USDA Forest Service Forest Health Protection, Southern Region Pine Needle Rust, caused by Coleosporium sp. The disease usually does not seriously damage trees, and is of most concern in Christmas tree plantings and nurseries. Goldenrod, asters, and other plants serve as the alternate hosts. Identifying the Fungus. The fungus has four stages.
Aeciospores infect the alternate host, which results in orange, powdery spores on the leaves.
Later orange, cushionlike objects, called telia, are produced on the underside of the leaf. Identifying the Injury. Although these are actually fruiting structures of the fungus, they are an obvious feature of infection. The spores from the aecial blisters infect the alternate hosts which produces urediospores on the leaf. These spores reinfect the alternate host, but not the pine.