Sweetfern blister rust
Damage, symptoms and biology
The fungus commonly infects jack pine seedlings or saplings. It causes swelling of the bark and the wood. The affected bark ends up rupturing, and this kills the tree. The fungus has several different stages of spores. A first type of fruiting body can be seen on the lower part of the bole of infected trees near the end of spring. The fruiting bodies are the most obvious sing of the disease. They produce swellings or nodules on the bole bark, which release orange spores. These spores end up infecting a small plant, called sweet fern (Comptonia peregrina (L.) Coulter). On this host, the fungus produces two new types of fruiting bodies. The most important type appears on the lower surface of needles as small thread-like structures. The spores discharged by these fruiting bodies infect new shoots of jack pine trees.
As they age, trees tolerate the presence of nodules on their bole; however, the pustules can serve as points of entry for decay fungi.