[Illustration: Fomes annosus fruiting bodies on stump.]
Annosus root and butt rot is caused by the fungus _Fomes annosus_. This
pathogen is common throughout coniferous stands of the North Temperate
Zone. Hardwoods may be attacked, but damage is usually of minor
consequence. In the South, the disease is most serious in pine
plantations on sandy soils with low organic matter. All species of
southern pine are susceptible. Slash and loblolly plantations are often
severely affected.
The disease gains entry into plantations by spore infection of freshly
cut stumps during thinnings. The fungus then spreads from the infected
stumps to residual trees by growth along the roots to points of root
contact. Residual trees usually begin to die within a few years after
thinning. The sporophores or fruiting bodies are generally found at
ground line or in the root crotch. Pines in initial stages of the
disease usually exhibit sparsely foliated crowns; however, white pine
with full crown may have extensive butt and root decay. Occasionally
trees may die rapidly with a sudden red discoloration of a nearly full
crown. Diseased trees are often found in groups or circular pockets in
the stand. The indication of _F. annosus_ decay may include the pink to
violet stain of incipient decay, the narrow elongated white pockets and
scattered black flecks in the wood of the early decay stages, and the
yellow stringy rot of the late stages of decay.
[Illustration: Infection center in pulpwood size pine stand.]
Control includes avoidance of planting on soils of low organic matter
and elimination of thinning. Stump infection following thinning or
harvest may be prevented using various methods.