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CORVALLIS, Ore. – Forestry researchers at Oregon State University have developed a computerized risk analysis system to help predict the vulnerability of specific sites to Swiss Needle Cast, a serious problem in Coast Range forests that can cut tree growth and causes losses of more than $200 million a year.

The model, which is now in prototype form and should be fully available to landowners by early next year, may be an important tool to help address a resurgence of the Swiss Needle Cast epidemic that has occurred just in the past couple years, almost doubling from its level in 2004.

Other initiatives are also under way in the Swiss Needle Cast Cooperative based at OSU, which was founded 10 years ago as a cooperative effort of private industry, academia and other government agencies.

“This new risk-rating model should be a reliable predictive tool so that landowners can make more informed decisions on what tree species to plant,” said David Shaw, an assistant professor in the Department of Forest Science at OSU, and director of the cooperative. “Some of our co-op members are pretty excited about its potential to help address this problem.”

Swiss Needle Cast, a fungal disease of Douglas fir that is native to the Pacific Northwest, is mostly a problem in areas within 20 miles of the ocean, where warm, wet conditions favor its growth. It’s a cyclical problem that is made more severe by warmer winters, wetter springs and extended drizzle.

Historically, the fungus was a minor concern in this region, which was dominated by hemlock and Sitka spruce trees, with only smaller amounts of Douglas fir. But with intensive forest management during the past century, the varied tree species were often harvested and replaced with a monoculture of Douglas fir, which grew well and commanded higher market prices.

“Other than with the concerns about Swiss Needle Cast, Douglas fir grows exceptionally well in the Coast Range, and in past decades a couple million acres were converted to it,” Shaw said. “But now we have a perfect storm of conditions favoring this fungus, with dense plantations of the trees it infects and favorable climate conditions.”

At its worst, Swiss Needle Cast can cut Douglas fir growth by up to 50 percent, causing new-growth tree needles to turn yellow and be “cast off.” As recently as 2004, efforts to change the mix of tree plantations had shown some success and cut the acreage of significant infection in half, to less than 200,000 acres. But a new survey shows the disease has made a dramatic recovery and once again is nearing peak levels, affecting 338,000 acres. A particular hot spot is the low elevation areas and hills around Tillamook, where conditions appear optimal for the disease.

“Most of what we’re seeing is probably variation driven by weather,” Shaw said. “This is not a problem we’re going to eradicate any time soon, so we have to develop ways to deal with it.”

The new model is being developed at OSU with funding from the Swiss Needle Cast Cooperative, by Jeff Stone, an associate professor of botany and plant pathology, and Len Coop of the Integrated Plant Protection Center. It can tell landowners whether a very specific plot of land will be at low, moderate or high risk to develop significant Swiss Needle Cast infection. This can help guide decisions on what to plant for future tree rotations. The model incorporates a diverse range of data about topography, climate, local weather patterns, historic disease problems and other relevant issues.

For those with existing problems, there are fewer options. Use of fungicides is effective but too expensive to use on a broad scale. OSU studies in the Swiss Needle Cast Cooperative have determined that thinning of the weakest Douglas-fir and replacement with hemlock or spruce can be of some value. It helps to avoid nitrogen fertilization, which favors the growth of fungus. And in extreme cases, some landowners may even consider conversion of their existing forest to different species.

Within five to 15 years, Shaw said, other research may produce Douglas fir varieties with improved Swiss Needle Cast tolerance, through studies that are now under way.

A series of workshops will be conducted next year to help private and industrial landowners learn more about the new risk-rating model and other steps to address this problem, Shaw said.