Enquiring eyes throughout Ohio are noticing sparse foliation on sycamores (American planetree) and to a lesser extent London planetree hybrids this Spring. Not to worry, the culprit is almost assuredly sycamore anthracnose disease. This fungal disease occurs every year, but is enhanced when there are cool, wet conditions during leaf emergence, conditions which were common throughout Ohio this year. If history is to be any guide, these planetrees will recover well, putting out new leaves which will make us forget how they look now by late June.
The fungus overwinters in twigs over the winter, with spores splashing to new foliage in spring. Leaves developing during warmer weather are less susceptible to infection. So, sprays are usually not warranted earlier for most planetrees and sprays applied now are even less warranted as the season progresses, since earlier infections will not be eradicated by these sprays and the tree should recover in any case.