How to Manage Pests
UC Pest Management Guidelines
Symptom expression depends upon how much of the root or crown tissues are affected and how quickly they are destroyed. Generally, crown rots advance rapidly and trees collapse and die soon after the first warm weather of spring. Leaves of such trees wilt, dry, and remain attached to the tree. Chronic infections, usually of the roots, cause reduction in growth and early senescence and leaf fall. These trees may be unthrifty for several years before succumbing to the disease. Phytophthora infections typically kill young trees because their root systems and crown areas are small compared to those of mature trees.
Periods of 24 hours or more of saturated soil favor Phytophthora infections. Conversely, good soil drainage and more frequent but shorter irrigations reduce the risk of root and crown rot. Rootstocks vary in susceptibility to the different Phytophthora species; none are resistant to all pathogenic species of the fungus, but Marianna 2624 and Myrobalan 29C rootstocks are somewhat resistant. The success of a rootstock may depend in part upon the species of Phytophthora present in the orchard.
The most effective ways to manage Phytophthora root and crown rot are to select a good planting site, select an appropriate rootstock, plant trees on a slight mound or berm to promote drainage away from the crown, and properly manage irrigation water. Avoid overirrigating in spring and fall when soil temperatures are most conducive to disease development and water use by the tree is low. Fungicides are available to treat soil around newly planted trees. Fall and/or spring foliar sprays with a phosphonate product offers suppression of Phytophthora during the critical fall, winter, and spring periods. If there is a history of Phytophthora root rot in the orchards and problems are anticipated, treatments may be warranted.
UC IPM Pest Management Guidelines: Apricot