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How to Manage Pests

UC Pest Management Guidelines


White mycelial mats are evident at or below ground in trees infected with Armillaria.

Pistachio

Armillaria Root Rot (Oak Root Fungus)

Pathogen: Armillaria mellea

(Reviewed 2/07, updated 2/09)

In this Guideline:


SYMPTOMS AND SIGNS

Roots infected with Armillaria mellea have white to yellowish fan-shaped mycelial mats between the bark and the wood. Dark brown to black rhizomorphs can sometimes be seen on the root surface. Although pistachio is susceptible to Armillaria root rot, the disease is infrequently reported. The relative susceptibility of pistachio rootstocks is unknown.

COMMENTS ON THE DISEASE

The fungus survives on dead roots.

MANAGEMENT

Armillaria root rot is only occasionally a problem in pistachio orchards. Management of this disease can be difficult and resistant rootstock may offer the best protection. Research indicates that Pistacia terebinthus and P. atlantica x P. integerrima hybrids are tolerant but P. atlantica and P. integerrima are susceptible. However, because pathogenicity and virulence in the natural population of the pathogen ranges from weak to severe, disease response may vary with different combinations of rootstocks and pathogen. Exposing an infected crown may help individual trees with the disease.

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pistachio
UC ANR Publication 3461
Diseases
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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