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Influence of a Benzimidazole-Tolerant Isolate of Ceratocystis ulmi on the Control of Dutch Elm Disease with Methyl 2-Benzimidazole Carbamate Phosphate. L. R. Schreiber, Supervisory plant pathologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Nursery Crops Research Laboratory, Delaware, OH 43015; G. F. Gregory, principal plant pathologist, U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station, Delaware, OH 43015. Phytopathology 70:444-446. Accepted for publication 12 November 1979. 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, 1980. DOI: 10.1094/Phyto-70-444.

American elm (Ulmus americana) seedlings 10.020.0 cm in diameter at breast height (dbh) were inoculated with either a benzimidazole-sensitive (WI) or a benzimidazole-tolerant (WIT) strain of Ceratocystis ulmi. When Dutch elm disease symptoms appeared, trees were injected with Lignasan BLP (methyl 2-benzimidazole carbamate phosphate) at either 0.8 or 4.0 g/2.5 cm dbh. Dutch elm disease symptoms were reduced below the control level only in trees inoculated with the WI strain and treated with Lignasan BLP at 4.0 g/2.5 cm dbh. Fungitoxicants were recovered from the symptom-bearing branches of a higher percentage of WI-inoculated elms than from WIT-inoculated elms. Decreased reisolation of the WI but not of the WIT strain occurred with increased fungicide concentration. The benzimidazole sensitivity of the WI and WIT strains remained stable, and the pathogenicity of the two strains did not differ significantly as measured by disease development from August 1976 through July 1978.

Additional keywords: systemic fungicides.