Patterns of Increasing Swiss Needle Cast Impacts on Growth of 20- and 40-year-old Douglas-fir from Tillamook

Currently, Swiss Needle Cast (SNC) is causing an epidemic west of the Oregon Coast Range from Coos Bay to Astoria. The most severely infected Douglas-fir trees are located on BLM land and Stimson Lumber plantations in Tillamook where environmental conditions are highly favorable for fungal development. Increasing severity of SNC has reduced the growth of naturally regenerated and introduced Douglas-fir stands since ~1984. Annual radial stem growth of 20- and 40-year-old Douglas-fir trees on Stimson Lumber land in Tillamook displayed a marked decline in growth rates in the most recent decade. The increase in SNC severity is associated with increasing winter temperature which enhances the proliferation of pseudothecia and inoculum abundance.