Armillaria Root Rot
Hosts, Symptoms & Signs
- aboveground symptoms: over time the foliage turns yellow, thins and branches die back; eventually the tree dies
- below ground, the roots are rotting leading to the above ground symptoms; infected conifers may exude resin at the base of the tree
Three signs to look for to diagnose Armillaria:
- the mycelial fan under the bark that can be seen when the bark of a dead tree is peeled back
- rhizomorphs on the roots and under the bark (rhizomorphs are thick strands of hyphae that are dark brown; they can look like shoelaces)
- mushroom clusters at the base of the tree in late summer and fall
- Armillaria fungus is soilborne
- colonizes the roots and causes root rot
- rhizomorphs can grow through the soil from one tree root to neighboring tree roots, infecting neighboring trees
- once the tree is dead, Armillaria can survive on dead roots and other wood for decades in the soil until a new host plant is found
- Armillaria can be a problem in areas where woodlands used to be
- Keep trees vigorous and avoid excessive moisture.
- Remove affected trees and remove as much of the roots as possible (roots can extend several feet away from the trunk).
- If Armillaria has been a problem in the past, plant resistant trees.