- Bailey County farm test indicates glyphosate-resistant Palmer amaranth.
- High rates of glyphosate unable to control weeds.
- Application errors not an issue.
PALMER AMARANTH 18 days after treatment.
Weed specialists have been warning for years that it isn’t a matter of “if” but a matter of “when” glyphosate-resistant weeds show up in West Texas cotton fields.
When is here.
Monti Vandiver, an integrated pest management specialist in Muleshoe, says a test he performed on a Bailey County farm indicates that glyphosate-resistant Palmer amaranth is present. He said herbicide failures in the past often could be attributed to extreme environmental conditions, application errors or mechanical failures.
“I took the application factors out of the equation,” Vandiver said, “and I was still unable to control the weeds with Roundup PowerMAX.”
One of his producers asked Vandiver to take a look at Palmer amaranth escapes in a field where the weed had not been a bad problem before.
“Field conditions were good for spraying,” Vandiver said. “I saw a lot of dead weeds, but I also saw a lot of live weeds, some live ones beside the dead plants. I tried to duplicate the usual rates.”
He applied Roundup PowerMAX at 22, 44, 66, and 88 ounces per acre. “I also used a 2 percent Roundup formulation and sprayed to runoff. I evaluated control on a weekly basis.”
He expected after 14 days to see all the Palmer amaranth plants dead. “I didn’t. I was not able to control the weeds. I killed some, but I didn’t kill many.”
He said the PowerMAX rates would equate to as much as one gallon per acre. “The spray to wet could be two gallons per acre.”
A bio-assay, he said, would be necessary to make certain the escaped weeds were resistant. “But it looks highly likely. We were not able to control them.”
He said escapes have shown up before. “But most of the cases go back to environmental factors, application error or a nozzle malfunction. This is the first case I know of in this area that application was not the issue. A product failure to control weeds was.”
The producer was very proactive in his efforts to manage the escapes, Vandiver said. “After the test, he brought in hoeing crews to clean out the weeds and remove them from the field to minimize potential for seed production.”
No one is certain how the infestation developed so quickly. “He (the producer) said he did not have problems with Palmer amaranth in this field last year. He did not spread manure or bring in hay.”
A neighbor, however, may have brought in hay from Missouri. That could be the source, Vandiver said, but no one is certain.
“It was a pretty rapid build-up,” Vandiver said. Resistance typically starts with just a few plants and spreads from there. This infestation appears to have developed from one year to the next. Last year’s drought, which hampered herbicide activity, also could have contributed to escapes, he said.
He urges farmers to be alert. “We will get aggressive with it,” he said. “We’re talking to chemical company representatives about lay-by materials. We may need to go back to products with multiple modes of action or back to how we did things in the ‘80s—yellows, pre-emergence materials and cultivation.”
That’s not an ideal option for the many farmers who have turned to herbicide-tolerant varieties and reduced tillage to reduce labor and to decrease erosion and moisture loss. “We encourage farmers to use every tool in the tool box,” he said.