What’s Wrong with My Sycamore?

By Robert Weaver

an image of sycamore leaves with anthracnose littering the groundIf the lawn beneath your sycamore tree looks like this this spring, you might be understandably concerned about the sycamore tree towering above it. Leaves shriveling and dropping by the basketful can certainly be disturbing, but in this case, it’s nothing to get too concerned about. In cool, wet springs, sycamores are susceptible to a fungus disease called anthracnose.

The symptoms of anthracnose usually appear when that cool, wet weather

an image of sycamore leaves exhibiting anthracnose symptoms

Sycamore leaves exhitibing anthracnose symptoms

(such as we’ve had in St. Louis this spring) coincide with the emergence of the young sycamore leaves. Both emerging and larger leaves will wilt, turn brown and fall from the trees. Cankers (sunken spots) develop on twigs and branches, and in severe cases can girdle the branch causing it to die.

an image of a canker caused by anthracnose fungus on sycamore

A canker/lesion caused by anthracnose

While these symptoms can concern homeowners, the damage is rarely significant to the long-term health of the tree. Healthy, mature trees will simply send out a new set of leaves, and with warmer weather, the fungus becomes inactive and by summer the tree will fully leaf out as if nothing had happened. Yearly repeated infections could weaken trees, cause “witches brooms” (twiggy clusters at a branch tip) or significant branch dieback, but again, otherwise healthy trees will not be too adversely affected. It’s mainly a short-term esthetic problem and maintenance issue (affected leaves and twigs will continue to fall through the early summer).

There are sprays to prevent the fungus, but these must be applied by a certified arborist, and are expensive and rarely necessary.  Other preventative measures include cleaning up the fallen leaf and twig debris and disposing of it, rather than composting to eliminate the source of new infection. Keep trees well watered during drought (sycamores are naturally a river bottom tree and need lots of water), and fertilize to maintain tree vigor.

If considering planting a sycamore, choose instead its cousin with similar appearance, the London plane tree, which is highly resistant to anthracnose.

Robert Weaver is editor of The Gateway Gardener magazine, Master Gardener, and has a degree in horticulture from St. Louis Community College-Meramec.