By LYNNETTE HINTZE

The Daily Inter Lake

The worst infestation of the pea leaf weevil in recent years is damaging pea fields throughout Flathead County.

“I’ve never seen damage like this in our area,” said Bob Stougaard, superintendent of the Montana State University Agricultural Research Center at Creston. “Peas are being hit pretty hard.”

Production pea fields at the Creston research center have 100 percent damage, he said, noting that every single plant has been damaged by the weevils.

Apparently spring weather conditions have a large impact on the timing and severity of pea leaf weevil damage, Stougaard said. When warm conditions — temperatures 68 degrees Fahrenheit or greater — persist for more than a few days in late April or early May, the weevils arrive in fields early.

“Early arrival corresponds to the potential for higher yield losses,” he said. “In years where cool weather persists, the arrival of the pea leaf weevil can be much later and the resulting yield impact appears to be lower.”

The infestation is affecting commercial pea growers — there are about 10 such growers in the Flathead — and may impact local gardens, he added.

“In every case, control decisions should be made on a field-by-field basis,” Stougaard said. “Young seedling plants are most susceptible to damage.”

Some defoliation can be tolerated once the plant has reached the six-leaf stage. There are a couple of threshold levels for treatment.

Insecticide should be considered when more than 25 percent of the leaves are notched or there are more than 0.2 to 1 weevils per plant. Another threshold is between the two- to four-leaf stage when a quarter of the plants have feeding injury and insects are present.

Stougaard recommends growers contact their local garden center or agricultural chemical supplier to inquire about which insecticides to use. He doesn’t know of any effective organic treatment that can be applied other than rotating and growing other crops.

The pea leaf weevil feeds on legume plants and spends the winter as an adult beetle surviving on alfalfa and other perennial legumes.

In the spring, adult weevils are attracted to feed on annual legume crops such as field peas, fava beans, lentils and beans. However, the weevils generally only negatively affect peas and fava beans.