Wafer ash (Ptelea trifoliate) which is also known as common hoptree or stinking ash has garnered considerable landscape interest in recent years owing to its native status in Ohio. It's also one of the few members of the Citrus (Rue) family (Ruaceae) found in the state. I've developed an interest in this small tree because it's a host for one of the subspecies of the two-marked treehopper (Enchenopa binotata) [See BYGL Alert! September 11, 2016, Small White Masses on Red Bud Stems]. It's also one of the few hosts for the relatively rare orange dog or orange puppy caterpillar which is the larval form of the eastern giant swallowtail butterfly (Papilio cresphontes).
However, wafer ash is also a potato leafhopper (Empoasca fabae) magnate. Heavy feeding damage by both the nymphs and adults can cause the normally dark green leaves to fade to white. Although this leafhopper is most often associated with damage to field crops, it is capable of feeding on over 100 plant species including trees and shrubs. The literature notes that red maple (Acer rubrum), burning bush euonymus (Euonymus alatus), and wafer ash appear to be particularly susceptible.
The potato leafhopper feeds on the underside of leaves where it uses its piercing-sucking mouthparts to suck juices. They also inject a toxin in their saliva that destroys plant cells or interferes with the plants ability to produce photosynthates. The destruction of plant cells on red maples causes new leaves to become distorted and dark brown necrotic tissue to form along the leaf edges; a characteristic symptom called "hopper burn." The damage on wafer ash is more subtle. Leaves first develop tiny, yellowish-white spots (stippling) that strongly resemble symptoms produced by other plant pests including spider mites (family Tetranychidae). Heavy stippling may coalesce to produce irregular yellow patches or more broadly faded leaves.
Potato leafhoppers are not able to survive winters in the north. New infestations are spawned each spring by the arrival of adults and nymphs that were carried north on storm fronts originating in the Gulf States. Once deposited in the north, the hoppers begin feeding and reproducing with each new generation requiring about a month to develop. Early populations are often so low the leafhoppers remain undetected. However, populations build with each new generation with the heaviest damage usually occurring late in the season.
Decisions to use insecticides to manage leafhopper populations on wafer ash should be seriously weighed against two important considerations. First, potato leafhopper damage to wafer ash probably causes little harm to the overall health of affected trees because the most serious damage occurs so late in the season. Also, year-to-year potato leafhopper populations are highly variable; damage seldom occurs over two successive seasons. Finally, as noted above, wafer ash is an important host to the relatively rare orange dog caterpillar which develops into the eastern giant swallowtail butterfly. Insecticide applications aimed at potato leafhoppers may also kill the caterpillars reducing the appearance one of our largest and most beautiful native butterflies in our Ohio forests and landscapes.