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Disease Control and Pest Management

Effects of Triadimefon on Growth and Ectomycorrhizal Development of Loblolly and Slash Pines in Nurseries. D. H. Marx, Institute for Mycorrhizal Research and Development, USDA Forest Service, Athens, GA 30602; C. E. Cordell(2), and R. C. France(3). (2)Forest Pest Management, Region 8, State and Private Forestry, USDA Forest Service, Asheville, NC 28804; (3)International Paper Company, Bainbridge, GA 31717. Phytopathology 76:824-831. Accepted for publication 21 January 1986. 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, 1986. DOI: 10.1094/Phyto-76-824.

Three or four sprays with the systemic fungicide triadimefon (Bayleton) each at 0.56 kg a.i./ha applied in May and June to control fusiform rust significantly suppressed ectomycorrhizal development by artificially introduced Pisolithus tinctorius and naturally occurring fungi, by twofold to threefold on loblolly and slash pine seedlings throughout the growing season compared with seedlings sprayed (17-41 times) with the fungicide ferbam. The average indices of P. tinctorius in the three nurseries after triadimefon and ferbam sprays were 2 and 69, respectively. Loblolly pine seedling growth was not significantly affected by triadimefon in two of three nurseries. Basidiocarp production by ectomycorrhizal fungi in triadimefon-treated plots occurred later in the growing season (September) and was 3-10 times less than in ferbam-treated plots. Residues of triadimefon and its metabolite triadimenol were detected in roots and tops of seedlings. These residues, especially triadimenol, were detected in one nursery up to 116 days after the last triadimefon spray in amounts sufficient to strongly inhibit growth of P. tinctorius and Thelephora terrestris in pure culture. The ED₅₀ of triadimefon on growth of P. tinctorius and T. terrestris was 0.98 and 1.66 mg/L, respectively; the ED₅₀ of triadimenol was 0.40 and 0.25 mg/L, respectively. Triadimenol residues ranging between 0.4 and 4.5 μg/g of root were detected up to 116 days after the last triadimefon spray.