Black Walnut Tree Disease


Black walnut trees (Juglans nigra) are famous for their beautiful wood products and for their delicious tasting nuts. Black walnut trees reach heights between 70 and 150 feet and are found throughout the United States and southern Canada. A hardy breed, black walnut trees may live to be 200 years old, but they are still susceptible to a variety of diseases.


Characterized by brown leaf spots and premature leaf fall, anthracnose often infects trees during the early summer months. Twigs and the nuts can be affected and damaged by anthracnose. It rarely causes severe damage to the trees but severely infected trees may lose all of their leaves. Control anthracnose by treating trees with fungicides in the spring and stop further spread of anthracnose by removing and burning infected leaves, branches and twigs.

Stem Cankers

Stem cankers are a disease caused by Fusarium sporotrichioides. This disease is one of the few that are serious and it can kill your tree. A canker is a dead, dark brown patch that will appear under splits in the bark. Stem cankers are often attributed to mower damage or pruning wounds. Cankers will heal over on larger trees but the wood may be stained and degraded. Smaller trees are cut and burned. Avoid fusarium infections by pruning trees between January and May and avoid pruning them from August through December.

Bunch Disease

This is a slow moving but serious disease that is caused by a virus-like organism which is spread from tree to tree by aphids and tree hoppers. It often affects only one branch and may require years to move through the other parts of the tree. Signs of bunch disease include cupped leaves, short shoots and weak wood, you'll notice branches and limbs break easily. Growth of the tree will slowly decline and the tree will eventually die. Branches infected by bunch disease must be removed immediately. If Bunch has moved to the base of the tree, remove the entire tree and kill the root system.


Blight causes black spots and holes in the leaves of the black walnut. Nuts are usually severely damaged and blight may cause the die-back of new shoots. Blight does the most harm during cooler, damp periods which is usually when trees begin to flower. Bacterial blight overwinters in normal healthy looking buds allowing it to quickly attack new spring growth. Treat blight by cutting off damaged parts of the tree and burn the infected stems, branches and nuts.

Powdery Mildew

Occurrences of powdery mildew are rare for the black walnut tree but this species of fungi may be found from time to time on trees in more humid conditions. Powdery mildew is a fungus that attacks the buds, young new shoots and leaves of your tree. It covers them with a powder like mass of spores which cause the leaves of the tree to turn brown and curl.Eliminate powdery mildew by using a proper solution of fungicide.

Keywords: black walnuts, walnut disease, black walnut disease

About this Author

Amy Deemer has been writing since 1992. Her articles on family life and pets have appeared in the family section of "The Herald Standard" newspaper. Deemer has an Associate of Arts degree in liberal studies from Westmoreland Community college.