Detractors will say it’s karma, but fans of Colorado blue spruce in the Midwest are seeing an increase in the rate of decline. And what’s causing it is actually called spruce decline. One of the first signs is the browning and thinning of lower branches. In a recent Michigan Radio report, Michigan State University plant pathologist Dave Roberts explains what’s happening.

“First of all,” he says, “we’ve taken a tree that is native to the Rocky Mountains, and we’ve transplanted it to Michigan, which is a completely different environment. And in that different environment, the tree is susceptible to a much greater variety of pests and diseases than it normally would be in its native habitat.” Although several types of spruce are affected, Colorado blue appears to be the most susceptible.

According to Roberts, Phomopsis canker appears to be prevalent. “That’s a disease I discovered in the late eighties and early nineties that was affecting many nursery stock trees,” he claims, and it has subsequently moved into the landscape, causing enough of a decline to kill many of the state’s Colorado blue spruce.

Other causes of decline may include Cytospora canker, which typically attacks the lower branches of mature spruces; needlecast diseases, which normally don’t kill trees unless they experience several years of defoliation; SNEED (Sudden Needle Drop or Spruce Needle Drop), believed to be caused by an opportunistic fungus; spruce spider mites; spruce adelgids and pitch mass borer.

Close monitoring of spruce can help to identify problems, but this may simply be a case of “right plant, right place.” Tell that to the millions of homeowners across the Midwest who’ve fallen in love with their spruce trees.

Read more: Battling Blue Spruce Burnout


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