African Sumac Limb Disease

Q. My African sumac tree has a fungus in it. I am thinking of cutting off the whole main branch because of the disease but it’s a guide branch and I hate to do that. Or can I just cut off the branch that broke? Any info you have would be greatly appreciated!

Bottom picture is limb of African Sumac reportedly dead. The top picture is the inside of the limb cut open to show the dead part inside.

A. The disease won’t spread to healthy parts of the plant. The rot or disease spreads internally inside the tree because it's what we call "saprophytic" and only attacks dead or very weak wood. There is nothing you can do to stop it.

Tree Biology

            The center of the tree is composed of dead wood. The only living part of the tree is a thin ring just under the bark. This living part is strong enough to stop the spread of this "saprophytic" disease. The only thing you can do to help your tree is to make sure that whatever you use to cut or prune the wood is as clean and sharp as possible.

Narrow crotch angles are not good in landscape trees. They are shaped like the letter "V". After time they start to split as their weight increases and rot can begin on the inside of the trunk.

Narrow crotches start to split during the wind and its internal dead wood begins to rot. This rotting will not affect the living parts of the tree. Only the dead parts.

            My guess is that this “rot” started at the top of a narrow crotch; where two limbs come together. Narrow crotch is making the letter V when you look at it. Week crotches can split in strong winds particularly if the inside of the tree has been starting to rot there. A strong crotch angle makes the letter “U” and less likely to start rotting in that spot and then split apart in strong winds.

             Prune it enough to shape the tree the way you want it. Just cut off the branch that broke very close to the next larger branch and let it heal and completely close it off in three or four years. It takes longer to heal if it’s not cut close to the trunk so there is no longer a stub remaining. If the tree looks healthy to you otherwise then don’t worry about it. Cut off the limb close to the trunk with a clean blade.