Issue link: http://read.dmtmag.com/i/64944
Early Robin cherries fall in the high susceptibility category when it comes to cracking, according to the Washington Tree Fruit Research Commission. said. Lesser factors in cracking are the stage of closure of stomates or lenticels, which can let water into the fruit, and the loss of the fruit's nat- ural protective coating. In the last stage of cherry growth, the triterpene coating diminishes as the fruit matures. Cherry cracking is also related to fruit turgor, which typically peaks in the early morning hours and is influ- enced by irrigation amounts and frequency. "That's why it's best not to let the orchard dry out because that can encourage more cracking," Hanrahan said. "Soil moisture should be kept at a more constant level with frequent irrigations to prevent drying out." Antisplitting materials Hanrahan has tested a dozen antisplitting materials in seven varieties, four replicates each, in 40 field trials the last four years. Orchards must have at least 10 percent cracking to yield data included in the trial, which has made the trial slow going as rain doesn't occur in every location every year. "I've set up a lot of trials, but not a lot of sites get to the 10 percent cracking level, so I only have a limited amount of data and cannot tell you about every material I've tried." Thus far, the two protective coatings of SureSeal and "That's why it's best not to let the orchard dry out because that can encourage more RainGard have consistently reduced rain-induced cherry cracking in Washington State trials, she said, adding that some of the other materials tested—BlueStim (glycine betaine), calcium nitrate, and VaporGard (di-1-p-menthene)—have not had enough rain in their trials to provide meaningful data. RainGard is made from natural fatty acids and lipophilic substances, developed and patented by Washington State University's Dr. Larry Schrader. SureSeal, developed and patented by Clive Kaiser of Oregon State University, is an elastic, organic biofilm made of a hydrophobic copolymer of stearic acid, cellulose, and calcium. The coating stretches as the fruit grows, but Hanrahan stresses that good coverage, to the point of dripping, is needed. She also found dur- ing trials last year that the material is very sensitive to the spreader-sticker or adju- vant used, and was only compatible with one particular product. However, the company is working to improve the spreader-sticker issue. SureSeal, at 1 per- cent solution, was applied twice—once at four weeks before harvest and again at two weeks before harvest. In one of the RainGard trials of Tieton cherries on Gisela 6 rootstock in Pasco, rain has occurred three years in a row. RainGard reduced cracking in all three years compared with the untreated control. While she often sees some reduction in cracking from the anti-splitting materials, they have never reduced cracking by more than 50 percent compared with the untreated control. "So you need to consider the suscepti- bility to cracking of the orchard when con- sidering if it's cost effective to apply these materials," Hanrahan said. A high-yield- ing block with ten tons per acre is proba- bly worth it, but maybe not for an orchard yielding three or four tons per acre. • Cherry cracking from rain changes from year to year and even within the same season, says Ines Hanrahan who has spent the last four years testing protective materials. GOOD FRUIT GROWER MAY 15, 2012 27 cracking." — Ines Hanrahan Photos courtesy of Washington tree fruit research commission