By now, everything that is going to green up, has greened up. So, if you have a plant that hasn’t green up, there’s likely an issue. But what if it’s one of your beautiful oak trees? Here’s what you need to know.

Oak trees are a one of the standard trees we find across Oklahoma. They are durable, and for the most part problem-free trees to have in your landscape. However, there is a disease that can kill a mature oak tree. It is called hypoxylon canker aka biscogniauxia canker.

Hypoxylon canker first hit our radar as a potentially important disease of trees in 1979. It was first found in Pushmataha County, but it is now active in much of the state. While it predominantly affects oaks in the red oak family, it can also be found on maple, hickory, pecan, golden raintree, and sycamore among others. And it is mostly found on mature trees rather than young ones. Part of the reason for this is because it tends to affect trees that are under some sort of stress. Stress factors can include drought, heat, root damage, and chemical injury among others.

Hypoxylon canker tends to enter stressed trees through a wound of some sort. In the beginning you might notice yellowing or wilting leaves. These symptoms by themselves are not necessarily cause for concern, especially in an Oklahoma summer. Next the disease progresses down the trunk and develops into a girdling canker which kills the entire tree. A girdling canker basically disrupts the flow of water and nutrients which causes the tree to die. When this happens, the tree seems to die almost overnight.

Hypoxylon canker fungi tend to grow under the bark. As it grows, it eventually loosens the bark which then separates from the tree, revealing what appears to be a white to brown, dusty looking mat. At this point the fungus is easily blown to nearby trees or carried from tree to tree by animals. Even splashing rain can spread the fungus among trees. As it ages, it darkens to be black in color.

Since there are no chemicals to treat for hypoxylon canker, the key to preventing it from damaging or destroying one of your trees is proper tree care and early detection. Proper tree care would include keeping trees watered during dry spells and making sure it has all the nutrients it needs. Also, be on the lookout for dying limbs with an area that has lost its bark and looks to be covered in powder.

If you suspect you have a tree that might have hypoxylon canker, send a photo of the affected area to our Diagnostic Lab for confirmation. If confirmed, you probably need to have the tree removed or at least the affected area removed as a start. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: 

USDA Forest Service - Region 8 - Southern , USDA Forest Service, Bugwood.org