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String Trimmers for Curbing Weeds in Row Crops

With the whir of a string-operated weed whacker, corn and soybean farmers can take a big step to reduce herbicide use that has the potential to contaminate surface water near streams, wetlands, and wells.

"The only way to avoid surface water contamination is to reduce herbicide use, and that's where the string trimmer comes in," says Bill Donald. He is an agronomist in the ARS Cropping Systems and Water Quality Research Unit located at the University of Missouri in Columbia.

Donald designed a system to cut weeds between crop rows—using a lawn-type string trimmer—and reduce herbicide application by as much as 60 percent.

ARS studies in 1993 and 1994 evaluated the surface water quality at Goodwater Creek, an agricultural watershed established as an experimental site by USDA in 1971. The conclusion of those studies was that most herbicides end up in surface water, rather than in groundwater.

"If farmers banded herbicides in a small, narrow strip over the crop row and mowed or whacked the weeds between rows of corn and soybeans, they could get the same yield as if there were no weeds," says Donald. "Four years of field research in Missouri substantiate this finding.

"The same system could apply to growing sorghum and cotton, but at this time these crops haven't been tested," he says.

Banding uses less herbicide per acre by treating only the crop rows. And the weed stubble left between the rows after using the weed whacker has an added benefit: it helps prevent erosion by holding the soil in place.

Donald is currently developing a prototype string trimmer that can be used on four rows at a time. -- By Linda Cooke, ARS.

William W. Donald is in the USDA-ARS Cropping Systems and Water Quality Research Unit, University of Missouri, 269 Agricultural Engineering Bldg., Columbia, M0 65211; phone (573) 882-6404.