“The FiberMax 1944 seems to be the right product at the right time for our farming situation — for help with several weed problems,” he adds.

He isn’t alone in his fight against glyphosate-resistant marestail, also called horseweed in some areas. It has been reported in cotton and grain fields in Virginia for the past several years.

Marestail emergence occurs both in the fall and the spring. Best control in Virginia appears to come by controlling the weed during the rosette stage, which usually occurs in March.

 A frequently used management system includes a burndown treatment applied in early March of glyphosate mixed with either 1.5-2.0 pints of 2,4-D or 0.5 pint of Clarity to control glyphosate-resistant horseweed.

Effective use of these materials requires some precise timing, which is not always easy at this time of year. Applications of 2,4-D must occur 30 days before planting.

Clarity should be applied 21 days before planting and one inch of rainfall must accumulate prior to planting.

To reduce spring emergence, the pre-emergence residual herbicide Valor can be applied with the burndown treatment in early spring.

Careful stewardship of Valor is also important, because the ppo-inhibiting family of herbicides, including Valor, has already been linked to resistance to waterhemp in the Midwest, a close cousin of Palmer amaranth.

Gramoxone and Direx with crop oil concentrate can provide fair to good control of glyphosate-resistant horseweed if applied under warm temperatures (greater than 70 degrees). This mixture should be applied at least 45 days before planting.

Using the new FiberMax variety seed with both glufosinate and glyphosate tolerance overcomes numerous timing and application restrictions in dealing with marestail, Davis says.

“We started out using straight Liberty in combination with Cotoran and other older herbicide chemistries, and we were doing a good job with most weeds.

“However, if we get rains in August or late summer, fall panicum just goes crazy. We needed something to control these late flushes of fall panicum and 1944 gives us the options we need,” he adds.

Though the Virginia grower battles herbicide resistance problems with ragweed and marestail, the big bully on the resistance block is Palmer amaranth, and that’s a battle Davis says he hopes to avoid.

Resistant Palmer pigweed has been reported in southeast Virginia, mostly along the North Carolina border and is not widespread.

“We don’t take any chances with Palmer pigweed, when anybody in our general area sees what looks like a pigweed that shouldn’t be there, we call each other and we pull those weeds and get rid of the seed,” Davis says.

rroberson@farmpress.com

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