Oak Wilt Disease

What is Oak Wilt?

2016 Oak Wilt range

Oak wilt disease is a fungus that infects and kills oaks trees. The fungus (Ceratocystis fagacearum) infects the tree through bore holes of oak bark beetles and a sap-feeding beetle. The fungus attaches to the beetles and gets a free ride from tree to tree. Once the fungus gets into the tree it stops the flow of water in the bark and plugs the vessels in the tree’s vascular system. This causes the tree to die.

All species of oak are susceptible to getting the disease but some species seem to be more tolerant than others. Red oak is more susceptible than white oak and other varieties.

 

Signs and symptoms.

Infected oaks will begin to show signs of wilting leaves. Leaves of infected trees will begin to turn brown around leaf edges and curl inward. Some leaves may fall off the tree when they are green and sometimes leaves will stay attached to the tree. Depending upon time of year, tree diagnosis can be very difficult.

Red oak leaf

Approximately one year after the oak tree has been infected a fungal mat, or pressure pad, can develop beneath the bark’s surface. This fungal mat is a source of infection. Picnic beetles are attracted to this spot on the tree. They will feed on the tree then transport the fungus to a healthy tree elsewhere.

Sap beetles (Family Nitidulidae)

Infected oak tree

Once a tree becomes infected there is no reversal. The whole tree will be affected and the outcome is tree mortality. One infected oak in an area can infect other trees surrounding it. Oak tree will graft their roots together in the soil and since the fungus is in the whole tree, including the roots, surrounding trees can become infected.

If a tree is infected during the early spring it is often dead by August or September.

Control methods.

Once an oak tree is infected there is no action that can save the tree.The best action is to be proactive in monitoring oak trees for signs of wilt and be prompt to remove any dead or dying trees and to break the root grafts between infected and healthy trees.

Root grafts can be severed by using a trencher down to 2 to 4 feet. Chemical application of soil fumigants can be done as well to kill the connecting roots. As soon as oak wilt is confirmed it is best to complete these practices to save and give the surrounding oak trees the best chance at survival.

What can you do to help?

While research shows that oaks can be infected any time of year, there is a period where oaks trees are safer from exposure to possible infection. Do not cut or trim any oak trees during warmer weather. These means only trimming or cutting down trees when it has been colder than 45 degrees for a few days in a row. Typically this period is November 1 to March 15th. It is important to limit impact to oak trees during other months of the year because the picnic beetles are more active. Since the picnic beetle is attracted to the smell of a fresh wound on the tree (trimming a branch or cutting it down) it is best to limit the beetles temptation.

If fungal mats or the beetles are found in diseased trees, a trenching perimeter should be established prior to removing the infected trees. The trees should be cut down and burned, chipped, or covered with plastic for a minimum of 60 days. This should include grinding the stump or covering the stump with dirt. 

Diseased trees can be used for firewood but must be covered for 60 days by a plastic tarp with the tarp edges buried in dirt. Tarping will ensure that spores and beetles cannot escape to infect other trees. This firewood should not be transported.

 

Want to read more?

Here are some links to other sites that we found helpful.

https://www.na.fs.fed.us/spfo/pubs/fidls/oakwilt/oakwilt.htm

http://www.michiganoakwilt.org/

https://treedoctor.msu.edu/oakwilt

https://www.extension.umn.edu/environment/trees-woodlands/oak-wilt-in-minnesota/

 

 

 

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