How to Manage Pests

UC Pest Management Guidelines

Grape

Armillaria Root Rot (Oak Root Fungus)

Pathogen: Armillaria mellea

(Reviewed 6/06, updated 2/14)

In this Guideline:


SYMPTOMS

Vines infected with Armillaria root rot become nonproductive and often die within 2to 4 years. Adjacent vines may develop weak, shorter shoots as they are infected by the pathogen. White mycelial mats can be found under the bark at the soil line. Dark, rootlike structures (rhizomorphs) may be seen growing in the soil near infested grapevine roots.

COMMENTS ON THE DISEASE

The fungus survives on diseased wood and roots below ground for many years. Healthy plant roots can become infected when they come in contact with inoculum, including rhizomorphs, from a preceding orchard crop or nearby oak trees. Flood waters sometimes spread infected roots in a vineyard. The fungus is favored by soil that is continually damp. Although the pathogen produces mushrooms, they are not considered significant in disease spread.

MANAGEMENT

Because there are no known Armillaria-tolerant grape rootstocks, preplant chemical fumigation of the soil is the only control for oak root fungus. Treatment is best undertaken in September to November when the soil is still dry. Several preparatory steps are involved:

Before planting or replanting in affected soil, remove, pile, and burn all diseased vines, tree stumps, and roots greater than 1.5 inch in diameter.

In treating portions of an existing vineyard, healthy appearing vines adjacent to those showing symptoms are often also infected and should be removed. If removed, include the area in the fumigation treatment.

Before fumigation with methyl bromide or sodium tetrathiocarbonate, dry out the soil as much as possible. The drier the soil, the deeper the chemical will penetrate and the more effective the treatment will be. Do this by withholding water during summer and by using cover crops (such as sudangrass or safflower) to further deplete soil moisture. Finally, deep-till the dried area, being careful not to spread any diseased roots.

Common name Amount per acre** R.E.I.‡
(example trade name)   (hours)

  Calculate impact of pesticide on air quality
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A. METHYL BROMIDE* Label rates See label
  COMMENTS: Preplant treatment. May only be used under a Critical Use Exemption. 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.
 
B. METAM SODIUM*
  (Vapam, etc.) Label rates See label
  COMMENTS: Apply in winter when soil moisture is high. Fumigants such as metam sodium are a source of volatile organic compounds (VOCs) but are minimally reactive with other air contaminants that form ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
 
** Apply with enough water to provide complete coverage.
* Permit required from county agricultural commissioner for purchase or use.
Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448

Diseases

W. D. Gubler, Plant Pathology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma County
L. G. Varela, UC IPM Program, Sonoma County
S. Vasquez, UC Cooperative Extension, Fresno County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Research Center, Parlier
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
Acknowledgment for contributions to Diseases:
G. M. Leavitt, UC Cooperative Extension, Madera County

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