Department of Plant Pathology

Several species of powdery mildews are obligate biotrophs of crops in the Cucurbitaceae. These pathogens rapidly colonize green tissues via asexual reproduction and can negatively affect host physiology. We conducted a field experiment to evaluate the efficacy of organic and synthetic fungicides (registered and experimental products) for control of powdery mildew in pumpkin cv. Sorcerer. Following six weeks of fungicide applications, disease incidence (percentage of infected leaves within a plot) and disease severity (colony density on the leaf surface) was generally lowest in plants treated with synthetic materials (quinoxyfen, penthiopyrad, triflumizole, and mixed programs of triflumizole/quinoxyfen, myclobutanil/quinoxyfen/ trifloxystrobin, and myclobutanil/penthiopyrad/ trifloxystrobin). ‘Soft-chemistry’ materials such as paraffinic oil, tea tree oil, hydrogen peroxide, and the biocontrol agent, Strepyomyces lydicus WYEC108, were less effective at managing disease when used alone. However, tea tree oil and S. lydicus substantially reduced disease incidence and severity when used in a program with quinoxyfen, suggesting that good disease management can be maintained while significantly reducing use of synthetic fungicides.