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Index : Pests
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- 7. Eucalyptus Insect Pest Cause Unwarranted Concerns - Top
- Many Eucalyptus trees around Tucson have been dropping leaves this spring due to the presence of tiny little insects with a strange-sounding name: Red Gum Lerp Psyllids. These small insects suck sap from Eucalyptus leaves, and like the Eucalyptus, they’re native to Australia. They have shown up from time to time here in Tucson, but this year they’re appearance is more widespread and on a larger number of trees. Still, their presence is more of a nuisance than a real threat to the health of our Eucalyptus.
Lerp Psyllids can be identified by the presence of white crystalline, scab-like dots that spot the leaves. These dots are called lerps, and under each lerp is an insect - the Psyllid. You can see the Psyllid nymph (immature stage) by simply pulling off the protective Lerp covering with your fingernail. They resemble small Aphids and are reddish bronze color in color. Adults are yellow to green in color and are winged.
Both Psyllid nymphs and adults feed by sucking out plant fluids from the leaf. Heavy populations of psyllids secrete copious amounts of honeydew. It is this secreted and dried honeydew that form the protective ‘lerp’ over the insect. Trees in some parts of Tucson were heavily infested earlier this spring, however, the rains we experienced in May washed most of the insects off the leaves, killing them. Some Eucalyptus did loose lots of leaves, but have begun putting out new growth. Too my knowledge, no trees have suffered serious injury.
Although several species of Eucalyptus can be attacked, the Psyllid’s favored host is the Red Gum Eucalyptus (E. camaldulensis), thus the name: Red Gum Lerp Psyllid!
In California, the Lerp Psyllid has been a serious pest, causing defoliation of many Eucalyptus. In their weakened sate, these trees are susceptible to other more serious insect pests, such as wood-boring beetles. In California, injections of systemic insecticides into the trunks of infected trees has been used to provide some measure of control.
Here in Southern Arizona no control measures for the Lerp Psyllid are warranted, according to Entomologists at the University of Arizona. Although these insects do show up from time to time, weather conditions, namely our Summer Monsoon rains, prevent the insects from developing.
Unlike Arizona, California summers are dry, enabling populations of Lerp Psyllids to build unabated. Their continual feeding for months on end, can cause continued defoliation and resulting injury to California Eucalyptus. However, recently a natural enemy of the Lerp Psyllid has been introduced from Australia to California. It’s a tiny parasitoid wasp that lays it’s egg n a suitable psyllid nymph. The egg hatches and consumes the Psyllid from within. The presence of this little wasp is already having an impact on the Psyllids reducing their populations and lessening the damage to Eucalyptus.
Rather than the Lerp Psyllid, Eucalyptus here in Southern Arizona are most at risk from extremely hot, dry conditions. Like all large trees it’s important to give them extra water in this extremely hot weather.
Once or twice monthly, deep water Eucalyptus and other large trees. The most effective method is to use soaker hose spread out under the tree, starting near trunk and spiraling out 10 or 15 feet beyond the spread of the branches. Open the hose bib to allow a slow flow of water through the soaker hose. Let the hose trickle out water for 6 to 8 hours overnight.
Water should penetrate the soil to a depth of 3 feet. A metal rod can be inserted into the soil to measure the depth of wetting. The probe can be easily pushed through wet soil, but will stop when dry soil in encountered. If the moisture hasn’t penetrated down 3 feet deep, then water longer.
Finally, if your tree looks thinner due to an earlier infestation of Lerp Psyllids, you can add some fertilizer at the time of watering to encourage new growth. Apply one-half pound of ammonium sulfate or other high nitrogen fertilizer for each inch of trunk diameter. Spread the fertilizer out under the tree and water to move the nitrogen into the soil.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona,
520-626-5161.
- Updated: July 3, 2005
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