Closer inspection of the affected spruce trees, infected needles have pale orange spore masses that erupt in the summer. These spores are wind blown from the needles to the surrounding area, and if they land on the leaves of Labrador tea, the next step in a complex life cycle can proceed. Spruce Needle Rust has a complicated life cycle. There are five stages, two that occur on the spruce tree and three on Labrador tea. The spores that the tree produces does not reinfect the tree, it can only infect Labrador tea. When the spore lands on Labrador tea it grows into the leaf, it grows and produces a spore type whose job it is to spread to other places on that plant or can be spread by wind to other Labrador tea plants nearby. This stage produces more affected Labrador tea plants. These spore types also are the stage that allows them to overwinter. In spring, another type of spore is produced on the Labrador tea, and coincides with the time that new needles are being produced on spruce trees. The spores are released from the Labrador tea leaves and travel by air. If they land on new, succulent needles, the spores grow into the tissues, infecting the tree.

Spruce trees are rarely killed by the Spruce Needle Rust, However, young trees can have growth effected and can reduces the chances that the tree will reach maturity. Since it is important that spruce trees be close to Labrador tea to trade spores in the life cycle, areas like bogs and tundra that are near trees increase the chances that Spruce Needle Rust will be found. The fungus can be noted in a particular area for a year or two, but is not epidemic every year. The fluctuating incidence of rust from year to year may be due to different weather conditions. Wet and cool weather is conducive for spore formation and spore disperal from Labrador tea, as well as infection of new spruce needles.