Spore Deposition by Heterobasidion annosum in Forests of California. R. L. James, Plant Pathologist, USDA Forest Service, Cooperative Forestry and Pest Management, Missoula, MT 59801. F. W. Cobb, Jr., Professor, Department of Plant Pathology, University of California, Berkeley 94720. Plant Dis. 68:246-248. Accepted for publication 19 September 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/PD-68-246.

Spore deposition of Heterobasidion annosum on fresh pine disks was studied in Jackson State Forest (JSF) in coastal northern California, Stanislaus National Forest (SNF) in the central Sierra Nevada, and San Bernardino National Forest (SBNF) in southern California. Highest spore deposition rates (to 796/m²/hr) occurred on the SNF; the SBNF had the lowest rates. Spores were deposited throughout the year on the SNF and SBNF. Lowest deposition rates occurred in the summer on the SBNF and in winter on the SNF. Greatest deposition occurred during winter on the SBNF and in autumn on the SNF. Diurnal patterns of spore deposition were studied on the SBNF, where most deposition occurred at night. Spore deposition was not correlated with air-pollution dosage gradients on the SBNF.