Herbicide resistance within small grain crops has been confirmed for common chickweed. Researchers have found that chickweed populations are demonstrating resistance to ALS-inhibitors. Additionally, chickweed management in alfalfa is also raising some concerns. Agronomy and Nutrient Management Farm Advisor Nick Clark said they are taking the same research approach to alfalfa that was taken with small grains.
“We’ve started challenging the weeds from the same populations with herbicides that are ALS-inhibitors but registered for use in alfalfa. They’re different active ingredients, but they target the same point in the weed,” said Clark. “They have the same mode of action. That means they act the same way on the weed in trying to kill it.”
As part of the research, Clark said they have enlisted the help of a graduate student to determine how widespread the issue is. Samples will be collected from other fields where growers are struggling with chickweed management. Another aspect of the study will be evaluating the type of concern chickweed is within production agriculture.
“Does chickweed actually pose a problem for the crop itself? In other words, is chickweed reducing the yield of small grain crops and alfalfa, or is chickweed diminishing the feed quality of these crops?” Clark noted. “We don’t really know the answers to these questions because, in the literature, there are very few studies that attempt to answer these questions.”
Some of the information that relates to the potential economic impact of poorly controlled chickweed can be contradictory. Clark said their work seeks to find some better clarity with data specific to California cropping systems. In the meantime, growers are encouraged to consider potential resistance as a factor when having trouble with chickweed management.
“Be diligent about selecting ALS-inhibitor herbicides in an herbicide recommendation. Make sure that there are some other weeds in there that are targeted by it, that you’re getting control out of it,” Clark explained. “If you’re having trouble controlling chickweed, maybe choose another mode of action; another herbicide group.”