“More and more acres are going to have to have something more than just glyphosate, and that often means a soil residual type of product,” says Aaron Hager, extension weed specialist, University of Illinois. “Tank mixing other herbicides with glyphosate will not always provide the weed control producers want or need.”

The glyphosate-resistant problem has been well documented in biotypes of some of the toughest weeds, including giant ragweed, Palmer amaranth and marestail. In fact, the number of documented glyphosate-resistant weeds went from zero in 1996 to 11 today. “We are at the cusp of having even more significant issues with glyphosate-resistant weeds,” Westberg says. “The number of acres will not get any smaller. It’s not a question of if you have a problem, but when.”

Experts stress that glyphosate is a very effective herbicide and, managed properly, can remain in the toolbox. “The industry’s push now is to enhance glyphosate’s effectiveness with multiple modes of action,” says Tim Keller, Dow AgroSciences product manager. “There is a growth in the preemergence and residual market.” 

Why preemergence herbicides? “Reducing early weed competition and starting with a clean field is the main advantage of a preemergence program,” says John Pawlak, Valent product development manager. “University research shows that reducing early competition helps boost yields.” Growers can then follow up with a post application of glyphosate, which should subsequently work more effectively.

Many growers may need to learn about preemergence products. “It’s been more than a decade since some producers have used these products,” says Gordon Vail, Syngenta herbicide brand manager. “We need to ensure producers understand how to use these products. They can be very effective, but not used the right way, you can get poor weed control and possible crop damage.”

In addition, new products with existing active ingredients can create some confusion. Growers need to know what is in a premix, how to apply it, and potential drawbacks of the chemistry.

“Producers also need to know the weed problems they have in the field,” Keller adds. “There are several products that are very effective on certain weeds, so it becomes more of a prescription approach to weed control.”

A drawback to preemergence products is that they are often tailored for a specific crop, which may limit a grower’s flexibility at planting time. Use of some of the chemicals requires preplanning because once a grower applies them for a certain crop, he cannot then change crops. However, now companies are looking at how existing chemistries can be adapted to both corn and soybeans.