New Bioherbicide Whacks Tomato Weeds

By Tara Weaver-Missick
June 8, 2000

Agricultural Research Service scientists have found a new bioherbicide that shows promise as an alternative to methyl bromide for controlling weeds in tomatoes.

The bioherbicide, Myrothecium verrucaria, comes from the sicklepod plant found primarily in the southeastern United States. ARS scientists recently reported that the fungus controls kudzu, a problematic weed in the South.

Common purslane, horse purslane, ground spurge and spotted spurge are serious weed pests in commercially grown tomatoes. Tomato crops have the highest consumption of methyl bromide of all crop uses. Tomato crops account for 23 percent of pre-plant methyl bromide use. About 3,773 tons are applied annually to the crop to control nematodes (tiny worms), insects and weeds.

Researchers C. Douglas Boyette and Hamed K. Abbas at the ARS Southern Weed Science Research Unit, Stoneville, Miss., treated plots with natural infestations of these weeds with Myrothecium before planting Beefsteak tomato seedlings. Myrothecium eliminated these weeds in several field tests.

Myrothecium was applied in place of methyl bromide. After 14 days, no weeds were found and the tomatoes prospered.

This research was part of an agency fast-track study to look for alternatives to methyl bromide, a widely used fumigant and ozone-depletor. Methyl bromide is scheduled to be banned in the United States in 2005, and worldwide by 2015. Worldwide, 72,000 tons of methyl bromide are used in preplant and postplant applications and fumigations.

The researchers are also examining several other possible natural alternatives to methyl bromide for controlling weeds, including Fusarium solani and Colletotrichum truncatum.

Boyette was scheduled to present these findings today at the Third International Weed Science Conference, Foz do Iguassu, Brazil, June 6-11.

ARS is the U.S. Department of Agriculture's chief research agency.

Scientific contact: C. Douglas Boyette, ARS Southern Weed Science Research Unit, Stoneville, Miss., phone (662) 686-5222, fax (662) 686-5422, dboyette@ag.gov.