A swift decline in tree health, as exhibited by branch and twig death, leaf discoloration and leaf drop might indicate the presence of the eucalyptus longhorn borer. Smaller diameter eucalyptus trees of all species can be killed in one year by the longhorn borer. Trees of larger diameter may die after repeated years of attack.
The most obvious indication of the borer is the presence of the adult or larval stage of the insect. Larvae are creamy white in color and have large circular heads and reach one and a half inches in length. Adults are blackish-brown beetles up to an inch in length.
Adult beetles first emerge from eucalyptus wood in late April and are active throughout the spring and summer months. Eggs are laid in clusters under loose bark on the live trees and on fallen or cut down trees and limbs. Eggs hatch about two weeks later and larvae tunnel into and below the bark where they feed.
It is important to restrict movement of eucalyptus wood to limit the spread of the beetle. Restrict pruning and removal of trees to the winter and early spring months when adults are not active.
The best treatment is to keep trees healthy to prevent the problem from occurring. Healthy trees can often drown beetle larvae with production of large amounts of sap.
Proper fertilization, irrigation, mulching and pruning will maintain the vigor of the trees and support their natural defenses against insect and disease pests.