How to Manage Pests
UC Pest Management Guidelines
Armillaria Root Rot (Oak Root Fungus)
Pathogen: Armillaria mellea
(Reviewed 6/10, updated 6/10, pesticides updated 9/15)
In this Guideline:
Roots infected with Armillaria mellea have white to yellowish, fan-shaped mycelial mats between the bark and the wood. Dark brown to black rhizomorphs sometimes can be seen on the root surface. All stone fruit rootstocks are susceptible sometimes to Armillaria root rot. The plum rootstock Marianna 2624 has some tolerance and may be useful in some situations.
The fungus survives within dead and living roots and as rhizomorphs in the soil.
Avoid planting nectarine orchards where forest or oak woodland has recently been cleared or where there is a history of Armillaria root rot. All rootstocks can be attacked by Armillaria mellea but some are less affected than others. Maintain the vigor of the trees to help resist Armillaria attack. Infested sites can be fumigated, but often this procedure will not prevent recurrence of the disease.Physical barriers to contain infection centers have been used successfully in orchards. Four-foot trenches are dug around the infection center and plastic tarp is laid inside the trench wall from bottom to top before the soil is replaced. The tarp prevents healthy roots from coming in contact with diseased ones, thus preventing spread of the disease.
Research on other tree crops has indicated that exposing an infected crown and upper root area of a tree infected with Armillaria mellea may help to slow the development of the fungus into the crown area. In spring, remove soil from around the base of the tree to a depth of 9 to 12 inches. Leave the trunk exposed for the remainder of the growing season. During the spring, summer, and fall, keep the upper roots and crown area as dry as possible. During winter, provide drainage if necessary so that rain doesn't collect in the hole. Recheck the hole every few years to make sure it has not filled in with leaves, soil, and other matter; the hole must be kept open and the crown and upper roots exposed.
Organically Acceptable Methods
Cultural controls are acceptable for use in an organically certified crop.
UC IPM Pest Management Guidelines: Nectarine
J. E. Adaskaveg, Plant Pathology, UC Riverside
Acknowledgment for contributions to Diseases:B. L. Teviotdale, Kearney Agricultural Center, Parlier
W. D. Gubler, Plant Pathology, UC Davis