Correcting Borer Damage to Apricot

Q. The ‘Royal’ apricot tree I planted three years ago, died. Someone at the nursery told me they thought it was borers. When I was digging the old tree out, I broke a branch and found a dead larva. I plan to replace the tree next week. Is there anything I should put in the soil at the time I plant the tree that gives it some resistance to borers and I can still eat the fruit? I would prefer a nonchemical solution to the problem.

Picture of flatheaded borer in apricot by reader. In the hot desert our most common borer problems are the Pacific flatheaded borer and Flatheaded apple tree borer which attack most ornamental and fruit trees indiscriminately.

A. Borers here are a problem in nearly all trees and shrubs, not just fruit trees. Peach is most susceptible and apricot and plum less but they are also attacked if conditions are right. Apple can be very susceptible to borers, particularly when they are young.

Flatheaded borer damage to ornamental plum.

            This borer is in three different forms during its lifecycle: egg, immature larva or “worm” (which causes typical “borer” damage) and the flying adult which is a 3/8-inch-long beetle. Adult beetles can fly and so find a mate using their sense of “smell”.

Adult beetle of Pacific flatheaded borer from Oregon State University.

            Females lay eggs on limbs of trees and shrubs. They use their sense of “smell” to find the best place for egg–laying. The smell which really turns on their egg–laying is the odor given off by sunburned but living wood. Dead wood doesn’t have the right odor. Only wood that is alive but damaged.

            Their eggs hatch on the sunburned limb in a few days and the newly hatched but small “worm” tunnels into the tree where it finds food and protection from predators while it grows. The food these worms eat is the young “wood” just under the bark which is full of sugars.

Early stages of sunburn on a tree. This is the stage that many borers are attracted to.

            Most of its time is spent inside the tree, not outside of it. The most effective chemical that controls this pest is a systemic insecticide either poured around the roots of the tree or sprayed on the leaves. It is one of the most widely used insecticides in the world commercially and labeled for fruit trees and even vegetables. You can find this product in a homeowner form at any nursery or garden store.

Whitewash is made from white latex paint now. You can make your own by diluting latex paint with at least an equal amount of water. It should be thin enough to apply but shade the trunk and limbs with white to reduce the heat buildup and UV light reaching the living "wood".

         

Diluted white latex paint applied to reduce sunburn

            This pesticide enters the tree and spreads through it (systemically) where it stays put and effective for about 12 months. Scientists are debating, but there are allegations it may play a role in the recent decline in bee populations. Personally, I have a problem with any systemic insecticide approved for use in protecting food from insects whether approved or not. Do not use it on food crops unless the label specifically says you can.

            One non-pesticide approach is painting the trunk and tree limbs with whitewash. It is not 100% effective but does help. An “organic” method is digging out these “worms” from damaged areas of the tree with a sanitized knife. Once removed, allow the tree to heal without applying anything to the wound.

Sap oozing from the trunk of borer infested tree

This is what the limb should look like after cleaning up the damage and removing "hiding places" for adult borers after they emerge.

            Look for borer activity the day after a good rain. Areas damaged by borers push out a dark colored, jelly-like ooze indicating where the pest is located. Start looking for the borer at this spot with a sanitized knife and remove any places where it can hide from predatory birds and other insects.