PESTICIDES FOR ORGANIC GROWERS

Organic certification, contrary to popular belief, does allow pesticides to be used in vegetable and berry production. However, the selection is limited compared to conventional production and it excludes most, but not all, man-made materials. The federal Organic Foods Production Act of 1990 mandated the development of a national list of allowed materials. This list is due to be published later this year.

With a relatively small array of pesticides to work with, organic growers must emphasize the use of cultural practices to minimize pest problems. Practices such as crop rotation, sanitation, stress avoidance, and selection of resistant varieties are the cornerstones of organic, as well as conventional, pest management.

When organic pesticides need to be used, the choices include botanicals, microbials, synthetics and minerals. Botanicals are plant-derived materials such as rotenone, pyrethrum, sabadilla, ryania, etc. Nicotine products, although natural, are not permitted due to their high mammalian toxicity. Botanicals are generally short-lived in the environment, being broken down rapidly in the presence of light and air. Thus, they provide pest control for only a day or two. Ryania and sabadilla may have some additional residual activity. Botanicals are generally broad-spectrum, so they kill beneficial insects too.

Some newer botanical insecticides include products made from extracts of Neem tree seeds. Azatin and Align are labeled for many vegetable crops. Azadirachtin, the active ingredient, has a very low mammalian toxicity. It works by inhibiting development of immature stages of many insects, and by deterring feeding by adults.

Microbial pesticides, formulated from microorganisms or their by-products, tend to have advantages over the botanicals in that they are safer to use, and are more selective in what they kill, so beneficials are not harmed. Bacillus thuringiensis or B.t. is perhaps the most widely used type of microbial insecticide. B. t. products contain a toxin made by a bacterium. B.t. has greatly expanded organic pest control effectiveness for insects like Colorado potato beetle, the cabbage worm complex and corn borer.

The major types of B.t. are the 'kurstake' strain for caterpillar pests (Dipel, Javelin, Thuricide, MVP, etc.) and the 'San Diego' or 'tenebrionis' strain for potato beetle larvae (M-One, M-Trak, Beetle Beater, Novodor, etc.).

For B.t. to be effective, you must use the right strain for the pest and apply it when small larvae are actively feeding. Because B.t. must be ingested by the pest, thorough coverage is essential. Use spray water with a pH between four and seven for best results.

Other microbials are available that work as fungicides, such as Mycostop, a soil drench derived from Streptomyces fungus, and Gliogard, derived from Gliocladium fungus. Both these products are labeled to control some root rotting organisms that cause damping off and similar problems in seeded crops.

Synthetics available to organic growers include soaps and horticultural oil. Soaps are fatty acids of potassium salts, which are formulated to be both insecticides (M-Pede, Safer's Soap) and herbicides (Sharpshooter). The latter are not allowed by all certification groups. Soaps work by smothering soft-bodied insects like aphids or thrips. Application directly onto exposed insects is critical to good control. Soaps can be phytotoxic to some crops, and harmful to some beneficials.

Horticultural and other dormant oils are petroleum-based but are an organically-allowed means of smothering scale and other insects. There is good evidence that horticultural oil in combination with bicarbonate salts (such as baking soda) can prevent powdery mildew on crops like cucurbits. All that's missing is a label for the use of baking soda as a fungicide.

Minerals such as sulfur and copper are the primary organic fungicides and bactericides used to prevent disease in the field. Some available formulations are Bordeaux mixture, tri-basic copper, copper hydroxide (Kocide), cupric oxide, copper sulfate, elemental sulfur, calcium poly sulfide (lime sulfur) and copper-zinc mixtures. With a good spray program and cultural practices that maximize leaf drying, organic growers may achieve effective prevention. In some cases, as with bramble and blueberry 'blights', these may be the materials of choice. Use these products with caution because of potential phytotoxicity, especially with temperatures over 80oF.

Diatomaceous earth is really a biological, as it is composed of one-celled diatoms, the "shells" of which act as a mineral dust which dries out certain soft-bodied insects. It is more widely used in post-harvest applications than in the field.

Although disinfectants are not typically considered pesticides, they are important to horticultural production. The synthetic materials, chlorine (bleach) or hydrogen peroxide are allowed organically as dilute solutions to disinfectant greenhouse surfaces and tools. Other synthetics may be permitted in special applications such as pheromone traps for monitoring insect pest populations, although the permissibility of this use varies among certifying bodies.

The so-called "beneficial" insects include predators and parasitoids such as lady beetles and various wasps, as well as certain nematodes that are used for insect control. These are all allowed organically. They are classified by regulatory agencies as biological controls, not as pesticides. Most suppliers of these organisms provide good information on how to best use them.

With organic pesticides, as all others, read the label carefully to be sure it applies to the crop and pest in question and to learn the most effective means of application. Remember that labels may change from year to year as crops and pests are added or withdrawn, or new application procedures developed.

Dr. Vern Grubinger, University of Vermont Extension System

The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension system does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law.Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations.The user of this information assumes all risks for personal injury or property damage.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, The University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.

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