Effects of Number and Timing of Chlorothalonil Applications on Onion Yield. M. E. Miller, Associate Professor, Texas Agricultural Experiment Station, Weslaco 78596. B. D. Bruton, USDA-ARS, Weslaco, TX 78596; and J. M. Amador, Texas Agricultural Extension Service, Weslaco 78596. Plant Dis. 70:875-876. Accepted for publication 18 February 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-875.

Chlorothalonil at 1.75 kg a.i./ ha and mancozeb at 2.69 kg a.i./ ha were applied to New Mexico Yellow Grano onions to determine the effects of the number and timing of chlorothalonil treatments on bulb yield. Bulb yields decreased linearly (Y = 31.45 – 0.77 X, P = 0.05) as the number of chlorothalonil applications increased. Yields of onions treated with 10 mancozeb applications and those of untreated controls did not differ significantly. No significant difference in yield was observed among treatments with equivalent numbers of chlorothalonil applications, indicating that the total number and not the timing of applications affected bulb yield.