Your 2016 Weed Management Plan Might Start in 2015

Look back at your growing year in 2015. If you had excessive rain, herbicide application delays, abundant weed escapes and/or fallow fields, your best plan for managing weeds in 2016 may involve a fall herbicide treatment in 2015.

Dr. Kevin Bradley at the University of Missouri has some important advice: Start planning now. Weeds, he points out, gained a big head start in 2015, particularly in his state.

“Missouri led the nation in unplanted acres, and a high percentage of those acres that weren’t planted were left fallow and grew up in weeds, and those weeds went to seed,” he explains. “Even in some fields that were tilled, waterhemp came back up and went to seed. I believe our soil seed bank is going to be tremendous in volume next year. Growers know what fields were weedy and they need to plan for it. Be prepared for the weed seed that are in the soil now.”

For soybean growers who have glyphosate-resistant marestail (or horseweed), Bradley recommends a fall burndown herbicide treatment. “That’s the number one reason people would need a fall herbicide application. We have trouble controlling marestail if we wait until the spring.”

Bradley says the foundation of any weed management program should be “start clean and stay clean.” For some growers this year that definitely means a fall burndown application. Many producers already see it as a prudent, standard practice, especially where they have a history of resistant marestail.

“Some farmers like the fall application because it gives them a shot at starting weed-free,” he adds.

Deciding whether to apply a fall burndown or wait until spring should partly be based on the climate and growing history in your area, particularly how much flexibility you will or won’t have to make spring herbicide applications on time.

“If you look at historical spring weather data in Missouri, we have a pretty low number of suitable field days in the spring,” Bradley says. “So, we have to plan for that and work around it as effectively as we can.”

Fall burndown applications in that situation are actually a form of insurance, reducing weed pressure early in case rains delay or prevent spring herbicide programs.

Starting clean is one thing. But for many growers this year the tough part was “staying clean” as the season progressed.

“Put together a plan,” Bradley continues. “If nothing else, this year showed us the critical importance of being prepared and acting when the window opens. With your herbicide program, make the most of every opportunity that presents itself.”

That means applying pre-emergent and pre-plant herbicides in a timely manner. Certain weeds have to be killed before planting even starts, Bradley stresses.

“If we don’t kill giant ragweed or horseweed that has emerged and we plant into that – and assuming it’s resistant – then we’re not going to kill it in the crop,” he says. “Our data shows that in a Roundup Ready soybean system we don’t have any recommendations that work as a post-emerge application if those weeds are resistant.”

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Other tips from Dr. Bradley include:

Always apply a FULL use rate of a pre-emergence residual herbicide that targets your most troublesome weeds. The labels of certain residual materials state that you can get by with a half-rate in Roundup Ready or Liberty Link soybeans. Bradley says that’s a bad idea, and he discourages farmers from cutting rates. The approach makes no sense, he adds. “Why would you reduce the rate of the only herbicide that’s working on weeds that glyphosate doesn’t control in those situations? Our best chance of controlling resistant waterhemp, for example, is to apply a full rate of the residual herbicide in the spring application timing.”

Spray coverage is critical with post-emergence contact herbicides, so adjust your sprayer to get optimal product performance. “The spray parameters for glyphosate aren’t going to get you the best performance from these contact herbicides. You need higher gallonage per acre and nozzles that provide good coverage. We’ve got to be willing to do the little things to make these products work.”

In addition to herbicide programs, Bradley recommends that growers consider additional tools for combatting resistant weeds, including cultural methods like narrow row spacings, optimum planting populations, crop rotation and cover crops where appropriate.

  • To see the complete text of Dr. Bradley’s article, click here.
  • For information on fall burndown of Palmer Amaranth, read this study from North Carolina State University.