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7 Weed Control Tips for 2018

You’ve probably heard of The Three Stooges: Larry, Curly, and Moe. Well, you may have a trio of stooges of your own in your fields. They just aren’t as funny.

If you have marestail, waterhemp, or Palmer amaranth, one or all of them may resist glyphosate or other herbicides.

Unfortunately, no help is on the way from any new corn and soybean herbicide modes of action.

“The amount of resources that has to be put into new mode of action development is significant,” says Ryan Lins, Syngenta research and development scientist. “That’s not to say it won’t occur in the next 10 years. But it will be difficult, given the regulatory climate and the fact it would be really expensive.”

The good news is you have strategies and tools available to help you manage these weeds and halt their spread. They include the following.

  1. Don’t let them get started in the first place. “Every path (toward prevention) leads back to point that if we use several (effective existing) modes of action, this prevents hard-to-control weeds from getting started in the field,” says Luke Peters, Dow AgroSciences product manager for U.S. corn herbicides.

  2. Hit them early. Preemergence residual herbicides play such a huge role in snuffing weeds early, says Ryan Rector, Monsanto Roundup technology development manager. They do cost money. Given tight margins, they are an easy place to cut. But Rector notes this is penny-wise and pound-foolish. Don’t expect preemergence residual herbicides to be foolproof. Preemergence residual herbicides still need water to activate. Acetochlor, for example, needs .25 inches of rainfall to activate in the soil. “Weather still always plays a factor,” says Rector.

  3. Come back with postemergence herbicides when weeds are small. Laying down preemergence residual herbicides can hold down weed flushes for six to eight weeks. Unfortunately in soybeans, this likely won’t take you into canopy. That’s where effective postemergence herbicides play a valuable role. Applying them when weeds are small is crucial, though. “Our recommendation is to control weeds when they are 4 inches or smaller,” says Rector.

  4. Consider cultural practices. For example, more Minnesota farmers are narrowing rows from 30 to 20 inches, says Lins. “Crop competition is part of managing weeds,” he says. In narrow rows, the crop canopy that emerges earlier can shade out weeds earlier.

  5. Don’t neglect drowned-out spots or prevented planted areas. Left unchecked, these areas incubate exploding waterhemp populations if plants go to seed. Each waterhemp plant can produce at least 250,000 seeds. This seed can spur future waterhemp plants that will haunt you in future years. Although it’s a pain, backpack spraying or hand rouging small waterhemp-infested areas can nix seed formation. “The key is to control those weeds,” says Rector. “Don’t let them set seed.”

  6. Watch for Palmer amaranth. This pigweed family member might not be Satan, but it certainly mimics the Evil One in your corn and soybean fields. Left unchecked, herbicide-resistant palmer amaranth can obliterate a field. “We are seeing it move into more northern regions, says Rector. “Keep that top of mind.”

  7. Learn from the past. Above all, think about what worked last year and what didn’t. “Take an opportunity to tweak the system to make it more effective,” says Rector.


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