What's new in 2013 herbicides

Every year, clever and witty sales pitches entice you to try brand-spanking-new corn and soybean herbicides.

Strip away the marketing veneer, though, and you'll find these products are often either mixes of existing herbicides or ones that include a new active ingredient from an existing site of action. This continues to be the case for 2013.

"We still have nothing new," says Mike Owen, Iowa State University Extension weed specialist. "There are a number of new herbicides (recently) introduced, but nothing that represents a truly new site of action."

The last new site of action in the corn and soybean market was the HPPD inhibitor (Balance Pro and Callisto), which first debuted in the late 1990s. A new site of action developed today would entail tens of millions of dollars in development costs and would incur company and regulatory scrutiny in a 10-year path to market commercialization.

"There are several companies investing in new herbicide development," says Owen. "As of now, no new announcements have been made regarding new site of action herbicide development."

The pyroxasulfone year

Still, new active ingredients that originate from existing action sites can be valuable tools in your weed-control arsenal. The standout for 2013 is pyroxasulfone.

Among weed scientists, there's an inside joke that pyroxasulfone is the most researched agricultural chemical known to man. Universities started testing this compound, known during the research phase as KIH-485, back in the early 2000s. It showed great promise for control of grasses and some small-seeded broadleaves. Pyroxasulfone has the same site of action – a long-chain fatty acid inhibitor – as that of metolachlor (Dual) and acetochlor (Harness and Degree).

"We started work with KIH-485 close to 10 years ago," says Owen. "The rates we looked at in the early days were higher than the rate that is registered," says Owen. It's likely the expense caused companies marketing pyroxasulfone in 2013 to use lower rates in current products, says Owen.

Even so, University of Missouri research shows pyroxasulfone provides better control of common ragweed, lambsquarters, and velvetleaf, compared to S-metolachlor.

It has excellent activity on pigweed species such as redroot pigweed, waterhemp, and Palmer amaranth, along with many grasses, says Kevin Bradley, University of Missouri Extension weed specialist. Pyroxasulfone can also be a key component as an overlapping residual herbicide to control pigweeds. In this program, a preemergence residual herbicide is followed by a postemergence mix of glyphosate and a residual herbicide.

"Cost increases, but you can get better weed control," he says.

Pyroxasulfone will be contained in three products for 2013 that include:

Anthem ATZ, a premix containing pyroxasulfone, fluthiacet-methyl, and atrazine, is also registered for corn. The atrazine component adds another site of action for weed-resistance management. FMC officials say the Anthem products have a 45- to 60-day residual period.

FMC is also pursuing an Anthem label for soybeans but had not received it at press time.

Other products

Instigate is a new premix of rimsulfuron (Resolve) and mesotrione (Callisto) from DuPont. DuPont is suggesting that this mix provides burndown activity as well as residual activity in corn, says Owen. Instigate's application range is from 14 days before planting up to the V2 corn stage. Restrictions include no applications of an HPPD inhibitor herbicide like Callisto following an Instigate application.

DuPont also registered Realm Q for corn last July. It's a postemergence premix of rimsulfuron, mesotrione, and isoxadifen, a safener to minimize crop injury potential from rimsulfuron. This product provides burndown activity as well as some residual control of some annual grasses and broadleaves.

Intimidator is a premix of S-metolachlor, fomesafen (Reflex), and metribuzin (Sencor) for preplant or preemergence use. Its weed spectrum is similar to a mix of Prefix plus metribuzin. Intimidator provides broad-spectrum weed control but will be generally less effective for residual control of giant ragweed compared with other broad-spectrum soybean herbicides, says Mark Loux, Ohio State University Extension weed specialist. Adding a few ounces per acre of metribuzin 75DF will improve marestail control, especially where lower rates of Intimidator are used, he says.

Matador is a premix of metolachlor, imazethapyr (Pursuit), and metribuzin for preplant or preemergence use in soybeans. Matador provides broad-spectrum weed control. It generally will be less effective for residual control of ragweed and marestail compared with other broad-spectrum soybean, says Loux. Mixing this product with additional metribuzin 75DF will improve residual marestail control and weed burndown, he adds. *