There Are White Spots on My Eucalyptus

Causes

• The cause of psyllid outbreaks is not known, but there are certain conditions that are commonly associated with their presence. They are often found on eucalyptus trees that are stressed by weather conditions, such as trees that receive too little or too much rain. The most persistent outbreaks tend to occur in low-lying areas during summer months. Ineffective natural control, in the form of biological predators, and a surplus of young, malleable leaves result in tree specimens that are both vulnerable and attractive to the psyllid at the same time.

Impact

• Psyllid adults and nymphs feed on eucalyptus leaf phloem sap. As this substance is sucked out of leaves, a sticky material, commonly referred to as honeydew, is excreted. This material can result in conspicuous sooty mold growth and premature leaf drop. In severe cases, trees may experience branch die-back and death. Defoliation weakens eucalyptus trees, leaving them increasingly susceptible to other, more threatening, insects and disease.

Biological Control

• The Australian parasitic wasp, Psyllaephagus bliteus, was widely introduced into the United States in the year 2000. The very small wasp feeds exclusively on the Red gum lerp psyllid. Scientists are optimistic that eventually, as the wasp spreads, it will effectively help control lerp infestations within American eucalyptus trees. Other natural potential natural predators, which are known to attack insects that are similar to the lerp, include ladybird beetles, minute pirate bugs, green and brown lacewings, syrphid flies, spiders and birds.

Cultural Control

• Stressed eucalyptus trees are more prone to psyllid infestation. Maintaining proper conditions can reduce likelihood of insect injury. Select a species that is well-adapted to climate and conditions where it is planted. The amount and frequency of watering will vary by tree variety and site conditions but in general, eucalyptus trees prefer infrequent but deep waterings. Avoid fertilizing infested eucalyptus and prune with care -- psyllid nymphs and egg-producing females favor the new growth that is stimulated by excess nutrients and pruning.

Chemical Control

• Oil sprays and soap sprays can provide some degree of temporary relief by killing adult, egg and nymph psyllids that are not covered by protective lerps. However, the results are limited and only temporary. Unfortunately, there are no selective herbicides formulated to kill only psyllids; consequently, the chemicals used are just as likely to kill psyllids as they are beneficial predators. Some formulations of the herbicide imidacloprid, which is available to home gardeners as well as professionals, may help manage psyllids, but there are limited studies concerning proper timing and overall efficacy of the product.