Seed-Treatment Fungicides for Control of Seedborne Ascochyta lentis on Lentil. Walter J. Kaiser, Research Plant Pathologist, Western Regional Plant Introduction Station, USDA, ARS, Washington State University, Pullman 99164. Richard M. Hannan, Biological Technician, Western Regional Plant Introduction Station, USDA, ARS, Washington State University, Pullman 99164. Plant Dis. 71:58-62. Accepted for publication 31 May 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, 1987. DOI: 10.1094/PD-71-0058.

The efficacy of chemical treatments and thermotherapy in controlling seedborne Ascochyta lentis was tested on naturally infected lentil seeds. Lentil plants from infected seeds had fewer branches, smaller roots and shoots, reduced vigor, and lower seed yields. In laboratory studies, the most effective of 12 seed-treatment fungicides were thiabendazole and etaconazole (CGA-64251), which reduced the incidence of A. lentis in lentil PI 438516 from 80.5% in the untreated seeds to 0 and 1.5%, respectively, in treated seeds. When fungicide-treated seeds were tested under field conditions, emergence of A. lentis-infected seeds treated with thiabendazole and benomyl was significantly greater than with the other treatments, and yields were significantly higher with the thiabendazole treatment. Seed-treatment fungicides that adversely affected plant growth, vigor, and yields included triadimefon, triadimenol, etaconazole, and thiram (as a soak treatment). There was some evidence of a phytotoxic response to thiabendazole at 3.0 and 6.0 g a.i./kg of seed. Mycelial growth of four isolates of A. lentis was completely inhibited on potato-dextrose agar amended with thiabendazole at 10 µg a.i./ml. Infusion of thiabendazole and benomyl into infected lentil seeds, using acetone or dichloromethane, was not effective in controlling seedborne. A. lentis. Treatment of infected seeds with aerated steam or hot water at 45—75 C for 30 min did not control A. lentis.