Armillaria Root and Butt Rot (Armillaria mellea)

From: Ostry, Michael E.; Wilson, Louis F.; McNabb, Harold S., Jr.; Moore, Lincoln M. 1988. A guide to insect, disease, and animal pests of poplars. Agric. Handb. 677. Washington, DC: U.S. Department of Agriculture. 118 p.

Importance- Armillaria causes a root and butt rot of poplars. This root disease may be more damaging under intensive management systems than in natural stands. Repeated harvests and vegetative reproduction from stumps may increase disease incidence and severity.

Look For: White mycelium under the bark of infected trees. Strands of dark brown to black fungus mycelium (rhizomorphs) resembling shoestrings, around infected roots, under the bark of infected trees, or in decayed wood. Honey-colored, gilled mushrooms at the base of infected trees for a few weeks in early fall. These mushrooms will then turn black and shrivel, persisting for several months.
Diseased Root	Mushroom Stage.

Biology- Armillaria overwinters as rhizomorphs or vegetative mycellium in infected live and dead trees. Armillaria root rot is usually associated with weakened trees. The fungus can spread from one tree to another by rhizomorphs that grow through the soil until they contact and infect a root of another tree. Mycelium of the fungus then spreads through the root system of that tree, causing root rot and eventually butt rot.

Monitoring- Examine dead and dying trees of stumps for Armillaria. This is especially important in nursery stool beds and coppiced plantations.

Control: Maintain high tree vigor by minimizing tree stress caused by other biotic agents as well as noninfectious diseases. Minimize the number of infected live and dead trees in new plantings by removing as much of the old root system as possible to reduce inoculum in the soil.
Butt Rot.	Rhizomorphs.

For Additional Information:

Prey, Allen; Robbins, Kathryn. 1979. Armillaria root and butt rot. Pest Alert NA-FB/U-6. Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Area State & Private Forestry. 1p.

Stanosz, G.R.; Patton, R.F. 1987. Armillaria root rot in aspen stands after repeated short rotations. Canadian Journal of Forest Research. 17:1001-1005.