Sulfur management and miticide use in winegrapes grown in California

Abstract

AbstractProper sulfur management in winegrapes may potentially reduce both insecticide/miticide use and the human/social problems associated with sulfur's impacts on air quality and odors, particularly in wine tourism regions. Data from California's unique Pesticide Use Report (PUR) database, which records agricultural pesticide applications on all crops throughout the state, are used to determine if either winegrape grower's choice of sulfur formulation (dust only, wettable only, or a combination) or overall sulfur use rates (pounds per acre planted) correlate with annual miticide and insecticide use in Fresno and Madera (hotter–drier) and Napa and Sonoma counties (cooler–damper). Annual sulfur use has declined by 36–55% in these counties from 1993 to 2009. In 2000, the greatest number of growers in each county were combination users; wettable users were higher in Napa (38%) and Sonoma (34%) than in Fresno (24%) and Madera (10%); and dust-only users varied little (15–19%) across the four counties. Data for 2005 and 2009 showed similar trends. The use of high-toxicity insecticides in Fresno was 387% higher than in Napa–Sonoma in 2000, but was 25 and 8% lower in 2005 and 2009, respectively. In Fresno, wettable sulfur users used less high-toxicity insecticides; while in Fresno and Madera dust users used less lower-risk insecticides than combination or wettable sulfur users. No significant differences in insecticide use were evident between the three sulfur use categories in Napa–Sonoma (P = 0.97). On average, dust users in Fresno–Madera used more high-toxicity miticides than combination or wettable sulfur users in 2000. That trend decreased in the data for 2005 and 2009. Average miticide use in Fresno–Madera was higher than in Napa–Sonoma by 1349% in 2000, 1103% in 2005 and 146% in 2009. Higher sulfur use intensities among individual growers in Fresno–Madera were positively correlated with greater use of high-toxicity miticides in 2000 and 2005, but not 2009. The comparable results for Napa–Sonoma were less clear. Since PUR data represent statewide information on pesticide use decisions in real-world farming scenarios, it can complement data from field and laboratory studies. Expanding these analyses to compare pesticide use by individual growers across years, or to correlate pesticide usage with any published mite field surveys may shed more light on the enigmatic relationship between sulfur fungicide use and mite outbreaks in winegrapes.