Latin name: Armillaria spp.
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.
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.
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.