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Early weed control keys corn yields

Gil Gullickson 07/18/2011 @ 1:49pm Crops Technology Editor for Successful Farming magazine/Agriculture.com

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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