A pest new to the Pacific Northwest may be causing yield losses in clover grown for seed.
Casebearer moths, native to Europe, were first found in North America in the 1960s, when the moth was found in the New York state and Eastern Canada, according to Oregon State University Extension agent Nicole Anderson.
In 2001 was it reported in Western Canada, when researchers in Alberta identified it as being responsible for seed yield losses of between 25 and 45 percent in first-year stands of red clover.
No data was available on yield losses in second year stands, as growers pulled stands out after the first year.
In 2012, a Canadian graduate student asked Anderson if she would put out some pheromone traps to see if the pest was present in Oregon. Anderson agreed to place traps in three fields, although she didn’t think she’d find the pest here.
To her surprise, Anderson found the pest in every trap.
“We literally stumbled upon the pest,” she said.
Red clover is the preferred host for the pest, Anderson said, but the pest also has caused yield losses in white clover in New Zealand and Tasmania. In 2013, Anderson found about 100 adults a week in red clover fields during the pest’s peak flight in June, but only two to three a week in white clover.
Larvae of the pest damage plants by chewing on seed heads and moving from floret to floret. Adult moths, which are 3 to 5 millimeters in length and metallic in color, lay eggs on the florets, Anderson said.
Researchers in Canada, New Zealand and Tasmania have tried several different pesticides on the pest with little success, Anderson said.
“This is not a good sign,” she said. “But we have some materials they don’t have, and vice versa.”
Growers in New Zealand have had some success controlling the pest with bio-control products, she said.
Anderson said she is unsure if the pest is causing yield losses in Oregon. Clover seed yields tend to fluctuate, so it is difficult to determine if the pest is a reason behind the fluctuation, she said.
“It’s something we now know we have, and it’s problematic in other places, so it is something we need to keep an eye on,” she said.