Oaks are one of the most majestic and beautiful trees on Earth and the emergence of oak wilt disease has threatened to destroy many of the mighty oaks we all love. In this article we’ll explore what causes oak wilt, which trees are susceptible, what homeowners can do to prevent it, and oak wilt treatment options.

Oak wilt is caused by a fungus (Ceratocystis fagacearum) that affects nearly all species of oaks and is particularly aggressive when contracted by Red Oaks. It has the potential to take out red oaks in just one season. This disease is a major problem in the eastern and central United States, including the greater Madison area and all of southern Wisconsin where we’re located.

Oak Wilt is caused by a fungus which invades the tree’s vascular system (right beneath the bark) and feeds off the tree’s translocating water. In order to eliminate the fungus, the tree blocks infected areas of the vascular system, eliminating necessary water from the fungus. Unfortunately, the tree is then unable to move water and nutrients to its leaves, slowly starving and dehydrating itself in the process. (Oof that sounds really terrible!)

All oaks are susceptible to Oak Wilt, however the Red oak subgenus, including Pin oak, Scarlet oak and Black oak are most affected. Trees in the red oak group generally die rapidly, usually within weeks or months after infection. Treatment will not save an infected red oak. Trees in the White oak subgenus, such as Burr oak and Chinkapin oak, can generally be treated for oak wilt and will recover within a year of treatment.

oak tree

Transmission and Symptoms

Oak wilt is transmitted primarily by sap-sucking insects and beetles which inadvertently act as vectors for the disease. However, overlapping root sections can also spread disease from an infected specimen through an entire stand if other susceptible trees are nearby.

Symptoms of oak wilt include:

  • abrupt leaf wilt during the growing season
  • browning of green leaves generally starting at the infection point in the canopy
  • leaf drop

Oak wilt symptoms in red oaks will typically appear in the upper canopy and progress inward and downward within a few weeks. At first, there may only be a single branch that dies, showing leaves that often bronze, or turn tan or dull green, starting at the tips or outer margins. The leaves will turn brownish and prematurely drop mid-summer.

Oak wilt symptoms in white oaks are similar but progress more slowly. Generally, a single isolated branch will begin to “flag” and leaves will turn brown. If left untreated for several seasons the dead areas will generally spread out from the area around the initial infection.

With red oaks, there is not much we can do if the tree is already infected, but in the case of white oaks, we must be sure to make a positive diagnosis by sampling and submitting the specimen to a local university tree lab for proper diagnosis since other factors or pathogens can cause similar dieback. Some examples include two-lined chestnut borer, soil compaction, storm damage, cankers, root rot or armalaria, and grade changes.

It is difficult to diagnose the issue quickly, as the fungus grows beneath the bark and the downfall of the tree is swift. This is why having a Certified Arborist from a local tree service out to your property to inspect your trees is incredibly important. If you live in the greater Madison, WI area you can contact us here.

man giving oak wilt treatment

Options for Oak Wilt Treatment

Don’t worry, if your tree is diagnosed as having oak wilt not all hope is lost, especially if it’s in the white oak family.

Red oaks must be removed as no treatment is available once the tree is infected. It is very important that the tree is left standing until the dormant season to reduce the risk of the pathogen spreading through any root grafts. Because of the dire results of infection, preventative/therapeutic treatments are a must for high-value Red oaks.

White oaks can be treated by tapping into the vascular system with a specialized pump setup that injects a liquid fungicide, Propiconazole, throughout the trunk and canopy. This will generally stop the progression of the disease and protect from reinfection for two years from the time of injection.

This treatment process is similar to an I.V. one might receive in the hospital. First, the proper dosage is determined with several techniques. Then the correct amount of injection sites are drilled in the root flare. The injection system (or I.V.) is plugged into the holes, filled with the appropriate dose of the chemical and pressurized enough to allow a gentle flow into the vascular system of the tree.

The benefits of this “I.V.” or direct injection method as opposed to other less-effective soil injected methods are many:

  • No chemical is released into the environment.
  • All of the prescribed chemical is delivered to the tree with no waste.
  • Adjacent plants will not be affected.
  • Beneficial soil microorganisms are left unharmed.
  • There is no chemical exposure to pets or children.
treating oak wilt

Oak Wilt Prevention

As a homeowner with beloved oaks on your property there are a few things you can do to help prevent oak wilt from infecting your trees.

Prune at the Right Time

Oak pruning must only be done in the winter by a trusted area tree service. Oak wilt is transmitted primarily sap-sucking insects. Therefore, pruning must be done in cold temperatures to avoid transmission.

Proactively Treat Your Trees

Many neighborhoods are lined with irreplaceable 80-200+ year old oak trees. Just like in modern health care, it is often better to be proactive than reactive. This is why a health assessment of your trees is necessary. If appropriate, therapeutic treatment of propiconazole fungicide may be prescribed to assure and infection can never take hold. Oaks can be proactively treated in the late spring or early fall with the I.V. method described above. This treatment will not help infected trees.

Hire a Professional

We know this is a lot of info and it can be challenging for an untrained individual to recognize these symptoms early enough to still be able to combat this tree disease and decide on a course of action for oak wilt treatment. Our primary piece of advice would be to contact a local tree service even if you just suspect something might be going on. When contacting a local arborist make sure to find a service that:

1. Specializes in disease diagnosis and treatment
2. Has Certified Arborists on staff and completing the evaluation and work.

Finding a company (like ours!) that has these basic requirements will assure you and your trees get the best care possible!

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