Annosum root rot has caused
significant losses of volume in managed southern pine stands on high hazard soils and eastern white pine in the mountains. Mortality and growth losses range from 2% to 25% of volume in managed high risk stands across the
South. In recreation sites where pine is a major component, damage by annosum root rot has resulted in hazard trees that threaten people and property. Orchard managers routinely use stump treatments to prevent loss of
Annosum root rot rarely becomes a problem in un-managed pine stands. When the disease is found in an un-managed stand, it is often associated with weakened or damaged
trees. The fungus colonizes living and freshly dead wood, persisting until the wood is completely decayed. The fungus does not replace other decay organisms in the wood. The relatively fast decay of
wood by other organisms in the South is why the disease stabilizes after 10 years and is not a big problem in regenerated pine stands. When forest mangers partially cut pine stands, they significantly increase the
probability of infection by the fungus. Thinning a pine stand on a high hazard soil increases the chance of severe loss from 75 to 85 percent. The risk decreases to 30 to 40 percent probability on moderate hazard
soils. Thinned stands on low hazard soils have a 10 to 20 percent probability of severe loss.
Southern pine plantations and natural stands that are located on low hazard
soil, and are free from annosum root rot, do not need to be managed for the disease. Stands located on medium to high hazard sites and stands of eastern white pine should be managed for the disease. All high value
stands, including orchards, seed production, and recreation areas, also need to be managed for annosum root rot.
Stump treatment is the primary method to control annosum root rot in a partially cut stand. The
only stump treatment currently available to managers is borax. Borax is used to prevent infection and must be applied to the stump surface immediately after the tree is cut. Once annosum root rot is established in a
stand, borax may not be a suitable treatment. Foresters will need to consult with a plant pathologist to determine the appropriate management response for infected stands.
Stump treatment is not necessary if a
stand is clearcut. Management strategies to reduce future infections of new stands include: (1) plant trees on a wide spacing (10' x 10' or greater) to delay thinning, (2) use stump treatments for partial cuts of stands at
high risk for disease, and (3) consider managing for tree species that are less susceptible to annosum root rot than loblolly, slash, and eastern white pine. Although longleaf pine is somewhat less susceptible than these
species, it is not resistant and will still require stump treatments for partial cuts on high hazard sites.
The following map shows the hazard rating for annosum root rot by the
general soil type. Well-drained sandy soils are associated with a greater incidence of disease and are classified as high hazard. Moderately-drained soils that consist of loam or silt are considered a moderate
hazard. Poorly-drained or clay soils are classified as low hazard. In the mountains, eastern white pine is very susceptible to infection by annosum root rot regardless of soil type.
Rate of Spread
Above-ground symptoms of annosum root rot usually are not apparent for two to six years after a partial cut. The spread of the fungus can continue through root contacts and grafts for up to ten years. The
growth rate of the fungus in the roots ranges from 0.5 to 2 meters per year. In a living tree root, the rate of spread by the fungus is reduced due to the host's attempt at resistance. The growth rate in a dead root is
more rapid than in a living root.