RESEARCH UPDATE
A wealth of ways to manage pests without pesticides

Entomologists report on new research into trap crops, refugia and other biocontrol methods

By Laura Sayre

February 22, 2005: A recent article by Joel Grossman in the IPM Practitioner (Sept/Oct 2004) highlights the wide range of Integrated Pest Management research being carried out in nearly every region of the United States, as reported at the annual meeting of the Entomological Society of America. While much IPM research is designed primarily to help conventional farmers reduce their use of chemical pesticides—especially the most dangerous compounds—more and more researchers are investigating principles, materials, and techniques with practical value for organic farmers.

Some of the most promising work focuses on trap cropping. Forrest Mitchell of the Texas Agricultural Experiment Station tested the effectiveness of squash trap crops for control of squash bugs, Anasa tristis. When planning trap crops, Mitchell said, farmers should keep in mind that squash bug feeding preferences among cucurbits run as follows (from most to least favored): squash and pumpkins > watermelons > cantaloupes > cucumbers > wild gourds. In addition, he noted, squash bugs feed on large plants in preference to small plants, so trap crops should be planted earlier than primary crops.

Mitchell emphasized that squash trap crops are highly effective for watermelons and cantaloupes, where they can offer better than 90 percent protection from squash bugs. They are less effective as trap crops for other squash plants, he said, but still offer good early-season pest protection and some later-season protection.

Elsewhere in the country, Richard Roush of the University of California at Davis reported that early potatoes grown at the margins of tomato, eggplant or later potato fields can serve as an effective trap crop for Colorado potato beetle. Once the trap potatoes are infested, they can be sprayed (by conventional farmers) or flamed (by organic farmers) to impact the CPB populations. Alternatively, trenches lined with black plastic can be constructed along field perimeters—since most CPB walk into fields early in the season, they get caught in the trenches and cannot escape.

In a different approach, researchers at Montana State University reported that farmers on the Northern Plains could protect crops from wheat stem sawfly (Cephus cinctus), a relatively new and very damaging pest, simply by setting their cutter bars higher when they combine. Scott Meers found that two parasitoids, Bracon cephi and C. lissogaster, overwinter in wheat stems and are harmed by standard harvest practices. Farmers can ensure adequate overwintering habitat for the parasitoids by leaving at least 1/3 of the wheat stem standing when they harvest, Meers said. Leaving more stem standing, especially within 7.5 to 30 meters of field perimeters, offers the beneficial species additional protection. Given sufficient habitat, the parasitoids can virtually eliminate sawfly damage.

Alan Cady of Miami University in Ohio studied the effectiveness of constructed refugia to encourage predatory ground beetle and spider populations in corn and soybean fields. Cady and his team built open baskets (1 meter x .5 m x .2 m) out of chickenwire, filled them with sterile wheatstraw, and placed them in and around the fields. They found that the refugia boosted predatory arthropod populations in both corn and soybean fields, and in the corn fields led to reduced insect damage, higher yields, larger ears, and greater stalk biomass. The effectiveness of the refugia appeared to be greatest within about 5 meters of the straw piles.

Finally, a group led by Donald Weber of USDA-ARS Beltsville has been working to develop textile-based, baited traps for adult corn rootworms, Diabrotica spp. The adult leaf beetles are strongly attracted to cucurbitacins, plant compounds produced by cucurbits. To make the traps, researchers extracted cucurbitacins from buffalogourd, Cucurbita foetidissima, and Hawkesbury watermelon, Citrullus lanatus, and then either sprayed or soaked a number of different textiles (including knit polyester, jute burlap, and cotton muslin) with the compounds. Some of the fabric panels were also treated with spinosad to kill the attracted beetles. Soaked burlap was among the most effective trap materials, Weber reported.

The Entomological Society of America's next annual meeting will be held Nov. 6-9, 2005, in Fort Lauderdale, Florida. Abstracts of papers presented at past ESA meetings can be accessed at www.entsoc.org/annual_meeting.