Foliar sprays generally are not recommended and will most likely not be cost effective. There are no selective insecticides that kill only psyllids. It is difficult to spray large urban trees without pesticide drift. The lerp covering may provide psyllid larvae with some protection from spray contact. Unlike many other insecticides, oil can kill psyllid eggs, in addition to other insect life stages.
Insecticidal soap helps to wash-off honeydew and kill psyllids.
Thorough foliar coverage is essential, so effective spraying may be limited to smaller trees. Soap or oil applications will likely provide only temporary control and application may need to be repeated after about two weeks. Certain systemic insecticides may control RLP, but this has not been verified. These implants are pesticide-containing plastic plugs that are pounded into holds drilled every few inches to encircle the trunk. Proper implant depth varies in part depending on the tree species and trunk diameter.