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Control of Leaf Rust on Spring Wheat by Seed Treatment with 4-N-butyl-1,2,4-triazole. J. B. Rowell, Research Plant Pathologist, Cereal Rust Laboratory, U.S. Department of Agriculture, University of Minnesota, St. Paul 55108; Phytopathology 66:1129-1134. Accepted for publication 2 March 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1129.

Seedling assays showed that 4-n-butyl-1,2,4-triazole (RH-124) was superior as a systemic protectant against wheat leaf rust in foliar, soil, and seed applications compared to triarimol, oxycarboxin, and benomyl. RH-124, however, had a relatively short duration of effectiveness inside the wheat plant. In field tests, the effective dosage for seed treatment with RH-124 was 20-25% of that required for the same level of effectiveness as a spray applied after rust was present. A seed treatment at 140 g/hectare(ha) effectively prevented crop losses due to leaf rust. Soil residues from spray applications at 280 and 560 g/ha suppressed leaf rust development on wheat planted in the succeeding season. Seed treatment with RH-124 had no discernible effect on plant development when seed was planted in moist soil, but stand densities and seedling growth were reduced when seed was planted in dry soil. More RH-124 was required for the same level of control of leaf rust on cultivar Kota than on the less susceptible cultivars Thatcher and Selkirk. The results indicate that seed treatment with RH-124 has a high potential for control of leaf rust on spring wheats in the north central USA.

Additional keywords: Puccinia recondita, Triticum aestivum, systemic fungicides.