Good Fruit Grower

July 1

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"The greater the severity of sunburn at harvest, the higher the incidence of delayed sunburn in storage," she said. She noted that delayed sunburn has not been effec- tively controlled or minimized with cold-storage inter- ventions like SmartFresh (1-methylcyclopropene), DPA (diphenylamine), controlled atmosphere regimes, or temperature. It is sometimes confused with similar-look- ing storage disorders, such as superficial scald that's not very pronounced and DPA burn. Why do we care, she asks? "The f.o.b. price for bright, green Granny Smith is around $30 per box compared to $18 per box for yellow Granny Smith. If you have a lot of this type of fruit in the bin at harvest already, I can guarantee you it will not be better after several months in storage. It'll have only gotten worse. That's why we care." Granny Smith is an important variety in Washington State, ranking fourth in the varieties grown in Washing- ton State. Production has been around 12 to 14 million boxes annually the last seven years, and the variety still enjoys relatively good returns. But the crop is not moved all at once, Hanrahan says. Typically, only about a third of the Granny Smiths in stor- age are shipped by January 1, according to data from the Washington Growers Clearing House Association. "That means that every day fruit are kept longer in storage, the clock is ticking and quality can be diminishing." Prevention Hanrahan used both shade cloth, a practice being tried in Australia to prevent sunburn, and sunburn pro- tectants (Eclipse and Raynox) to reduce sunburn in the field. The shade cloth trial, though small, provided inter- esting results that warrant further study. The shade cloth provided 99 percent protection from sunburn. However, although fruit size was the same in both the shade cloth treatment and the control, titratable acidity was lower, and soluble solids slightly less. "You do have physiological effects from the netting," she said, adding that a small amount of bleaching or white areas were observed on fruit. Prevention of delayed sunburn requires an integrated approach that involves: • adequate canopy density (holes in canopy can lead to sunburn, especially in a V-trellis system) • fruit position • careful thinning (removing outer exposed fruit often creates a new cull fruit underneath) • row orientation • protective measures (hydrocooling, shade cloth, protective chemicals) • good coverage of protective chemicals • monitoring fruit during season Growers using a V-trellis should ensure that protective chemicals are reaching their target. In some of her trials, she's found that nozzles needed adjustment in V-trellis applications because the upper half of the canopy was not getting adequate coverage. In a V-trellis trial, sunburn incidence in the upper half of the V-trellis was 46 and 47 percent with protective chemicals applied, but was only 11 and 6 percent in the middle half of the canopy. "It wasn't an efficacy problem, but a problem in getting good coverage," she said. Sunburn begins to show by the end of July or early August. "If you look for sunburn at this time, you can still influence the final outcome," she said, encouraging grow- ers to monitor their orchards for sunburn. "By looking at your fruit, you can see if you got your coverage right or not. And you still have time to make a change if need be." But it takes more than walking down the orchard rows when monitoring for sunburn. Hanrahan suggests that growers need to pick fruit off the tree from susceptible locations and compare samples to clean fruit because it's very hard to discern yellowed fruit on the tree. "You can never see the sunburn if you try to just look at fruit on the tree." • 18 JULY 2012 GOOD FRUIT GROWER www.goodfruit.com

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