Sycamore Anthracnose is a tree disease that is caused by the fungus Apiognomonia veneta. This disease affects sycamore trees, but there are some varieties that are resistant (namely the London planetree). While rarely fatal, the disease negatively affects the look of the tree and, with repeated years of infection, can affect its overall health.
The most common signs of Sycamore Anthracnose are (1) heavy leaf and twig drop in late spring, (2) a thinning crown, (3) distorted limb growth, and (4) "witches' broom" growth. Cool, wet, spring weather will aggravate the spread of this disease.
To stop this vicious cycle and to nurse the tree back to health, a two-fold approach is recommended. On one hand, the tree is injected with a fungicide that moves up into the small one- and two-year-old branches where the disease overwinters. In addition to the injection, a soil treatment is recommended with a mixture of fertilizer, bio-root stimulants, phosphite, and a systemic biological fungicide.
Large amounts of bark falling off of a sycamore tree is not a sign of Sycamore Anthracnose. Sycamore trees lose their bark (it’s called exfoliating) as a part of their normal growth process. While the exfoliation does appear to be worse in certain years than others, and although there has been very little agreement over the years as to what causes it, there is a definite agreement that Sycamore Anthracnose is not the cause.