Peach twig borer,
Moths of the peach twig borer measure approximately 7.5-13 mm (0.3-0.5 inches) and have forewings that are steel gray and lightly fringed. The hindwings are a lighter shade of gray and more fringed than the forewings.
Eggs are oval and yellow or orange. After hatching, larvae of peach twig borer are white with a black head. Mature larvae are brown with dark and light bands that alternate on the abdomen; a feature that distinguishes this pest from other larvae that attack stone fruits.
Pupae are roughly 6.5-10 mm (0.25-0.4 inches) long and, unlike many moth species, do not pupate in a cocoon. Rather, peach twig borer pupation occurs in sheltered places on the tree, sometimes inside of infested fruit within the stem cavity.
- The peach twig borer is a species of moth that attacks stone fruits (Prunus spp.) such as peach, plum, apricot, and nectarine.
- Peach twig borer larvae are easily distinguished from other stone fruit pests by the alternating dark brown and white bands on the abdomen.
- Larvae can feed directly on fruit or on shoots. There are many management options available to combat peach twig borer infestations.
Peach twig borer larvae. Note the alternating bands of brown and white on the abdomen, which easily distinguishes larvae of peach twig borer from other stone fruit pests. They can attack different parts of the host plant and cause wilting of newly emerged leaves and disfiguration of fruit. Young trees are the most susceptible to infestations. Image credit: H. Audemard, INRA, Montfavet, Bugwood.org
Peach twig borer larva in a peach. Frass and entry holes are also visible. Image credit: Eugene E. Nelson, Bugwood.org
External signs of peach twig borer infestation include entry holes and the presence of frass on the fruit surface. Image credit: Eugene E. Nelson, Bugwood.org
Damage to the inside of a peach caused by feeding of peach twig borer. Image credit: H.J. Larsen, Bugwood.org
Wilting of young shoots on a peach tree in the spring due to peach twig borer attack. Image credit: G. Morvan, INRA, Montfavet, Bugwood.org
Life history and habits
Larvae overwinter in cells under thin layers of bark in bark cracks or in limb crotches. Overwintering sites contain visible collections of frass and wood chips due to larval feeding. Upon emerging in the spring, larvae feed on newly emerging leaves, shoots, and blossoms. After pupating, adults from the overwintering generation emerge in early spring and mate.
Female moths lay as many as 90 eggs singly on the surface of developing fruits, twigs, or the underside of leaves close to veins. During early July and late August, moths tend to lay eggs on maturing fruit. The eggs can hatch in as little as 5 days, depending on temperature, and there can be as many as three generations in a single growing season.
Signs of peach twig borer infestation include flagging or wilting of new growth in the spring. As larvae burrow deeper into shoots the branches wilt and die. This is likely to be more severe on younger trees, with stunted growth and declines in tree vigor occurring as terminal branches continue to die. Young trees are especially susceptible when under attack by high numbers of larvae.
Later in the season, larvae continue feeding on shoots or on fruit near the stem, on adjacent fruits, or on portions of the fruit in contact with leaves. Fruit disfiguration occurs when larvae feed along the sides. Infested fruits will also contain small exit holes, sometimes with protruding sap.
During bloom, trees should be monitored to determine whether the pest is present. Peach twig borer activity is visible when shoots are roughly 25 mm (1 inch) long and leaf shoots are wilted. Feeding at the base of flowers may also be visible. It is important to inspect multiple trees throughout the orchard. Shoots should also be examined in mid-June to look for the first summer generation of larvae. When these symptoms are present, additional control measures will likely be needed later in the season.
Moths can be detected with pheromone traps deployed in orchards during early May.
Upon detection, infested shoots should be pruned out in the spring and summer. This will help decrease densities of the pest and lower the likelihood of severe infestations later in the growing season. Early season controls should be considered when dead shoot tips from the previous growing season are present.
There are several natural enemies that can attack peach twig borer, ranging from ants to parasitic wasps, and even mites. Preserving these natural enemies can help suppress peach twig borer populations, as well as populations of other pests such as the green peach aphid.
Early sprays applied during pre-bloom and shortly after bloom will target young larvae and provide the best control of twig borer. However, spraying should be delayed until the first summer generation of larvae emerge in order to conserve natural enemies of the green peach aphid. There are several insecticides available to combat peach twig borer infestations and they should be rotated in order to prevent the development of resistant peach twig borer populations. Degree day models can be useful in determining the timing of sprays. For more information on degree days and insecticide options, consult the Washing State University factsheet and PNW Pest Management Handbook.
Brunner, F., Rice, R. E., 1993. Peach Twig Borer. Washington State University. Available http://treefruit.wsu.edu/crop-protection/opm/peach-twig-borer/
Hasey, J. K., Day K. R., and Tollerup K. E. 2015. Peach Twig Borer. University of California Agriculture and Natural Resources. Available https://www2.ipm.ucanr.edu/agriculture/peach/peach-twig-borer/
PNW Pest Management Handbook. (n.d.). Peach and Nectarine – Peach Twig Borer. Oregon State University. Available https://pnwhandbooks.org/insect/tree-fruit/peach-nectarine/peach-nectarine-peach-twig-borer
Utah State University. (n.d.). Peach Twig Borer. Utah State University – Extension. Available https://extension.usu.edu/pests/ipm/notes_ag/fruit-ptb