Good Fruit Grower

May 15

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Cherries SPLITTING S Preventing everal years of field trials have yet to find a sure-fire material that completely prevents cherries from cracking after rain. But a few antisplitting materials do help reduce the amount of cracking and are worth applying, especially if the blocks are high-yielding with expected high returns, says a Washington Tree Fruit Research Commission scientist. As cherry harvest nears, nothing gets the adrenaline going for a cherry grower quite like a forecast of rain. A year's worth of effort can be quickly diminished if rain comes at the wrong time, causing fruit to split and crack. In some years, cracking incidence can be high in an orchard, while other years, fruit in the same orchard escapes major problems. Rain-induced cherry cracking is a complex combination of factors that Protective materials might be worth applying in high-yielding cherry blocks, says a Washington State scientist. by Melissa Hansen are constantly interacting with each other and changing within the orchard, said Dr. Ines Hanrahan, project manager for the Research Com- mission. Genetic factors involve the cracking susceptibility of cherry cul- tivars; physiological factors, like tree age, use of plant growth regulators, and frequency and amount of irrigation; morphological factors include stage of fruit development, skin thickness, and chemical composition of wax; and environmental factors include frequency and amount of rain, temperature, humidity, and such. Causes of cracking "We know that cherries have a double sigmoidal growth curve and that most growth occurs in the last few weeks before harvest," Hanrahan said during a session of the Northwest Cherry Institute's annual meeting held in Yakima, Washington. "That's also when cracking suscepti- bility develops—in the last growth stage, and it peaks at harvest." However, her research shows that there are sev- eral different patterns present in cherry varieties grown in the Pacific Northwest, such as: a) fruit of the same variety can become highly susceptible four weeks before harvest, or b) they may never reach high cracking potentials. "The incidence or amount of cracking varies tremendously and depends on hundreds of factors," she said. Her research shows that crack- ing susceptibility within an orchard doesn't necessarily increase in a linear fashion as the fruit matures. Cracking susceptibility varies from block to block, by variety, year to year, and within the season. Scientists around the world have studied how water enters the cherry to cause the splitting, with inconclusive results. Her work has looked at water uptake throughout the fruit development process, and she hasn't observed changes in water uptake rates per unit of surface area as the fruit matures. Instead, she's found a relatively consistent rate of uptake through fruit development. "Most believe that the majority of water uptake happens by diffusion of osmosis through the cherry fruit skin," she noted. "However, based on data obtained last year, we have reason to believe that the main route of uptake is indeed the pedicel/fruit juncture," she SureSeal, a new protective coating, at right, patented by Oregon State University that stretches as the fruit grows, needs complete fruit coverage—to the point of dripping off fruit—to be effective. 26 MAY 15, 2012 GOOD FRUIT GROWER

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