Speak for the Trees: Recognizing Tree Pests and Diseases

September 19, 2025

By: Erin Parker, Interpretive Services Supervisor

The trees in our backyards, cities, and throughout the Metroparks are a critical piece of our environments as they provide shade, filter water, host wildlife, and connect us to nature. Trees may seem like a permanent backdrop, slow-growing and ever-present, and tree problems like pests and disease may seem to sneak up on most people. But many tree species are susceptible to a variety of insects, fungi, and other disease. Early detection and awareness about these pests and problems may help prevent the spread.

Tree Pests and Diseases in Southeast Michigan

Beech Leaf Disease:

American beech, the tall, smooth-barked giant of southeast Michigan’s forests are under threat from a disease that first shows up in the leaves of the trees. As you are looking upwards into the canopy, leaves may appear to be striped with darker stripes inside the lighter green of the leaf. This disease first appeared in Ohio in 2012, and is likely spread by a non-native nematode, or small (often microscopic) worm. While many nematodes are beneficial, feeding on bacteria, fungi, and other microscopic organisms, some can cause harm. Beech trees can be killed as the disease impacts their leaves year after year, reducing their ability to photosynthesize. There is currently no treatment for beech leaf disease, which makes monitoring and reporting the spread critical.

Oak Wilt:

Another of Michigan’s important tree species are all of the oaks- these trees feed wildlife, provide shade, and live for centuries. Oak wilt is a fungus that particularly harms red oaks and, like beech leaf disease, there is no treatment and infected trees die from the fungal infection.

Luckily, with care, oaks wilt spread can be slowed. The fungal infection spreads through roots of trees, which means once it gets into one tree, it can slowly spread to and kill all the trees in an area. The fungus can also be spread by beetles moving from tree to tree or people moving firewood from place to place. The biggest preventative measures that people can take are to not prune oaks during their spring and summer growing season, April 15-July 15, and to not move firewood. Reporting signs of oak wilt, which appears as wilting and dropping of leaves that have turned yellow or brown can also help protect neighboring trees. Sometimes diseased trees can be removed and trenches dug that break up the connections between the roots of nearby, still-healthy trees.

Spongy Moth:

Another oak pest, this one in the form of a voracious moth caterpillar, is the spongy moth. These hungry caterpillars can defoliate oaks, though they have cyclical population spikes with some years and crashes other years.

There are many ways to reduce or prevent spongy moth outbreaks. Look for their fuzzy-looking tan egg clusters on tree trunks, fencing, and even outdoor furniture. The egg masses can be scraped off and soaked in soapy water to destroy them before discarding. Traps, made of burlap wrapped around a tree trunk, can catch the caterpillars as they attempt to crawl upwards to the leaves. The caterpillars can then be collected and destroyed.

Spotted Lanternfly:

Another insect pest that is just reaching Michigan is the Spotten lanternfly. This colorful insect may look like a moth or butterfly, but it is actually a planthopper that feeds on plants like grape and tree-of-heaven. These sapsuckers can harm plants directly, by feeding heavily, and also cause a secondary problem when their sugary waste secretions build up on plant surfaces and grow a sooty black mold.

This new-to-Michigan pest has been found in several southeast Michigan counties and, while the planthoppers don’t travel long distances as adults, their egg masses can be laid on nearly any hard surface and then moved inadvertently by humans. Keep an eye out for their eggs that look like old, graying chewing gum and, like the spongy moths, scrape and soak them before disposing of them.

Action Steps

Your Metroparks have a lot of trees to manage! According to Chief of Natural Resources and Regulatory Compliance: “We have been surveying for spotted lanternfly for the past 3 years in parks we determined were most likely to have the pest due to the parks’ proximity to known spotted lanternfly locations. This survey work is funded through the Michigan Invasive Species Grant Program. So far, we have not yet found spotted lanternfly in the parks. Additionally, our natural areas crew annual treats tree of heaven through the park system. Not only is this an invasive and aggressively spreading tree, but it’s the preferred host plant for spotted lanternfly.”

Anyone in southeast Michigan can help protect trees by observing and reporting signs of tree pests and diseases, as well as following protocols like not moving firewood and not trimming oaks during their critical April 15-July 15 growing season.

Jimmy Provost, Metroparks’ Natural Resources Supervisor added: “Tree diseases and pests don’t understand park boundaries. So, it is important to know what to look for in your own yard, and also to take actions to reduce the spread of diseases and pests. A big thing that homeowners can do is limit the trimming of oak trees to fall and winter months since oak wilt spreads through open wounds or cuts on oak trees.”

We can all do our part to speak for the trees by recognizing and reporting any problems they notice.

Read on for resources, more information, and where and how to report instances of tree pests and diseases.

Resources and Further Reading:

Learn to identify and report invasive species at the Midwest Invasive Species Information Network

https://www.michigan.gov/invasives/id-report/insects/spotted-lanternfly

Michigan Invasive Species Grant: Spotted Lanternfly and Tree of Heaven

https://www.michiganoakwilt.org/

https://www.michigan.gov/invasives/id-report/insects/spotted-lanternfly