Forest and Wildlife Extension

Forest Health Notes

A Series for the Non-Industrial Private Forest Landowner

Elytroderma Needle Cast
(Elytroderma deformans)

Host: Ponderosa pine, rarely lodgepole pine

Quick ID:

• Narrow, long black spots on 2-year-old needles
  
• Reddened, dead 1-year-old needles ("flags")
  
• Current season needles green
  
• Witches' brooms
  
• Inner bark of older twigs has dead patches

Field Identification

Tree: In the spring, needles infected the previous fall die and turn red-brown. This color fades through the summer. At the tip of the twig, the current year's needles remain green. If the tree is infected year after year, witches' brooms, or abnormal proliferations of many small twigs which appear as a mass of twigs and foliage, may form. These are more compact and rounded than the witches' brooms from dwarf mistletoe infections, and have upward-turning branches and many dead needles. Twigs that have been infected for more than three years have small patches of dead tissue under the inner bark.

Fungus: Dull black, elongated fruiting bodies appear as spots on dead needle surfaces in the late summer.

May be confused with: Dwarf mistletoe, Dothistroma needle blight, Lophodermella needle cast.

Disease cycle: Elytroderma needle blight is the most important foliage disease of ponderosa pine in Washington. Windborne spores are disseminated from the hysterothecia in late summer and autumn, infecting the current year's foliage. The fungus grows from the needle into the twig without initially killing either one. The following spring, the needles die and new hysterothecia form on the dead needles.

Infections in the woody twigs can remain for many years, reinfecting needles that produce spores that infect other trees. The spread of the disease in the twigs causes the characteristic brooming and deformation.

Predisposing agents: Cool temperatures and high humidity in the late summer and fall promotes infection by the windborne spores. Certain sites that typically have these conditions such as around lakes, in stream bottoms, in canyons, near meadows and in other cool moist areas have more problems with the disease, especially as the air recirculates in the stand. Elytroderma is itself a predisposing factor for Armillaria root disease and bark beetle attack as it weakens the tree.

Impact: Infection becomes damaging around 3,500 feet of elevation in Washington, though it occurs at lower elevations. The damage from this disease occurs mainly as growth loss and predisposition to disease and bark beetles, although infections year after year can kill the tree. No information is known about the disease's impact in terms of cubic feet lost each year, but trees with 30% to 60% of the crowns infected lose 52% to 65% of normal diameter growth, and trees with more than 60% of the crown infected lose 93% to 99% of normal diameter growth.

Management: In immature stands, good spacing should be maintained but large openings in the stand should not be created. Severely infected trees should be removed when thinning (do not leave trees with flags within 6 feet of the leader). Infected branches should be pruned if it is economically feasible to remove sources of inoculum. In mature stands, it is important to avoid hasty action as infection can occur without catastrophic loss. Watch the stand carefully for signs of more serious damage (bark beetles, Armillaria, etc.). When harvesting damaged or diseased trees, carefully inspect the residual stand taking care to remove all infected trees.

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About Forest Health Notes

Forest Health Notes were prepared by Donna Dekker-Robertson, Peter Griessmann, Dave Baumgartner, and Don Hanley, Washington State University Extension. The assistance of Robert L. Edmonds and Robert I. Gara, University of Washington College of Forest Resources, is gratefully acknowledged.

Insect or disease treatments should always be part of an overall forest management planning process. It's a good idea to have a forest management plan for your property. This tool will help you prevent problems and keep your forest healthy. For information on forest stewardship educational programs, contact your local WSU Extension office. For information on technical assistance and financial incentive programs, contact the Washington Department of Natural Resources. The Natural Resources Conservation Service will assist landowners in developing conservation plans.