August 20, 2014

What is Killing the Spruce Trees of Michigan?

Back in 2011, agriculturalists from Michigan State University began noticing something odd: many of the state’s spruce trees, especially its’ Colorado and Engelman spruces, were thinning out, losing needles and even branches at an unusual rate. The trees were thinning from the bottom up, looking very much like the result of a needlecast disease or a shoot blight. However, if the cause were either of those ailments, that would mean that that particular ailment had, unexpectedly, become much more widespread in the area than ever before. Curious as to the cause of the issue, the MSU agriculturalists took some of the effected branches for observation. Outwardly the plants had few symptoms, looking more or less normal minus the obvious damage that had been done. However, when they peeled back the bark on the branches the agriculturalists found cankers, or infected areas. Generally, cankers are immediately visible, so their presence beneath the bark of the tree complicated matters. The agriculturalists began experimenting, trying to deduce the cause of the cankers.

The agriculturalists hypothesized that the cankers were likely caused by a fungal infection, and after testing various possibilities, they arrived at a fungus known as phomopsis. This fungus was involved in several outbreaks in the past, most notably in Wisconsin in the 80s and Michigan in the 90s, but both of those outbreaks occurred in nurseries and tree farms. This was the first time that phomopsis had effected trees in the wild, at least in such a major way. So what might explain this unusual development? Was the fungus actually responsible for the tree’s decline or was it only invading them once they had been weakened by another agent? Are there environmental factors at play? Three years later these questions have still not been answered in any kind of satisfactory way. The trees continue to thin and weaken. Though defoliation is still commonplace and cankers are still widespread, actual branch death is less common. Regardless, this outbreak continues to be an issue throughout Michigan.

There is actually a potential solution to the problem: a chemical called thiophanate methyl which can effectively kill phomopsis fungus. However, because the cankers are beneath the tree’s bark combating the problem with an exterior agent like a chemical spray could prove extremely difficult, if not impossible. As such, a viable solution still has not been found to combat this issue, and 27% of randomly studied spruces throughout Southeast Michigan currently suffer. Thankfully, diseased spruces are in the minority in Michigan. Most of the state’s spruce trees are completely healthy. However, the effects of this phomopsis outbreak have been felt throughout the state. The least effected types of spruces are the Norway and White varieties, and yet even these trees have been found to occasionally have cankers. Recently, the same problem has sprung up in Minnesota, with thousands of trees dying from the influence of phomopsis. Even as the problem becomes more widespread we are no closer to discovering a cure. Until this matter is cleared up watch your spruce trees carefully for signs of phomopsis fungus.


Steve Scheuring, Horticulturalist

Twin Oaks Landscape, Inc.

August 2014