, and
kill soil insects (e.g., grubs, borers, etc.). Good timing of eggplants for the length of the rotation. Whether crop
these nematodes is essential if they are to work. They can be rotation is effective or not and the length of crop rotation
some-what effective, but environmental conditions, stage of required are listed under each crop/disease combination. If
pest, initial infestation rate, etc. will affect how well they work. the table lists two years, plant a different crop for two years
before planting the original crop again (Table 4).
Beauveria bassiana (Bb) is a fungus that attacks insects.
As an insecticide, it has been concentrated so that it can be Tillage - Decay of plant debris can be hastened by tilling
sprayed on insects to induce infection. It works best on the debris into the soil. The sooner the plant debris is buried,
young immatures – small caterpillars or nymphs under the sooner decay starts and the pathogens die out. Therefore,
humid (> 70% relative humidity) conditions. It does not it is often wise to till a field in the fall. The deeper the debris
work well on adults or large immatures. is buried, the better. Moldboard plowing may be advisable.

10

To avoid soil erosion, a cover crop can be planted over the Attention to timing is critical for successful weed
winter. Alternatively, some growers may want to remove management. In most cases, the smaller the weed, the easier
plant debris and compost it. In such cases it is critical to it is to control. Some cultivation tools work well only on
remove roots as well as tops and make sure the compost very small weeds, others can kill larger weeds as well. The
becomes hot enough to kill the plant pathogens that may be timing of control in relation to crop growth is also important.
present. Whether tillage is likely to be effective or not is Most vegetable crops show little yield loss if kept weed-free
listed under each crop/disease combination (Table 4). As a from 3 to 6 weeks after planting. Those weeds that emerge
general rule, composting will not be effective unless plant soon after the crop is planted are likely to reduce yield. Make
parts can no longer be recognized. controlling such weeds a priority. Late-emerging weeds may
need to be controlled to prevent additions of seed to the soil,
Resistant Varieties are an organic growerʼs best friend. to ease harvest operations, or for appearance. Strategies,
If at all possible, use resistant varieties to avoid disease practices, and technologies which aid in weed control are
problems in the first place. Some varieties are listed as included below.
partially resistant or tolerant. Whereas resistant varieties
show very few symptoms of the disease, partially resistant
varieties may show symptoms, but yield is unaffected.
Growers should note that some varieties are resistant to only
certain races of a pathogen. Find out what races of a patho-
gen are in your area by asking your seed representative or
Purdue Extension educator. Unfortunately, resistant varieties
are not available for all situations. In addition, varieties that
are resistant may lack desirable horticultural characteristics
or consumer preference. The availability of resistant varieties
is listed under each crop/disease combination (Table 4).

Saving Seed - It may be tempting to save seed from
your favorite varieties for use in future years. All vegetable
growers should realize, however, that there are certain
dangers to saving seed. Many diseases can be seed borne.
This means that a disease that was present in the plant can
be carried in the seed and thus may cause disease problems These watermelon varieties differ in susceptibility to
when planted. In addition to plant disease problems, saved Fusarium wilt. Organic growers should choose resistant/
seed may not have the characteristics of the original variety. tolerant varieties whenever possible.
Saving vegetable seeds requires special skills and equipment.
Prevention - Minimize weed seed additions to the soil.
Other Remedies - Organic growers may spray certain Weed seeds can live for many years in the soil, but some
substances as a treatment for plant disease. Such treatments buried seeds die or are eaten every year. If the addition of
are targeted at foliar diseases and are ineffective in control- weed seeds can be avoided, the number of viable weed seeds
ling root diseases. Depending on the organic certification decreases and it will be easier to control the remaining
process, such chemicals may include copper, bicarbonate weeds. This really can make a difference. Weeds that have
salts, and polymer films. Copper and polymer films leave escaped early season weed control measures and are about
some residue on the leaves and therefore may be used as a to flower, or have flowered, should be killed and, if they
preventative treatment. These chemicals should be applied have flowered, removed from the field to prevent maturation
on a weekly basis during the time diseases threaten. Salts and dispersal of the seed back into the field. Weeds can also
of bicarbonate, however, cannot be used as a preventative be brought into a field in manure, compost, hay, straw,
treatment. Substances such as ammonium or sodium or animal feed, and other material. Whenever you apply
potassium bicarbonate may have a toxic activity on fungi something to a field, make an effort to learn whether there
existing on the leaf. A concentration of one of these bicar- are weed seeds present, and evaluate benefits of the material
bonate substances at 0.5% (weight to volume) or less should versus potential for causing a weed problem.
not have any phytotoxic effects.
Cover Cropping - Plant cover crops to compete with
weeds. A fallow field grown up to weeds is a source of weed
Weed Management seed for itself and the rest of the farm. A cover crop instead
of a fallow, will reduce weed growth by competing for light
Organic growers manage weeds using a combination and nutrients, thereby reducing weed seed production.
of methods. The mix of weed species in a field changes in
response to the cropping practices used over a period of Flame Weeding - A hot flame passed quickly over
years; the weed species and types most adapted to the small broadleaf weeds provides a one-time kill of emerged
practices in use will increase in number, and those poorly seedlings. Equipment designed for field use can be pur-
adapted will decrease. As organic practices are adopted, the chased. Flame weeding can be performed after planting but
mix of weed species will probably change; weeds that were before crop emergence, to kill weeds that germinate before
difficult to control will become manageable, and weeds the crop. This is particularly useful in crops which take a
hardly noticed before will become the problem weeds. The long time to emerge, such as carrots. After crop emergence,
more diverse the weed management program, the better directed flaming can be used to selectively kill small weeds
chance that no weed will be well-adapted to it. in certain crops such as sweet corn, onions, and potatoes.

