By Extension: What is going on with that tree?

By Valerie Grant, Forestry & Natural Resources

Someone recently asked if western larch trees grows on the hills in Tillamook. They observed that the trees were turning yellow green this spring much like a western larch might in the fall. The thin yellow Douglas-fir trees might look a little like a larch but they’re not, they have a disease called Swiss Needle Cast.

Swiss Needle Cast is the common name of a disease caused by a native fungus that attacks Douglas-fir needles. The small black dots on the underside of the needles are fungal spores plugging up natural openings, giving them a soot coated appearance. The trees look yellow and thin with many missing needles and the disease can cause significant growth losses. Swiss Needle Cast symptoms started to show up in the 1980s along the Oregon Coast. The disease symptoms are associated with mild winters and warm wet springs (fog, drizzle and rain), and Douglas-fir plantations in the western hemlock-Sitka spruce zone.

So what is being done about it? The Swiss Needle Cast Cooperative, a partnership between Oregon State University, Oregon Department of Forestry, US Forest Service, Bureau of Land Management, and private forest landowner partners installed long-term monitoring plots in coastal Oregon and north-western Washington, where researchers are studying the disease. A new guide will be published later this year to assist landowners in making disease management decisions.
While this disease is no joking matter, causing significant economic losses, for a tree nerd like me its funny to confuse the two tree species. Douglas-fir is an evergreen conifer retaining its needles year round, while larch with its many evergreen characteristics is deciduous, its needles turning brilliantly yellow and naturally casting in the fall.

Western Larch

Western larch does not occur in Tillamook County aside from the occasional tree planted in a yard or a park. It is found in the northeast part of the state at higher elevations.
If you notice that the trees in your woods are looking unusual give the Extension office a call. We can help connect you with the Master Gardener’s to assist with identification. As an Extension Forester, I can help connect you with resources or other professionals to help you manage your woods to meet your objectives like productivity and wildlife habitat.

By Extension, Your Connection to the Programs, People, and Publications from OSU Extension Tillamook County
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