This is one of Minnesota’s most common diseases on ornamental trees, specifically spruce trees. This fungus is called Rhizosphaera (needle cast in laymen’s terms). This fungus is pretty much everywhere on the lawn. The fungus splashes up to the lower portions of the tree through moisture and works its way upward over many years. Because it’s a “slower” mover than other diseases, people usually don’t notice it until a lot of damage is done. The distinguishing characteristics are needle loss on the lower portions first, browning to purplish coloration of the needles, and tiny black spores on the base of the needle. Usually the needle loss on the bottom and purple needles are what’s easily spotted. These pictures without a doubt confirm Rhizosphaera (Rise-o-sphere-a).
These trees are not done for, but this is more serious than Anthracnose and these trees need immediate attention. To improve the health of these trees, a number of things need to happen.
1.Try to avoid sprinklers splashing water onto the trees. Because the fungus begins on the ground, a sprinkler will actually carry the spores up from the ground onto the tree.
2. Prune diseased branches off and raise braches up that are near the ground. Even “healthy” looking spruce trees need the bottom branches raised up to avoid ground contact and to increase air flow. Remember, prevention is always better than reaction.
3. Try to avoid planting spruce trees next to each other where they might eventually touch. Think long term and the potential size they might get. If the customer prefers evergreens, then mix up the variety. Maybe include pine, fir, cedar, or other types of conifers mixed with the spruce so the disease doesn’t spread. In this case, the disease won’t spread from tree to tree that are so far away, only trees that are basically touching. However, the fungus comes from the ground so the other trees are still susceptible.
4. If the disease is confirmed, which in this case it is, 2 fungicide treatments must happen in the spring. BRAVO has already started these applications and the first application would need to happen within the next week to be the most effective. Most of the time it takes 1-3 years of spring time treatments to be completely effective. It’s important to note that the diseased needles will not recover, but the treatments will stop the spread to other needles.
5. Unlike anthracnose, which usually shows up in the spring then disappears; this fungus will persist for many years. These trees are older and have probably lived with Rhizosphaera for many years. I would strongly suggest a spring and fall fertilizer deep root application to begin the rejuvenation process. The spring fertilizer promotes growth and the fall fertilizer is to boost the immune system of the plant and used typically for trees that have gone under tremendous stress.
At this point, taking these actions will be less costly $ than removing and replanting. These would be good candidate trees to take action.
Information provided by our Friends at Bravotree:
Phil JubertCertified Arborist #IL-5190A BRAVO Forestry www.bravotree.com