11

An advantage to flame weeding over cultivation is that it Mulching - Mulch is a material covering the soil
does not disturb the soil, and so does not stimulate germi- surface. To control weeds, the mulch must block nearly all
nation of additional dormant weed seeds. the light that reaches the soil, so that weeds which emerge
underneath the mulch do not have enough light to survive.
Stale Seedbed - A stale seedbed is prepared several Non-degradable black plastic mulch and wavelength selec-
weeks to months prior to crop seeding, weeds are allowed to tive mulches are acceptable in some organic programs,
emerge, and they are killed while still small by very shallow provided the mulch is completely removed from the field at
cultivation, flame weeding, or other non-selective method. the end of the season. Mulches of organic material such as
Depending on the length of time before planting, one or straw, paper, newspaper, and cardboard, or killed cover crop,
more flushes of weeds may emerge and be killed between are effective if they block sufficient light. Using mulch in
seedbed preparation and planting. The final kill should occur combination with no-till planting of vegetables into undis-
as close to the planting date as possible. This technique turbed soil has looked promising in a number of trials. For
reduces the number of weeds that germinate after the crop is example, people are experimenting with no-till planting into
planted. Its success depends on the weed spectrum and the a killed winter rye cover crop. In addition to controlling
timing of planting. It has proven useful in reducing popu- weeds, plastic and organic mulches influence other aspects
lations of summer annual broadleaves such as lambsquarters of the system. Black mulch, and to a greater extent, Infra Red
and pigweed. Transmitting (IRT) mulch, increase soil temperature, which
speeds growth of warm season crops, leading to earlier and
sometimes higher total yield. Organic mulches typically
decrease the soil temperature. This lower temperature can
delay warm season crops, if mulches are applied before the
soil has warmed up. It can also provide a better environment
for cool season crops during the summer months. Organic
mulches which have a high carbon to nitrogen ratio such as
straw, paper, or cardboard, may reduce the amount of
nitrogen available to the plant as they begin to decompose.
Additions of nitrogen-rich organic fertilizers may be needed
to overcome this problem. Mulches provide additional
benefits, including keeping the crop clean, reducing loss of
soil moisture to evaporation, and (if organic) adding organic
matter to the soil.

Mowing - Mowing can reduce competition and seed
Cultivation is an important part of weed control. production. Most weeds will regrow after mowing and so
repeated mowing is necessary to be most effective. As with
Cultivation - Cultivate using mechanical and hand tools any practice, weeds species adapted to mowing will increase
designed for the particular crop and weed stage. For more in number if it is practiced repeatedly over a number of
information on cultivating equipment, see the resources years.
listed at the end of this publication.
Living Mulches - See the soil fertility section for a
Crop Rotation - Rotate crops and planting dates to discussion of living mulches. Once established, a living
disrupt weed life cycles. Summer annual weeds such as mulch can compete with weeds and reduce weed seed
pigweed and nightshade will do best in crops which are production. An unmanaged living mulch can have much the
planted about the same time as these weeds normally same effect on a crop as weeds, competing for light, water,
germinate, such as the warm season crops of peppers, and nutrients, and reducing yield.
tomatoes, etc. Winter annual weeds such as shepherdspurse
and pepperweed will thrive in crops planted in late summer Biological Diversity - Encourage biological activity to
or fall. Perennial weeds such as Canada thistle or bindweed reduce weed seed survival. Weed seeds are eaten by a variety
are well-adapted to perennial crops, such as a sod crop, or of soil organisms, attacked by microbes, and eaten by
untilled fields, such as no-till operations. Organic growers insects, rodents and birds. The more biological activity in the
can plan rotations so that a weed species favored in one year soil and environment, the fewer weed seeds will be left to
will not be favored in another year. germinate. Practices such as adding organic matter to the
soil, using organic mulches, rotating crops, planting a variety
of crops, and cultivating diversity along field edges all
promote biological activity.

12

Tomato Hornworm Colorado Potato Beetle

Bean Leaf Beetle Striped Cucumber Beetle
These line drawings represent insect
pests common to vegetable production
in Indiana. More information on these
and other pests can be found in the
Adult Wireworm Imported Cabbage Worm Purdue Extension publication E-65.

