[ScienceDaily Aug. 16, 2012] — Even as crops resistant to 2,4-D herbicide are being developed, populations of weeds are also developing a resistance. A 2,4-D-resistant variety of the waterhemp weed has been found, and its spread could lessen the impact of a herbicide widely used in grassland and crop production. Despite worldwide use of 2,4-D since the 1940s, only 17 weeds were previously known to be resistant to it. The journal Weed Science reports the discovery of 2,4-D-resistant waterhemp by a grower in Nebraska. Although scarce 30 years ago, waterhemp is now a major problem for crop production in the midwestern United States. This is the sixth mechanism-of-action herbicide group to which waterhemp has developed resistance. After 10 years of treatment with 2,4-D, waterhemp was no longer effectively controlled in a Nebraska native-grass seed production field. The highest doses of 2,4-D that were used in an on-site field study, 33 lb ai/A, were insufficient to control 50 percent of the waterhemp population. [Photo: Waterhem plant by Aaron Hager, University of Illinois] Comment
Researchers gathered waterhemp seeds from this field and performed greenhouse testing against a susceptible waterhemp variety. Twenty-eight days after treatment with the herbicide, visual observation and dry weight values showed a 10-fold resistance in the affected sample. Researchers also found a reduced sensitivity to the herbicide dicamba.
Corn, soybeans, and cotton resistant to 2,4-D are under development; some are already under USDA consideration for nonregulated status. Engineered crop ... biotechnology will bring about an increase in the use of the 2,4-D herbicide.
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