Sirococcus clavigignenti-juglandacearum is responsible for dieback and decline of butternut. It was first described in 1923, but reports of the malady go back to the turn of the century. The casual organism was at first thought to be Melanconis juglandis, a weak pathogen found throughout the butternut range. However, Sirococcus clavigignenti-juglandacearum has recently been found to produce a canker that leads to the decline; M. juglandis is secondary.
- The first symptom of decline is branch dieback; M. juglandis usually is found fruiting on the dead twigs. Annual stem and branch cankers form and normally the bark splits at the point of the canker. Typically bark turns white around the canker and black substance oozes from the canker. Cankers develop throughout a tree, but commonly occur on the main stem, at the base of trees and on exposed roots. Epicormic branching is common, and tufts of live branches form along the bole before the tree dies. No sexual stage of the fungus is known. The asexual spores are spread locally by blowing rain and by possibly by insects and birds. The mode of long distance spread is unknown.
- Ecological Threat
- Butternut dieback probably is responsible for the present scarcity of butternut in the eastern states. The disease is now causing severe losses in the Midwest and is seriously threatening the survival of the species. It is now present in the entire natural range of Juglans cinerea.