By: Dave Scharfenberger, Board Certified Master Arborist WI-0131B
Given the dry conditions we have seen the past few years I have been asked one question more than any other: “We have a Colorado blue spruce that is about 25 feet tall and some of the lower branches are beginning to die. What is wrong?”
Cytospora canker is the culprit. This is the most predictable problem we see in the landscape. There are other diseases on spruce, such as needlecasts, however, cytospora is the most common. It usually kills all of the lower branches on a once beautiful tree.
Cytospora is a fungal disease that is spread by air and waterborne spores. Once in the branch cambium, the fungus causes a canker (infection) to develop. These cankers exude a white resin material that is a very useful sign in diagnosing the disease. This gummy ooze is the tree’s response to wounding. The enlarging canker will eventually encircle the branch and kill it.
Lower, older branches are typically (but not always) the first to be infected. The needles on the affected branches can appear purple at first, then turn brown as they die. It often starts with only a branch or two, then progresses over time to what can be a large percentage of the tree. Trees of all ages can be affected. I have seen it in trees only a few years old, but it is most common on trees over 20 years old.
The key factors for disease development are stress and wounding. Many stresses can weaken urban trees: drought, too much water, winter injury, insects, mechanical injury (mowing equipment), construction, etc. Drought stress, in particular, is probably the biggest factor in encouraging cytospora canker in our area.
Since there is no cure for this devastating disease, prevention is the key. The best way to prevent cytospora is by keeping your spruce tree as healthy and as vigorous as possible — avoid tree stresses. Install a large mulched bed under the tree to retain moisture and insulate the roots from summer heat. This will also create a very beneficial layer of decaying organic material that the roots can utilize. The mulch area should go beyond the drip line to reduce mower damage to lower branches where the disease often starts. Water the tree, if needed, during dry periods (always check under the mulch before watering, overwatering kills roots and weakens the tree). This is easiest with a soaker hose at the base rather than a sprinkler, because wetting the foliage can help spread the disease. Fertilize the tree every 1-2 years to keep it as vigorous as possible. Additional treatments like micorrhizae soil injections may also be recommended.
If your tree has cytospora canker, all of the above steps need to be taken. Furthermore, the infected branches have to be pruned out, with the pruning tools being disinfected to prevent spreading the disease. If all these steps are taken, the disease may stay in remission.
Cytospora canker is a devastating disease that destroys many valuable spruce trees every year. The key is to protect the tree ahead of time with proper care to prevent stress in the plant. Watering is critical. If you have questions about your spruce, please call the Certified Arborists at Wachtel Tree Science & Service.
© Copyright 2005 – Wachtel Tree Science & Service, Inc.