Spore Deposition of Heterobasidion annosum in Thinned Coastal Western Hemlock Stands in Oregon and Washington. R. L. Edmonds, Professor, College of Forest Resources, University of Washington, Seattle 98195. K. B. Leslie, Graduate Student, and C. H. Driver, Professor, College of Forest Resources, University of Washington, Seattle 98195. Plant Dis. 68:713-715. Accepted for publication 20 February 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-713.

Deposition of spores of Heterobasidion annosum was studied in both commercially and precommercially thinned stands of western hemlock (Tsuga heterophylla) at five coastal locations in Washington and Oregon. Petri plates containing selective medium were exposed at approximately monthly intervals from April 1981 to June 1982. Average spore deposition rates were higher in precommercially than commercially thinned stands, with the highest average rate (19,557/m²/hr) occurring at Seaside, OR. The maximum spore deposition rate was 44,353/m²/hr in a precommercially thinned stand at Tillamook, OR. Deposition rates in precommercially thinned stands were higher at the southern sites (Cathlamet, Seaside, and Tillamook) than the northern sites (Sekiu and Hoquiam). This trend did not occur in commercially thinned stands. Deposition rates were, in general, highest in autumn and spring and lowest in winter and summer.

Keyword(s): root disease.