Aphid Squash Bug

Japanese Beetle

16

Additional Sources of Information on Organic Vegetable Production:
Books Rodaleʼs Successful Organic Gardening: Controlling Pests
Great Garden Formulas: The Ultimate Book of Mix-it- & Diseases. Rodale Press, Book Readersʼ Service, 33 East
Yourself Concoctions for Your Garden. Rodale Press. Book Minor St., Emmaus, PA 18098.
Readersʼ Service, 33 East Minor St., Emmaus, PA 18098. <www.rodalepress.com>
<www.rodalepress.com>
Sustainable Vegetable Production from Startup to Market, by
The New Organic Grower, by E. Coleman. Chelsea Green V. Grubinger. NRAES-104. Natural Resource, Agriculture
Publishing, Chelsea, VT. & Engineering Service, Cooperative Extension, 152 Riley-
<www.chelseagreen.com> Robb Hall, Ithaca, NY 14853-5701.
<www.nraes.org>
Pests of the Garden & Small Farm: A Growerʼs Guide to
Using Less Pesticide, by M. L. Flint. Pub. 3332, Division of Vegetable Insect Management with Emphasis on the
Agriculture & Natural Resources, Univ. of California, 6701 Midwest, by R. Foster and B. Flood. Meister Publishing
San Pablo Ave., Oakland, CA 94608-1239. Company, Willoughby, OH.
<www.ucpress.edu> <http://meisterpro.com/mpn/>
(Not written for organic production, but includes alternative
methods of control for pests.)

18

Purdue University Extension Publications Commercial Sites
E-21 Managing Insects in the Home Vegetable Garden Organic Gardening
E-30-W Cucurbit Insect Management <http://www.organicgardening.com>
E-65 Vegetable Insect Identification The Natural Gardening Co.
E-74 Flea Beetles <http://www.naturalgardening.com>
E-95 Managing Striped Cucumber Beetle Populations on Organic Trade Association
Cantaloupe and Watermelon <http://www.ota.com>
E-96 Managing Insect Pests of Potato Individuals and Organizations
E-97 Management of Insect Pests on Fresh Market Hoosier Organic Marketing Education
Tomatoes <http://members.iquest.net/~cvof/home/homeinfo.htm>
E-98 Managing Insects in Commercially Grown Sweet Noahʼs Ark – An Organic Growers Homepage
Corn <www.rain.org/~sals/my.html>
E-99 Managing Insect Pests of Commercially Grown Organic Ag Info
Cole Crops <http://www.organicaginfo.org>
BP-61 Preventing Seedling Diseases in the Greenhouse Organic Consumers Association
<http://organicconsumers.org/>
ID-56 Midwest Vegetable Production Guide for
Commercial Growers Organic Materials Review Institute
<http://www.omri.org>
ID-101 Animal Manure as a Plant Nutrient Resource
The Organic Vegetable Gardening Guru
WQ-16 Land Application of Manure
<http://members.aol.com/ovgguru/ovgguru.html>
AY-277 Calculating Manure and Manure Nutrient
Rodale Institute
Application Rates
<http://www.rodaleinstitute.org>
AY-281 Soil Sampling for P, K, and Lime Recommendations Sustainable Earth
<http://www.sustainableearth.net>
Many of these are available on the Web at
<http://www.ces.purdue.edu/extmedia> Organic Certification - Educational Organizations
Also, single copies of these can be obtained through Purdue Hoosier Organic Marketing Education
Media Distribution Center, 1-888-EXT-INFO. 8364 S. State Road 39
Clayton, IN 46118
Other Extension Publications Phone: (317) 539-4317
Cultivation Equipment. IPM Fact Sheet 102FSNCT, Cornell E-mail: cvof@iquest.net
Cooperative Extension, Resource Center, 7 Business and <http://members.iquest.net/~cvof/home/homeinfo.htm>
Technology Park, Ithaca, NY 14850. (607) 255-2080.
<http://www.cce.cornell.edu/publications/catalog.html> Organic Certification - Certifying Agents
Indiana Certified Organic
Information on the Internet 8364 S. State Road 39
Sites at Land Grant Universities Clayton, IN 46118
Univ. of California, Davis Phone: (317) 539-4317
<vric.ucdavis.edu/selectnewtopic.organic.htm>
Ohio Ecological Food and Farm Association
Univ. of Wisconsin: Healthy Farms, Healthy Profits
9665 Kline Road
<www.bse.wisc.edu/hfhp>
West Salem, OH 44287-9562
Federal and State Government Sites Phone: (419) 853-4060
Appropriate Technology Transfer for Rural Areas (ATTRA) E-mail: organic@oeffa.com
<http://attra.ncat.org>
Many publications about organic growing online.
National Organic Program
<http://www.ams.usda.gov/nop >
This site has the National Organic Rule (standards) online.
Indiana Organic Certification Standards
<http://www.IN.gov/oca/other/organic_rule.html>
Indiana Organic Certification Accreditation Law
<http://www.IN.gov/legislative/ic/code/title15/ar4/
ch12.html>

19

REVISED 8/03
It is the policy of the Purdue University Cooperative Extension Service, David C. Petritz, Director,
that all persons shall have equal opportunity and access to the programs and facilities without regard to race,
color, sex, religion, national origin, age, marital status, parental status, sexual orientation, or disability.
Purdue University is an Affirmative Action employer. This material may be available in alternative formats.
1-888-EXT-INFO
http://www.ces.purdue.edu/extmedia/

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