Got Resistant Marestail? It’s Not Too Early To Pull The Trigger

Glyphosate-resistant marestail is becoming a nightmare for soybean growers through the South and Midwest. An aggressive winter annual weed, marestail emerges in the late fall, and if you don’t control it early, it can eat up soybean yields and profits.

But new research shows that fall burndown applications can be the most effective way to control this troublesome weed. If anything, 2015 proved to be a useful and often painful learning experience for growers battling marestail.

“If growers wait until spring applications, conditions can be too wet like it was this year,” explains the University of Nebraska’s Dr. Amit Jhala. “We had almost double our usual rainfall early in the season, so growers couldn’t apply their early spring herbicides.

“By the time they planted soybeans, marestail was 4 to 6 inches tall, so managing that glyphosate-resistant marestail was a significant challenge. We don’t really have many effective post-emergent control options for the resistant marestail in soybeans and we now have resistant marestail in more than 2 million acres in Nebraska.”

Jhala has evaluated fall burndown programs to improve marestail control. He has compared various fall treatments and in some cases has paired them with various early spring herbicide mixes. He wanted to see which options provided the best control of marestail and other winter annual weeds.

“We’ve looked at treatments where we have only burndown programs like glyphosate applied alone or combined with 2,4-D or dicamba,” he says. “We compared these more traditional burndown treatments to other tank mixes that contained residual materials like flumioxazin-based herbicides, and premixes like 2,4-D, dicamba plus flumioxazin.

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“So with this kind of approach we’re not relying on a single herbicide site of action. That’s important because we’re using a lot of 2,4-D and dicamba now as a fall or early spring burndown and we don’t want to create a lot of selection pressure on the weeds.”

The results show that adding a residual herbicide such as flumioxazin to the fall burndown treatment gave superior control of glyphosate-resistant marestail and other troublesome winter annual weeds.

For more information on scouting winter annual weeds click here.