Down the Garden Path
Richard Hentschel, Extension Educator
Just about this time every year, homeowners that have a Sycamore tree in the home landscape begin to notice problems. Leafing out late or seeing a second set of buds and then leaves form is not normal. While Sycamores seem to be the worst, the disease called anthracnose also infects other trees as well. Anthracnose is favored by cool wet spring weather with temperatures for several days in the low 50's, something we had a lot of in the Fox valley.
On maple and what is left of our ash trees, the damage is limited to leaf blight symptoms. On maple tree leaves, the cells turn black between the veining and the leaf retains much of its normal shape. If you still have ash in the yard or younger ash trees growing from seed, the disease causes a distortion in the leaflets causing them to curl sideways.
Sycamores are impacted more heavily as anthracnose also causes stem and twig cankers which leads to those stems and twigs dying. These lesions can grow all away around a stem, girdling and killing any growth the other side of the cankers. As the cankers developing, they restrict water and nutrition to any parts of the twig trying to grow. The first set of leaves will fall while green in the spring too. Once the weather dries and warms with temperatures above 60 degrees, the pathogen causing anthracnose can no longer survive in that environment and that allows the sycamore to produce new buds, leaf out for the second time, and remain leafed out for the rest of the summer.
It is impractical to attempt fungicide treatments on large trees, where a newly planted tree may warrant the sprays. Fertilizing in Early spring or after dormancy has begun in the fall can help the trees restore lost food reserves that went to creating that second set of buds. Watering in the hot summer months will benefit the trees too. An important time to water is late in the season. Seasonal sanitation includes picking up infected leaves and twigs. On younger and smaller trees, pruning can remove a portion of the cankers as well.
Sycamores are being grown by nurseries as a replacement for the ash trees we have lost. When looking for ash tree replacements, consider a sycamore that has some anthracnose resistance in its DNA. There are two kinds of sycamores grown, one better than the other for resistance. The American sycamore is more likely to contract anthracnose that of the London plane tree or the Oriental plane tree. There are cultivar selections available of the London plane trees that have good resistance. The one I have seen for sale in our area is "Liberty".
About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.