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Expect Multiple Weed Problems in Crp Land

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Written Thursday, January 18, 1996  

After staying fallow for 10 years, land coming out of the Conservation Reserve Program (CRP) is bound to have a variety of weed problems when farmers start planting row crops on it.

Ohio State weed specialist Mark Loux says farmers will have to tackle perennial grasses and legumes, brushy plants, small trees and perennial broadleaf weeds when CRP contracts expire. The seriousness of the weed problems may depend on how the land was managed while the land was idle, he says.

"The problem is that fields have been managed in various ways," says Mark Loux. "What helps favorably is if it's been mowed every year in the program."

While annual mowing keeps down brush and small trees, it may not have controlled perennial broadleaf weeds that thrive in undisturbed soils. Also, CRP rules required farmers to keep the land in cool- or warm-season grasses or legumes, which will need to be burned down.

Farmers planning to grow crops in 1997 can begin working on their land this summer, Loux says. Spot treatments can be used on brushy plants, including multiflora rose, from late spring through early fall. Crossbow is effective on small trees when applied after leafing. Mowing, allowed after August 1 will help reduce brush and small trees.

Loux recommends a two-step herbicide treatment to kill the cover crop and perennial broadleaf weeds. Apply at least 1-1/2 quarts per acre of Roundup plus 2,4-D or Banvel in the fall. In the spring, apply Roundup and/or 2,4-D again before planting corn.

Loux emphasizes that both fall and spring applications are essential. One application before planting won't be enough, he says.

Loux says farmers should plan to spend $15 to $20 per acre for chemicals in the fall and $5 to $10 in the spring. These figures do not include application costs.

Loux says farmers who cannot make a fall application can apply high rates of Extrazine and Gramoxone in the spring, but they should expect less control than if they did spring and fall applications.

The build-up of weed populations when the land was idled will determine the extent of further weed problems, Loux says. Left undisturbed, weeds such as giant foxtail spread seeds across the field, leaving a "pretty good seed bank," he says.

"It all depends on how messy it was before you go in there and on how good a job you do on weed control," Loux says. "Do what you have to do for weed control."

Generally expect high populations of giant foxtail in lands converted from CRP to crop production. Control preplant weed escapes with a postemergence chemicals, Loux says.

An economical approach to controlling foxtail in soybeans would include a preplant application of either Prowl, Canopy or Scepter to control or suppress grasses, followed by a postemergence treatment such as Select, Assure, Fusion or Poast Plus for later-emerging foxtail plants. Postemergence options for grass control in corn include Accent or the use of Poast Plus on one of the new sethoxydim-resistant (SRC) corn hybrids.

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