Organic vegetables are usually more expensive than conventionally grown produce. One of the reasons for this is that the choice of pesticides that organic growers may use is limited (yes, they are allowed to use certain pesticides). For example, in 2012 researchers from Auburn University found only two organic pesticides — Entrust® (spinosad) and PyGanic® (pyrethrins) — were effective against the yellowmargined leaf beetle (Microtheca ochroloma) on crucifer crops such as cabbage. However, these pesticides may have negative impacts on beneficial insects and they can be expensive, so many organic vegetable growers are reluctant to use them.
Now the Auburn researchers, Rammohan Balusu and Henry Fadamiro, along with colleagues at the University of Florida (Elena Rhodes and Oscar Liburd) have published research in the Journal of Economic Entomology which may offer organic cabbage growers an alternative. Planting turnips around the perimeter of the cabbage crop, they found, reduced beetle numbers and crop damage.
Turnips seem to be more attractive to the yellowmargined leaf beetle palate than cabbage, so instead of eating the cabbage, the beetles dined on the turnips. This pest-management technique is known as “trap cropping.” One crop (the trap crop) is used to lure insects away from the crop being grown for harvest (the cash crop).
“The data from the research station trials, which showed significant reduction in insect densities and crop damage in cabbage plots bordered by turnip, indicate that the use of turnip as a trap crop is an effective control method for M. ochroloma when cabbage is the cash crop,” the researchers wrote.
Trap cropping might help decrease the costs associated with organic farming, resulting in lower retail prices for organic food.
“Trap cropping tactics used for control of yellowmargined leaf beetle are very important in organic systems where there are limited tools available for pest management,” they wrote. “Trap cropping may reduce or eliminate the need for insecticide application in the main crop, thereby reducing the cost of pest control, eliminating the overuse of a single insecticide that eventually results in the beetle becoming resistant to that insecticide, and reducing impacts on non-target beneficial organisms like predators (lady beetles) and pollinators (bees).”
While the researchers have shown that trap cropping may be a beneficial tool for cabbage growers, their research isn’t done.
“In a follow up study,” they wrote, “we have identified the chemicals (volatile organic compounds) that attract yellowmargined leaf beetle to its preferred cruciferous plants. We are working to develop these attractive compounds as lures for use in monitoring and managing yellowmargined leaf beetle in vegetable farms.”
Funding for their study was provided by the USDA NIFA Organic Agriculture Research and Extension Initiative Program (Grant No. 2011 – 51300 – 30634).
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