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Early weed control keys corn yields

There's some good news on the weed-control front in corn.

“Corn is traditionally a heavy preemergence (herbicide) market,” says Shawn Potter with Syngenta. “Farmers are predisposed to using preemergence residuals on corn.”

Nixing weeds right at the start frees corn from early-season weed competition for water and nutrients.

There's more, Flash back to your high school physics class. Remember when you separated white light with a prism to reveal colors of the visible light spectrum?

Research by Clarence Swanton, a University of Guelph weed scientist, shows that the way light is reflected influences early growth patterns and ultimately yield. Weeds growing next to emerging corn reflect a type of light called far red light back to the corn. This triggers the corn plant to start shading weeds by quickly growing and putting on leaves.

So is this a problem?

Unfortunately, this is done at the expense of developing roots. Corn plants with no early-weed competition direct resources into growing roots. Later on, these roots enable corn plants to better access water and nutrients more than plants that fight weeds early.

Swanton also found that plants battling early-season weeds grow parallel to the row. This results in a slow-closing canopy and a reduced ability to shade weeds.

Meanwhile, corn plants with no early-season weeds grow perpendicular to the row. This translates into rapid canopy closure, better growth, and more effective weed suppression between rows.

“There can be up to a 6% to 10% yield loss from weeds in corn when they reach a 9- to 12-inch height,” says Gary Schmitz, Midwest regional technical manager for BASF Crop Protection.

That's why a preemergence residual herbicide that suppresses early-weed growth pays dividends.

“The days of straight (postemergence) glyphosate are over,” says Carroll Moseley, Syngenta Crop Protection herbicide brand manager. “We don't recommend straight glyphosate applications, especially with heavy waterhemp or pigweed pressure.”

The impact from far red light reflecting off weeds can occur even under seemingly optimum growing conditions.

“Early in the season, there can be enough water, nutrients, and light for the plant, but something is taking place causing the plant to grow differently,” says Moseley. “It has to do with (far red) light reflected back to the plant.”

Some Of The Perks

Besides curbing yield loss, residual preemergence herbicides also add another mode of action to the herbicide mix. This can help forestall weed resistance to glyphosate.

Another perk is fewer weed seeds can spur future weed infestations. “As you get more residual protection from weeds, you can reduce the weed seed bank,” says Potter.

That's something to consider as you start planning for next year's 2011 seed and chemical offerings. Harvest is a good time to eye your fields for herbicide performance and what you may do differently next year.

This year entailed several new herbicides and premixes. One new one was the Kixor stable from BASF. This PPO-inhibitor herbicide includes a new active ingredient, saflufenacil. Corn is included as a crop with two Kixor products, Integrity and Sharpen.

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Sharpen, which contains saflufenacil, is a burndown herbicide that has activity only on broadleaves. It's used primarily in burndown situations with glyphosate.

A good niche is glyphosate-resistant horseweed, says Aaron Hager, University of Illinois Extension weed specialist. Sharpen gives consistent residual weed control of seven to 10 days, he adds.

Another plus is farmers can plant the same day they apply any Kixor product.

“On most soils, there's no seven-day setback like there is with a burndown containing 2,4-D,” says Schmitz. He adds it also has three to five times quicker burndown of broadleaves than 2,4-D-glyphosate burndown mixes.

Integrity is a mix of saflufenacil and Outlook (dimethenamid-P). This preemergence residual product gives a broad spectrum of grasses and broad-leaves without the need for atrazine. It's designed as a setup for a two-pass program containing a postemergence herbicide application, says Kevin Bradley, University of Missouri Extension weed specialist.

Callisto Xtra is a new premix from Syngenta used by farmers for the first time in 2010. It contains Callisto (mesotrione) and atrazine. It's positioned in glyphosate-tolerant corn as a glyphosate additive, says Mike Owen, Iowa State University Extension weed specialist. Callisto Xtra gives postemergence control of some annual grasses and broadleaves, and also provides residual control of some broadleaf weeds. Callisto Xtra should not be applied to corn taller than 12 inches.

Prequel preemergence herbicide from DuPont gained approval late in 2009 for use this year. It contains an HPPD inhibitor (isoxaflutole) and an ALS-inhibitor herbicide (rimsulfuron). It's a burndown product that also provides residual control of winter annuals, grass, and broadleaf weeds.

“Its multiple modes of action enable it to control glyphosate-resistant weeds,” says Jeff Carpenter, corn portfolio manager for DuPont Crop Protection. “It's designed as a setup treatment, to be complemented with an in-crop herbicide like our Q line of herbicides (such as Accent Q or Resolve Q).”

Capreno is a postemergence corn package mix from Bayer CropScience that obtained registration in 2009 for use in 2010. It combines tembotrione (the active ingredient in Laudis) and thiencarbazone-methyl (an active ingredient in Corvus). Thiencarbazone-methyl is a new ALS inhibitor, while tembotrione is an HPPD inhibitor. Capreno is designed to be a one-pass postemergence product covering a wide grass and broadleaf spectrum.

“It combines the flexibility of traditional two-pass programs, too,” says Brent Philbrook, herbicide product development manager for Bayer CropScience. “It can be used alone or with tankmix partners.”

Capreno was primarily available this year in Michigan, Minnesota, North Carolina, South Carolina, Virginia, and Wisconsin. Limited supplies were available in other central and eastern Corn Belt states. Capreno will be available across the Corn Belt in 2011.

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