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How to Manage Pests

UC Pest Management Guidelines


Phytophthora Root And Crown Rot

Pathogens: Phytophthora spp.

(Reviewed 2/07, updated 2/09)

In this Guideline:


Pistachio is subject to root and crown rots and trunk and branch cankers. Trees show poor vigor; leaf yellowing, wilting, and scorching. And shoot and branch dieback. Infected roots become necrotic, with dark brown to black discoloration of the cortex and stele. Small roots eventually disintegrate. Cankers develop at the root crown, which may extend above the soil line. Infected pistachio bark turns brown to black. Active cankers often ooze and release a light cream exudate in balls, strands, or puddles. The exudate is not diagnostic because other diseases and/or injuries to the trunk will result in sap release.

Occasionally, Phytophthora spp. cause perennial cankers on trunks and scaffolds. Such cankers stop at the union of the scion and the rootstock. Such cankers often lead to tree death.


The pathogens survive in soil and can be carried in irrigation water obtained from surface sources. Prolonged periods of saturated soil are optimal for the pathogen to infect roots. Disease development is enhanced in poorly drained soils, where orchards receive long durations of flood irrigation, or in trees in lower spots or along creeks and natural drainage creeks in the orchard. Several species of Phytophthora are known to attack pistachio roots and crowns.


Fungicides are not currently registered for control of Phytopthora root and crown rot in California pistachio. Control of this disease can best be achieved using strict planting practices and water management. Plant on raised berms in well-drained soil to allow for rapid water drainage following irrigation or rains. Although the disease is not a major problem in California, growers have been loosing trees due to Phytophthora canker, although in general the Pistacia rootstocks are considered not very susceptible.


[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pistachio
UC ANR Publication 3461
T. J. Michailides, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

Statewide IPM Program, Agriculture and Natural Resources, University of California
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