Agriculture: Cherry Pest Management Guidelines

Armillaria Root Rot (Oak Root Fungus)

  • Armillaria mellea
  • 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 sometimes can be seen on the root surface. All stone fruit rootstocks are susceptible to Armillaria root rot.

    Comments on the Disease

    The fungus survives on dead roots.

    Management

    Generally, once a cherry tree trunk becomes infected with Armillaria mellea, it cannot be saved and should be removed.

    Preparation and Timing for Treatment

    Before planting or replanting an orchard site, 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 re-treatment 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. Treat Armillaria from late summer to early fall.

    Common name Amount per acre REI‡ PHI‡
    (Example trade name) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.
     
    PREPLANT
     
    A. METHYL BROMIDE* Label rates See label NA
      COMMENTS: For preplant fumigation. Use allowed under List of Approved Critical Uses. 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 to 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.
     
    B. METAM SODIUM*
      (Vapam, etc.) Label rates 48 NA
      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.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
    * Permit required from county agricultural commissioner for purchase or use.
    NA Not applicable.
    Text Updated: 09/15
    Treatment Table Updated: 09/15