Comparison of Fungicide Application Methods for Systemic Control of Sugar Beet Powdery Mildew

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Abstract
Several methods of applying 4 systemic fungicides to control sugar beet powdery mildew [Erysiphe betae, E. polygoni] were tested in the greenhouse and field over a 5-yr period. When applied as seed treatments, benomyl, ethirimol and triadimefon had no effect on yield or disease levels under field conditions. However, when used as a preplant soil treatment, triadimefon at 1.12 kg/ha reduced disease levels and resulted in yields comparable to S-sprayed controls. When applied as foliar sprays (0.28 kg/ha) twice during the growing season, nuarimol and triadimefon provided disease control comparable to that of 2 sulfur applications, each at 44.8 kg/ha. All foliar sprays protected leaves for approximately 4-6 wk and required repeated applications for effective control. When applied directly to the crowns of 8-wk old sugar beets, low-concentration (5%) granules of nuarimol (0.56 and 1.12 kg/ha) or triadimefon (0.56, 1.12, and 2.24 kg/ha) resulted in low levels of disease throughout the season and in yields as high as or, in some trials, significantly higher than the S sprays tested.