How to Manage Pests
UC Pest Management Guidelines
Phytophthora Root and Crown Rot
Pathogen: Phytophthora spp.
(Reviewed 8/06, updated 3/09, pesticides updated 10/15)
In this Guideline:
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.
Proper water management is the key to controlling root and crown rot. Do not allow water to accumulate or stand around crowns of trees. Provide adequate drainage or leave unplanted low spots in the orchard, areas that flood frequently, and places where water penetration is poor. Plant on berms. Once Phytophthora is present in your orchard, the pathogen will remain; eradication is impossible. Avoid introducing infected plant material, infested irrigation water, or infested soil on farm equipment into uncontaminated soil. Periods of 24 hours or more of saturated soil favor Phytophthora infections. Conversely, good soil drainage and more frequent but shorter irrigations (e.g. pulse irrigation) 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. Thus, the success of a rootstock may depend in part upon the species of Phytophthora present in the orchard. In general, MM 104 and MM 106 are more susceptible than are M 9 and M 26. Fungicides can help minimize losses.
UC IPM Pest Management Guidelines: Apple
W. D. Gubler, Plant Pathology, UC Davis
Acknowledgment for contributions to Diseases:B. L. Teviotdale, Kearney Agricultural Center, Parlier