Publication tackles new pest causing concern in western Oregon

CORVALLIS, Ore. – A new and potentially troubling pest that feeds in winter has shown up in agricultural crops, lawns and ornamental plants in western Oregon, and the Oregon State University Extension Service has developed a new publication to help address it.

Called the winter cutworm, the pest moves and feeds in large masses during fall and winter and can cause significant damage in a short amount of time, said Jessica Green, an entomologist with the OSU department of horticulture and co-author of Winter Cutworm: A New Pest Threat in Oregon.

This is of particular concern in the Willamette Valley where a wide array of crops, including rye grass and grains, are grown during these months, she said. Damage from the winter cutworm, which is the larval or immature phase of the large yellow underwing moth (Noctua pronuba), appears as wide swaths of dead pasture, grass seed fields and lawn.

Like related cutworms and armyworms, winter cutworms hide in the soil around the base of plants and emerge at night to feed. Typically, plants show notched foliage or stems eaten off at ground level.

“The winter cutworm encompasses both cutworm and armyworm behavior because it cuts foliage like a cutworm, and moves en masse like an armyworm and clears everything in its path,” Green said. “That’s troublesome.”

The pest was noticed this year by homeowners because the cutworms gather by the hundreds on patios and entryways. So far, large populations of the pest have been seen in western Oregon and southwest Washington with damage ranging from nuisance to severe defoliation of ryegrass fields.

Adult moths, which don’t bother plants, have been detected in Oregon since 2001, sometimes in high numbers, but widespread damage by larvae has not been reported until this year. Why the larvae just now became a problem, and the potential risk it poses to crops, is unknown, Green said.

The larvae look like many other cutworms, but are distinguished by the dark markings that run down each side of the body. Much more striking, the 2-inch adult moths have bright yellow to orange bottom wings with thick, dark margins.

The Extension publication, which includes full-color photographs and graphics, helps with identification and also contains information about biology, distribution and potential control measures.

Native to Eurasia, Noctua pronuba made its way to Nova Scotia in 1979. It rapidly traveled down the East Coast and by 2000, the moths migrated to Illinois, Wisconsin, Colorado and Wyoming and then to Oregon.

As with other pests, combining cultural, biological and chemical management tactics is likely the best approach. Tilling, for instance, brings the larvae to the surface and exposes them to predators. Rotating crops and keeping down weeds may help. Homeowners should maintain healthy lawn by mowing, watering and fertilizing regularly. For chemical controls, refer to the Pacific Northwest Insect Management Handbook. Always check the label to make sure the product is registered for use on your crop or site.

Also contributing to the publication were Amy Dreves, entomologist with OSU Extension; Brian McDonald, senior research assistant in the horticulture department; and Ed Peachey, weed specialist with Extension.

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Jessica Green

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