As the battle to control glyphosate-resistant weeds intensifies, growers are turning to chemistries that fell out of favor when Roundup Ready soybeans and corn took hold of the marketplace. Those chemistries are preemergence herbicides, which are seeing a surge in demand.

“Preemergence products were almost completely abandoned by soybean growers,” reports Dan Westberg, BASF market manager. When preemergence herbicides were widely used a decade ago, total annual herbicide sales were $1.6 billion. Today, herbicide sales have dropped to less than $800 million a year.

 

Residuals market grows

“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.

 

Resistant-weed fighters

As companies continue to search for new modes of action, existing chemistries are getting a makeover in response to the resistance issue.

In 2010, BASF launched Kixor, and growers applied the family of products containing the active ingredient on more than 10 million acres. “That is a reflection that producers wanted a product that controls glyphosate-resistant broadleaf weeds,” Westberg says. “It has been a tremendous success.”

DuPont expects to introduce Leadoff to the mid-south market after the product receives regulatory approval. Leadoff is for fall burndown application in corn and soybeans to control winter annuals.

Valent’s Valor can be applied in the spring up to seven days before planting corn and up to three days after planting soybeans. It also can be applied in the fall. Valent will introduce an additional preemergence herbicide in 2011 called Fierce, which contains flumioxazin (the active ingredient in Valor) and pyroxasulfone.

Monsanto is partnering with several herbicide suppliers, including Valent, FMC and MANA Crop Protection, to encourage the adoption of a preemergence or postemergence herbicide program. Announced this fall, Roundup Ready Plus will offer producers rebates of up to $6/acre if they use select products in the Residual Rewards program.

Monsanto’s Warrant is a postemergence herbicide that can be applied on soybeans from the first trifoliate to the first reproductive stage. It is for the residual control of small-seeded broadleaf weeds and grasses.

DuPont’s Prequel controls winter annuals and provides contact and residual action in corn. It is designed as a setup treatment for the control of weeds like waterhemp and wooly cupgrass. “We have had a lot of interest in this chemistry in the heart of the Corn Belt,” says Jeff Carpenter, DuPont corn portfolio manager.

The crop protection industry has pushed the resistance message for several years, and experts say it’s starting to resonate. “More and more producers are starting to see problem weeds in their fields and are tackling the problem with other modes of action,” Vail says. “That’s being reflected in increased usage of preemergence herbicides.”

With no new active ingredients expected, a multifaceted approach to combating weed problems is critical. “We can’t simply tank mix our way out of this issue,” Hager says. “Producers need to consider what type of residual program they might need even before they put seed in the ground.”