Common chickweed is a normally occurring weed in many cropping systems. However, the issue has become more problematic in small grain production systems over the past couple of years. Frequent reports have been coming in indicating that a certain class of herbicides was exhibiting poor control. Agronomy and Nutrient Management Farm Advisor Nick Clark said they have been responding to the calls and investigating the problem.
“We asked a lot of questions about how the applications were made and we looked at other weeds that were out in the field. We looked at how the crop was performing. Mainly because there’s a lot of reasons why an herbicide application wouldn’t work,” Clark noted. “The big concern that we were hearing from the pest control advisors was they thought there might be a problem we call genetic resistance to the herbicide that they were using.”
The herbicide type that is raising concern among PCAs and growers is ALS-inhibitors. Clark said they agreed that it was a “suspicious occurrence” after assessing production records from where these issues were occurring. Based on the information that was collected, “it was just too hard for us to rule out the possibility…that there might be genetic resistance,” Clark noted.
Studies began to evaluate the issue further. Common chickweed seeds were collected from the fields exhibiting control problems. Using ALS-inhibitor herbicides under more controlled conditions, tests indicated “there’s a high probability that we’re seeing instances of genetic resistance,” Clark explained. In one instance, an herbicide applied at eight times the top label rate still could not achieve control.
“We’re going to repeat the study because we understand how sensitive of an issue this is. We want to make sure that we’re crossing all of our T’s and dotting our I’s before we make any strong conclusive statements,” said Clark. “Again, we don’t know the breadth of this problem. It’s something that we’ve noticed in the southern San Joaquin Valley, but that’s a big question that we’re asking. Additionally, we’re trying to figure out what the economic impacts of a problem like this might have. Certainly, we don’t have that answer yet. We’re still trying to figure it out. Hopefully, it’s not a problem at all.”
About the Author
