Soft and Juicy Peach Bark May Mean Borers

Soft and rotting trunk of young peach tree. Definitely borers. Young fruit trees like peach and apple are very susceptible to borers in the desert and oftentimes don't survive a one time attack. Older trees can recover better.

Q. I recently planted a 15-gallon peach tree that I had in a planter pit all winter. I noticed that the bark was soft and almost rotting at the joints with some sap coming out. I am afraid that this can be borers but can’t say with certainty.

A. Judging from the picture you sent with all the dried sap coming from the tree and given it’s a peach, I am 100% certain this is borer damage. This damage started last year. Borer adults in southern Nevada  are beetles that fly and don’t bother a tree until it’s time for the female to lay its eggs.

Sap oozing from a newly planted fruit tree after a rain from borers.

            Adult beetles lay their eggs on all sorts of weakened and newly planted trees and shrubs, mostly on parts of the tree at least 1 inch in diameter and in full sun. The tiny larva from the egg tunnels inside the plant just under the bark, protected from predators and usually in the spring. Here it feeds on the rich sap it finds transported from the leaves and roots. As it continues tunneling and feeding under the bark, it gets larger as it creates more and more damage from feeding.

If the borer hasn't girdled or gone most of the way around the trunk or limb sometimes you can save it without an insecticide by removing all the damaged area with a sharp, sanitized knife.

            The most susceptible plants in our hot and dry desert are the small and newly planted trees and shrubs. These borers prefer fruit trees and landscape plants in the Rose family. This includes most common fruit trees and many different landscape plants. Probably peach is the most susceptible.

Plants will oftentimes produce new growth or suckers below the damage from borers or from its base.

            Once these plants get large enough to produce their own shade then borer problems lessen until they get a bad pruning job. Bad pruning jobs open them up to sun damage again and it starts all over.

Pyracantha dieback from borers. Don't expose the trunk or limbs to direct sunlight in the desert on these plants.

            What to do? Because they are hidden from site when tunneling inside young trees,  borer larvae are difficult to find. It’s easier to see their damage the day after a rain and the tree is sopping wet. Oozing sap from the trunk and limbs in areas exposed to intense sunlight is a pretty clear indicator of borer damage. Take a sharp, sanitized knife and surgically remove the young larva. It’s been suggested to soak the tree with a hose and water if it hasn’t rained.

There he or she or it is! Sometimes when you excavate the damaged area with a sharp sanitized knife you will see them busily eating away at the soft juicky rich sapwood just under the bark.

            Systemic insecticides applied to the soil around the tree will kill this larva inside the tree without using a knife. The most effective insecticide for doing this job as the insecticide “imidacloprid” listed in the ingredients. One example is the Bayer product referred to as “Tree and Shrub Insect Control”. Read the label on how to apply it as a “soil drench”, protect your hands and eyes, and follow the directions exactly for best results.

Remember insecticides are a LAST resort when you have no other choices left. Apply imidacloprid as a soil drench (ingredient on the label) after the tree has flowered to protect honeybees.

            I caution people to apply it after the tree or shrub has finished flowering in the spring. Because it is a systemic insecticide that can last for several months, I also caution people not to eat any fruit harvested for 12 months after its application.