Header image courtesy of USDA Forest Service-Rocky Mountain Research Station – Forest Pathology, USDA Forest Service, Bugwood.org.
If sections of your spruce tree are looking yellow or orange, especially during the summer months, it may be suffering from a disease called spruce broom rust.
Thanks to a rainy summer this year, property owners have been noticing some orange sections on their spruce trees. This orange patch is a witches’ broom and is most likely something called spruce broom rust.
In this article, we’ll cover:
- What causes spruce broom rust
- How to identify it on your trees
- What to do if you spot it on your trees
- And more
Keep reading to learn more about this fungal disease.
What is Spruce Broom Rust?
Spruce broom rust is a disease caused by a fungus called Chrysomyxa arctosphyli. It is found on blue and Engelmann spruce trees here in Colorado and in Northern Arizona, and on black, Sitka, and white spruce trees in Alaska and parts of Canada.
The spruce needles turn yellow and form a witches’ broom, or cluster of branches, once infected, which is from where the disease gets its name.
Interestingly, spruce broom rust and the fungus that causes it need two hosts to survive. In our area, that other host is bearberry, sometimes called kinnikinnick (or any plants in the genus Arctostaphylos). If there is a bearberry plant within 1,000 feet of a spruce tree, it can become the secondary host for the fungus.
How is Does the Disease Spread?
The fungus spreads through spores carried by the wind. As we mentioned, the fungus needs two hosts, a spruce tree and a bearberry (Arctostaphylos uva-ursi) plant. Both hosts are needed for the fungus to complete its lifecycle.
Spores are released from an infected spruce tree, and the wind takes them to a bearberry plant. The leaves of this plant become infected and turn a purple-brown color. Spores are created on the bearberry plant, and the wind carries the spores to spruce trees, where it infects young needles. The infected needles become witches’ brooms, and the cycle repeats.
Fungal diseases are more likely to spread when there is a lot of moisture, so spruce broom rust is more common after a wet spring or summer.
Orange needles in a clumping form are signs of spruce broom rust on this Engelmann spruce tree. Image courtesy of USDA Forest Service – North Central Research Station, USDA Forest Service, Bugwood.org.
Does my Tree Have Spruce Broom Rust?
Only blue and Engelmann spruce trees are infected by this disease here in Colorado, so first determine if your tree is a spruce tree.
One of the symptoms of this disease is a witches’ broom or a tight cluster of needles. The witches’ broom turns yellow or orange in the summer and brown in the fall. It may stick out slightly and is often on the top section of the tree.
Some infected needles may fall off the witches’ broom during the fall months. You can see what this looks like in the header image on this page.
Spruce broom rust can often be confused with dwarf mistletoe.
Check out this gallery of images of spruce broom rust from forestryimages.org to help you better identify the symptoms.
A witches broom caused by spruce broom rust in a white spruce tree in Colorado. Joesph OBrien, USDA Forest Service, Bugwood.org.
Can you Prevent or Treat Spruce Broom Rust?
At this time, there are no treatments available to prevent or stop this fungal disease. No fungicide, for example, has proven effective.
So what should you do if you spot this disease on your trees?
The good news is that this fungal disease is a cosmetic issue, meaning that it won’t significantly harm the health of your tree.
You have two options: prune or ignore.
Pruning out spruce broom rust
The witches’ brooms that are a symptom of the disease are easy to spot thanks to their strange shape and different coloring. You can choose to have the witches broom pruned out of the tree. Keep in mind, however, that the witches’ broom is often attached to the main stem (trunk) of the tree, so at times an entire section or top of the tree may need to be removed.
There is also no guarantee that another witches’ broom won’t form in future.
If you choose this method, we recommend pruning during the cold months when the tree is dormant. Contact LAM Tree Service for more information.
Leaving the disease as-is
The other option is to leave the witches broom caused by the spruce broom rust alone. There are some benefits to this method, especially for our local wildlife. Birds and other small animals like to use witches’ brooms in trees as a place to rest or nest.
Removing bearberry plants
There is another option to prevent spruce broom rust, and that is to remove all bearberry plants from a 1,000-foot radius of all spruce trees. This option is not feasible for most property owners and can be a costly solution.
Bearberry gets its name because the berries are a food source for bears, which is another reason you may not want to remove the plant. Birds and butterflies also count on bearberry plants as a source of food and nectar.
Can it Cause Serious Issues to My Tree?
Spruce broom rust is seen as a mostly cosmetic issue, only affecting the way that the tree looks. If it becomes too infected, it can slow down growth and can impact the overall health of the tree.
It becomes more of an issue when the trees are grown for commercial purposes, such as logging.
On most properties, however, it is rarely the direct cause of a tree’s demise. Whether or not your trees have any signs of disease, keeping them healthy and well-maintained are the best ways to improve their longevity.
LAM Tree Service Can Help
Whether you are trying to determine if your trees have spruce broom rust or some other disease, you’d like to prune out a witches’ broom, or you want to improve the general health of your trees, LAM Tree Service can help!
Contact us to schedule an inspection or to learn more about our plant health care services. We have the knowledge, training, and experience to help your trees stay healthy.
