Integrated Pest Management
Shothole Borer
Shothole borer damage on tree limb.
Shothole borer gummosis.
HOSTS
- Most fruit trees
- Many ornamental trees, including hawthorn, cherry, and others
DESCRIPTION
Shothole borer is a bark beetle that can attack trees under stress, or with existing bark wounds. They feed in galleries just beneath the bark. Adults are tiny, brown-black beetles, about 3 mm in size. Larvae are small, creamy-white and legless, with dark brown mouthparts.
BIOLOGY
In Utah, there are 2-3 generations per year. Regardless of the number of generations, adults fly almost continuously from spring to fall, so trees can be attacked at any time. Shothole borer overwinters as larvae inside the tree, and adults emerge starting in April-May. Adults fly to weakened or stressed trees, and bore under the bark to create a short, parental “egg gallery” in the sapwood. Larvae hatch and feed in individual galleries for 6-8 weeks, pupate, and then emerge as adults for the second generation. The larvae of this generation overwinter in the wood and pupate in spring.
SYMPTOMS
- Tiny, perfectly round exit holes
- Clear tendrils of gum exuding from entrance or exit holes
- Boring dust (frass) in the bark crevices
- Yellowing and wilting foliage
- Branch dieback
GENERAL MANAGEMENT
Because shothole borers preferentially attack stressed or injured trees, management strategies aimed at keeping trees healthy are important. For example, deep watering should be done once a week during hot summer months (July, August) and less frequently in the cooler months.
Other management strategies include:
- Protect tree bark from winter injury.
- Apply white tree wrap on the trunk from December to April, or paint trunks with a 50% white latex paint/50% water solution.
- Replace or remove old, diseased, injured, weakened, or stressed trees.
- Prune dead or dying branches.
- Remove and burn, chip, solarize, or debark infested branches, stumps or trees, as old wood can attract beetles.
INSECTICIDES
Insecticide applications for shothole borer are generally not recommended. Additionally, there no products available that include shothole borer on the label. However, chemical products may be used IF the tree or tree type (fruit, or ornamental trees) is listed on the label.
Options include carbaryl, bifenthrin, permethrin, or spinosad (organic) once a month throughout the season. Systemic insecticides (such as imidacloprid) are not effective against shothole borer.