What gardeners should know about organic insecticides!

by Ayanava Majumdar, Alabama Cooperative Extension Service

Organic insecticides are critical tools to insect control, especially in the hot and humid south where insect pests never seem to rest. Even in the dead of winter, insect pests such as the yellowmargined leaf beetles can be active in the soil on a warm winter day (just look under some turnip plants and other host plants for deep brown larvae that may be in the ground). In most cases, vegetable plants have should be protected early in the season with a variety of integrated pest management tactics. Insecticides are the last resort for pest management in a sustainable system. With latest advances in IPM technologies, there are several types of organic insecticides to choose from, namely, physical desiccants, contact and stomach poisons, and products with volatile action. Below is a brief description of modes of action and usage tips.

  • Kaolin clay and diatomaceous earth are natural desiccants and abrasives that are readily available in farmer coop stores and other retailers. These products form a layer over the plant parts that confuses insects or abrades their exoskeleton making them vulnerable. These insecticides should be reapplied after a heavy rainfall or periodically to protect new plant growth.
  • A large majority of garden insecticides, be it organic or conventional, are contact poisons meaning they have to be applied timely when the target insect is most active and in the right dosage. Common organic contact insecticides include vegetable and horticultural oils, botanical insecticides like neem, natural pyrethrin and Chenopodium ambrosioides, and microbial extracts like spinosad. Spinosad-based products are good for quick kill of caterpillars and small pests in organic situations. Many of the paraffinic oil containing products (Suffoil-X, TriTek) can slow down small insect pests to prevent an outbreak. Do not over-use spinosad and pyrethroid based products to prevent insecticide resistance.
  • There are also some beneficial fungi that infect insects and they are available in the form of products called Botanigard and Botanigard Maxx, Mycotrol-O, BioCeres (all containing Beaveria bassiana), PFR-97 containing Isaria fumosorosea, etc. They act by piercing the exoskeleton of insects and then causing septicemia.
  • Gardeners will recognize Bacillus thuringiensis (Bt) as a commonly available product with product names such as Thuricide, Monterey B.t., Agree, etc. Bt is actually a stomach poison that is specific to caterpillars for the products mentioned. When using Bt, spray timely on small caterpillars and spray thoroughly many times till the pest population crash.
  • Some insecticides are volatiles, meaning, they deter insects by their strong smell thereby masking plant cues. Unfortunately, these products may not last very long in poor weather conditions. Some gardeners make their own formulations using mixtures of garlic, chilies, and herbs that may give the same effect. Garlic Barrier and Cinnamite are some commercial formulations available for purchase online.
  • We highly recommend contacting the farmers cooperative stores for product support and consultation. Alabama Farmers Cooperative can also provide you a copy of the new Urban Garden IPM Toolkit for beginning farmers or gardeners (see below).  Some excellent online vendors for organic insecticides include Arbico Organics, Garden Alive, Forestry Distributing, Do-My-Own, and Amazon.
  • For further information, do not forget to visit the Alabama Vegetable IPM website (www.aces.edu/vegetableipm) or directly contact a Commercial Horticulture Regional Extension Agent.

Home and Urban Garden IPM Toolkit is Now Available!

A brand new Urban Farm IPM Toolkit is now available for urban farmers and community gardeners. This wheel slide chart has both conventional and organic insecticide listings for nearly 20 different crops. This publication also has listing of common insect pests with images that may help when scouting garden vegetables. Email bugdoctor@auburn.edu to get your own copy.

Click here to see what it looks like.

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