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Control of Dutch Elm Disease in Artificially-Inoculated American Elms with Soil-Injected Benomyl, Captan, and Thiabendazole. R. J. Stipes, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061; Phytopathology 63:735-738. Accepted for publication 20 December 1972. DOI: 10.1094/Phyto-63-735.

Benomyl, captan and thiabendazole at 124.8 g per tree each were injected under pressure into the Lodi loam rhizosphere of nine completely-randomized three-year-old American elms (Ulmus americana) prior to inoculation with Ceratocystis ulmi. Mean percent foliar symptoms after 14 months were 4, 23, 55 and 76 in benomyl-, thiabendazole- and captan-treated and control trees, respectively. Disease control in benomyl-treated trees was superior and highly uniform. Bioassays of solvent-extracted leaves from treated trees sampled 2 days after fungicide application revealed the presence of fungitoxicants. Vascular discoloration was present in at least half of the trees from each treatment, and biopsy tissues from benomyl-treated trees yielded the least number of C. ulmi cultures. Fresh weight of tops of manually-defoliated benomyl-treated trees was more than twice that of any other treatment, including fungus-inoculated, non-fungicide-treated controls. The surfactant adjuvant, Tween 80, used at 1% (v/v) with each fungicide did not appreciably affect disease control. Residual fungitoxicants were detected in all treated soils 17 months after application. Benomyl offers promise in controlling Dutch elm disease by soil injection prior to infection.

Additional keywords: fungitoxicant residues.