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Desert GArdener: Controlling pests

June 14, 2001

The redgum lerp psyllid, Glycaspis brimblecombei, found infesting eucalyptus trees in El Centro has now moved to other locations through the Imperial Valley. This psyllid, a native of Australia, has spread rapidly throughout California where susceptible species of eucalyptus are grown.

Psyllids are plant-juice sucking insects similar to leafhoppers and aphids. The redgum lerp psyllid forms a protective cover called a "lerp," during its nymphal (immature) stage.

Lerps are composed mostly of crystallized honeydew (a sugary fluid) resembling small, white, hemispherical caps that grow up to one-eighth inch diameter and one-eighth inch tall. The nymph beneath each lerp is yellow or brownish and looks similar to a wingless aphid.

Older nymphs stay beneath their lerps and generally don't move.

Adult lerp psyllids are slender insects that are about one-eighth inch long and are similar to adult leafhoppers. Their bodies are light green with orangish and yellow blotches and they have clear wings that are usually held rooflike over their abdomen.


The adult of this species differs from other psyllids in California, possessing relatively long, forward projections on its head below each eye. Females lay tiny, yellowish, ovoid eggs singly or in scattered groups.

Female lerp psyllids prefer to lay their eggs on succulent leaves and young shoots, but all psyllid life stages occur on new and mature foliage.

Lerp psyllid start out as eggs that hatch into nymphs and gradually grow into adults. Young nymphs excrete gelatinous honeydew from their posterior end, eventually forming lerps. Older nymphs are concealed underneath their lerps.

Developmental time from egg to adult varies from several weeks during warm weather to several months during the cool season. We can expect two to four generations a year in Imperial County.

Psyllid nymphs and adults feed by sucking plant juices through their strawlike mouthparts. High populations of psyllids secrete copious amounts of honeydew. This clear sticky liquid fouls surfaces beneath heavily infested trees. A blackish sooty mold grows on the honeydew-covered surfaces.

High psyllid populations can cause severe leaf drop, creating an annoying mess of sticky leaves. Extensive defoliation weakens trees and increases tree susceptibility to disease and to other pests such as eucalyptus longhorned beetle.

Relatively little is known about controlling this new pest. Biological control is being investigated as a long-term solution. Redgum lerp psyllid in California is attacked by several natural enemies, but it's not known if these natural enemies are important in helping to control this pest in California.

Planting resistant species can prevent this psyllid from being a problem. Only certain species of eucalyptus are attacked by redgum lerp psyllid.

The primary host of the redgum lerp psyllid is the river red gum (Eucalyptus camaldulensis); in addition, sugar gum (E. cladocalyx) and white gum (E. viminalis) trees are heavily infested in some locations. Lemon gum (Eucalyptus citriodora), blue gum (E. globulus), E. lehmannii, E. nicholii, and E. rudis can also become infested in California.

Other species that may be susceptible based on reports from Australia include Eucalyptus blakelyi, E. bridgesiana, E. dealbata, E. nitens, and E. tereticornis. The complete host plant range in California is not yet well known.

Certain eucalyptus species are avoided by this psyllid. Eggs laid on certain other eucalyptus species are unable to complete their development and psyllid populations do not build to bothersome levels.

Minimize tree stress by providing eucalyptus with proper cultural care and protecting trees from injury. Nitrogen levels in foliage may increase when eucalyptus are stressed and increased foliar nitrogen increases reproduction and survival of psyllids. To minimize stress, provide trees with adequate water during summer and fall. Drought stress increases damage to trees from both lerp psyllids and eucalyptus longhorned borers.

Avoid fertilizing eucalyptus. Use slow-release nutrient formulations if other plants near the drip line of eucalyptus require fertilization. Psyllid nymphs and egg-laying females prefer the abundant, succulent new shoot growth stimulated by excess nutrients, especially nitrogen, that occur following the application of quick-release fertilizer formulations.

The effectiveness of insecticide against this psyllid has not been investigated in California, but systemic soil-applied insecticides, such as imidacloprid, may prove effective against this pest.

The lerp covering may provide psyllid nymphs with some protection from spray contact. Also, it's difficult to spray large urban trees without pesticides drifting off-target.

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