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Rate of Spread of Ceratocystis wageneri in Ponderosa Pine Stands in the Central Sierra Nevada. F. W. Cobb, Jr., Associate professor, Department of Plant Pathology, University of California, Berkeley 94720; G. W. Slaughter(2), D. L. Rowney(3), and C. J. DeMars(4). (2)(3)Research associate, and statistician, respectively, Department of Plant Pathology, University of California, Berkeley 94720; (4)Research entomologist, Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Berkeley, CA 94701. Phytopathology 72:1359-1362. Accepted for publication 7 April 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1359.

Ceratocystis wageneri, cause of black stain root disease, typically spreads locally from disease foci, sometimes producing infection centers of ≥10 ha in ponderosa pine stands. To determine rates of spread and the influence of stand-site variables on spread rate, the enlargement of 52 infection centers was determined from aerial photographs taken during an 1115 yr period. Average rate of radial spread for all centers was 1.0 m/yr, but it varied from 0 to 7 m/yr. Often, under apparently favorable conditions, annual rates of ≥3 m were sustained for the entire study period. Such rates can lead to substantial losses in pines with rotation ages of 5080 years. Of the four stand-site variables studied (mortality-center size, ponderosa pine stand density, species composition, and soil moisture drainage class), only ponderosa pine density was strongly associated with spread rate. Rate of generation of new centers in the 2,225-ha study area for a period of 3 yr was only one center per 1,000 ha per year. Besides yielding data useful in developing pest management strategies, the results illustrate the efficacy of sequential aerial photography as a research tool.

Additional keywords: root disease, Verticicladiella wageneri.