   Thinning Deciduous Fruit Crops - May 18, 2016 Jeff Schalau, Agent, Agriculture & Natural Resources University of Arizona Cooperative Extension, Yavapai County Many fruit trees across Yavapai County have set a fruit crop this spring – that’s great news for backyard orchardists. However, deciduous fruit trees often set more fruit than they can support to full ripeness. Excessive fruit crops compete for available carbohydrates (stored energy) and this can result in smaller fruit. Excess fruit can also weaken the tree and make it more susceptible to pests, diseases, limb breakage, and leads to alternate bearing (a cycle where the tree bears excessively one year and little or none the next year). Thinning fruit is the intentional removal of developing fruits and aids in the prevention of the above listed problems. Thinning immature fruit at the proper time allows each remaining fruit to grow larger without reducing tree vigor. In addition, remaining fruit will receive more sunlight improving fruit color and flavor at harvest time. Proper pruning also keeps trees smaller requiring less labor and ladder climbing during thinning. Some fruit species will drop developing fruits naturally in what is known as the “June drop”. Species that do not typically require manual fruit thinning are cherries, figs, persimmons, pomegranates, citrus, and many nut trees. Peaches, nectarines, plums, apricots, apples, and pears should be manually thinned before the June drop to ensure a high quality crop and avoid the problems listed above. Timing of thinning varies with growing season and time of fruit ripening. In general, stone fruits (peaches, nectarines, plums, and apricots) should be thinned when they are ¾ to 1 inch in diameter and pome fruits (apples and pears) should be thinned when they are between ½ to 1 inches in diameter. Thinning too early can result in split pits in stone fruits and thinning too late reduces the likelihood of remaining fruit will increase in size. The amount of fruit to thin is dependent on species and the overall amount of fruit on the tree. Apricots and plums are relatively small and should be thinned to 2 to 4 inches on each branch. Peaches and nectarines should be thinned to 3 to 5 inches. If the pollination was ideal, fruit set will be excessive and additional thinning will be required. Conversely, if the fruit set was light, but the fruit set was heavy on a few branches, then less thinning is required because the branches without fruit are contributing carbohydrates to the overall crop. There are two methods of fruit thinning: by hand or by pole. Hand thinning is more thorough and accurate than pole thinning, but is slower and more labor intensive. Hand thinning allows the orchardist to leave fruit sufficient space so they don’t touch at maturity. If a long branch has a heavy crop, thin more heavily, especially near the terminal end. Remove doubles (two fruits fused together) and small or damaged fruit. Pole thinning is used on large trees and uses a long a pole to touch flower clusters and remove a portion of the fruit. A rubber hose or other soft material is attached to the pole end to reduce scarring of branches and harm to desired fruit. With experience you can learn to strike a fruit cluster once or twice – just enough to properly thin the cluster. While thinning your orchard, you can also monitor for pests, disease, and abiotic (environmental) stress such as sunscald. Remember to fertilize your fruit trees during the growing season. Nitrogen is the only nutrient necessary to apply unless other deficiency symptoms are present. The first application should occur just after the leaves have emerged (now if you have not done it yet). The second application should be in mid-July and the third and final application in mid-September. The University of Arizona Cooperative Extension publication Backyard Fruit Production at 3,500 to 6,000 Feet is linked with the online edition (see URL below) and contains fertilizer recommendations for deciduous fruit trees and contains example calculations. I recommend applying ½ of the yearly total in spring and ¼ of the yearly total during subsequent fertilizations. Backyard Fruit Production at 3,500 to 6,000 Feet and an Excel spreadsheet to assist with fertilizer calculations are both linked below. Follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call the Master Gardener help line in the Camp Verde office at 928-554-8992 or e-mail us at verdevalleymg@gmail.com and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. Additional Resources Backyard Fruit Production at 3,500 to 6,000 Feet University of Arizona Cooperative Extension, revised 2015. extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1162-2015.pdf Fruit Trees: Thinning Young Fruit by C. Ingels, P.M. Geisel, C.L. Unruh, and P.M. Lawson. 2001. University of California Agriculture and Natural Resources Publication 8047. 2001. homeorchard.ucdavis.edu/8047.pdf Deciduous Fruit Tree Fertilization Calulator by J. Schalau, 2012. decidfruittreefertcalc.xls  |