AMES, Iowa - The sycamore tree is one of Iowa’s largest trees, found mainly in the eastern and southern parts of the state. It’s a great tree to have on a landscape, but it can run into problems.
ISU Extension and Outreach horticulturists can help handle issues connected to sycamore trees.
Why is my sycamore tree dropping its leaves?
The leaf drop is likely due to anthracnose. Anthracnose is a common fungal disease of sycamore, ash, maple, oak and other trees.
Sycamore anthracnose is caused by the fungus Apiognomonia veneta. Anthracnose is most severe in years with cool, wet spring weather. Infections occur during rainy periods when mean daily temperatures are 50 to 55 degrees Fahrenheit.
Symptoms of anthracnose on sycamores include brown blotches on leaves, death of young buds and shoots, and leaf drop. In cool, wet springs, affected sycamores may lose most of their initial foliage.
Fortunately, the sycamore trees will continue to produce additional leaves and shoots through early summer. Foliage that develops in late spring and early summer shouldn’t become infected as warmer, drier weather suppresses anthracnose. Most sycamores should have a good canopy of leaves by late June or early July.
While anthracnose may cause extensive defoliation, it does not cause serious harm to healthy, well-established sycamores. Fungicide treatments are rarely warranted.
The leaves on my sycamore have a bleached appearance in late summer. Why?
The bleached appearance may be due to lace bugs. Lace bugs are sap feeding insects commonly found on the leaves of shade and ornamental trees in Iowa. The most commonly affected trees are hackberry, sycamore and oak. Adult lace bugs have attractive wings that are beautifully sculptured with an intricate pattern of veins resembling lace, hence the common name.
Lace bugs feed on the underside of the leaves. They pierce the leaf epidermis with their sucking mouthparts and cause the characteristic pale yellow, scorched or “bleached” discoloration on the upper leaf surfaces. The underside of heavily infested leaves will be speckled with small, black, shiny “varnish spots” (excrement). While lace bugs are present throughout the summer, damage symptoms usually don’t develop until August or September.
Lace bugs also have the annoying habit of dropping onto people and pets as they walk/sit under infested trees. While lace bugs are harmless, their presence in the hair, on arms/legs, or clothing can be quite annoying.
Lace bug damage varies greatly from year to year, mainly in response to variations in natural controls and weather conditions. Severe feeding may cause premature leaf drop, but healthy, well-established trees are not seriously harmed. Spraying infested trees with an insecticide in late summer is of little or no benefit to the trees. Further, spraying when it is too late for effective control may cause more harm than good by killing the insect’s natural enemies.