Anthracnose on Shade Trees

Anthracnose on Shade Trees - Solution Guide

Anthracnose is a common disease caused by several species of fungi in several genera, including Discula, Apignomonia, and Colletotrichum.


Leaf spots are the most common symptom. Spots that form are typically tan to brown or black blotched areas on leaves, which develop commonly, but not always, adjacent to the leaf veins. Frequently, the infected area will expand outward to the leaf margin causing irregular, brown patches, and distortion of the leaf.

Susceptible Tree Types Include:

  • Sycamore
  • Flowering dogwood
  • Maple
  • Ash
  • Birch
  • Black walnut
  • Hornbeam
  • Buckeye
  • Elm
  • etc.

Anthracnose Infections:

  • During winter, the causing fungi exist in diseased leaves and stem tissue and on the ground in fallen, infected leaf debris. Spore-causing pathogens are ubiquitous in the environment and can travel decent distances.
  • In early spring, infectious spores are produced, which are then carried by rain and wind to newly emerging leaves. Additional new spores are produced from recently infected leaf tissue, causing further spread of the disease during the growing season.
  • Temperature and rainfall are the key factors determining an anthracnose infection's severity. Average daily temperatures between 50-60°F during bud break and early leaf development are responsible for spore production and infection spread. Weather dependence means higher or lower average temperatures during this period will reduce disease severity. Frequent rain aids the dispersal of spores and allows for a more significant number of infections. Symptoms most commonly occur sporadically only during conducive weather patterns.

Although spotting and leaf dropping during severe infections can cause the tree canopy to appear unsightly, Anthracnose is not fatal. It is a disease classified as a cosmetic nuisance. Weak, stressed, newly planted trees or trees that have been previously infected are most susceptible to this disease.

Anthracnose Management:

  • Practice proper sanitation. Rake and clean up all fallen leaves to reduce future reinfection. Burn, bury, or send leaves to the landfill. Do not compost disease-infected leaves since compost bin temperatures rarely get high enough to kill pathogens.
  • Keep trees healthy. Feed trees as recommended. Deciduous shade trees and evergreen trees are typically done in early spring with a granulated, slow-release balanced fertilizer, with subsequent applications of fresh compost or aged manure in late spring or late summer to help boost beneficial microbe populations.
  • Perform proper annual pruning. Since other disease infections such as canker can lead to general tree stress and weakness, proper pruning should be done as needed, while trees are dormant. Follow basic pruning rules, always with clean, sterilized cutting tools.
    • First, prune out any diseased or damaged wood using thinning cuts whenever possible or cut limbs back by several inches into healthy wood. Do not keep potentially diseased wood lying around. Burn, bury, or send it to the landfill.
    • Next, remove any rubbing or crossing branches.
    • Lastly, remove low-hanging limbs, suckers, water sprouts, or branches for cosmetic or safety reasons.
  • Water trees consistently. Watering trees during growing seasons is often overlooked, especially during drought and high heat. Trees can become easily stressed in those conditions. Newly planted or immature trees are especially susceptible to stress-inducing conditions. It is best to follow the 1-inch of water per week, per tree rule of thumb, with newly planted trees.

Suppose an Anthracnose infection persists yearly despite proper sanitation and maintenance measures. In that case, you may enlist a certified arborist's help to assist with a more advanced treatment program.