University of Maryland Extension Entomologist Galen Dively offered an overview of organic insecticides at January's Mid-Atlantic Fruit and Vegetable Grower's Conference. Here's a recap of Dively's remarks from Scott Guiser, Penn State Extension horticulturist.
In prefacing his comments, Dively noted that, in organic systems, insecticides are tools of last resort – after all non-chemical approaches have been employed. This often puts the products at a disadvantage because they frequently work best on immature stages of a pest's life cycle.
More effective organic products
Here's what the Maryland entomologist considers to be more effective products labeled for organic use:
Azadirachtin products, such as Neemix and Aza-Direct are extracts of oils found in the Neem tree. These insect growth regulators prevent insect molting (slow) and also serve as feeding deterrents and repellents. Fair to good control of beetles (cucumber, Colorado potato, Mexican bean, and flea) is reported. However, with cucumber beetles, even minimal feeding can transmit the bacterial wilt organism to cucumber and cantaloupe.
Pyrethrum is the naturally-derived insecticide commonly marketed as Pyganic. Quick
knockdown, but very short residual activity are key traits. Fair to good control of aphids, whiteflies, thrips as well as knockdown of cucumber, Colorado potato and flea beetles were noted.
Azera is a new combination of a pyrethrum (like Pyganic) and azadirachtin (like Aza-Direct/Neemix). Control of Japanese beetle, aphids, imported cabbage worm, leafhoppers and cucumber beetles was improved over use of azadirachtin alone in recent studies. It even provided good squash bug control if timed to target nymphs, just after egg hatch. The limitations of one ingredient are partially covered by the other.
Bacillus thuringiensis (Bt) products are well known for their ability to control lepidopteron (caterpillar) larvae such as imported cabbage moths in cole crops. Good spray coverage and repeat applications are important. Some Bt strains control non-lepidopterons. Not all Bts are alike, and some aren't labeled for organic production.
Spinosad, sold as Entrust to the organic market, provides very good control of caterpillars and thrips. Fair to good control of flea beetles and Mexican bean beetle was noted. Some growers note control of Colorado potato beetle.
Soaps and oils provide good knockdown of soft-bodied insects such as aphids and mites. Repeat applications and excellent plant coverage are important. Oils provide more residual activity than soaps, but this effect still is short lived. Both soaps and oils have phytotoxcity potential.
Plant extracts such as d-limonene (citrus) and rosemary extras disrupt insect neuroreceptors and act as anti-feedants. Fair to good control of aphids and spider mites are reported.
Mineral dusts (kaolin clay), sold as Surround, repel and/or irritate insects and disrupt feeding and egg laying. Maryland research showed that Surround applied alone or in combination with sulfur, Azera or Trilogy provided 55% to 86% stink bug control. Residue from Surround may not be acceptable for some fresh market crops.
Dively recommends the following for improving the efficacy of organic insecticides:
- Use 50 to100 gallons of spray solution to ensure good plant coverage.
- Arrange nozzles (such as drop nozzles) to improve plant coverage.
- Monitor pH of spray water and buffer as needed.
- Calibrate sprayers.
- Apply controls when pests are in the early stages of development.
- Consider adjuvants to increase coverage and efficacy.