Researchers have confirmed common chickweed herbicide resistance with a certain class of herbicide materials. Agronomy and Nutrient Management Farm Advisor Nick Clark said the conclusion was reached after multiple studies were conducted.
“Yes, there are some populations of common chickweed in California that we have found in small grain crops which are resistant to certain ALS-inhibitor herbicides. That’s been documented now,” Clark explained. “As far as we can tell it’s the first documented case west of the Rocky Mountains in North America.”
The issue of resistance was first suspected last year after multiple reports from growers and pest control advisors (PCAs) indicated a problem. Seeds were collected and tested against multiple different ALS-inhibitor herbicides. “We did it a total of three times. Each time we did it we were not able to control the chickweed,” said Clark.
Rising Concern in Other Crops
Common chickweed is also a problem in alfalfa, which is commonly rotated with small grains in a dairy forage crop system. Growers and PCAs have been pointing out similar management problems in alfalfa crops. Clark said they are taking a similar approach to the issue as they took with small grains. Researchers are looking at ALS-inhibitors registered in alfalfa to test for potential chickweed herbicide resistance.
“We’ve had one run of that study, or we’ve challenged the weeds one time with those herbicides that are registered in alfalfa. We were not able to kill them this time. But in tradition, we are going to repeat that study to try and confirm our preliminary results,” Clark noted. “Right now, as far as that handful of herbicides that are registered in alfalfa that are ALS-inhibitors, we’re saying that it’s suspected that these populations of chickweed might also be genetically resistant to control with those particular active ingredients as well.”
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