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Delimitation of Lesions of Fusarium Hypocotyl Rot of Pine by Soil Microsite Environmental Determinants. K. H. Brownell, Stauffer Chemical Co., P.O. Box 760, Mountain View, CA 94040; R. W. Schneider, Department of Plant Pathology and Crop Physiology, Louisiana State University, Baton Rouge 70803. Phytopathology 75:58-60. Accepted for publication 12 June 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-58.

Moisture and temperature in the top 3 cm of soil were tested for effects on the development of Fusarium hypocotyl rot of Pinus lambertiana, lesions of which occurred at a mean soil depth of 1.7 cm. Several factors were found to be involved in the depth restriction of lesion formation. Soil water potential and temperature were more favorable for fungal development with increasing soil depth, which would increase the probability of lesions occurring at greater depths. However, hypocotyl tissue was predisposed to localized infection by the higher temperatures that occurred in the top 3 cm. This predisposition did not persist after the heat was discontinued. Plant water stress of the magnitude found in the field did not predispose plants. This knowledge has been used to control the disease by manipulation of the soil environment at the microsite by earlier planting dates and partial shading.

Additional keywords: Fusarium oxysporum, sugar pine.