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Anthracnose Disease of Trees

May 12, 1999
Each spring, we see spotting and blighting of the leaves, buds, and sometimes stems of sycamore, ash, maple, oak, elm, walnut, and several other tree spe-cies. This disease is anthracnose, caused by one of many fungi that are present in cool, wet conditions as tender leaves are first developing from the bud. Cer-tainly not all of the trees just mentioned are affected, but anthracnose will show its ugly head on susceptible trees that happen to put out new leaves in cool, wet conditions. The disease is most prevalent in the spring because the cool, wet conditions that prevail then are conducive to fungal development while slowing plant tissue development. Leaves that emerge in warmer, drier conditions usually escape the disease.

Recently, the Plant Clinic has received reports and samples of anthracnose on ash trees. Initial leaf expansion was great. The leaves looked healthy for about two weeks; then a tremendous amount of leaves with brown to black spots and blotches fell from the tree. Usually, the trees still appear healthy but thin-ner. Yes, this is probably anthracnose; and, no, we donít recommend a fungicide.

Unless anthracnose fungi have repeatedly hit a tree in the past, we do not recommend the use of fungicides. Anthracnose diseases do not kill trees. Some defoliation may occur, but refoliation with healthy leaves follows in warmer weather. Concentrate on boosting tree vitality, which will promote new growth. Remove dead or dying branches, water in periods of drought, and mark calendars now to fertilize affected trees in the fall.

Central Illinois has also experienced the usual amount of sycamore anthracnose. That species is not really as slow to leaf out as some might think. Look closely at the leaves to see that many are already brown, dry, and dead. Donít fretómost of these trees are huge, old trees that will outlive most of us. Sycamore anthracnose takes several forms including leaf blight, bud blight, shoot blight, and cankers.

For more on anthracnose diseases of shade trees, consult Report on Plant Disease No. 621.

Author: Nancy Pataky


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