This beetle, native to Asia, was likely introduced in southeast Michigan in the early 1990’s and has spread rapidly since then. This beetle is the reason why whole areas of forest are dead and is probably why the ash trees in your yard have died.

Although most of the mature ash trees in our area are likely to die, there is hope for the future. Injections can be very effective at preserving individual trees, many of which are still alive as they are more resistant to the beetle.

The US Department of Agriculture has been releasing parasites that feed on the ash borer since 2007. These natural enemies of the ash borer could reduce their population to the point where ash trees can make a comeback across the landscape. Private landowners can participate in the effort; click here for more info.

Emerald Ash Borer

Oak wilt is a very serious disease that can kill large, mature oak trees in less than a year. It is caused by the fungus Bretziella fagacearum. Red oaks are more susceptible than white oaks, but all oak species are at risk of infection.

This map is almost 8 years old, but since oak wilt spreads slowly its range has likely not expanded much past what’s indicated. While it is not yet widespread in our area, it has been detected nearby and likely occurs sporadically in the Southern Tier.

Oak wilt is primarily spread by nitidulid beetles that are very quickly drawn to pruning wounds during the warmer months, so the best thing we can to do slow the spread of oak wilt is do not prune oaks during spring, summer, or early fall. . This pamphlet is an excellent resource for more information on oak wilt.

This disease has a complex mix of causes, mostly attacks by two different insects (Cryptococcus fagisuga and Xylococculus betulae) and two different fungi (Neonectria faginata and N. ditissima). The effects can range from swift mortality to chronic infections that slow growth and make the tree susceptible to other stresses. It almost always leads to death of the infected tree.

Trees infected or killed by beech bark disease commonly break during high wind events (see picture). Because of this, trees near houses, playgrounds, etc., should be inspected for disease development and monitored for stability.

A lot of spruce trees in our area are struggling, particularly Colorado blue spruces. Maybe you’ve seen some that look like the one in the picture? These trees evolved in an area with dry conditions and colder temperatures at night; our humid summers and warm nights are perfect for the diseases that have been killing them.

It’s likely that there are multiple infections affecting any one spruce tree. Some fungal diseases like Rhizosphaera and Stigmina needle casts, Diplodia shoot blight, and Phomopsis tip blight can be treated with a couple applications of fungicide if the infection is caught early. Relatively easy on small trees, but likely impractical on large ones. Other diseases like Cytospora canker are more serious and harder to control. Insect pests such as gall adelgids and spider mites can also be treated, but controlling infestations on larger trees may be cost-prohibitive.

The best way to keep a spruce tree healthy is to prune branches up at least 6-8 inches from the ground and do whatever you can to maximize the amount of sunlight and airflow so that these diseases can’t take hold.

Cedar-Apple rust

Tar spot is a common problem on maple trees, particularly Norway maple (why “Norway maple” instead of “Norwegian maple”? I couldn’t tell you, doesn’t make sense to me either). The symptoms are black, tar-like splotches on leaves. This disease can look quite serious and even cause defoliation of a tree, but it rarely poses a threat to a tree’s health. It can be especially widespread during years with cool, wet springs as these conditions favor the growth of the fungus that causes the disease, Rhytisma acerinum.

Tar Spot

Here is a more detailed list of tree pathologies and management options for curious souls