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Potato Enemy #1--the Colorado Potato Beetle

Cool Weather Fungus Could Put Potato Pest on Hot Seat

By Jan Suszkiw
May 20, 1998

Spraying potato plants with the fungus Beauveria bassiana can kill hungry Colorado potato beetles so less insecticide is needed. The rub: Summer's heat can squelch Beauveria before it gets started.

Studies conducted by Agricultural Research Service microbiologist Phyllis Martin and co-workers last summer in Maryland suggest Beauveria will perform best in early spring, or cooler regions like Maine. Summer temperatures that climb above 86 degrees Fahrenheit can kill the fungus or prevent it from germinating into forms that infect and kill potato beetles.

Martin reports on her findings at today's American Society for Microbiology meeting in Atlanta, Georgia. She and ARS colleagues Robert Schroder and Ashaki Shropshire conducted field studies on Maryland's Eastern Shore and at Beltsville, Md. Their work is part of an ongoing project with Polish and Czech Republic scientists. The goal: develop an integrated approach to managing the beetle, which resists some insecticides.

The pest costs U.S. potato, tomato and eggplant growers about $150 million annually in losses. It's just as destructive abroad. Beauveria is one of several natural alternatives scientists are testing. Other alternatives include Bacillus thuringiensis bacteria, beneficial insects and a commercial dye.

Last year, Martin's group treated half-acre potato plots with a registered commercial Beauveria strain from Mycotech Corp. They treated each plot four separate times from May to July. Overseas, their colleagues followed suit, later reporting an 84 percent drop in larval beetle populations. But in Maryland, no such reduction occurred.

By growing Beauveria in test-tube experiments at ARS' Insect Biocontrol Laboratory in Beltsville, Martin concluded temperature was the deciding factor. In Maryland, Beauveria often faced 100-plus degree temperatures. But Poland's average daytime temperature of 74 degrees F. proved more forgiving, allowing the fungus to survive on plants longer and kill leaf- eating larvae.

Scientific Contact: Phyllis Martin, USDA-ARS Insect Biocontrol Laboratory, Beltsville, Md., (301) 504-6331, fax (301) 504-6973,

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