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New Bioherbicide Controls Several Weeds

By Tara Weaver
October 29, 1997

A fungal compound--normally undesirable because it can promote food spoilage--killed jimsonweed and other pesky broadleaf weeds in lab studies at USDA's Agricultural Research Service.

Weeds in corn, soybeans and other row crops cost farmers billions of dollars in losses and reduced crop yields. But the fungus-produced compound, known as AAL-toxin, could reduce farmers' reliance on synthetic weed-killing chemicals if it passes additional tests and is developed as a commercial product.

ARS has patented AAL-toxin as a bioherbicide--a nature-based weed killer. The agency and DuPont Agricultural Products, Newark, Del., have a cooperative research and development agreement to test and further develop AAL-toxin for agricultural uses.

AAL-toxin is produced by the fungus Alternaria alternata f. sp. lycopersici. ARS scientists found that the AAL-toxin kills a number of weeds that are pests of row crops such as soybeans, cotton, rice and corn. Weeds that succumbed in lab tests include duckweed (Lemna species), jimsonweed (Datura stramonium), black nightshade (Solanum nigrum), prickly sida (Sida spinosa), redroot pigweed (Amaranthus retroflexus) and northern jointvetch (Aeschynomene virginica).

Some A. alternata fungi are known to promote spoilage of fruits, vegetables and grains. But use of AAL-toxin to kill weeds doesn't pose a hazard to the crops and should be safe for the environment and wildlife.

AAL-toxin affects broadleaf weeds, but not grasses. It can be used before or after weeds emerge and is effective as a spray, mixed with water or alone, according to Hamed K. Abbas. He and colleagues conducted lab studies at ARS' Southern Weed Science Research Unit in Stoneville, Miss.