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What's new in 2013 herbicides

03/28/2013 @ 4:27pm

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:

  • Zidua from BASF. This formulation contains pyroxasulfone as its sole active ingredient. You can apply Zidua on corn early preplant (up to 45 days before planting), preplant incorporated, preemergence, early postemergence, and in the fall. Zidua is not yet labeled for soybeans, but BASF is pursuing that label. Zidua's residual lasts for six to eight weeks, depending on rate.

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