Is your evergreen tree showing signs of distress? It might be suffering from needle rust or needle cast disease. Evergreen trees sometimes struggle with various needle diseases that cause discoloration and can eventually result in serious damage to the tree. Read on to learn more about needle diseases and how to prevent them.
Needle Rust Disease
Needle rust is a disease that causes fresh evergreen needles to turn yellow. In the fall and winter, the needles start to develop yellow splotches. When temperatures increase, the fungus creates spores that spread the disease. Eventually, affected needles die and fall off the tree.

Sometimes old needles may show discoloration, but this is nothing to be concerned about. However, if new growth on the tree is discolored, your tree might be struggling with needle rust disease.
This disease is caused by a variety of different fungi. The spores of the fungus are orange and spread in windy conditions in the spring and summer. To infect the trees that they land on, the spores need moisture, so you can prevent needle rust disease by keeping moisture levels low. Make sure there is plenty of airflow among the branches by keeping it pruned. You should also make sure the tree gets plenty of light.
If your tree is already struggling with needle rust disease, you should prune out affected sections of the tree, then dispose of the diseased evergreen needles. While fungicide may help keep the disease from spreading, it is unlikely to cure it entirely.
Needle Cast Disease
Needle cast is another fungus that affects evergreen trees. It causes the needles to turn brown and drop off the tree in late fall and winter. The fungus spores spread by rainwater and wind in the spring/summer. The bottom branches of the tree are usually affected first.
Young trees are especially susceptible to needle cast disease. If the tree is struggling or very young, over time it can die from needle cast damage.
If you leave the fungus untreated, it will continue to spread throughout the tree and to other trees. Fungicides can help, but they won’t eliminate the fungus entirely. The only way to get rid of the fungus is to prune out affected parts of the tree. However, the best way is to prevent it in the first place. You can prevent needle cast disease by doing the following:
- Plant disease-resistant tree varieties.
- Keep plenty of space between the trees in your yard for good air circulation.
- Water your trees properly because healthy trees are less susceptible to disease.
Stewarts offers a variety of tree treatments to help with diseases, insects, and more. Call or text our office at 801-226-2261 and ask to speak with one of our ISA-certified arborists for more information about our tree services and a free quote.