Pacific Northwest wheat and pulse growers are turning to new strategies to control mayweed chamomile, a weed that is developing resistance to Group 2 herbicides.
“It worked too well, and when things work well, people tend to overuse them,” said Drew Lyon, weed science professor at Washington State University. “If you use a particular mechanism of action over and over again, you eventually shift the population to those individuals that are resistant.”
Group 2 herbicides block the function of an enzyme essential to protein synthesis in the weed.
WSU, Oregon State University and the University of Idaho recently released an extension publication about managing the weed, also known as dog fennel.
The weed is more of a problem in pulse crops, particularly in lentils, so Lyon expects more problems as farmers turn to pulses in response to low wheat prices.
Winter wheat can lose 5-10 percent of its yield to the weed, but if mayweed chamomile goes to seed, the seed can survive in the soil.
Spring wheat tends to come up at the same time, so mayweed chamomile can mean a loss of up to 25 percent of the crop.
“The real key to controlling this is trying not to let it produce seed,” Lyon said. “Once that seed bank’s filled up, you have a problem for quite some time.”
Early moisture this year delayed most pulse planting, helping to reduce the weed in those crops. But “a fair bit” still can be found in winter wheat, Lyon said.
The weed tends to be more of a problem in higher rainfall zones.
Tillage can be effective. Lyon recommends putting the seed down deep and then not plowing again for eight to 10 years.
No-till farmers can switch to herbicides using different modes of action, stop raising pulses or switch to more competitive pulses. Peas are more competitive against the weed than chickpeas, which fare better than lentils.
“If you’re going to grow a pulse crop, you grow a pulse crop that’s as competitive as possible, and that would be peas,” Lyon said. “Of course, chickpeas and lentils have probably the better price, so there’s some incentive to go ahead and plant those.”
Some different chemistries have proven successful, but Lyons cautions that reports of resistance to other herbicides are already starting to come in.
“Growers need to be careful about their use and try to rotate crops and herbicide chemistries,” he said.