Locally severe in west central Montana and along the Clearwater River near Orofino, Idaho. May be widely distributed.
New shoots are killed by the canker-causing fungus. Severe infections may lead to death of trees of all sizes.
Stunted new shoots or flagged branches with drooping red or gray needles occur anywhere in crown (fig. 94). Needles are infected as they emerge from the sheath. Infected needles are stunted and may have a resinous droplet associated with the infection point. The fungus commonly girdles the entire new shoot by the end of summer. Infections may continue to develop into year-old tissues as well, but evidence of this is often subtle. Cambium of infected shoots is resinous and discolored (fig. 95). Minute, round, black fruiting bodies are produced on twigs, bases of needles, or on cone scales.
Western pine shoot borer and gouty pitch midge damages are similar in appearance to Diplodia blight. Shoot borer and pitch midge are generally restricted to saplings and evidence of the insects are found in damaged shoots.
Peterson, G. W. 1981. Diplodia blight of pines. USDA For. Serv., For. Ins, & Dis. Leaflet 161, 7 p.
Field Guide to Diseases and Insect Pests of Idaho and Montana Forests, USDA Forest Service Northern Region, Publication Number R1-89-54