Elytroderma needle cast, also known as Elytroderma disease, is a fungal disease of pine trees. It is especially common on ponderosa pine. Elytroderma needle cast is caused by the fungus, Elytroderma deformas. The fungus infects and kills the foliage of susceptible trees. The disease seldom culminates in tree mortality. However, successive defoliations can weaken trees, and render them more prone to failure.
Distribution & Range
Elytroderma needle cast occurs throughout the range of ponderosa, lodgepole, jack, and pinyon pine. It has been reported in the Western, Central, and Eastern United States, as well as the Western Provinces of Canada.
Ponderosa pine is the preferred host of Elytroderma deformans, but infections may also occur on lodgepole pine, jack pine, and pinyon pine.
In summer and fall, fruiting bodies, or stromata, on infected trees rupture, and release spores, which are disseminated to susceptible trees by air currents, and splashes of rain, where they initiate new infections. If conditions are sufficiently moist, the spores penetrate the expanding needles, and germinate within one to two days. Once the fungus has become established, it develops within the needle tissue. In early summer, the infected needles turn reddish-brown, and expire. By mid to late summer, fungal fruiting bodies form on the dead needles. These fruiting bodies appear as black, elongated lines, which split open during rainstorms, and release spores. The spores are dispersed to nearby trees to begin the cycle anew. Infections are most common in areas where rainstorms frequently occur. Dry weather tends to suppress spore production. Dense plantings are more prone to infection.
Symptoms of Infection
Persistent infection of vigorous branches often results in the formation of small to large brooms with upward turning branches, and an abundance of dead needles. The brooms caused by Elytroderma needle cast are compact, and rounded, which differentiates them from witches’ broom. The brooms contain discolored needles, many of which are shed by fall. The infected needles initially turn a reddish-brown, but become paler during the summer. The basal portion of the infected needles will remain green. By the following spring, the infected needles will be straw-colored. Branches that have been infected for three or more years tend to develop small patches of dead tissue beneath the inner bark. Brown, resinous legions may form in the phloem of infected twigs. The black fruiting bodies appear near the base of infected needles in spring. Elytroderma needle cast infections can significantly defoliate trees. Small trees may be permanently deformed. When an infection is severe, tree growth is inhibited, and the entire crown of the tree may die back. In these situations, the tree generally succumbs to the infection. Infected trees are vulnerable to infestation by bark beetles, and other insects.
- Thin the crown of susceptible trees to improve air circulation, and promote the rapid drying of foliage.
- Selectively cull moderately, and severely infected trees. Remove trees that have been extensively defoliated.
- When planting, select resistant tree species, such as Douglas-fir.
- Infected branches can be pruned to remove sources of inoculum.
Photo courtesy of Government of Canada, Natural Resources