Botrytis bunch rot is an important grapevine disease in California. Twenty eight fungicide programs were evaluated for control of bunch rot in a field experiment in a Chardonnay (clone 4) vineyard in the Carneros region of Napa Valley, California during 2009. Four fungicide applications were made from bloom to harvest with the final application made just prior to heavy rainfall. Disease was rated three weeks following the final application. Disease developed rapidly during the month of October, approaching 60% infected berries in untreated vines. Most fungicide programs failed to give a large (>3 fold) reduction in disease severity, but many partially lowered disease severity. Several products reduced disease to less than 10% severity: fenhexamid (alone and with tetraconazole), fluopyram + tebuconazole and fluopyram + tebuconazole alternated with trifloxystrobin + tebuconazole. Tetraconazole and cyprodinil alone, mineral oil, other soft chemistry products, and boscalid + pyraclostrobin did not effectively control disease.

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.