Identifying and Managing Sycamore Blight on Sycamore Trees
Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent
Do you want the good news of the bad news first? The bad news is that many of our area sycamores are infected with sycamore blight this spring. The good news is that sycamore blight seldom kills a tree. Well, it's good news for those of you who like sycamore trees. Most of you know that sycamores are not my favorite type of tree. One reason that sycamores don't hold my esteem is that they get sycamore anthracnose .
Sycamore anthracnose, also know as sycamore "blight", is a fungus disease which commonly attacks the leaves and twigs of sycamore trees. The cool, wet weather this spring has been ideal for the development of this disease. The fungus survives the winter in cankers (which look like small wounds) on the branch twigs and also on fallen leaves and twigs. During cool (55 degrees Fahrenheit), wet spring weather, the spores of the fungus develop in these cankers. The spores are blown and splashed by the rain onto newly expanding buds, shoots, and leaves. The spores germinate and the fungus infects and kills plant tissue.
The first symptom of sycamore blight is usually sudden browning and death of single leaves or clusters of leaves as they're expanding in the spring. It’s easily mistaken for frost or wind injury.
A quick look around the area, and you’ll easily find a large number of sycamore trees that are quite sparse and appear to be leafing out very slowly. Many of these are affected by “blight.” As our weather turns warmer (hopefully), the trees will form new leaves but the foliage will not be as dense as in other years.
If our cool and wet weather persists, later leaf infections may also occur. Symptoms of these later infections appear as brown dead spots which start at the base of the leaf or at avein on the leaf. The brown spots then follow the veins outward.
Control of anthracnose on susceptible trees is difficult, mainly because of the large size ofmost sycamores. Recommended cultural control consists pruning off and destroying infected twigs and dead branches and also raking up and disposing of all the fallen leaves and dead twigs. Both of these actions are designed to remove the organism that lives through the winter and produces spores the next spring.
Spraying with a fungicide to protect expanding buds and leaves from the fungus can be done in the spring as the buds begin to swell andjust start to break open. This is most practical where trees are young and small enough for you to be able to achieve good coverage when spraying. Adequate coverage is difficult to achieve on large trees, even for competent applicators with good equipment. Recommended fungicides are applied at bud‑break and then again at ten to fourteen day intervals during periods of wet weather. Remember that good coverage is essential for effective control.
I should note that sycamore and plane trees vary in their susceptibility to the disease. Oriental plane trees are resistant while native sycamores are not. There are some cultivated varieties of Oriental hybrids that are known to be resistant to the disease. These varieties are "Bloodgood," "Columbia," and "Liberty." If you must plant a sycamore, plant one of these resistant varieties.