Cause Davisomycella medusa, a fungus. The disease is on lodgepole, Jeffery, and ponderosa pine. It is prevalent in pure open stands east of the Cascade Range and is more intense after a drought. Spores disperse in summer and fall and infect current-season needles. Symptoms occur after a 2- to 4-year latent period.
Symptoms Fungal fruiting bodies (hysterothecia) are seen easily in late spring and early summer as elongate, black bumps on most of the needle. Infected foliage fades to a greenish white to straw color and eventually is cast. The entire tree's growth decreases.
Can easily be confused with other needle cast diseases. Needle cast diseases are identified by microscopically examining fruiting bodies and spores. Needle casts can also be confused with annual (normal) fall needle drop. Most conifers shed some of their oldest needles in the fall. These old needles often turn yellow or brown before falling off.
Cultural control
- Provide good air circulation; do not crowd plants.
- Practice good weed control so lower needles are not kept moist for extended periods of time.
- For high-value trees, remove and destroy fallen needles that collect in branch crotches and on the ground.
Reference Bega, R.V. 1978. Diseases of Pacific Coast Conifers. USDA Agriculture Handbook 521. Washington, DC: Superintendent of Documents, U.S. Government Printing Office.