We have received several calls to the Iowa State University Plant Disease Clinic regarding shade trees that have suddenly dropped most of their newly-developed, green leaves. Hackberry trees seem especially prone to shedding their green leaves, although oak, hickory, and many other species also have been reported to drop green leaves this time of year.
Although somewhat alarming, shedding of green leaves is a fairly common occurrence in the spring. It is most likely caused by cold springtime temperatures, and it is not usually associated with disease or insect damage. In most cases, the trees soon develop a new flush of green leaves and recover completely.
This article originally appeared in the 5/28/2004 issue.