By Erin Marissa Russell and Matt Gibson
The peach twig borer is one of the biggest pest problems for stone fruit orchards, attacking not only peach trees, but the trees of other stone fruits, such as nectarines, apricots, and plums. The peach twig borer wouldn’t be that big of a problem for fruit farmers if it was just a pest known for boring into the twigs and branches of stone fruit trees, as it is known to do.
Unfortunately, the peach twig borer doesn’t stop at just the twigs, as later in the season, the pest is known to also bore into the fruit, attacking peaches, nectarines, apricots, and plums, sometimes destroying entire crops in the process.
Not to be confused with the peach tree borer, a pest known for boring into the trunk of peach trees, the peach tree borer causes damage to the trees that can become a problem after long periods of infestation, while the peach twig borer can cause new growth to die back and damage stone fruit harvests within the first year of an infestation.
Identifying Peach Twig Borers
Young peach twig borer larvae are off white with black heads. As they mature, larvae become brown with rotating light and dark bands or stripes around their abdomen. Adult peach twig borer larvae are around a half-inch long. The pupae, which form in protected locations on infected trees, or sometimes in the stems of infested fruits, lack a cocoon, and are small (one quarter-inch to just under one half-inch long) and brown.
Adult peach twig borer moths are quite small, measuring under a half-inch long, with metallic gray, speckled forewings. The long, thin forewings are fringed, but not as much as the hindwings, which are a lighter gray color. The antennas on their heads make it look as if they have snouts. The peach twig borer’s eggs are orange or yellow, oval, and found on the surface of twigs, leaves, and occasionally the fruit of stone trees.
The damage caused by peach twig borers is due to their feeding on shoots or the fruit of infested trees. Twig injury is most prevalent on new, young growth, especially on young, developing trees, as the pest’s feeding kills terminal growth, often resulting in unwanted lateral branch development. As the fruit becomes ripe, it becomes more prone to attack from the pests, as the flesh is softer and more easily penetrable. Peach twig borer damage to fruit usually occurs between the color change and harvesting. The pests bore into the fruit near the stem or near the suture line and feed just beneath the surface of the skin.
Preventing Peach Twig Borers
Environmental and cultural controls can allow gardeners to suppress or minimize the population of peach twig borers in their trees. When these coping methods are in play, gardens are less likely to require insecticides or other harsh treatments.
- Predatory Insects: It’s possible to keep peach twig borer populations at a minimum with the use of beneficial predatory insects. There are several varieties of parasitic wasp from the Chalcididae family that gardeners can deploy. Certain ants from the Formica family have also been used against peach twig borers to great effect. Such as Formica aerata, the gray field ant. Other predators of the peach twig borer include chalcid wasps from the Copidosoma family, the braconid wasp Macrocentrus ancylivorus, and the grain mite (sometimes called the itch mite) Pyemotes ventricosus.
- Pruning Shoot Strikes: At the end of spring and beginning of summer when shoot strikes first appear, gardeners have the opportunity to curtail summer generations of the peach twig borer and miss out on the damage they would cause. Simply prune away these shoot strikes as soon as possible, and any associated peach twig borer larva will be done away with as well. Be vigilant during the end of winter and beginning of spring in watching for old shoot strikes, as if you see them, early season controls should be used.
- Pheromone Traps: While traps won’t do anything on their own to stave off an infestation of peach twig borers, you can use them to monitor the associated moths and help you determine whether other controls are needed. Hang your traps between six and seven feet high in susceptible trees, and position them between one and three feet from the outer drip line of the tree. You should make the rounds to check your pheromone traps twice each week. Bait traps for peach twig borers with a pheromone lure, which should be stored in the freezer. Prevent contaminating your lures by never handling traps for two different species of insect at the same time. Using latex gloves or forceps whenever you need to handle the lures is another best practice that will help avoid trap contamination. Never keep a trap you used for another species and attempt to repurpose it with a different type of lure. Place your pheromone traps at the beginning of May in order to monitor for peach twig borers.
Treating Peach Twig Borers
While many gardeners turn to insecticides to defend their trees from peach twig borers, there are options that have lower toxicity. Microbial products or those that regulate insect growth can be carefully administered so they are timed with egg hatching and the feeding of new generations to be extremely effective.
- Botanical Bt: Bacillus thuringiensis, also called botanical Bt, is an all-natural method of pest control that gardeners can depend on to overcome a peach twig borer infestation. However, in order to be effective, the botanical Bt must be used as soon as the peach twig borers are seen in the garden. For it to work, botanical Bt must be applied before the borers have had a chance to tunnel into the wood of trees or their fruit. Botanical Bt is a soil-based bacteria that makes use of the microbes that occur naturally in soil to keep insects at bay. It works because the Bacillus thuringiensis bacteria produce a protein that is toxic and fatal to the larva of some insects, despite being safe to use around children and pets.
Whenever possible, gardeners should strive to avoid insecticides as a treatment for peach twig borers. Some of the potential insecticides that fight peach twig borers have harmful side effects, such as being detrimental to surface water quality or causing a health risk for beneficial wildlife like aquatic invertebrates, bees, raptor birds, and other animals that are not part of the insecticide’s target species. With careful monitoring and use of the alternative treatments we’ve discussed here, there’s no reason gardeners should need to rely on potentially harmful insecticides to keep their trees free of peach twig borers.