Kill weeds before you kill the turkey

Although Texas and Oklahoma are neighboring states, they don’t always have the same weed problems, especially for winter wheat. Oklahoma fields recently have been invaded by grassy weeds, including cheatgrass and annual ryegrass. For many growers, that ryegrass has been exhibiting increased resistance to herbicides. More than 15,000 acres of wheat have ryegrass that displays some level of resistance, and it seems to be getting worse.

“Ryegrass has developed resistance to ALS-type inhibitor herbicides, and unfortunately, a few fields have cheat that is resistant to those same herbicides,” says Tom Peeper, a Worth distinguished professor of agronomy, Oklahoma State University, Stillwater.

Key Points

• Oklahoma and Texas wheat producers face different weed problems.

• Applying herbicide before Thanksgiving is important in Oklahoma.

• Texans need preplant control for kochia, bindweed and mustard weeds.

Texas growers also have problems with grasses, but they don’t generally become issues until well after planting. Broadleaf weeds, including mustard weeds, bindweed and kochia, are bigger problems at planting.

Herbicides provide good weed control at or before planting, and newer formulations provide better control than previous generations. For summer bindweed control, dicamba, 2,4-D and glyphosate have proven effective.

“Paramount can also be effective against bindweed. Apply it to emerged bindweed in the summer, and apply it again in the fall just prior to planting wheat,” says Brent Bean, Texas AgriLife Extension agronomist at Amarillo.

Spray before Thanksgiving

An important aspect to herbicide control is timing, especially for recurring weed problems. Many problems can be eased by spraying early, before weeds take over fields. “Kill the weeds before you kill the turkey. If you’re spraying for weeds after the first of January, you need to spray before the first of Thanksgiving,” Peeper says.

Oklahoma growers are finding options severely limited in the face of herbicide-resistant ryegrass, and many of the herbicides have been rendered ineffective. Many growers are rotating to alternative crops to reduce ryegrass populations, especially in western Oklahoma. One alternative is canola, a crop that has dramatically increased in Oklahoma and Kansas in recent years.

“This year, we’re up to 85,000 acres of canola, and weed problems are thinning out so much [growers] are considering increasing acres of canola,” Peeper says. He offers two options for winter canola rotations. Conventional canola controls grassy weeds with herbicide applications, and Roundup Ready canola works against broadleaf weeds and grasses.

Not all growers can rotate crops, and there are plenty of preventive weed control measures for growers interested in continuing wheat production.

One of the most important is seed cleanliness, especially during storage. Even a few weed seeds can create bigger problems, so stored seed must be as clean and weed-free as possible to protect the integrity of next season’s crop.

Certified wheat provides an alternative to farm storage if field wheat contains too many weeds. Certified wheat is typically cleaner than standard wheat, but there are no guarantees, so screening is important. If any weed seed is present, it may not be a good idea to buy it.

“The first place herbicide-resistant weeds show up is at the seed dealer, because growers are careful about spraying, so there’s a chance of herbicide resistance,” Peeper says. “Take a screen when buying wheat and look at what comes out. There is no sense in buying new weeds.”

Find more weed control options by contacting a county Extension agent.

Brazil writes from Clermont, Fla.

This article published in the August, 2010 edition of THE FARMER-STOCKMAN.

All rights reserved. Copyright Farm Progress Cos. 2010.