You might’ve noticed there’s something strange going on with the spruce trees in your neighborhood.
It’s called spruce decline and it’s mostly affecting Colorado blue spruce.
Spruce decline is pretty much what it sounds like – the lower branches on the tree start turning brown and dying.
So what’s causing spruce decline?
"Tree Doctor" Dave Roberts is a plant pathologist from Michigan State University. Roberts studies plant diseases and he says there are several things contributing to spruce decline throughout the Midwest.
“First of all, 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,” Roberts says. “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.”
Roberts says the Colorado blue spruce is the species of tree most affected.
“It seems to be a magnet for all sorts of diseases and pests,” he says.
One disease hitting spruce trees particularly hard right now is Phomopsis canker.
“That’s a disease I discovered in the late eighties and early nineties that was affecting many nursery stock trees,” Roberts says. “And that disease has subsequently moved out into our landscapes and is virtually causing such a decline in many Colorado blue spruces that the trees are dying.”
The blue spruce, especially, is dealing with many different issues at once, and Roberts says that’s why we’re seeing so many affected trees.
“It’s very widespread,” Roberts says. “In fact, I’ve heard some scientists say there won’t be another blue spruce in 10 years in Michigan, and I think that’s a gross exaggeration. Frankly, these trees are over-planted, as they have been for the past 40 to 50 years because of their great blue color.”
How to know if your tree is affected
Roberts says trees suffering from spruce decline won’t look healthy.
“What you’re going to see are bare branches — a gradual decline in these trees, with bare branches, needle loss, sometimes the tops die in them,” he says. “And eventually, there’s so many dead branches in these trees, that people find them unsightly as they continue to decline.”
Keeping trees healthy
If you have a tree suffering from spruce decline, Roberts says the first step is to determine which specific diseases or pests the tree is suffering from. He recommends hiring a professional arborist to figure out what's wrong.
“Then we can apply certain pesticides to control them,” he says. “And the unfortunate thing about that: it almost takes pesticides today to maintain a very good looking Colorado blue spruce.”
Roberts says if you want to plant new trees, you should avoid planting blue spruce.
“If you have an existing blue spruce that you want to keep, certainly pesticides can be applied. But if you’re installing new trees, we probably should go to different species,” he says.
We’ve heard that advice a lot in recent years: diversifying and planting a mix of trees in our yards and cities can help keep new diseases and pests from wiping out all the trees on the block.
That was Roberts’ advice when he found the emerald ash borer in ash trees, for example.
But he says he doesn’t think people have been following that advice.
“I just recently found another new disease in Michigan called trellis rust on pear,” he says. “And what happened with the emerald ash borer is that Bradford pears and so forth were planted back in where ash trees were and now we’ve got a new rust disease being introduced into Michigan from Europe. And that is now affecting the Bradford pear very drastically.”
For more information on spruce decline, see this document.