Issue link: https://read.dmtmag.com/i/114539
Grapes Grape powdery mildew infection chain and fungicide timing { Preventing MILDEW Protectant Target sprays during the plant's most susceptible time: from prebloom to four weeks after fruit set. Visible symptoms Sporulation { { Infection Curative Target fungicide sprays early in the disease cycle to prevent infection. Eradicant Antisporulant KEY: Green—low infection risk Yellow—medium infection risk Red—high infection risk SOURCE: Washington State University by Melissa Hansen O nce you see a problem with powdery mildew in your vineyard, you're already too late. Washington State University extension specialists want grape growers to focus on prevention, rather than wait for symptoms to trigger their action. Most pest management programs use economic thresholds to guide action or spray decisions, but disease management programs typically don't fit the economic threshold concept, says WSU's Dr. Michelle Moyer, statewide viticulture extension specialist. The economic threshold, also called the treatment or action threshold, is a predetermined pest density/population level at which control is needed to prevent the pest from reaching an economic injury level. "Thresholds are a concept of integrated pest management," Moyer said during a statewide wine grape convention held in Kennewick, Washington, in February. "It's a point where if you have x number of mites or leafhoppers, you must take action or you'll see an economic loss. But thresholds don't exist for powdery mildew or botrytis bunch rot because disease management is usually based on prevention and is not curative or reactionary." Some pathogens are monocyclic, meaning they develop through just one generation per year, and take a long time to build up in the vineyard. Crown gall and Eutypa dieback in grapes are examples of pathogens that growers can tolerate somewhat in the vineyard because the disease can take years to reach economic injury levels. But powdery mildew and botrytis are polycyclic, developing through multiple generations during the growing season. "It's the difference between simple interest banking being monocyclic and compound interest as polycyclic," she said, adding that polycyclic diseases can multiply exponentially. "With polycyclic pathogens that build rapidly, you can't tolerate an initial level. You have to focus on preventing the disease from showing up, because by the time you see it, it's too late." "With powdery mildew, you don't spray based on what you see, but on what you're trying to prevent." Avoid the Orchard of No Return Replant disease can take the profit out of any orchard. Soil fumigation services offered by Trident manage replant disease and other soil-borne pathogens. Trident offers custom applications of Telone® C17, Telone C35, and Pic-Clor 60. • Row and broadcast applications available • Specializing in tree fruit, hops, grape, berry, and nursery crops Telone® II, Telone C-17, and Telone C-35 are registered trademarks of Dow AgroSciences LLC. Telone II, Telone C-17, Telone C-35, and Pic-Clor 60 are restricted-use pesticides. Soil Fumigation Specialists Serving the Northwest for 29 years orchardfumigation@tridentag.com NORTHWEST, WA: EASTERN WASHINGTON: EASTERN WASHINGTON: THE DALLES & HOOD RIVER, OR: 38 March 15, 2013 GOOD FRUIT GROWER Tim Purcell..........Mobile 360-630-4285 Robert Rauert ....Mobile 509-728-2004 Jason Rainer .......Mobile 509-731-5424 David Sbur ..........Mobile 971-563-8848 Window of susceptibility The grapevine follows a physiological calendar of development during the growing season. Within this calendar, there are times when the vine is more susceptible —Michelle Moyer to powdery mildew. She cited research from Cornell University that shows grape clusters are most susceptible to powdery mildew from prebloom to about four weeks after fruit set. To determine this, Cornell scientists inoculated clusters with powdery mildew in the vineyard at various stages of development and measured disease incidence at harvest. Clusters inoculated at prebloom and when the fruit was BB-sized were completely rotted by harvest. However, the later the cluster was COLD AIR DRAIN® Frost Protection COST EFFECTIVE! Most systems have a 100% payback in the first year. Minimal site prep. Fuel efficient. No maintenance contracts. POWERFUL! State-of-the-art propeller sends cold air up approximately 300 ft. VERSATILE! Size & power options available to meet your needs. Targeted protection for frost pockets, swales, slopes, valleys, etc. Use alone or with wind machines, water, or heaters. FREE COMPUTERIZED FROST ANALYSIS & PRICE QUOTE! SHuR FARMS® Frost Protection 1890 N. 8th Street, Colton, CA 92324 877.842.9688 or 909.825.2035 info@shurfarms.com www.shurfarms.com www.goodfruit.com