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The most common, and quite devastating, disease of spruces is known as cytospora canker, named after the old scientific name of the causal fungus. (The fungus is now officially known as Leucostoma kunzei, but that is surely more than most rational beings would like to know.)
Cytospora canker disease attacks mostly mature specimens of Colorado blue and norway spruce. It is classified as a canker disease because it causes localized necrotic areas under the bark (which is the definition of a canker). Remember: people get cancers, trees get cankers.
Since the disease works under the bark, it is not possible to control the disease by spraying. And since the host is a conifer, when you drill a hole into the trunk and try to force a water-based chemical into tree vascular tissue, you have to work against a globby stream of sticky pitch. Does any chemical get into the tree? We're not entirely convinced although our chemical providers assure us it is possible. Do treatments protect the trees? We don't know. As far as we know, there have no scientific studies conducted to test the efficacy of treatments. We do see trees get better, but that may be because the concerned property owners are out there giving their spruces verbal encouragement.
Diseases of Spruce Trees
Cytospora Canker
Cytospora: note the lack of new growth on infected branches and the contrast between infected and uninfected limbs
Rhizosphaera needle-cast
Typical rhizosphaera damage
When the old inner needles on blue spruce turn an alarming purple-brown in late summer or fall, it is often due to a fungus called Rhizosphaera needle-cast. This disease can become established most any time during the growing season if and when environmental conditions favor its development. Since the newest needles are unaffected, tree health is not generally at risk; and as new growth emerges in subsequent seasons, the damage becomes masked. Several protective sprays in early spring can help prevent the spread of this disease.
The plot thickens
Outside of remnant bogs, spruce trees are not native to southern Michigan. They are better adapted to mountainous or more northerly environments than they are to our muggy summers and clay soils. Yet everyone wants to grow them.
None of the diseases on spruce trees are easy to control, nor are the problems always easy to identify.
In the spring of 2006 we started seeing ailing spruces with symptoms that did not match the textbook descriptions of the common problems. Branches in full sun were often bare, yet showed no signs of the white pitch usually associated with cytospora canker. Often the needles would be brown or absent except for a small spurt of new green growth at the branch tips.
We called upon a plant pathologist from Michigan Extension who admitted that the Extension office had received many calls and e-mails regarding needle drop. "MSU Diagnostic Services has received samples from several affected trees and has not identified an insect or pathogen cause. The circumstantial evidence points to an environmental problem, likely drought stress last year."
Drought stress can be a problem on spruces trees. In addition we note that two more fungi were recently found to be associated with spruce needle drop in the midwest. It is not clear if the fungi are the cause of the condition. “Sudden needle drop” or SNEED (you got to love it!) is the name given to the defoliation of branches in association with the fungus Setamelanomma. Another fungus, in the genus Stigmina, can only be positively identified by inspecting for the feathery (vs. unfeathery!) spore-producing structures under high magnification.
Even though we can't always identify the exact causal agent, we have seen many spruce trees improve after being sprayed with broad-spectrum fungicides in the spring.
above and below: unidentified damage on spruce
