How to Manage Pests
UC Pest Management Guidelines
Armillaria Root Rot (Oak Root Fungus)
Pathogen: Armillaria mellea
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 fungus survives within dead and living roots and as rhizomorphs
in the soil.
Avoid planting peach
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. 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. 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
Before fumigating, remove all infected trees, stumps, and as many roots
greater than 1 inch in diameter as possible. Healthy-appearing trees adjacent
to those showing symptoms are often infected also. Removal of these adjacent
trees and inclusion of that ground in the soil fumigation may be advisable.
Infected trees, stumps, and roots should be burned at the site or disposed of
in areas where flood waters cannot wash them to agricultural lands. Complete
eradication is rarely achieved, and retreatment may be necessary in localized
areas. If the soil is wet or if it has extensive clay layers to the depths
reached by the roots, fumigant treatment may not be successful. The greatest
opportunity for eradication occurs on shallow soils less than 5 feet in depth.
Fumigate from late summer to early fall.
||Amount to Use
|When choosing a pesticide,
consider information relating to environmental impact. Not all registered pesticides are listed. Always
read label of product being used.
||COMMENTS: Must be
applied under a Critical Use Exemption. For preplant fumigation. Before
fumigating, dry soil by withholding water during summer and using cover crops
such as sudangrass or safflower. The drier the soil the better for deep
penetration. Deep-till the area after drying. If the soil is dusty, wait for
an early rain before ripping and fumigation. Ripping a dry soil that is silty
can result in large clods on the surface. Inject methyl bromide 18–30
inches deep with chisels and cover with gas-proof cover. Increasing the dose
tends to increase the depth of penetration, but it cannot be relied upon to
penetrate wet soils, especially if soils are high in clay. Do not remove the
cover for at least 2 weeks and aerate 1 month before planting. Fumigants such
as methyl bromide are a source of volatile organic compounds (VOCs) but are
not reactive with other air contaminants that form ozone; methyl bromide
depletes ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
||COMMENTS: Trees must
be in the ground at least 1 year before treatment or injury may occur. See label for treatment timing.
UC IPM Pest Management Guidelines: Peach
UC ANR Publication 3454
J. E. Adaskaveg, Plant Pathology, UC Riverside
R. A. Duncan, UC Cooperative Extension Stanislaus County
J. K. Hasey, UC Cooperative Extension Sutter/Yuba counties
K. R. Day, UC Cooperative Extension Tulare County
Acknowledgment for contributions to Diseases:
W. D. Gubler, Plant Pathology, UC Davis
B. L. Teviotdale, Kearney Agricultural Center, Parlier
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