Black Knot on Oklahoma Redbud Trunk

Asked April 6, 2020, 3:36 PM EDT

My redbud was planted about 18 months ago. It had a great showing it's first spring, but this spring, only half the canopy bloomed. There is a black knot on the trunk that is oozing. Canker keeps popping up as a possible issue, but wanted to get another opinion. Thanks!

Collin County Texas

1 Response

As you have probably found, the most common disease of redbud is called "Bot canker". This disease is named for the causal fungus, Botryosphaeria dothidea. The disease occurs when the tree is stressed by some environmental condition, such as lack of water. Pruned branch stubs are usually where the fungus infects the tree. Although the swollen, bleeding wounds on your tree may be infected, I do not believe this is why your tree is slow in breaking bud. Some diagnostic protocols are necessary to assess your tree, some of which I can help with. For example, are the bare twigs supple when you bend them? If they snap, then the tree is indeed dying back. If they are supple, then the buds on the tree may yet emerge. Even so, the late emergence indicates the tree is probably under stress. When wounds on trees bleed as yours are, there are several potential reasons, all related to the growing and planting conditions. The tree may have been planted to deep? You should be able to see the "scaffold" roots growing from the base of the trunk along the soil surface for at least an inch or two. If not, the tree will look like post standing in the ground, meaning it is planted too deep. What is your soil drainage like? Redbuds prefer well drained soil, and would not do well where they have "wet feet". Is the turf growing right up to the base of the tree? There should be at least a foot around the base of the trunk where the is bare soil or a very light layer of mulch - again, the base of the tree should not be constantly moist or have to compete with the turf. Finally, redbuds tolerate sunlight, but are usually found on forest edges under larger trees where they get several hours of shade during the day. Keep all of these issues in mind and hopefully they will help you deal with the tree.