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Weedy fields this fal result of various facatorsl
<p> Weedy fields this fal result of various facatorsl.</p>

Weedy fields this fall may include herbicide-resistant plants

Dry weather, rushed planting, some missed herbicide applications and the increased presence of glyphosate-resistant weeds has left some Texas High Plains cotton and grain fields a bit more weedy than usual this fall.

The combination of dry weather early and during the growing season, rushed planting, some missed pre-emergence herbicide applications and the increased presence of glyphosate-resistant weeds has left some Texas High Plains cotton and grain fields a bit more weedy than usual this fall.

“I’ve seen some bad fields, some that will be hard to harvest,” says Gaines County AgriLife Extension integrated pest management specialist Manda Anderson. “I think we have some resistance but we also have some issues with application.”

Mother Nature, Anderson says, was not cooperative. “Soil was very dry and humidity was so low plants couldn’t take up the product. Application timing was also an issue.”

She says another contributing factor would be some farmers “not getting yellows down. That’s not an expensive system if we get the products out at the right time. Starting clean is the key to good weed control.”

She says if weeds are present before planting, “burn them down. Also, treating small weeds is important. A 4-inch weed target is the key. Weeds are tough and will not take up herbicides as effectively as they get bigger.”

Anderson said weedy fields result from several factors. “But we have to use herbicides other than Roundup (glyphosate). It’s also important to get a second application on.”

Monti Vandiver, IPM specialist for the Northwest region, in Muleshoe, has also noticed a significant number of escapes, both herbicide-resistant and weeds that were missed for one reason or another.


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“I have definitely seen resistant weeds,” Vandiver says, “but I also believe other issues have played a significant role in weed control failures. In some cases, it has become convenient for us to blame resistance when weeds are not controlled by glyphosate.”

Regardless of the reason, a more prescribed approach to management will improve control, he says. “Whether a control failure was actually a result of resistance or not, if production practices which combat resistance development are implemented dividends will be paid in the future.”

Texas AgriLife Research agronomist Wayne Keeling, at the Research and Extension Center in Lubbock, says he’s seeing two distinct issues this fall, “escapes and resistant escapes.

Resistance documented

“We first discovered resistant pigweed in the Southern Plains in 2011; we saw more of them in 2012; and we’ve seen even more this year.”

He says fields with escaped pigweeds scattered across the field should be a warning sign. If weeds are pretty much uniformly present across the field, weather problems or application issues are more likely to be the reason for escapes.

Weather played a big part this year, he says, especially in dryland cotton where pre-emergence herbicides may not have been activated properly due to dry conditions. Also, with significant drought in place at planting time some dryland farmers may not have gotten those pre-plant or pre-emergence materials applied on time or at all.

He said some grain sorghum fields were “planted late and fast,” and may not have received usual herbicide applications. Some of those fields were planted to replace failed cotton acreage. “We see a lot of fields where farmers killed a lot of weeds,” Keeling says, “but not all.”

He says some fields south of Lubbock had high infestations of tumbleweed that were “tough and hard to kill.”

He recommends that farmers who still have time before harvest should look for resistant weeds and destroy them before they go to seed and create even more trouble next year. “Also, for future reference, do the best job possible on herbicide application.

“Since resistance is getting worse, farmers need to go back to using those residual materials and clean up the fields,” he says. “Be on guard for those resistant escapes and get back to using a full complement of herbicides. And if we get back to a more normal weather pattern, we can do a little better job. But we need to consider a blanket application of Treflan to all acres.”

Paul Baumann, AgriLife Extension state weed specialist in College Station, discussed the increasing need to follow a systems approach to weed management at Stiles Farm field day last summer.

“We are putting chemistries under more pressure, so we have to do what we can to preserve the program and products and consider our best options. We need a prescription approach to weed management.”

Baumann said farmers must look to other chemistries “without abandoning a good product. Use products with different modes of action.” Farmers have many good options, including pre-plant and pre-emergence residual herbicides.

He also warns farmers not to leave suspected resistant weeds in the field in the fall. “We cannot afford to leave one weed of the amaranth species in the field. We can’t let it go to seed.”

Some other troublesome weeds are not as critical. “Johnsongrass, Texas panicum, etc., are different. But if you see a careless weed, get it out.”

He cautions farmers to be wary of pigweeds that survive late into the season and get to be “too large to control. Pull it out; hoe it out; get it with a cultivator. One pigweed plant can shed 500,000 seeds or more. That can cause problems for several years. We have to get it out before it goes to seed.

“And then it is critical to use a Treflan material for the next crop. That chemistry still works, and we are thankful for that with all the resistant issues.”



More from Southwest Farm Press:

Weed issues necessitate production changes

Resistant weeds changing the way we farm

Prevention is best strategy for resistant weed management

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