Shade tree anthracnose

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Spring rains that coincided with leafing out of our oaks and sycamores have set us up for another big year of shade tree anthracnose. Many samples and images of oak and sycamore anthracnose are being submitted to Diagnostic Services as well as county Extension offices. Folks in the landscape industry are looking for some new and improved way to prevent anthracnose, unfortunately, there is no silver bullet.

Anthracnose is a fairly generic disease name. Many different plants – vegetables, perennials, annuals, trees – get diseases commonly referred to as anthracnose. When we talk about shade tree anthracnose, we are referring to diseases caused by several different, but closely related, fungi. Oak anthracnose is caused by Apignomonia quercinia (good luck pronouncing that), while A. veneta causes sycamore anthracnose. Both of these pathogens blight foliage and in some cases create cankers on twigs, resulting in dieback. Anthracnose foliar lesions are large, irregularly shaped areas of necrotic tissue along the leaf margins and between the veins. Leaf blighting typically begins on lower branches and spreads upward. With a hand lens you may be able to see the fungal fruiting bodies along the veins of infected foliage.

Newly emerged foliage is more susceptible to infection. Last year I spoke to many landscape managers and homeowners that had experienced the damage caused by anthracnose. Many of these people were desperate for fool-proof control recommendations. As a rule, fungicides are not recommended for control of shade tree anthracnose. Large well-established trees that are otherwise healthy can withstand the damage without serious long-term affects. In time, severely infected plants will push forth a new flush of growth from buds that would otherwise have remained dormant.

Some examples where chemical control might be appropriate include protection of smaller trees or trees that are not well established, or in “show case” areas where for aesthetic reasons it is important to maintain a disease-free tree. Applications of Protect T/O, Camelot, thiophanate-methyl or Spectro will help protect foliage from infection. Refer to the fungicide label for application rates and intervals.

If you are not inclined to use fungicides to manage this disease, remember that sanitation is also important. Fallen leaves should be raked up and removed, spores of the pathogen remain viable on this dead foliage throughout the winter. In the spring humidity and rain help spread spores to the newly emerging foliage. Where possible it is helpful to prune and destroy dead twigs and branches from the trees during dormancy (This is probably impossible with large trees.). Some references indicate that white oak is more susceptible to infection than other oak species. Likewise, there are a few anthracnose tolerant cultivars of sycamore available.

If you are interested in learning even more about anthracnose, The University of Nebraska has a nice Extension publication that compares anthracnose on several shade trees and includes photos. It can be found on the Internet at:

http://ianrpubs.unl.edu/plantdisease/g1200.htm

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