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May 12, 2015

Anthracnose of Shade Trees

Gail Ruhl, Senior Plant Disease Diagnostician, 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 affect many trees, including ash, maple, sycamore, white oak, walnut, birch, elm and dogwood. Each species of tree is infected by a different species of fungus, thus the fungus does not spread from oak to maple or maple to ash or ash to sycamore. A different fungal species is also responsible for dogwood anthracnose.

Symptoms are especially severe in years with cool, wet spring weather. The symptoms will vary depending on the type of tree and the stage of leaf development at the time of infection: leaf spots or blotches; twig dieback and wilting; and browning or death of emerging leaves are possible symptoms for certain tree species. Premature leaf drop often occurs with anthracnose diseases, however, most of the trees infected with anthracnose usually show good resilience, and are not permanently damaged by this early season leaf blight.

Symptoms of sycamore and ash anthracnose are prevalent this year.

Sycamore anthracnose causes severe blighting of newly emerging leaves and shoots (Figs 1,2). Twig and branch cankers, shoot blight, leaf blight (Fig 3) and leaf drop are all symptoms of the fungus that causes sycamore anthracnose. Leaflet drop, as well as dead tissue along leaf veins or at the leaf edges are symptoms for ash anthracnose (Fig 4). Although defoliation may be so great that anthracnose-infected leaves practically carpet the walks and lawns nearby, healthy trees will leaf out again in a few weeks time. Defoliation early in the year does not affect overall tree health since trees have plenty of time to produce new leaves to supply the energy reserves necessary to survive the winter.
 
Anthracnose symptoms on maple and oak (figs 5,6) range from leaf spots to enlarged blighted dead areas along veins and sometimes, with oak, to shoot blight.

Anthracnose infected trees need to grow more actively than they normally would in mid-summer to replace lost leaves. Thus, cultural practices that include maintaining a balanced fertilization program and watering during drought stress periods are important for the active growth required in the current season and for the regeneration of carbohydrate reserves In preparation for the dormant season. For additional management suggestions for anthracnose and other leaf spot diseases please refer to the following Purdue publications:
Anthracnose of Shade Trees - BP-9-W (pdf file)
Dogwood Anthracnose BP-48 
Leaf Diseases BP-143-W (pdf file)

​Click images to enlarge

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Fig. 1- Sycamore anthracnose
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Fig. 2- Sycamore anthracnose
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Fig. 3- Sycamore anthracnose
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Fig. 4- Ash anthracnose
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Fig. 5- Maple anthracnose
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Fig. 6- Oak anthracnose​