Successful Management of Powdery Mildew in Pumpkin with Disease Threshold-based Fungicide Programs. M. T. McGrath, Department of Plant Pathology, Long Island Horticultural Research Laboratory, Cornell University, 3059 Sound Avenue, Riverhead, New York 11901-1098. Plant Dis. 80:910-916. Accepted for publication 13 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0910.

Triadimefon applications initiated after disease detection (integrated pest management [IPM] schedule) controlled powdery mildew as well as a preventive schedule in four field experiments (1989 to 1992) and in four commercial pumpkin fields (1992). Yield and fruit quality were similar among IPM and preventive schedules. The action threshold used to initiate the IPM schedule was at least one leaf with powdery mildew symptoms per 50 old leaves examined. For both the IPM and preventive schedules, the systemic fungicide triadimefon was applied every 14 days combined with a protectant fungicide, chlorothalonil, applied every 7 days. Symptoms were observed in all experiments 6 to 12 days before the threshold was reached in each plot. When the threshold was reached, actual disease level ranged from an average of four to 50 colonies on the 50 leaves examined per plot. The first application under the IPM schedule was made 2 to 4 days after the threshold was reached. Thus with the decision criterion used there is time for detection and management response. However, triadimefon applications initiated 1 week later were not always as effective.

Keyword(s): cucurbits, disease threshold, Sphaerotheca fuliginea