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7 steps to better weed control

Gil Gullickson 11/01/2011 @ 3:07pm Crops Technology Editor for Successful Farming magazine/Agriculture.com

Getting your crop off to a quick start hinges on your ability to nix weed competition. (After all, you want a nice clean field at the start and not a waterhemp-choked one like this one.) Here are seven factors to keep in mind as you plan next year's weed-control program this year.

1. Don't shave herbicide rates

This can enable some weeds to survive and to compete with crops for sunlight, moisture, and nutrients.

“Any surviving weeds are competing for moisture and sunlight,” says Jeff Springsteen, marketing manager for selective corn herbicides for Bayer CropScience. “You want to take out that competition as soon as possible.”

It's also a bad idea from a herbicide-resistance standpoint. Herbicide-resistant biotypes exist in every weed population. It may be one in 1 billion, perhaps one in 10 billion. However, a below-label rate gives these biotypes a chance to survive and to multiply to where they can be a severe problem down the road.

“We see problems with resistant weed populations when people shave rates,” says Carroll Moseley, herbicide brand manager for Syngenta Crop Protection. “That's why we are so adamant that end users (of herbicides) go by rates on the label.”

2. Mix up modes of action

Using multiple herbicide modes of action is another way to keep resistant biotypes from developing. Weed resistance to glyphosate and other herbicides developed from using the same herbicide over and over again.

“I think the days of stand-alone glyphosate in corn are few,” says Moseley. “There are some areas of the country where straight glyphosate works well. But I don't think we will continue to go down that path. People are getting the message about switching modes of action.”

3. Consider preemergence herbicides

They can nix early weed competition and reduce pressure on later postemergence applications.

Lack of rainfall for activation is one concern for preemergence herbicide. However, some of the newer herbicide technologies enable herbicides to last longer without precipitation.

“We have had Corvus on the ground for over two weeks without a rainfall, and it has worked its way into roots and shoots of weeds,” says Springsteen.

Bear in mind, though, that factors other than rainfall, such as herbicide placement and herbicide rate, can influence activation, says Aaron Hager, University of Illinois Extension weeds specialist. Full rates have a greater likelihood of longer residual control than lower rates, he adds.

4. Watch your speed

One perk regarding modern herbicides is that they require less water as a carrier. “Corvus, Balance Flexx, Laudis, and Capreno work well at 10 gallons per acre,” says Springsteen.

Low water requirements enable applicators to spray more acres before they have to refill.

However, less water also translates into slower speeds to ensure that optimum application occurs. In the chemicals listed above, 5 mph to 7 mph is the recommended speed,” says Springsteen.

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