Tree bark rust

Scots pine blister rust

There are approximately 5,000 species of rust fungi known. All of them are parasitic fungi that live on trees and shrubs. Scots pine blister rust is caused by two species of rust fungi – Cronartium flaccidum and Peridermium pini. Signs of the disease are black, resinous sores on pine branches and trunk. The areas of the bark affected by the infection appear burned and are greyish-black in colour. The branches and trunk do not thicken in diseased areas, but the unaffected areas do thicken, and the pine develops a cancerous scar that increases each year. Most trees that grow in humus-rich soil become ill and die.