What is Fusarium Canker?
The fusarium fungus causes cankers in walnut trees in the Midwest and parts of the east. It enters the tree when the spores splash onto the tree during a heavy rain. It usually enters on the lower part of the trunk, but it can also infect branches and upper parts of the trunk. The disease causes cracks on the bark and dark, depressed, elongated scars. Trees with fusarium canker disease usually have sprouts around the base. The cankers cut off the tree’s circulation so that branches and stems above the wound die. As the canker enlarges and spreads around the tree, more of the circulation is lost and eventually the entire tree dies. After the tree dies, one of the sprouts can take over as the main trunk, but it takes years for the sprout to grow into a productive nut and shade tree.
Treating Fusarium Canker
There is no way to save a tree with fusarium canker disease on the trunk, but you can help a tree with cankers on branches. Prune away damaged branches, cutting them several inches (8 cm.) beyond the canker. Make sure you cut all the way back to healthy wood with no discolorations. Diseased prunings can spread the disease, so haul away or burn branches you prune from the tree. The best way to prevent the spread of the disease is to cut down and burn all walnut trees with fusarium cankers. You can distinguish fusarium from other types of cankers by the dark color of the wood inside the canker and under the surrounding bark. Use good sanitation when pruning a tree with fusarium canker disease. Disinfect small tools by dipping them into 10 percent bleach solution or 70 percent alcohol solution for 30 seconds. Spray large tools with disinfectant. Clean, rinse, and dry tools thoroughly before putting them away.
