Good Fruit Grower

February 1

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Horticulture Adjust Honeycrisp crop EARLY Overcropping Honeycrisp will result in poorly colored, poor-storing, and poor-tasting fruit. by Geraldine Warner ecause of Honeycrisp's tendency to fruit prolifically, growers are advised to start adjusting the crop load during winter pruning. "This variety has too many flower buds in the on year," Dr. Terence Robinson told participants at a Washington State University Honeycrisp Fruit School last December. Anything that can be done to reduce the bud load will help avoid biennial bearing and improve fruit quality, he said. When the crop load is too high, the tree cannot pump enough carbohydrates into the fruit, and it will lack color and the ability to resist storage rots. "Fruit from heavily cropped Honeycrisp trees are definitely smaller, greener, and poor tasting," Robinson said. "You'd think if you left them on the tree they'd eventually get ripe, but they don't have enough resources put into them, so delaying harvest does nothing. What you get B Terence Robinson is crummy little fruit that goes into the bin without any quality. Crop load management has to start with pruning." Robinson has developed a four-step precision pruning concept: Do rough pruning, removing the largest two or three limbs from each tree, leaving the smaller-diameter fruiting wood. Estimate the number of buds. 1 2 3 Decide how many fruit you want. Five to six fruit per square centimeter of trunk cross-sectional area would be a moderate crop, and Robinson does not recommend more than eight. He has developed a plastic gauge that fits around the trunk and shows the appropriate fruit number for the tree size. It is available from Valent USA. Use detail pruning to reduce the number of spurs. In New York, where there's the risk of bud damage from spring frosts, growers might want to leave 1.5 times the target fruit number, but some people take a more aggressive approach and prune down to the actual target fruit number, he said. The closer you can prune to the actual number of fruit you want, the better the physiological response of the tree. 4 Thinning Robinson said he's found that Honeycrisp is easy to chemically thin when the trees are young and still have some vigor, and can be overthinned with MaxCel (6-benzyladenine). But the variety becomes harder to thin as the trees mature. Even after aggressively pruning to reduce the number of buds, growers might still need to apply successive chemical thinning sprays. For example, supposing the grower wants 100 fruit per tree. Robinson would recommend pruning the tree down to 150 buds, each of which have the potential to produce five flowers, making 750 potential fruit. He would then recommend a bloom thinner of ATS (ammonium thiosulfate) or lime sulfur and fish oil, with the goal of having 300 flowers remaining. A petal fall spray of NAA (naphthaleneacetic acid) plus Sevin (carbaryl) might reduce the flower number to 200. With another NAA and Sevin application when the fruit are 10 to 12 millimeters in diameter, the number could be reduced to about 120. It would then take just a little touchup hand thinning to remove the remaining 20 fruit. To promote return bloom, he recommends four summer sprays of NAA every ten days, but avoids applying it after July 10 for fear of increasing fruit drop. Robinson said some rootstocks, such as Budagovsky 9 and Geneva 41, promote return bloom. "Over the course of ten years, it's made a huge different in yields by not having off years," he said. Plan ahead Dan Griffith, horticulturist with G.S. Long Company in Yakima, Washington, emphasized the importance of planning ahead. He starts working with growers in January through March to plan their chemical thinning programs. Otherwise, he said, decisions are made too quickly in April when the grower might be sleep deprived 14 FEBRUARY 1, 2014 GOOD FRUIT GROWER

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