Clare County forest update

August 2, 2018

Usually native pests and diseases will not kill trees unless they are already sick, weakened or damaged. These pests have been present in the ecosystem and our native plants have adapted to them. Invasive species do not have this balance and that is what makes them so destructive. Proper identification can help you treat or manage a disease or issue early on and prevent further damage.

Oak Wilt
Oak wilt (Bretziella fagacearum) is an invasive fungal disease that is first spread by native beetles, and then through roots of connected trees. All species of oak are affected. Red oak is the most vulnerable, and white oak somewhat resistant. Infected red oaks will usually die within 1 month of infection. White usually dies one branch at a time over several years.

Prevention is the best tool against oak wilt. Since the fungus-carrying beetles are attracted to sap from open wounds, avoid pruning or damaging oak trees from mid-April to mid-July. This period has the highest risk of infection. There is little to no risk of infection in late fall-winter when trees are dormant. In fact, the beetles that spread oak wilt can be active anytime the temperature is over 40 degrees F.  Once a tree is infected with oak wilt, it can spread to other oak trees due to underground root connections.

If you suspect that you may have oak wilt, you can send branch samples to MSU Diagnostic Services. Oak wilt treatment involves trenching to break root connections, tree removal, and possibly even fungicide injections. The Natural Resource Conservation Service (NRCS) has cost share available to help landowners with the cost of oak wilt treatments.

Beech Bark Disease
Beech Bark Disease is another insect/fungus disease. The beech scale insect (Cryptococcus fagisuga) is an invasive, aphid-like creature that feeds on the sap of the beech tree. It creates a white waxy, coating to protect itself that can be seen on the tree trunk. When thousands of scale insects feed on a tree they make holes that allow the tree to be infected with a native fungus (Neonectria spp). This fungus will kill large branches and eventually the whole tree.

Beech scale can be treated with a systemic insecticide. This can be injected into the tree or spread at the roots, so it is taken up through the tree. Without the beech scale insect, the tree won’t get infected with the deadly neonectria fungus. The Michigan DNR has also been working with the US Forest Service to breed beech trees resistant to beech scale. Some of these have been planted in Ludington State Park where beech bark disease was first discovered in Michigan.

White Pine Weevil
The majestic white pine is our state tree, but you may notice that some of them have crooked trunks or forked tops. This is usually a result of the native white pine weevil. This insect burrows into the top tip of a white pine and eats the tender shoot. This kills the very tip of the tree. It will soon wilt and turn brown. This wouldn’t be that big of a deal, but all the remaining side branches will begin to grow upward to become the new top. Multi-stemmed trees are less aesthetically pleasing, structurally weaker, and reduce timber quality. White pine weevil will attack other species of pine and spruce also.

If you are planting many white pines, consider planting them in the shade or under tree canopy. White pine will tolerate shade while the weevil does not. Small trees can be corrected by pruning. Prune out the extra branches and leave one branch to become the new top. If damage too high to reach, don’t worry too much. This weevil doesn’t really damage the health of the tree, just the aesthetic and timber value.

Gypsy Moth
The caterpillar of the gypsy moth has been causing damage to oak trees in our area. They will also feed on maple, aspen, apple, birch, beech and more, although oak is their favorite. The caterpillars feed on the leaves of the trees and can completely defoliate them.  Gypsy moth is an exotic species that has become “naturalized”, meaning native predators and parasites prey on it. Even so, outbreaks still occur. These usually only last a few years and may reduce on their own. Trees can survive multiple years of defoliation before they would be killed by gypsy moth.

How do you know if a caterpillar is a gypsy moth? First of all, gypsy moth caterpillars do not make tents in trees, those are eastern tent caterpillars, or “tent worms”. Gypsy moths have long hairs, that come out of knobs along the length of their body. They also have five pairs of blue spots and six pairs of red spots along their back. Eastern Tent Caterpillars have blue markings along their sides and a white stripe down the center of their back.

By July and August, the gypsy moths will have emerged from their cocoons and started laying eggs. Female moths are about an inch long, whitish tan, and cannot fly. Male moths are beige to dark brown and about half an inch long. You are much more likely to see the female moths because they stay on the trees.

Clare County operates a Gypsy Moth Suppression and Control Program that is administered through the Conservation District. The county was surveyed for egg masses in Fall 2017 to determine where the highest populations were. In late May 2018, the most infested areas of the county were sprayed to reduce gypsy moth caterpillar populations. Be on the lookout this fall for yellowish tan, fuzzy, football shaped egg masses. Once our Egg mass surveys are completed in October, it is safe to remove them. If you suspect gypsy moth, please contact the Clare Conservation District.

Additional info sources
MSU Extension
MSU Diagnostic Services NRCS
Michigan DNR  
Michigan Oak Wilt Coalition

For more information on forest health or to schedule a FREE site visit to your forested property with the Conservation District Forester, call Nia Becker at (989) 539-6401 or email at Visit to learn more about our local conservation district.

Share This Post

Error, no group ID set! Check your syntax!

Leave a Reply

Your email address will not be published. Required fields are marked *