The Black Walnut tree is one of the most hardy trees in the United States, able to resist most diseases. Insects pose a danger primarily to the nuts and young leaves, but there are certain diseases that can threaten the health of the tree. Fusarium canker is the worst of these, and can ruin the wood of an entire tree if left unchecked. Bunch disease is a virus that severely weakens the walnut tree --- it can be spread by insects, making it a danger in groves. Anthracnose can attack the leaves and shorten a tree's life.
The Black Walnut tree is one of the hardiest trees in North American. It is found widely throughout the United States and has many natural resistances in its leaves, bark and nuts that effectively fight off both disease and insects. These resistances are so strong that smaller plants have a difficult time growing underneath the tree because of the chemicals released by its roots. Because of some chemicals, the bark it used in some natural remedies. There is no known disease that can fully destroy the Black Walnut. However, some diseases affect it, especially when the tree is very young or very old, making it more susceptible.
The most damaging disease for a Black Walnut tree is known as Fusarium canker, which is a rot that infects the trunk. It can sometimes become so prevalent that the trunk itself is compromised, and dies or is chopped down. When this occurs, the tree can survive through new sprouts coming up from the roots.
The canker begins as damaged areas around the base of the trunk and grows from there. Strong trees might be able to recover from the canker and heal the damaged places, but it will still damage the valuable wood. The disease is caused by spreading spores, and can most easily infect wood where the bark has been cut or peeled off.
Bunch disease is a spreading virus that can be carried by insects throughout tree groves. This is a very slow disease that spreads through the sap, weakening the tree and causing it to produce rapid, green growth easily ruined by cold and weak limbs. There is no cure for Bunch disease, and if it spreads all the way through the tree system the infected plant must be removed, including the roots.
A simple disease that affects only the leaves, Anthracnose is not a threat to the Black Walnut, but can cause leaves to spot and wither, leading to premature decay. There has been no sign that Anthracnose causes any serious damage or restricts the growth of the tree.
Although Black Walnut trees are resistant to disease and insects, there are other dangers that can pose a threat to their health. Deer enjoy feasting on the tender parts of the Black Walnut tree, and should be kept away from the young shoots. Insects like the webworm and the walnut caterpillar can infest the nuts and other insects somtimes eat young walnut leaves.