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CORVALLIS, Ore. - A microscopic parasitic roundworm is costing Pacific Northwest wheat growers $51 million in lost revenue each year because it's cutting grain yields by an average of about 5 percent, according to estimates by Oregon State University researchers.

Called the root-lesion nematode, the transparent, eel-shaped roundworm lives in the soil and feeds on the roots of wheat, barley, oats and many other crops. This limits the crops' ability to take up nutrients and water, leaving plants with smaller heads and yellowed leaves.

"The presence of nematodes is usually confused with root rot, viruses or lack of nutrition because the effect on crops looks the same," said Dick Smiley, a plant pathologist at OSU's Columbia Basin Agricultural Research Center in Pendleton. "But nematodes often go undetected because they're not well-known, and they're transparent and thinner than a human hair."

Researchers have detected the root-lesion nematode in about 90 percent of fields sampled in Idaho, Montana, Oregon, and Washington, according to Smiley, who has studied the pest since 1999. Population densities of nematodes high enough to reduce yields have been detected in 60 percent of fields sampled in Oregon and Washington. The roundworm wreaks the most havoc in drier areas where wheat and barley grow.

Most nematodes are beneficial to agriculture by helping decompose organic matter. Some, however, are parasitic to plants or animals. They spread easily, hitchhiking to new locations via the wind, animals, farm equipment and boots. It's nearly impossible to eradicate them once they're established.

Another harmful roundworm, the cereal cyst nematode, is also damaging wheat, barley and oats in the Pacific Northwest. First identified in western Oregon in 1974, it is now found in eight western states.

Wheat farmers in Idaho, Oregon and Washington are estimated to lose $3.4 million in revenue each year to cereal cyst nematodes, according to OSU calculations. Researchers arrived at the figure by considering a range of factors, including the percentage of fields infested with damaging densities of nematodes, as well as the yields and farmgate value for crops in these infested areas.

OSU scientists are studying crop management strategies to mitigate the worms' impact. The most effective tactic they've found is a three-year crop rotation where farmers skip two years between wheat plantings.

Rotations vary depending upon which nematode is causing problems. Root-lesion nematodes are well-managed by planting winter wheat the first year and spring barley the second year and then letting the field go fallow the third year. Cereal cyst nematodes are best-managed by rotating wheat or barley with broadleaf crops.

Crop damage can also be alleviated to a limited extent by applying extra fertilizer and water. There are no chemicals legally available for wheat and barley growers to kill the two types of nematodes.

OSU researchers have also tested more than 20 wheat, barley and oat cultivars to determine how badly yields are reduced. Most Pacific Northwest wheat varieties don't resist harmful nematodes.

In OSU's tests, nearly every variety suffered severe root injury. Only the hard red spring wheat WB-Rockland prevented cereal cyst nematodes from reproducing while also maintaining consistent yields. UI Stone, a soft white spring wheat, and Buck Pronto, a hard red spring wheat, allowed nematode populations to thrive but still produced a steady crop.

Additionally, University of Idaho, Washington State University, U.S. Department of Agriculture, and commercial wheat breeders are crossing sources of resistance with a number of wheat varieties to create new cultivars that can potentially stand up to the cereal cyst and root-lesion nematodes.

OSU researchers recommend growers have their soil tested for nematodes. Addresses for testing labs, as well as information about management strategies for farmers, are available in two OSU Extension factsheets at http://bit.ly/OSU_ExtBulletin3 and http://bit.ly/OSU_ExtBulletin2.

The U.S. Department of Agriculture, Washington State University and the University of Idaho are collaborators with OSU on its cereal cyst nematode research.