Northwest berry Foundation

Management Detail

Armillaria Root Rot

in Raspberries

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Latin name: Armillaria spp.

Description:

Reason for Concern:
1) Rare in caneberries.
2) Age, Armillaria species and type of host plant, influence characteristics and severity of an Armillaria root rot infection.
3) Environmental conditions affect disease severity.

Identification/Symptoms:
The first visible disease symptom is cane decline and dieback: leaves turn yellow, wilt, and die. This may occur only on one side of the plant or in 1 or 2 canes. Groups of plants are usually infected and show symptoms, correlating with the location of inoculum in the soil. Infected main roots and crowns often have whitish to cream-colored fungus just under the bark. The mycelia are fan-shaped, about as thick as a piece of paper; and have a characteristic mushroom odor. The disease spreads through the soil by root-like structures that resemble shoestrings. In fall, Armillaria sometimes produces large, yellow-brown capped mushrooms with a ringed stem just below the cap around infected plant bases.

Disease Cycle:
The fungus spreads through soil by tiny root-like structures that kill the outer layer of blackberry roots and decay the inner layer. The fungus survives on woody host roots long after the host dies. When infected plants are removed, infected roots that remain below ground serve as an inoculum for future plantings. Infection occurs when berry roots directly contact partially decayed tree roots. Infection can also occur when roots contact the tiny root-like structures that grow out from partially decayed roots and through soil. Once roots and crowns are infected, whether living or dead, they serve as a source of inoculum for neighboring blackberries. The fungus is native and can be found on newly cleared land that had a previous native plant host or on land that was formerly in orchard production.

Links:

Scouting:

  • Cane dieback and wilting are common.
  • Mycelial fans can be observed beneath the bark of the root crown of infected plants.
  • Dig down about a foot below the soil line and use a pocketknife to remove thin layers of bark from the root collar.
  • Mycelial fans are thick, white layers of fungus that adhere to the root bark and/or the wood beneath the bark.
  • Look for mushrooms around the base of the plant in the fall. While this can help in detecting an infection, it is not a reliable diagnostic tool because many fungi produce similar fruiting bodies. (should this be part of another bullet?)
  • An assessment of plant health should be made in conjunction with the diagnosis of Armillaria root rot because the pathogen often infects plants that have been weakened by stress or other agents.

 
Cultural Controls:

  • Infected plants and native vegetation should be removed and destroyed. Be certain to remove all roots pencil size or larger from the soil.
  • Use caution with sawdust mulches. They can be a source of innoculum.
  • Avoid movement of soil to reduce the spread.

 

For information about chemical controls, check with our Pesticide Guide.

images


Mushrooms at base of canes - photo by T. Peerbolt


Mushrooms at base of canes - photo by T. Peerbolt


Mushrooms at base of canes - photo by T. Peerbolt


Typical mushroom and hyphae of armillaria - photo by T. Peerbolt


photo by T. Peerbolt


photo by T. Peerbolt

 

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Northwest Berry Foundation

Northwest Berry Foundation

© 2016

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