VIEW ARTICLE

Disease Control and Pest Management

Effect of Soil Solarization on Populations of Selected Soilborne Microorganisms and Growth of Deciduous Fruit Tree Seedlings. J. J. Stapleton, Department of Plant Pathology, University of California, Davis 95616; J. E. DeVay, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 72:323-326. Accepted for publication 6 May 1981. 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, 1982. DOI: 10.1094/Phyto-72-323.

Two fallowed field sites of differing soil type in the San Joaquin and Sacramento valleys in California, were treated by soil solarization (covering of moist soil with clear polyethylene sheeting to achieve high soil temperatures) for 4.5 wk in the summer. Soil samples from solarized and nonsolarized plots were periodically collected and assayed with selective media for population densities of certain microorganisms. Plots were planted with English walnut and cultivar Nemaguard peach seeds after solarization. Population densities of Agrobacterium spp., fluorescent pseudomonads, Gram-positive bacteria, and fungi recoverable on PDA were greatly reduced immediately following solarization. Actinomycetes and thermophilic/thermotolerant fungi were affected to a lesser extent. Agrobacterium spp. and populations of Gram-positive bacteria remained significantly depressed in solarized soil after 6–12 mo. Fluorescent pseudomonads and “total” fungi quickly recolonized the treated soil, while actinomycetes and thermophilic/thermotolerant fungi attained higher population densities following soil solarization. After one growing season, there were no detectable differences in stand counts of peach or walnut seedlings. However, peach seedlings grown in solarized soil showed increases in plant height of 25% and fresh weight of 42%, and walnut seedlings showed increases in height and fresh weight of 26 and 58%, respectively, compared with those grown in nonsolarized soil.