Farmers battling glyphosate-resistant horseweed in the Delta states have a new tool that promises to provide effective burndown of the troublesome weed while leaving a few extra dollars in their pockets.

The new product, Oracle-brand dicamba, can be applied to horseweed or marestail and other winter vegetation up to 21 days before cotton planting or 30 days before soybeans, according to James Oliver, president of J. Oliver Products, LLC, Hernando, Miss.

Oracle brand dicamba is a product of Gharda Chemical Ltd. of Mumbai, India. It is distributed through Gharda Chemical's U.S. branch, located in Newton, Pa. EPA granted a Section 3 registration for Oracle with the plant back to cotton restrictions in early February.

“Most universities are recommending an application of 24 to 32 ounces of glyphosate tank-mixed with 8 ounces of dicamba preplant burndown for glyphosate-resistant marestail,” says Oliver.

Once considered a problem primarily in the Delmarva area of Delaware, Maryland and Virginia and a few counties in west Tennessee, glyphosate-resistant marestail has been confirmed in parts of Arkansas and some counties in north Mississippi. Missouri growers have also encountered problems with glyphosate-resistant ragweed.

Writing in “Agronomy Notes,” Tom Barber, Extension cotton specialist with Mississippi State University, suggested that growers apply burndown herbicides at least four weeks before planting.

“Glyphosate-resistant horseweed has become a major problem in many of our cotton-growing areas in the Delta,” he said. “In these fields where horseweed is present, you need to pay close attention and burndown with a phenoxy-type herbicide mixed in the tank.”

Barber said Clarity or dicamba at 8 ounces per acre is his first choice because cotton is not as sensitive to the product as to 2,4-D, “and the label is very clear on the pre-plant interval of 21 days plus 1 inch of rain.”

If growers elect to use 2,4-D, he said, they should apply the full rate of 32 ounces per acre and wait at least 30 days before planting cotton. Better control of horseweed may be obtained with either chemical if the horseweed is in the two- to four-leaf stage, rosettes are less than 2 inches across and the weed is actively growing.

Oliver said Oracle is now registered in all cotton-producing states except California. Growers are cautioned to observe state regulations for applying burndown herbicides when using Oracle or other products.

“Some Oracle that was sold last year does not have the new plant back to cotton labeling with the product,” said Oliver. “Growers and applicators can obtain that labeling from their farm chemical retailers.”