In soybeans, early-season weed competition poses a potential 6 percent to 10 percent yield loss. In corn, weeds allowed to reach 4 to 6 inches in height can reduce yield potential by 3 percent and 7 percent, respectively. The potential losses due to weeds total almost $10 billion, based on current national projected yields and commodity prices.

Growers should plan preemergence applications of a residual herbicide now to help prevent that from happening.

"If you miss weeds early, they get bigger and tougher to control, potentially requiring multiple applications and/or higher use rates for effective control," said Dan Westberg, Ph.D., technical market manager with BASF. "That early-season weed competition ends up costing farmers more money and diminishes their yield potential."

Thomas Bauman, Ph.D., Purdue University weed scientist, noted that a field always has its highest yield potential when weeds have yet to appear.

"We recommend eliminating that early season weed competition so you get a higher yield," said Bauman. "The other thing it does, particularly for some of our larger growers who are farming literally thousands of acres, is provide a bigger window for a timely post-application because we control that earlier flush of weeds."

Tough weeds such as waterhemp, Palmer amaranth, and giant ragweed are highly competitive and, particularly with the spread of glyphosate resistance, can be difficult to manage once they get out of control. Post-emerge options can be limited, especially in soybeans.

"Weather also can make post-emerge applications difficult, since it can be unpredictable and keep applicators out of their fields when they most need to be there," Westberg said. "That's why we hear from growers that it can be easier to control weeds earlier in the season, when application timing isn't as difficult to manage."

Additionally, by eliminating early-season weed competition and allowing a wider, more effective post-emerge application window, a preemerge application of a residual herbicide helps protect a grower's seed and fertilizer investments.

A preemerge application also provides an opportunity to introduce a different site of action in a herbicide program to reduce the potential for resistant weeds to develop.

"We look at the best management practices to recommend, and number one would be different sites of action," said Kevin Bradley, Ph.D., University of Missouri weed scientist. "My recommendation for a different site of action comes in the form of a preemergence herbicide, because it is the most efficacious and economical for you."

Recently released results from two years of crop protection research trials showed that the weed-control benefits from a preemerge application of a BASF product helped increase soybean yields by an average 2.3 bu/A over a 2,4-D plus glyphosate preemerge application.2 In corn, a preemerge application of a BASF product increased yields by an average 19.5 bu/A.3

For more information about weed resistance management, visit http://agro.basf.us/stewardship/herbicide-best-practices.html.