Land Stewardship Technician Mark Peters wrote this blog post. He just finished his second season with us and will be returning to Michigan State University for his senior year, studying Forestry. Drop a comment to help us thank Mark for his contributions to keeping the natural areas in our parks beautiful!

We have probably all heard of oak wilt and that we should be on the lookout for it. But what is it and why should we care?

Oak wilt is a fungal disease than can kill oak trees very quickly. While there are no reports of oak wilt in Oakland Township, according to the Michigan Department of Natural Resources interactive map, there have been numerous confirmed cases in Oakland County, primarily on the western half. The easiest way to prevent its spread into the township is to avoid moving firewood and to avoid damaging oak trees during the growing season.

Oak wilt prevention is especially relevant here in “Oak”land Township where we have many oak woodlands and forests. In fact, one of my favorite areas in our parks is Lost Lake Nature Park. The open oak woodland is a fantastic place to go for a walk and appreciate some of the beautiful oaks that the township has to offer.

What is Oak Wilt?

Oak wilt is a fungus that kills oaks by interfering with the vascular system within the tree. Specifically, it clogs vessels in the sapwood of affected trees. This prevents the movement of water up from the ground into the rest of the tree, causing it to wilt and eventually die. Some oaks are more susceptible to oak wilt than others. Trees in the Red Oak group, which generally have bristle-tipped leaf lobes, are especially vulnerable, dying in as little as a few weeks. Trees in the White Oak group, which have rounded leaf lobes, are generally less vulnerable due to their ability to more effectively quarantine diseased wood, preventing the fungus from spreading throughout the vascular tissue. In some cases, just some branches of these white oaks may die instead of the entire tree.

Symptoms usually start with leaves at the top of the infected tree beginning to turn brown at the tips and, as the name would suggest, starting to wilt. Additionally, there may be darker streaks in the wood under the bark and in the branches. The most definitive way to identify the disease occurs after the tree dies, when the fungus will form mats under the bark which can push outward and crack the bark. These will produce a sweet odor and a sticky sap which will attract picnic beetles. The picnic beetles feed on the infected tree, picking up the fungal spores, then move on to other trees and spread the infection. Firewood from these infected trees can also spread the disease by providing an easy source for these beetles to feed and infect other trees.

Oak wilt can also spread below ground through root grafts. A root graft occurs when the root systems from different trees come into contact with each other and fuse together, allowing nutrients, and the fungal infection, to flow between them.

While the wilting of leaves is one of the most obvious signs of oak wilt, wilting does not always mean that oak wilt is present. Other factors such as bacterial infection or insect damage may also cause wilting leaves. The only way to be sure that it is oak wilt before fungal mats form is for samples of the affected tree to be sent to a lab and analyzed for presence of the fungus. If you think you may have a case of oak wilt Michigan State University has information on sampling procedures and can test samples for oak wilt.

Why Should We Care About Oak Wilt?

Now that we know what oak wilt is and how to spot it, why is it important? Oak wilt is important to be aware of because it can kill large areas of oaks if it is not caught, since it will continue to spread through picnic beetle activity and root grafts. Oaks are very valuable trees; they provide both food and habitat to a wide variety of insects and animals. Oak trees are also commonly planted ornamentally as landscape trees. Their loss could lead to major negative impacts on the surrounding ecosystem as well as making a large impact visually. It is important to be vigilant with preventing damage to oak trees during warm months (March to October) because there are no ways to cure afflicted trees. Keep a constant eye out for symptoms because if you catch a new infection early the surrounding trees can be often be saved.

The process for managing an oak wilt infestation is quite intensive. It usually involves selecting a buffer of visibly healthy trees around infected ones and using equipment to dig a trench (optimally two trenches) around this buffer deep enough to sever the roots. This trench is normally installed during the dormant season with a vibratory plow pulled by a tractor and must be at least 5 feet deep to ensure effective treatment, preventing the spread of oak wilt through grafted roots. The trees within the buffer zone are often killed to prevent additional spread and spore production. Small, single tree locations of oak wilt may be effectively treated pulling the stump of infected trees.

An Ounce of Prevention

This is a lot of information, but what can you do? The biggest way that people can help is to make sure that you are not spreading the infection and to keep an eye out for potential occurrences. One of the primary way so make sure that you are not providing a way for the fungus to travel is the proper handling of potentially infected wood. If you are dealing with potentially infected wood you should ensure that it is completely dry before the next spring to prevent formation of spore mats. Firewood should also not be moved long distances to prevent new cases of oak wilt appearing from potentially infected wood.

As an additional precaution, oak trees should not be wounded, whether that is by pruning or otherwise, from March until early November as the beetles that spread the fungus are most active within this period. If damage to oak trees isn’t avoidable, or happens from storm damage, immediately paint the bare wood with tree sealing paint or any latex paint. Picnic beetles can arrive at damaged trees within minutes!

If you want more information, check Michigan State University Extension, Michigan DNR, and the Michigan Oak Wilt Coalition. The DNR website also has an interactive mapping tool where you can report potential cases.

Information from Michigan State University Extension and Michigan DNR