Culprit: Armillaria mellea (A generic catch all for many varieties of Armillaria)

Armillaria is a common soil inhabiting fungus, commonly affecting Quercus, Prunus, Malus, Acer and Pinus. (Not limiting lists there are other genus’s also affected).
Common occurrence of Armillaria can be found throughout hardwood and coniferous forests. It spreads by a series of brownish – black string like rhizomorphs, which can actually travel quite a distance from the host plant. Evidence of infection is similar to other root troubles; loss of vigor, premature fall leaf coloration, dieback and even complete failure.

White mycelial fans grow below the bark in the cambial zone at the base of the trunk and in the larger roots, the fruiting body of Armillaria is a tanish, honey colored mushroom growing in colonies on decayed wood as well as live trees.

Due to its wide spreading nature and profusion in the landscape young trees planted in an area know to have hosted Armillaria will most likely be a candidate to host this fungal party. There is no chemical control for Armillaria therefore control is limited. By removing all wood in the landscape affected by the fungus, including roots and stumps, as well a selecting varieties of ornamental trees and shrubs that show resistance to the fungus will help in limiting the spread of this fungus to other plants.

 

Armillaria mellea – Mycelial Fan

 

Armillaria mellea – Rhizomorphs