In the past few weeks the Plant Clinic has received several calls about hackberry trees dropping their leaves. Other trees in the area, including maple and oak, have been unaffected. Recently we received two different samples from affected trees. Leaves are spotted with areas where the epidermis appears sunken. Some of the leaf margins are necrotic in a patchy pattern, not a uniform edge burn. New growth is healthy.
Many fungal leaf spots can infect hackberry in wet spring weather, but our lab work found no pathogens associated with the spotting and edge burn on these leaves. Fungal leaf spot was ruled out. Also, damage was not consistent with any insect-feeding injury.
There was some speculation that the cause might be chemical sensitivity on the part of hackberry--a sensitivity not shared by maples or oaks. Conversations with horticulture nursery specialist Dr. David Williams and weed science specialist Dr. Marshal McGlamery lead us to strongly question this theory. We have no proof that chemicals are to blame.
It is very likely that this earlier leaf drop was caused by a cold weather snap, probably when buds were first opening. Other trees may have been further along with less tender leaves when the cold temperatures occurred. That the injury happened suddenly and over a wide area are further clues to environmental injury. This is not a definite diagnosis, but it appears to best explain the injury we have seen. The good news is that hackberries are recovering with healthy new growth.