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Effects of Metalaxyl on Growth and Ectomycorrhizae of Fraser Fir Seedlings. C. M. Kenerley, Former Graduate Research Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27650. R. I. Bruck, Assistant Professor, and L. F. Grand, Professor, Plant Pathology and Forestry, North Carolina State University, Raleigh 27650. Plant Dis. 68:32-35. Accepted for publication 13 July 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-32.

Effects of metalaxyl on growth and ectomycorrhizae of Fraser fir seedlings were examined at two nurseries and in a natural Fraser fir stand. Dry weights of roots and shoots of seedlings at the Linville River Nursery were found to have a significant (P = 0.01) linear and quadratic response to metalaxyl. Lateral root length, number of ectomycorrhizal tips per centimeter of lateral root, and percentage of short roots ectomycorrhizal were significantly greater among metalaxyl-treated than among untreated seedlings at the Linville River Nursery. The number of sporocarps of Laccaria proxima, a putative ectomycorrhizal fungus of Fraser fir, increased with increasing dosage of metalaxyl. Dry weights were significantly greater (P = 0.01) for treated seedlings in their first year of growth at Wolf Mt. Nursery than for untreated seedlings on one sampling date but not on other dates. Dry weights of seedlings in their second year of growth at the Wolf Mt. Nursery or in a natural stand of Fraser fir were not affected by applications of a single rate of metalaxyl. Ectomycorrhizae were found earlier in the growing season on metalaxyl-treated than on untreated seedlings at the Wolf Mt. Nursery. Average organic matter content of soils was considerably higher in the natural stand (12.3%) and at the Wolf Mt. Nursery (4.3%) than at the Linville River Nursery (0.5%), which may account for the difference in responses to metalaxyl.