The Purdue Plant and Pest Diagnostic Laboratory

What's Hot at the P&PDL for
May 27, 2010

Anthracnose on Ash

Gail Ruhl, Department of Botany & Plant Pathology, Purdue University

Anthracnose is the common name for a type of leaf spot and canker disease caused by certain kinds of fungi.  Anthracnose diseases, each caused by a different fungus, affect many trees, but are particularly prevalent on white oak, ash, maple, walnut and sycamore.

Anthracnose infections occur when periods of cool wet weather coincide with leaf emergence. The fungus that causes this disease overwinters in diseased leaf litter and stem tissue.  The fungus becomes active when temperatures warm up again in the late winter and early spring, producing fungal spores that are carried by rain and wind to newly emerging leaves.  These spores germinate and initiate new infections.  Additional spores are produced from these early spring infections, and so the cycle of infection, sporulation, and infection repeats.

The symptoms will vary depending on the type of tree and the stage of plant development at the time of infection. On ash, infected, young ash leaves may wither and turn black while older ash leaves will exhibit brown, marginal, half-moon shaped discoloration. Although leaf drop occurs, defoliation does not usually affect overall tree health since trees have plenty of time to produce new leaves and make the energy reserves needed to survive the winter.

Chemical controls are unnecessary since ash anthracnose seldom causes significant damage to trees. In addition, fungicides do not cure infected leaves, and spraying after seeing symptoms is a waste of time and money.

Please refer to publication BP-143 for additional information on leaf diseases.

See two of our previous articles:

Sycamore Anthracnose

Leaf-spotting diseases are flourishing with all of the rain

Click image to enlarge

on ash tree

Ash anthracnose

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service