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San Joaquin Valley grape growers reduce fungicide sprays

The Issue

Powdery mildew is the No. 1 grapevine disease in California, and sulfur is the most common fungicide used to manage it. Growers like sulfur because of its low cost and ease of application, and because it doesn't promote powdery mildew resistance. Used alone, sulfur requires frequent application, and can cause phytotoxicity and health concerns. Other fungicides, when combined with sulfur, can promote fungicide resistance. Growers can reduce these problems by implementing the UC Davis Powdery Mildew Risk Index (PMI), which helps pinpoint the best times to apply fungicides. Due to hot weather, San Joaquin Valley growers have the most to gain by integrating the PMI into their programs.

What Has ANR Done?

The UC Cooperative Extension viticulture advisor met regularly with San Joaquin Valley grape growers, focusing on powdery mildew disease. Using local weather data from the Fresno-Madera Weather Network, the advisor has shown growers how to implement and organize the PMI to develop spray programs using fungicides of their choice.

The Payoff

Growers save time and money, and help improve air quality

Once growers see the exceptional results enabled by the PMI, they often commit entire vineyards to the new program. On 40-acre plots, growers can reduce costs, per eliminated application, of $149 when using dusting sulfur, $282 when using wettable sulfur, and $689 when using a sterol inhibitor such as fenarimol. Many growers have eliminated three sprays when conditions were right.

Clientele Testimonial

The Fresno-Madera weather network is one of the single most important Cooperative Extension services for California’s raisin growers. It has saved us substantial amounts of time and money, while reducing pesticide applications.
-Peter Miroyan, Fresno raisin grower


Supporting Unit: Fresno County

Fresno County, Madera County and Integrated Pest Management
Stephen Vasquez, former viticulture advisor, UCCE Fresno County