Biorational Pesticides

Pesticides vary in their toxicity and in their potential ecological impact. Pest control materials that are relatively non-toxic to people with few environmental side effects are sometimes called “biorational” pesticides. These fit well into an IPM strategy, which relies on monitoring for early detection of pests and emphasizes the use of selective products that provide control while minimizing negative effects on beneficial insects that suppress pests. The term ‘biorational’ is a qualitative term intended to help provide information and guidance for decision making. All pesticides have some toxicity; always read and follow the label regarding agricultural use requirements and personal protective equipment. All of the pesticides listed as biorationals in the tables below carry the signal word “Caution”, the least toxic classification, on the label. None are federally restricted-use products. Most have dermal and oral LD₅₀ values over 2,000 mg/kg.

Some, but not all, biorationals are approved for use on crops that are certified organic under the National Organic Program. For a given active ingredient, some products or formulations may be approved for use in certified organic crops, while others are not. Products that are generally approved for organic production are designated "OMRI" or "OMRI listed," which indicates they are listed on the website of the Organic Materials Review Institute (https://www.omri.org/about-products-list). Growers should consult with their certifying agency to be sure which products are approved for use.

Table 10 lists biorational insecticides and biological controls for insect management. Table 11 lists biorational fungicides and biological controls for disease management. The major categories of biorationals include botanicals, microbials, minerals, and synthetics.

Botanicals are plant-derived materials and include pyrethrin, azadiractin and neem oil, garlic, capsaicin, and vegetable oil. Botanicals are generally short-lived in the environment, as they are broken down rapidly in the presence of light and air. In general, these products require thorough coverage, application at the first signs of disease, and frequent repeated dosages to be effective. Products derived from the seeds of the Neem tree, including azadiractin and neem oil, are selective and have low mammalian toxicity. Garlic and capsaicin act primarily as repellents and thus need to be reapplied as long as pests are present. They are registered for use on a wide range of crops and pests. However, none are listed in this Guide for commercial use unless they carry the proper agricultural use requirements on the label. Vegetable oil may be derived from soybean, corn or other plants; the only labeled product for commercial use is produced from soybean oil. 

Microbial pesticides are formulated microorganisms or their by-products. They tend to be selective, so specific pests may be controlled with little or no effect on non-target organisms. Microbial insecticides include bacteria (Bacillus thuringiensis and spinosad) and fungi (Beauvaria bassiana). While these active ingredients are generally approved for organic crops because of their natural origin, certain formulated products are prohibited because the inert ingredients or procedures used to make the product may be prohibited. Microbial pesticides are often living organisms that require specialized storage and application procedures. These include beneficial fungi and bacteria (Streptomyces, Gliocladium, Trichoderma harzianum) that compete with plant pathogenic fungi, produce toxic metabolites, or actively parasitize pathogens. Their effectiveness in University research trials has been inconsistent because of variations in environmental conditions and disease pressure. Microbial fungicides perform best in a greenhouse environment where they can establish and flourish. Control of plant pathogenic organisms on the leaf surface is especially problematic, as the competing organisms may have difficulty becoming established due to dessication and exposure to sunlight. These materials have a limited shelf life, must be protected from temperature extremes, and must be applied correctly (with plenty of water and under the correct environmental conditions) to be effective.

Minerals and synthetics. Some biorational pesticides are minerals, mined from the earth and minimally processed. Kaolin clay, insecticidal soap, and iron phosphate are examples. Minerals that are heated, chemically reacted, or mixed with surfactants may be considered synthetics. Synthetics include growth inhibitors or insect growth regulators (IGR), materials that interrupt or inhibit the life cycle of a pest.