Controlling weeds is becoming increasingly difficult. Success requires a multipronged strategy that keeps weeds at bay during the growing season and limits their ability to pressure fields in coming years.

To accomplish this, growers must make timely herbicide applications: 

  1. A burndown or tillage to start with a clean field.
  2. A preemergence application of effective residual herbicides.
  3. Timely postemergence applications featuring multiple herbicide modes of action.

Using multiple modes of action is vital to control current weed pressure while limiting the development of herbicide resistance that can cause heavier pressure in future years.

Weather muddies the waters
This spring, although temperatures were plenty warm over much of the Corn Belt, many growers had to pull in the reins because of wet fields. When possible, take time for an effective burndown.

“When it’s wet, some growers may consider skipping the burndown,” says David Hillger, Ph.D., Enlist field specialist for Dow AgroSciences. “A rainy spring can make it difficult to clean up fields before planting. Still, it’s usually best to delay planting and take time for a burndown. Soybeans in particular are somewhat forgiving of planting date.”

The value of residuals
Residual herbicides go a long way in helping the crop establish a good stand. Growers in the northern Corn Belt are finding preemergence residuals help keep tough weeds under control, reports Steve Snyder, an Enlist field specialist who covers Wisconsin, Minnesota and the Dakotas.

“Waterhemp and glyphosate-resistant giant ragweeds are two of our most challenging weeds,” Snyder reports. “Growers are using preemergence products such as Sonic herbicide to control these weeds in soybeans before applying postemergence herbicides.”

Snyder notes a good preemergence herbicide program delays weed emergence and expands the window for effective postemergence application.

Timing postemergence treatments
No matter how good a herbicide is, it’ll work better if it’s applied before weeds get too big.

“Weeds are more of a challenge when they get above 6 or 8 inches tall,” Hillger says. “Ideally, we want to treat them at 3 or 4 inches, especially marestail and Palmer amaranth, which are two of our biggest concerns in the Corn Belt.”

Weed resistance is forcing farmers to learn to be more flexible.

“We have to be willing to rotate modes of action to maintain the efficacy of our herbicide tools,” Hillger says. “We’ll need a multiyear approach on herbicides. We understand the value of rotating crops; we need to realize the value of rotating modes of action.”

Read the label
Snyder points out that this requires farmers to follow herbicide labels. “We may have two products with different brand names, one that we use on corn one year and the other that we use on soybeans the next. But if they offer the same mode of action, we’re taking a chance on weeds developing resistance to that mode of action.”

Hillger and Snyder note the Enlist weed control system is designed to support a weed management plan that features multiple modes of action. Enlist crops are tolerant to three postemergence herbicide modes of action. Farmers can treat Enlist soybeans with Enlist Duo herbicide, a combination of new 2,4-D choline and glyphosate, as well as glufosinate. They can treat Enlist corn with Enlist Duo and the FOP family of grass herbicides.

“The Enlist weed control system offers flexibility,” Hillger says. “It provides growers an ideal way to control weeds this year and down the road.”

For more information, Snyder urges farmers to visit Enlist.com.