Good Fruit Grower

May 15

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10 MAY 15, 2016 Good Fruit Grower W hen it comes to dwarfi ng and preco- cious rootstocks, the greatest impact on commercial production has come in the apple industry, with research to develop new cultivars going back nearly 40 years in the United States. For sweet cherries, interest — and current cultivars like Gisela and Krymsk — came later, though growers continue to seek root- stocks that will produce high volumes of high-quality fruit on labor-friendly dwarfi ng trees. Michigan State University's cherry rootstock program has been working to improve effi ciency and reliability of such fi nished tree propagation, while aiming to improve virus sensitivity, among other things. The project is see- ing some results, and it's growing in planted plots and data, with additional plantings planned in the Pacifi c Northwest. MSU is pursuing patents for these cherry rootstocks, as several West Coast nurseries have plant material ready for propagation. Meanwhile, researchers are examining how each rootstock performs with different cultivars and in different training systems, soils and growing con- ditions. Five rootstocks are of key interest — Crawford, Lake, Clinton, Cass and Clare, all named after Michigan counties. The project, led by MSU researcher Dr. Amy Iezzoni, has the support of the Washington Tree Fruit Research Commission, the Oregon Sweet Cherry Commission and the Michigan Cherry Committee, which also has pro- vided support to develop Armillaria resistant rootstocks as part of her work. Iezzoni visited the Pacifi c Northwest in April to exam- ine the plots in Wenatchee and Mattawa, Washington, and The Dalles, Oregon, and gather data with cooperat- ing researchers. Following a six-year trial at Washington State University in Prosser, Washington, additional trials were planted in 2015. Four of the rootstocks are in their second leaf, with the fi fth, Crawford, planned for planting next spring. Scions are Regina, Early Robin and Sweetheart. Control rootstocks, which varied by site, were Gisela 5 and 6 and Krymsk 5 and 6. Washington sites At McDougall and Sons' Legacy Orchard east of Wenatchee, Washington, the training system is a super slender axe in an angle canopy trellis, with 12 feet between rows. Spacing between trees varies by rootstock — 2 feet for Clinton, 1 foot for Cass, Lake and Clare — with a range of 1,800 to 3,600 trees per acre. The result is the large rootstocks are 4 feet apart under each arm of the trellis, and the more dwarfi ng are 2 feet apart under each arm of the trellis. The orchard has drip irrigation with fertigation. The trees' outer bark was girdled at 10- to 12-inch intervals and some individual buds notched just above the buds by Dr. Stefano Musacchi, Washington State University pomologist. Following the gentle girdling, there were four Promalin (benzyladenine and gibberellic acid) treatments timed to precede warm weather (over 70 degrees Fahrenheit). Iezzoni noted the impressive bud breaks that were occurring as a result of the girdling and Promalin treatments. The target was for trees to be hitting the top trellis wire, around 11 feet from ground level, by the second leaf, Musacchi said, and that was happening almost Cherries Michigan State pursues patents for improved cherry rootstocks using plantings in the Pacifi c Northwest. by Shannon Dininny "It's wonderful to see them growing with such vigor." —Amy Iezzoni Breeding better rootstocks

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