Leaf wetness was measured continuously in the lower, middle, and upper canopy of one mature and one young Douglas-fir tree at five sites situated along an elevational gradient from west side of Coast Range of Oregon to west side of Cascade Range of Oregon. This dataset is associated with the following publication: Lan, Y., D.C. Shaw, P.A. Beedlow, E. Lee, and R.S. Waschmann. Severity of Swiss needle cast in young and mature Douglas-fir forests in western Oregon, USA. FOREST ECOLOGY AND MANAGEMENT. Elsevier Science Ltd, New York, NY, USA, 442: 79-95, (2019).