Soon it will be time to thin excess fruit on fruit trees, according to my fruit tree guru, Michael Janik. He writes, “Thinning is an essential step in producing larger, tastier fruit and will also help prevent damage from insects.”
Of the common fruits, only cherries don’t need thinning. Ideally, thin when the fruit is 1/4-3/4 inch in diameter. After the fruit is an inch in diameter, it’s too late to improve fruit quality.
Michael pointed out a technique for thinning: “First lightly run your fingers over the fruit; a good number of the fruits will fall off as some fruits weren’t completely fertilized or the tree is selectively pruning itself. Then, remove any damaged/deformed fruits.”
Apples and pears form in clusters. Leave the largest fruit of the cluster and remove the others. There are guidelines for the distance left between fruit: http://homeorchard.ucdavis.edu/8047.pdf.
Another important topic Michael covered in his recent newsletter was pests, both insects and diseases.
Many fruit tree pests are common in spring and summer. Aphids, including wooly apple aphids, are likely. Root weevils, so called because their larvae live in the roots of plants, will chew pinking shear-like edges on leaves. Pear or cherry slugs, which are the larvae of sawflies, will rasp the tissue off leaves creating a lacy appearance. Michael calls codling moths “the most damaging pest of apples and pears.” The moths are the parents of the worms (caterpillars) that invade apples and pears. For detailed information on codling moth, go to http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7412.html or http://utahpests.usu.edu/ipm/htm/fruits/fruit-insect-disease/codling-moths06.
Apples and pears are susceptible to a bacterial disease called fire blight. The signs of this disease are a watery, light tan ooze that comes out of small to large areas of dead bark and then turns into dark streaks on branches or trunks. Flowers, shoots and/or young fruit can shrivel and blacken. Infected flowers and flower stems wilt and turn black on pear trees and brown on apple trees.
If you prune any of this damage, disinfect all tools with isopropyl alcohol or Lysol to avoid spreading this highly infectious, damaging disease from limb to limb or tree to tree.
For information on managing fire blight, see my publication: http://www.unce.unr.edu/publications/files/ho/2001/fs0156.pdf.
Powdery mildew, a common fungal disease, can infect growth tips of limbs with a dull gray coating. Prune off the infected portion back to a branch or bud, dispose of the affected sprouts, and spray a disinfectant on pruning tools after use.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.