Waterhemp resistance to 2,4-D herbicide has been confirmed in a Nebraska field used in grass seed production. The resistance was previously reported but made a news splash this week because specifics were printed in the Weed Science journal published by the Weed Science Society of America (WSSA).

Formulations of 2,4-D herbicide have been used since the 1940s, and waterhemp is the 18th weed identified to have some resistance to 2,4-D globally, reported WSSA. And this is the sixth mode-of-action herbicide group to which waterhemp has developed resistance.

Waterhemp was a weed seldom found in fields of Midwestern crops a decade ago. But recently a high percentage of waterhemp has become resistant to glyphosate herbicide, which has been continuously used in Roundup Ready corn and soybean production fields. There has been an explosion of the weed in many fields.

Resistance to 2,4-D should have been predicted in the Nebraska field because the herbicide had been used in the field for 10 years continuously. Continuous use of any herbicide promotes weed resistance.

Researchers verified the 2,4-D waterhemp resistance in the Nebraska native-grass seed production field. The highest doses of 2,4-D that were used in an on-site field study were 33 pounds of active ingredient per acre, which were insufficient to control 50 percent of the waterhemp population, WSSA reported in a news release.

“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,” WSSA further explained.

Dow AgroSciences has submitted a registration data package for corn with a trait that will allow its new formulation of 2,4-D, which is also being evaluated by the EPA for registration, to be applied postemerge over the corn. The company has guaranteed that it will promote high stewardship principles for maintaining the effectiveness of its 2,4-D choline with Colex-D technology. A logical progressing of EPA approval/registration indicates there might be some Enlist Weed Control System 2,4-D choline-resistant corn hybrids available in 2013.

Soybeans and cotton resistant to this new 2,4-D formulation is also under development for registration no earlier than 2015.

Full text of the article appearing in the Weed Science journal is available by clicking here.

To read Dow AgroScience's response to the finding, click here.