Summertime is Borer Damage Time

In the middle of summer this is what catches your eye. Limb dieback. Borers in peach tree.

This is the time of year when borer damage in trees and shrubs is most obvious. Limbs are dying. Their damage can be seen from a distance now but they’ve been working hard feeding on the inside of trees and shrubs for months. The telltale sign of borer damage is a single limb or branch with leaves that turn brown and the branch dies. That’s during dry weather which happens a lot here.

Sometime borers will catch your eye because the bark is peeling off the trunk.  Borers in ash tree.

            Borer damage is often times associated with damage to plants from intense sunlight, sometimes called sunburn or sunscald. Damage is often times seen on the hot exposures of a trunk or the upper sides of limbs. A good strategy is cautiously prune plants that get borers. These include many fruit trees, pyracantha, Arizona cypress, loquat, several types of landscape trees and shrubs.

They either cause or are attracted to plant parts damaged by the sun like the upper surface of branches or the south or west sides of the trunk.

            One borer in a small branch can kill it. But it takes two or three borers feeding in the same area of a limb to cause a larger branch to die the same season it is attacked. It’s probable that borers were present in trees, chewing away on the soft succulent inside just under the bark, for years before obvious summer dieback is seen.

The larva (borer) of the adult beetle can be found feeding on the inside of the tree, just under the bark. Borer in Red Bird of Paradise.

            Resistance to borers depends on the health and age of the tree. Healthy trees withstand several attacks by borers before damage is seen. Smaller sized trees are easily killed while larger ones are more resisitant. Sometimes trees are healthy enough that damage is never seen and they “outgrow it”.

            The best time to inspect a tree for borer activity, even if you don’t suspect anything, is immediately after a rain. The rain “softens” the surface of limbs or the trunk. Tree sap associated with the feeding of borers oozes from the trees, at the damaged area, resembling varnish remover oozing from the trunk or limbs.

Sap, either dried or still gooey, can be a dead giveaway of borer activity in some trees. Some trees are just naturally "gummy" and so you cant tell.

            If there is a lot of “varnish remover” coming from a limb or trunk, then there is heavy damage in those areas. Take a sharp, sanitized knife and remove the bark from the trunk or limb. The borers, or flat headed “worms”, lie just beneath the surface in those damaged areas. Remove them and cleanup the wound and let it heal. If damage is too severe, remove it.