VIEW ARTICLE

Disease Control and Pest Management

Effects of Methyl Bromide Dosage on Microorganisms in Soil Before and After Growth of Nicotiana glutinosa. David E. Millhouse, Graduate research assistant, Department of Plant Pathology, University of California, Riverside 92521, Present address of senior author: BASF Agric. Res. Farm, P.O. Box 758, Dinuba, CA 93618; Donald E. Munnecke, professor, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 71:418-421. Accepted for publication 3 April 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-418.

Soil fumigation for various periods with a controlled concentration of methyl bromide (MB) in a moving airstream affected the populations of various microorganisms. In soil fumigated with 27,000 μl of MB per liter of air, soil fungi and Pseudomonas spp. were eliminated within 16 hr; Streptomyces spp. were greatly reduced within 64 hr and were undetectable in soil fumigated for 128 hr; but aerobic bacteria and Bacillus spp. were only slightly affected by treatment for 128 hr (the longest time tested). Soil was treated with 32,000 μl of MB per liter of air for various times, planted with Nicotiana glutinosa, and microbial populations also were determined in nonfumigated soil planted with N. glutinosa. Microbial populations of soil in which plants had been grown increased as the time after fumigation increased. After 89 days, populations of fungi in soil fumigated for 32 or 128 hours were as great as those initially found in nonfumigated soil. Penicillium spp. and Trichoderma spp. were the dominant fungi isolated from soil after fumigation for longer than 8 hr. Recolonization of fumigated soil by Streptomyces spp. was rapid; after 38 days, numbers were greater in soil fumigated for 32 hr than those in nonfumigated soil Recolonization by Streptomyces spp. was slow in soil fumigated for 128 hr and populations after 89 days were still lower than those in nonfumigated soil. Populations of aerobic bacteria and Bacillus spp. were greater in soils fumigated for 32 or 128 hr than in nonfumigated soil at all sampling periods. Fluorescent Pseudomonas spp. were not isolated from fumigated soils in which N. glutinosa was grown, but they were present in planted nonfumigated soils.