A tree expert and friend of Maple Leaves Forever, Carl Mansfield, looked into this question for us:
I checked a few references to confirm my best Guess as to what may be causing the terminal die-back, dead twigs and discolored, curled and dead leaves that are evident in the photo that accompanied the email you shared with me. From my experience with maple trees lined out in the nursery environment, there are several insects that can cause this type of damage when the buds break and new growth begins in the spring time on Maples and several other deciduous species. Two pests that we monitored for were:
- The potato leafhopper, Empoasca fabae attacks a wide variety of native and ornamental plants. It produces symptoms of injury on both leaves and twigs. Several generations can be present on the tree at the same time. When it is sufficiently numerous, it can cause curled, dwarfed and distorted leaves, and can kill twigs and small branches, most often in the upper crown of the affected tree. In birches and maples, the potato leafhopper feeds on the terminals and tender twigs. This injury may result in dead twigs and shortened, swollen internodes as well as pale distorted leaves that often exhibit dead margins. This leafhopper overwinters in the egg stage on the twigs of the host trees. When laying eggs the ovipositor of the female cuts slits into the twig tissue often completely circling the twig. This damage injures or kills the twig. The leaf hopper, Alebra albostriella is not as common as E. fabae. It feeds on birch, hickory, oak and maples. Some authors have given it the common name, maple leaf hopper.
- The tarnished plant bug, Lygus lineolaris also causes damage to maples. The adults go into hibernation in the fall, and become active in the early spring, about the time the first leaves begin to form. The nymphs suck plant sap from newly developing leaves which later turn into distorted shapes. They continue to feed on the host plants until they mature as adults. Enzymes secreted in the siliva are thought to cause the effectsdamage to the buds and leaves. Adults are capable fliers and readily move about to lay eggs on a variety of hosts. There are two to five generations per season depending on geographic location.
My suspicions are that leafhoppers may be the primary cause of the leaf/stem damage reported. They caused the most significant damage to our maple limers and larger trees. I cannot suggest a control measure as there are very few products (pesticides) available to the public. One reference suggested that leafhoppers were not an annually reoccurring pest (populations can be cyclic) and that controls may not be necessary. My experience has been otherwise.
Your customer may be able to Google these insects to find more information on these pests and to determine if the damage is comparable.