Managing Soilborne Pathogens of White Pine in a Forest Nursery. S. A. Enebak, Department of Plant Pathology, University of Minnesota. M. A. Palmer, and R. A. Blanchette. USDA Forest Service, North Central Forest Experiment Station; and Department of Plant Pathology, University of Minnesota, St. Paul 55108. Plant Dis. 74:195-198. Accepted for publication 10 September 1989. 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, 1990. DOI: 10.1094/PD-74-0195.

In a forest tree nursery, 100% methyl bromide (MB), 100% chloropicrin (CP), combinations of MB and CP, and dazomet significantly reduced populations of soil fungi. Captan, thiram, a combination of captan and thiram, and covering seed with silica sand had no effect on fungal populations in soil. Nine months after fumigation, populations of soil fungi remained lower only in plots treated with MB and/or CP. Preemergence mortality of eastern white pine (Pinus strobus) was greatest when seed was covered with silica sand (49%) and least when soil was treated with 100% MB (21%). Postemergence damping-off was greatest when soil was treated with captan (19%) and least when soil was treated with 67% MB and 33% CP (1%). Plots treated with MB and/or CP had the highest seedling stand densities, averaging 232 seedlings per 0.5 m², compared to 125 seedlings per 0.5 m² in plots treated with dazomet and an average of 53 seedlings per 0.5 m² in plots treated with captan, thiram, captan and thiram, or silica sand and in the control plots. Seedling taproots were significantly longer in soils treated with MB and/or CP than in all other treatments. The colonization of root tips by mycorrhizal fungi did not differ significantly among treatments on seedlings examined in June or July 1987.