Anthracnose of shade trees

Quick facts

  • Anthracnose is a common disease of shade trees that results in leaf spots, cupping or curling of leaves, and early leaf drop.
  • In Minnesota, anthracnose is most common in cool wet spring weather. 
  • Anthracnose is not a significant threat to the health of the tree and does not require treatment in most cases.

What is anthracnose?

Twisted green oak leaves with brown ends
Oak anthracnose

Anthracnose is a common fungal disease of several different shade trees, that results in a wide range of symptoms including leaf spots, blotches or distortion, defoliation, shoot blight, and twig cankers.

In most cases, anthracnose does not cause permanent damage to established trees.

If a tree loses the majority of its leaves multiple years in a row due to anthracnose, this can weaken the tree and make it more susceptible to other pest problems.

Trees affected by anthracnose in Minnesota

Most fungi that cause anthracnose can infect only one type of tree. For example, fungi infecting ash trees will not be able to infect maple or oak trees.

  • Ash

  • Birch
  • Black walnut, butternut
  • Buckeye
  • Elm
  • Hornbeam
  • Maple
  • Oak

Anthracnose symptoms

A young green twig with distorted leaves and brown patches
Ash anthracnose
  • Tan to brown irregular shaped spots or blotches on young leaves; often located close to leaf veins.
  • Infected leaves may be distorted, cupped or curled.
  • Severe infection can result in leaf drop in spring. A second growth of leaves occurs by midsummer.
  • Infections on mature leaves are irregular tan spots, often associated with minor wounds like insect feeding. Leaf distortion is rarely seen in these infections.
  • Infections on green twigs can be small orange brown blisters to a brown band encircling the young twig resulting in shoot death. These infections are most common on young twigs of oak (Quercus spp.) and ironwood (Ostrya virginiana).
  • Disease is often most severe on the lower and inner branches of the tree but may progress up through the canopy.
  • In Minnesota, the disease is most common during cool, wet spring weather.

How to manage anthracnose of shade trees

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Rebecca Koetter and Michelle Grabowski, Extension educator

Reviewed in 2018

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