What is Oak Wilt Disease?
Oak wilt is a common name for the fungus Ceratocystis fagacearum. Thought to originate somewhere in Latin America, this fungus entered the United States as an invasive species and spread quickly across the country. In recent years, it has become increasingly common in Michigan, where growing numbers of homeowners and others who care for oak trees struggle to contain the disease.
Oak wilt attacks both red oaks and white oaks, though it causes the most damage to red ones. It enters a tree either through the root system or when carried by a beetle. Once inside, it makes leaf tips turn brown; this discoloration then spreads inward to the base, causing the leaf to wilt and defoliate. It also causes a mat of fungus to develop beneath the tree, and it may lead to discoloration in any sap the tree produces. If left unattended, oak wilt can kill a red oak tree in a matter of months. White oaks tend to resist this disease longer and have a higher chance of surviving, but they can still be severely damaged.
Can Oak Wilt be Treated?
Yes, but only up to a point. If a tree has been infected with the fungus, you can get a professional to inject it with fungicide, which will suppress the infected tree's symptoms. But there are some serious limitations to this treatment method, including:
Effectiveness- While fungicides suppress the symptoms, they don’t actually get rid of the disease, and it doesn’t stop it from spreading to other trees. It also only works for two years, after which point you’ll need to inject it again.
Cost- Injecting the fungicide is highly expensive. When you add in the fact that you’ll have to inject it multiple times, many homeowners feel it is not worth using.
Timing- Fungicide only works if you inject it shortly after an infection has started. If the oak wilt has already spread throughout the tree and caused serious damage, it won’t make much of a difference.
With these limitations in mind, many homeowners and other oak tree caretakers choose not to bother with treatment for infected trees. Even those who do recognize it is not enough to stop oak wilt from harming their trees. Instead, they wisely make prevention the centerpiece of their strategy for dealing with the fungus.
Oak Wilt Prevention Tips
Preventing oak wilt involves limiting the avenues for infection. To do this, you must:
Separate the Roots- Because oak wilt can spread through roots, you have to keep each tree's roots from coming into close contact with those of other trees. You can do this by spacing the trees carefully. If a tree becomes infected, you must quickly cut its roots off from the others.
Time Your Trimming- Beetles tend to attack your trees shortly after you have trimmed or pruned them, and if they’re carrying oak wilt disease at that time, they’ll spread it. You should thus take care of all pruning and trimming during the months when the risk of oak wilt is lowest. In Michigan, this is from November until the middle of March. You should also make sure to sterilize your pruning and trimming tools before you use them.
Paint Wounds- Whether due to trimming and pruning or natural damage, your trees may develop wounds, which are vulnerable to infection through beetle attacks. But you can stop beetles from attacking by painting over those wounds.
Debris Care- Be careful where you put clippings, trimmings, and other debris from your trees, as they could contain fungus. Generally, you should burn this debris, bury them, chip them, or cover them in plastic at a location far from your oaks. This is especially important if you suspect that the trees that produced the debris contain oak wilt fungus.