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 their 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, scablike 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 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 forms 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 lose lots of leaves but have begun putting out new growth. To 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).
In California, the lerp psyllid has been a serious pest, causing defoliation of many eucalyptus. In their weakened state, these trees are susceptible to more serious insect pests, such as wood-boring beetles. In California, some measure of control has been provided by injections of systemic insecticides into the trunks of infected trees.
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.
California's summers, on the other hand, are dry, enabling populations of lerp psyllids to build unabated. Their continual feeding for months on end can cause continued defoliation and result in 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 its egg in 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 psyllid populations and lessening the damage to eucalyptus.
Eucalyptus in Southern Arizona are most at risk from extremely hot, dry conditions. As with all large trees, it's important to give them extra water in this extremely hot weather.
Once or twice a month, deep-water eucalyptus and other large trees. The most effective method is to use a soaker hose and deep-water the tree with a trickle overnight. Water should penetrate the soil to a depth of 3 feet.
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 1/2-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.
Contact John Begeman at 520/626-5161, e-mail address jbegeman@cals.arizona.edu
- Updated:
July 8, 2005
[e-Mail me the articles] -
[Search our articles]
- [contact
us ]
