Ash: Anthracnose

categories: Ash Ash Diseases Ornamental trees Ornamentals

revision date: 2024-06-05 02:07

Ash anthracnose on leaves.
Ash anthracnose
Photo by: R.S. Byther


Anthracnose is a fungal disease of leaves and twigs of many ash species, including black, green, red, velvet, and white ash. Symptoms of anthracnose arise in spring on succulent, expanding shoots and leaves as water-soaked spots that may enlarge and coalesce rapidly. Young leaves may be severely deformed (curled, puckered, or twisted) by infections occurring during development. Later symptoms include the presence of small to large irregular brown lesions on the leaves, usually along the midrib or main veins. Half or more of a leaf may be killed. Twigs may develop cankers and die back. The fungus may be visible as small brown specks on the lower surface of infected leaves or as pustules on infected twigs. Infections of mature, more resistant leaves are often limited to small brown spots. The fungus may infect and girdle twigs, also and cause premature leaf drop. The disease is favored by prolonged moisture at the time leaves are developing. Symptoms appear on lower part of tree; in severe cases, they can progress to the top of the tree. Defoliation in several successive years may lead to dieback.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

  • Avoid overhead watering.
  • Do not compost diseased material.
  • Prune and destroy diseased branches, when practical, to reduce overwintering of disease.
  • Rake and destroy fallen leaves during summer and fall.
  • The Modesto variety of velvet ash is the most susceptible. Green ash is relatively resistant.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

If fungicides are needed, apply in spring during budbreak and early shoot growth when wet weather is expected. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.