Issue link: http://winesandvines.uberflip.com/i/172581
OCTOBER NEWS Options to Control Powdery Mildew Annual field day looks at efficacy of fungicide treatments C ourtland, Calif.— Grapegrowers, vineyard managers, consultants, pest control advisors (PCAs) and ag chemical suppliers inspected the results of 90 different fungicide spray treatments to control powdery mildew Aug. 7 as part of a University of CaliUC Davis plant pathologist fornia Cooperative Extension Dr. Douglas Gubler noted that (UCCE) vineyard field trial organic oils continue to be very conducted by the University effective against fungus, but they of California, Davis, Departcan slightly delay fruit maturity. ment of Plant Pathology. UC Davis plant pathologist Dr. Douglas Gubler, an expert on grape fungal pathogens and diseases and a frequent lecturer at industry meetings, oversees the annual research trial that has been conducted in the same Chardonnay vineyard for 28 years in cooperation with grower John Baranek of Herzog Ranch in the Clarksburg American Viticultural Area. The vineyard near the Sacramento-San Joaquin River Delta is an excellent test site, with powdery mildew (Erysiphe necator) disease pressure each season because the weather in the area is cooler and the vineyard is near a body of water. The 90 treatments tested in 2013 included synthetic, biological and organic fungicides in different combinations, and with varying application rates and timing. Applications were made beginning in early April, and final treatments were applied the week of July 15. Gubler noted that organic oils such as JMS Stylet Oil (a paraffinic oil), PureSpray and Safe-T-Side, which work as contact fungicides with a smothering or barrier effect to PM growth, continue to be very effective products, particularly when used early in the season to knock back the fungus. One caution with these oils is that they can slightly delay fruit maturity, as the oil will block and shut down leaf stomata to reduce carbohydrate accumulation. A general recommendation is that different classes of fungicides with different modes of action be used alternately during the growing season and from year to year in an integrated program to prevent disease resistance and improve efficacy. Soft chemistry, natural and biological products can be used when disease pressure is low to moderate to practice good integrated pest management (IPM) and still get good disease control. A final report with results of disease severity and incidence for each treatment will be posted on the website for the UC Davis Department of Plant Pathology within the next two months. Copies of annual PM field trial reports going back to 2003 are currently posted at plantpathology.ucdavis.edu/cooperative_extension. —Jon Tourney 20 W in es & V i ne s O C TOB E R 20 13