This is mostly excretionary structure of crystallized honeydew produced by the larvae as a protective cover that closely resembles armored scale insects. The psyllids produce large amounts of honeydew, which stains the ground beneath trees. A blackish sooty mold grows on the honeydew-covered surfaces. In severe infestations, thousands of lerps cover the ground and understory, giving the appearance of hail. The lerps and honeydew stick to shoes of pedestrians.
Heavy infestations cause severe leaf drop.
Honeydew and sooty mold are bothersome to people, but probably do not have a serious adverse effect on tree health. However, extensive defoliation weakens trees and increases tree susceptibility to wood-boring pests such as eucalyptus longhorned beetles. These beetles, if successful in attacking trees weakened by RLP, can kill branches or entire trees. Successfully attacked eucalyptus will turn completely brown. RLP is implicated in serious outbreaks in native vegetation in Australia.