Good Fruit Grower

July 2016

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18 JULY 2016 Good Fruit Grower M ummy berry is a disease that suits its name, turning plump blueberries into white, wrinkled berries that fall to the ground and serve as a winter home for the causal pathogen. In early spring, those mummy berries develop into small mushrooms, called apothecia, which release spores to be spread by wind to infect healthy plants. It's one of the most signifi cant diseases of highbush blueberries in the Northwest. There are management options available for both conventional and organic growers, but they have been unable to consistently control the disease. In Oregon, commercial losses can range from 33 percent to 85 percent, with organic losses routinely reaching near 100 percent of the crop. Researchers are working to help blueberry growers forecast for and better recognize the signs and symptoms of mummy berry. Those efforts include a particularly novel idea that, if successful, could carry over to help growers recognize other pests and diseases. Knowing when to spray Understanding the cycle of the disease is key, researchers say. Mummy berry has two stages of infection. Primary infections occur when spores infect emerging leaf and fl ower buds in the spring. These "strikes" fi rst appear as dark brown discoloration of leaves. Secondary infections occur when spores infect the fl owers and fruit from within, which causes the wrinkled, pumpkin-shaped berries that give the disease its name. Researchers at Washington State University are targeting the fi rst phase of infection in hopes that by improving the timing of fungicide applications, growers can better control subsequent disease development in the fi eld. "Right now, growers are starting applications around bud break, and then continuing on a calendar schedule," said Dalphy Harteveld, a postdoctoral research associate at WSU's Northwestern Washington Research and Extension Center in Mount Vernon, Washington. "We'd like to refi ne that process, to use fungicides only when they're needed and actually reduce the amount of fungicide that's used to control the disease." Specifically, Harteveld is working to develop a model that identifi es the weather factors that control spore release. With two years of data already gathered, Harteveld plans to collect data again this year to build the model and begin testing it next year. "In the mummy berry cycle, there are specific susceptible phases when fl ower clusters and leaf clusters get infected. Initially, I thought that would be about the same time for each, but that's not the case," she said. "The timing of the development of these two features may actually affect whether disease develops in those plants." There's a window of time in which the mushrooms produce the spores — about 10 days, maybe two weeks if the conditions are right. But the mushrooms don't all come up at the same time, so over the spring, growers could have a month or fi ve weeks that spores are coming up and being dispersed. However, fewer spores are dispersed at the beginning and end of that window, and because different blueberry Summer Fruits Researchers aim to improve control for blueberry disease. by Shannon Dininny courtesy Jay Pscheidt Researchers are working to help blueberry growers forecast for and better recognize the signs and symptoms of mummy berry, as seen in top photo. Here, infected green berries show no symptoms unless they are cut open. The fungus begins to fi ll the carpels of the infected berry on the left while seeds form in the healthy berry on the right. Managing mummy berry courtesy daLPhy harteVeLd

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