Diseases of ponderosa pine (
Annosus root and butt rot
Annosus root and butt rot is caused by the fungus Heterobasidion annosum, a member of the Polyporaceae family that produces a perennial, woody bracket-like conk (the fruiting body) (photo 1). It causes root and butt (the butt is the base of the tree) rot on a wide host range of trees throughout the world, especially conifers. In Arizona, its main hosts are white fir, subalpine fir and ponderosa pine, but may occasionally be found on Douglas fir and Englemann spruce. There are two types of annosus, one which favors true fir and the other pine, displaying little crossover.
As with other root disease or decay fungi, spread of annosus is from roots of diseased trees to those of healthy ones. It starts in a tree or stump and spreads slowly outward in all directions, resulting in a slowly enlarging group of dying and dead trees. The oldest kills are located at the center of infection with a fringe of recently killed and dying trees around the outer edge. In the southwest, these “centers” of disease are small in size, typically less than 1 acre on average. Regeneration is often killed near infected stumps.
Root disease is referred to as a disease of the “site”
because root decay fungi colonize dead and dying trees and remain in
dead roots and soils for many years. Many of these fungi have the ability
to act as both pathogens in live trees and saprophytes in dead wood
material. So not only are the current trees affected, but also trees
that become established in the future. Some root disease fungi have
been shown to remain alive and active in infested sites for more than
50 years.
Symptoms of decay in wood begin as yellow-brown to red-brown stain (photo
2), eventually becoming a white stringy mass in later stages
of decay. The wood is completely degraded in the final stages of disease
and the butt of the tree is hollow (photo
3). Decay may extend several meters up the trunk. Heterobasidion
annosum can be identified by its conks found on the underside of
decayed roots of living and standing dead trees as well as stems and
roots of windthrown trees. The upper surface of the conk is dark brown
to black and the lower surface is white to cream.
In landscapes or highly maintained forest areas of the southwest, prevention of annosus root rot includes thinning out infected trees, favoring the regeneration and development of resistant tree species, and (rarely) treatment or removal of stumps. Infested sites should be replaced with tree species that are not hosts for the pathogen. In areas where true fir is impacted and older ponderosa pines are not, replace fir with young ponderosa pine. In some areas it may be a matter of maintaining trees at less than 120 years of age in order to have a healthy and safe forest. Annosus root disease is serious on pines in a few localities and under certain site and stand conditions. At sites where pines are being impacted by disease, hardwood species such as oak should be planted.
Although root-to-root contact is the primary means of spread from diseased to healthy trees, freshly cut stump surfaces are the major site of initial infection into a site. Treating freshly cut stump surfaces with a light coating of granular sodium tetraborate decahydrate or disodium octaborate yetrahydrate can prevent stump infection by H. annosum. Currently, the only borate products registered for annosus control are Sporax® and Tim-Bor®.
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Info on ponderosa and diseases, etc
http://www.na.fs.fed.us/pubs/silvics_manual/Volume_1/pinus/ponderosa.htm
Images from U. S. Forest Service:
http://www.forestryimages.org/browse/subimages.cfm?sub=519
August 3, 2011