BLOOMINGTON, Ill. – Have you noticed sycamores have had an unusual leaf-out this spring? You are seeing a symptom of a group of fungal diseases, anthracnose, which worsen when weather conditions are cool and moist and make the tree look like it is dying says University of Illinois Extension horticulture educator, Kelly Allsup.
Anthracnose is a common fungal disease amongst our Illinois trees that is usually only a cosmetic problem meaning it usually does not kill the tree. Trees that are the hardest hit by this disease are ash, maple, white oak, sycamore, walnut, and dogwood. Anthracnose attacks young growth.
The disease appears as brown lesions on the leaves along the veins and leaf curling. Severely infected plants can lose their leaves but are usually able to recover with a second flush of leaves in the early summer. Small black dots can be seen on leaves and cankers can be seen on the branches. Anthracnose is so common in our Illinois landscape, that the “witch’s broom” appearance of Sycamores’ attacked buds, shoots, and twigs is an identifying characteristic.
Several fungi cause anthracnose. The Anthracnose that affects your sycamore is not the same fungi that affect your dogwood.
Dogwoods get two types of anthracnose when weather permits. Dogwood anthracnose is not as common but is more severe than spot anthracnose. Dogwood anthracnose causes shoot dieback, large tan lesions with a purple border (greater than a ½ inch), cankers on twigs, bark peeling, and can kill the tree.
Spot anthracnose presents as a white spot with a purple border and usually only affects the leaves. Dogwood anthracnose is difficult to control. Dogwoods in clay soils, exposed to high winds and drought, and located in shadier conditions are more likely to succumb to fungal issues.
Clean up leaf litter and prune out diseased branches that host the anthracnose spores over winter. Remove the debris from your property. Only compost the leaves if you actively manage your compost and can ensure that all leaves are worked into the compost as the heat will kill off the fungi (over 140 degrees). Otherwise, burn, bury, or remove the property infected leaves.
Good plant management can help reduce symptoms: watering during times of drought and a light fertilizer treatment.
If problems persist or you are looking to replace a tree, consider planting a more resistant species. London planetree (another name sycamores go by) cultivars like ‘Bloodgood,’ ‘Liberty,’ and ‘Columbia’ tends to be less susceptible than the American sycamore. Kousa dogwood and hybrids of kousa dogwood and flowering dogwood show more resistance.
As with most diseases, by the time you see the symptoms, fungicide treatment is ineffective. The Pest Management for the Home Landscape Manual produced by University of Illinois Extension suggests chlorothalonil and Copper octanoate for sycamore anthracnose. If symptoms are severe, treat next spring to reduce symptoms. Morton Arboretum says three applications are necessary, beginning in early spring when buds start to open, then two additional treatments in two-week intervals.
Preventative treatment for dogwood and spot anthracnose suggested by University of Illinois Extension include pesticides containing chlorothalonil, myclobutanil, potassium bicarbonate, propiconazole. Spot anthracnose is sprayed just before flowering bracts are fully open and dogwood anthracnose is sprayed when leaves are emerging. Two to three follow up treatments are recommended. Pesticides are usually not warranted; cultural practices should be addressed first.
For more information on this topic or additional Extension programming, please visit go.illinois.edu/LMW or contact your local Extension office.
— University of Illinois Extension
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