April 15, 2020

Contact: James Wieferich, 517-284-5866

Trees at higher risk of oak wilt now through mid-July

If you have oak trees – especially red oaks – now is the time to be wary of oak wilt spores carried by flying beetles.

From April 15 to July 15, oak trees are at high risk for oak wilt, a serious fungal disease that can weaken white oaks and kill red oak trees within a few weeks of infection.

“The guidelines against pruning oak trees during this period are a way to help prevent the spread of the disease,” said James Wieferich, forest health specialist in the DNR’s Forest Resources Division. “Unfortunately, many people learn not to prune or otherwise wound trees from mid-April to mid-July only after they lose their oaks to oak wilt.”

Fungus travels by insects, through root grafts
Once a tree is infected, the fungus also can move to neighboring red oaks through root grafts. Oaks within about 100 feet of each other – depending on the size of the trees – have connected, or grafted, root systems. Left untreated, oak wilt will continue to move from tree to tree, killing more red oaks over an increasingly larger area. As more trees die from oak wilt, more fungal spores are produced, which allows the beetle to carry infection to new locations.

Oak wilt was first identified in the 1940s and is now widespread across Michigan. Red oaks are most susceptible to the disease. These trees have leaves with pointed tips and include black oaks, northern red oaks and northern pin oaks. Trees in the white oak group have rounded leaf edges and include white oaks and swamp white oaks. They are less susceptible.

Symptoms most often appear from late June until September. Affected trees will suddenly begin to wilt from the top down, rapidly dropping leaves, which can be green, brown or a combination of both colors.

Take steps to reduce risks to your trees
The high-risk period of infection occurs from April 15 to July 15, so it's important to avoid pruning or injuring oak trees during this time. If you have a tree that gets damaged during the risk period, immediately cover all wounds with tree-wound paint or latex-based paint.

Don’t move firewood, especially if it comes from oaks that may have died from oak wilt, as firewood can harbor the fungus. If you suspect your firewood is infected by oak wilt, you can help slow the spread by burning it, chipping it or debarking it before April. Once the firewood has been dried over a year and/or all the bark loosens, the firewood can no longer spread oak wilt.

To minimize the risk of oak wilt infection caused by logging damage, the DNR restricts cutting of red oak trees on state-managed land between April 15 and July 15.

The DNR recommends private forest landowners exercise caution during this period and, whenever possible, delay harvesting activity in oak forests until after July 15.

What to do if you suspect oak wilt
• Report infections at Michigan.gov/ForestHealth using an interactive map.
• Contact a local DNR forest health specialist for more information at DNR-FRD-Forest-Health@Michigan.gov or 517-284-5866.
• Michigan State University’s Diagnostic Clinic also can verify oak wilt infection. Find instructions at PestID.MSU.edu/ or call 517-355-4536.
• Get help from an oak-wilt qualified specialist. Visit MichiganOakWilt.org for a listing and more information.
• Learn more about invasive species in the state at Michigan.gov/Invasives.

Oak wilt – Please be aware!

Oak wilt (caused by the non-native fungus Ceratocystis fagacearum) is catching the attention of natural resource professionals and landowners across Michigan. In West and Northwest Michigan, oaks are amongst the most common and dominant species in many forests. Oak wilt is now wreaking havoc on our oak resource in Michigan, particularly those in the “red oak group” (those with leaves that have “pointed” tips, such as northern red oak, black oak, and northern pin oak). This fungus, which is related to the fungus that caused Dutch Elm Disease, kills oak trees by clogging its water transport system, thus causing the wilting of the leaves that is seen in infected trees. Once oak wilt has infected an oak tree, it can spread underground to neighboring oak trees via root grafts, and it can spread aboveground from sap-feeding beetles that carry the fungal spores to other trees. As oak wilt becomes more prevalent in Michigan, proper education about how to identify this disease and practices that can help slow the spread, will be necessary to help save the oaks that so many of us value.

So what can you do?

1) Learn how to identify which oak species are on your property. Oak wilt mainly infects oaks in the “red oak group”, and this includes trees that are otherwise perfectly healthy. Oaks in the “white oak group” can be infected but they are typically resistant.

2) Pay close attention to your “red oak group” trees. If you see the leaves suddenly turn a yellow or bronze color AND drop from the tree, then contact a professional who is qualified to determine if you have oak wilt. This changing of leaves and shedding of the leaves typically happens from mid-summer to early autumn, and the progression is very sudden.

3) There are other diseases and pests that affect and kill oak trees so please contact a qualified professional if you are not sure.

4) DO NOT cut or prune your oak trees from April to August as these wounds can attract the sap-feeding beetles that spread oak wilt. If pruning or cutting is absolutely necessary during this period, please make sure that you apply a tree dressing compound to the wound immediately following cutting. ALSO, do not move infected oak firewood!

For an excellent bulletin about oak wilt with more details, written by Michigan State University Extension, please go to http://msue.anr.msu.edu/resources/oak_wilt_in_michigans_forests

If your property is in Manistee, Mason, or the western half of Lake County and you think you may have oak wilt or would like more information about this disease, contact Josh Shields, Forestry Assistance Program (FAP) forester with the Manistee and Mason-Lake Conservation Districts, at 231-889-9666 (Office Phone), 989-220-9236 (Mobile Phone), or via email at joshua.shields@macd.org.