Good Fruit Grower

March 15

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T he team of researchers who developed the pollen tube growth model for thinning apples at blossom time is led by plant pathologist Dr. Keith Yoder, horticulturist Dr. Gregory Peck, and research specialist Leon Combs, supported by research specialists and graduate students who work with plant growth regulators. The team at Virginia Tech spent a decade develop- ing the model. They have worked with apple growers in Washington State and are now working to utilize the models for eastern growers, who face greater challenges as they try to grow apples organically in a humid climate. "The pollen tube growth model can be used to improve bloom thinning application timing in the East as well as the West," they say. "Hopefully, with fi ne-tun- ing of rates and optimal timing and other approaches, more thinning can be achieved with minimal fruit rus- setting." Yoder and Peck are familiar speakers at various venues as they explain the thinning model they devel- oped and why they like it. Last year, both spoke at the International Fruit Tree Association meeting in Boston, and they spoke at the Mid- Atlantic Fruit and Vegetable Convention in January. Yoder and Peck would like to see organic apple pro- duction grow and prosper—in the East as well as the West—and thinning is a major problem for organic growers whose only chemical thinning method is fi sh oil and liquid lime sulfur applied during bloom. The Virginia Tech scientists decided to build on that and develop a thinning program that would work for all apple growers—organic and conventional. "In apple production, crop thinning during bloom produces the largest fruit, the greatest return bloom in the following year, and reduces biennial bearing," Peck said. "Ideally, growers would allow set of the king bloom, then apply bloom thinner and prevent further set of later blossoms." Application timing is important. For a fl ower to be fer- tilized, a live pollen grain must extend a pollen tube about 8 millimeters to the ovule, and it takes about 48 hours 20 MARCH 15, 2014 GOOD FRUIT GROWER Crop Management Honey Lite Nectarine Royal Lynn Cherry Kylese-Cot Aprium® Dave Wilson Nursery (209) 874-1821 Fax 874-1920 Toll Free 800-654-5854 Far mer Proven ™ Since 1938 POLLEN TUBE growth model makes blossom-time apple thinning MORE PRECISE Golden Delicious pollen tube growth As pollen tubes elongated, thinning treatments were applied April 3 after king bloom set, to prevent further pollination, and April 5 to prevent TSPPMREXMSRSJRI[P]STIRMRK¾S[IVW SOURCE: Greg Peck and Keith Yoder. Data gathered at Virginia Tech's research center in Winchester, Virginia. 100 90 80 70 60 50 40 30 20 10 0 10 9 8 7 6 5 4 3 2 1 0 Hourly temperature (F) Cumulative hourly growth Temperature (F) Hourly cumulative growth March 29 March 30 March 31 April 1 April 2 April 3 April 4 April 5 Average style length Thinning model explored for eastern growers. by Richard Lehnert

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