Good Fruit Grower

February 15

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T art cherry growers in Michigan got a surprise last year when European brown rot appeared in their orchards. "The extent of infection observed in some orchards was surprising on Montmorency," said Dr. George Sundin, Michigan State University tree fruit pathologist. "It will take growers two to three years of intense activity to reduce inoculum lev- els in orchards that were affected." Overwhelmingly, the U.S. tart cherry industry is dominated by the red- skinned, white-fleshed Montmorency variety. Some growers have diver- sified, adding the Euro- pean-type, dark-fleshed, less-sour Balaton variety. Montmorency is more resistant to European brown rot than is Balaton. Super-optimal conditions "Balaton was ham- mered in 2013 by Euro- pean brown rot," Sundin said. "It is not usually an issue on Montmorency, so it's likely that conditions last year were super-optimal for infection." Unlike American brown rot (Monilinia fructicola), European brown rot (M. laxa) is not a problem on the fruit—at least under Michigan conditions—but it does attack flowers and spurs. "The lack of fungal sporulation activity closer to harvest is a huge bonus for growers. In Europe, it does go to the fruit," Sundin said. "The European brown rot pathogen is very highly sensitive to environmental conditions," he said. It takes a wetting event, followed by relative humid- ity above 80 percent for more than 16 hours for infection to occur. Trees with light freeze damage may be more sensitive to infection, he said. Infection occurs more fre- quently in orchards that are surrounded by windbreak trees that result in slow drying conditions, and also in low 24 FEBRUARY 15, 2014 GOOD FRUIT GROWER Diseases & Disorders Infection starts in the flowers, then moves into shoots, which wilt and die. These dead shoots provide the source of new infection the following year. Brown rot surprises cherry growers Tart cherry growers need to watch out for European brown rot as bloom arrives. by Richard Lehnert PHOTO COURTESY OF GEORGE SUNDIN "The lack of fungal sporulation activity closer to harvest is a huge bonus for growers. In Europe, it does go to the fruit." —Dr. George Sundin

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