The beetles damage trees by boring holes into them and laying eggs. When the eggs’ hatch the larvae emerge and eat the bark. They also drill tunnels through the trees which can kill them.
These bugs only attack Eucalyptus trees which are quite common in California. They are most likely to attack sick trees and trees during droughts. In Southern California they do a lot of damage during the hot summer months when trees don’t get enough water.
Spotting Longhorned Borers
It is actually fairly easy to tell if borers are attacking your trees. If the damage is heavy you can actually hear their larvae inside the trees chomping away at the wood. This is a scraping sound similar to a saw or other tool hacking away at wood. If you hear strange sounds coming from a Eucalyptus it could be the borer.
Another way to spot them is to look for holes in the tree that ooze black liquid. There also can be dark black trails of gunk left on the tree’s bark. Spotting the borer is vital because they can kill a Eucalyptus if they girdle the tree or completely remove a strip of bark around its trunk.
Controlling the Borer
The best way to control Longhorned Eucalyptus borers is to keep trees healthy and well watered. Generally, the bugs leave trees that are well watered alone. A good way to do this is to use a hose root feeder especially during droughts and dry seasons. Put the feeder in the ground a few feet from the trunk to be the most effective.
Simply watering the tree without a sprinkler is a waste of time. You will have to apply water directly to the roots. This can be done with a hose root feeder which can be purchased at any hardware store.
Remove any dead or dying Eucalyptus trees as soon as you notice them because this is where the borer lives. If you use Eucalyptus as firewood cover it with plastic and keep it away from healthy trees because the borer can live in those logs as well. Try and dry the firewood out by covering it with clear plastic and put it in a place where it can get a lot of sunlight. This should kill any beetles in the wood.
There are also some insecticides that can control the borer. These will have to be applied as soon as an infestation is noticed to be effective.
Affected Species of Eucalyptus
Experts at the University of California at Davis have identified some species of Eucalyptus that are more susceptible to this pest than others these are the Blue Gum, Flooded gum, Kari gum, Manna gum, Round-Leaved or Red-Flowered eucalyptus and the Sydney Blue Gum.
There are also some species less likely to be attacked by the Eucalyptus Longhorned Borer. These are the Hybrid, Lemon Gum, Red Ironbank, Red River Gum, Sugar Gum and Swamp Mahogany. If you are planting new trees, it might be a good idea to plant these species especially in areas with water shortages.