Ponderosa Pine Diseases

Caused by the fungus Elytroderma deformans, elytroderma disease is perhaps the most important and damaging disease of the pine tree in the Pacific Northwest. This disease causes the needles to turn reddish brown during their second year. Left untreated, the needles fade and are obscured by new growth until late summer, when it becomes difficult to distinguish them from older needles, and eventually fall off the tree. The infection causes crown thinning, reduces plant vigor and increases susceptibility to other pests and diseases, including bark beetles and root diseases.

A number of rust diseases attack ponderosa pines, including Western gall rust, comandra blister rust and sweetfern blister rust. Symptoms of Western gall rust, which is caused by Endocronartium harknessii, include galls or woody swellings on stems and branches that cause stem malformations in young pines and increase their susceptibility to breakage in heavy wind. Comandra blister rust, caused by the pathogen Cronartium comandrae, causes stem and branch dieback and the gradual death of the tree. Initial symptoms of sweetfern blister rust include swellings on branches and stems that cause girdling.

Although different types of heart rot diseases attack the pine tree from the inside out, red rot, caused by Polyporus anceps Peck, is perhaps the most damaging heart rot disease of ponderosa pines. Heart rot diseases damage the inner wood of ponderosa pines, causing them to turn pulpy and rot. Exterior symptoms of heart rot diseases include fungilike growths called conks surrounding branch junctions. Damaged branches don't offer any resistance when cut from the tree and break easily, as if waterlogged.

Annosus root and butt rot, tomentosus root rot and black stain disease are root diseases commonly associated with ponderosa pines. In most cases, symptoms of root diseases aren't apparent until extensive damage has occurred. Once the roots are damaged, symptoms of rot of the stems, branches and foliage appear as the tree begins to die. The fungi responsible for root diseases spread to surrounding trees at points of root contact, thereby causing damage to trees in groups.

Ponderosa pines are susceptible to a variety of needle diseases, including pine needle cast, needle cast and dothistroma needle blight. Symptoms of diseases include paling needles that eventually fall off, and thin crowns with clusters of dead or discolored needles. As the disease progresses, older needles shed, thereby causing "lion's tail" branches, with only terminal foliage remaining.