The peach tree borer (Synanthedon exitiosa) is a highly destructive pest that targets stone fruit trees across North America, including peaches, plums, cherries, and apricots. This insect is the larval stage of a clearwing moth, not a beetle. The caterpillar-like larvae are a major threat, causing damage by boring into the wood of the tree. The urgency of treatment is high because the borers feed beneath the bark, disrupting the flow of water and nutrients, often resulting in the decline or death of susceptible hosts.
Recognizing a Peach Tree Borer Infestation
The most definitive sign of an infestation is gummosis at the base of the tree trunk, usually at or just below the soil line. This symptom appears as thick, gooey masses of sap mixed with reddish-brown, sawdust-like material called frass (the insect’s excrement). The larvae feed on the cambial layer, the living tissue just under the bark. The tree produces gum in an attempt to seal the wound, but young trees are often completely girdled and killed by this feeding activity.
The adult pest is a clearwing moth, often mistaken for a wasp due to its steel-blue body and transparent wings. Female moths have a distinctive orange band around their abdomen, while males have narrow yellow bands. Adults are active during the day, emerging and laying eggs in the summer, typically from late June through August. The larvae overwinter beneath the bark and resume feeding in the spring.
Direct Eradication Strategies
Once an active infestation is confirmed, direct intervention is necessary to remove the larvae. The larvae are protected inside their tunnels for most of their life cycle, making surface treatments ineffective. Treatment approaches fall into mechanical, biological, and chemical categories. These methods target the pest at different life stages or accessibility points.
Mechanical Removal (Worming)
Mechanical removal, or “worming,” involves physically destroying the larvae inside their tunnels. This is a practical method for small infestations or individual backyard trees. To perform worming, carefully remove the soil from around the trunk base to expose the feeding area. A thin, stiff wire, such as a straightened coat hanger, is inserted into the borer holes, which are marked by gummy frass. The wire is probed into the tunnel until the larva is pierced and crushed.
This method requires a delicate touch to avoid causing further injury to the trunk’s cambium layer. A pocketknife can also be used to scrape away bark and physically extract the larvae, but this must be done with extreme care to prevent girdling the tree. This direct approach is best performed in the late summer or fall when the larvae are still small and before they inflict their most extensive feeding damage the following spring.
Biological Control
Biological control involves using beneficial nematodes, specifically the entomopathogenic species Steinernema carpocapsae. These microscopic, parasitic roundworms are applied in a water suspension directly to the trunk base and surrounding soil. They actively seek out and penetrate the borer larvae, releasing symbiotic bacteria that kill the pest from the inside.
Nematode application is most effective when the soil is moist and temperatures are between 60 and 85 degrees Fahrenheit, typically in the late summer or early fall when the new generation of larvae has hatched and is active. The area should be irrigated beforehand and kept moist after application to ensure the nematodes can move through the soil profile to find their hosts. This method is considered a safe and effective biological tool for reducing borer populations without the environmental impact of broad-spectrum chemicals.
Chemical Control
Chemical management relies on preventive trunk sprays to kill the newly hatched larvae before they bore into the protective inner wood. Once the larvae are inside the tree, insecticides are largely ineffective. Products containing active ingredients like permethrin or carbaryl are commonly recommended for homeowner use, provided the product label explicitly lists peach tree borer control.
Timing the application is critical, as the spray must coincide with the peak adult moth flight, generally occurring in late summer or early fall. A thorough saturation of the trunk from the ground line up to the lower scaffold limbs is necessary, applying the spray every two to three weeks during the egg-laying period. It is important to read and strictly follow all label directions regarding application rates, pre-harvest intervals, and safety precautions, ensuring that the spray is directed only at the trunk and not the fruit.
Long-Term Tree Health and Prevention
Maintaining a vigorous, healthy tree is the primary defense against peach tree borers, as stressed or injured trees are more susceptible to attack. Proper cultural practices significantly reduce the risk of future infestations.
Preventing Trunk Damage
Preventing mechanical damage to the trunk is essential, as wounds created by lawnmowers, string trimmers, or pruning shears provide easy entry points for newly hatched larvae. The area immediately surrounding the trunk should be kept clear of grass and weeds. This helps maintain a dry, hot surface environment unfavorable for egg survival and larval entry. Keeping the area clear also makes visual inspection for frass easier.
Using Physical Barriers
Physical barriers can prevent female moths from laying eggs on the bark near the soil line. Wrapping the trunk base with a protective barrier, such as fine mesh screening or hardware cloth, excludes adult moths from the most vulnerable area. The barrier should be secured at the top and extend a few inches below the soil surface for maximum effectiveness.
Promoting Tree Health
Ensuring the tree receives adequate water and proper fertilization promotes overall health. This allows the tree to better withstand and compartmentalize minor borer damage. Newly planted trees should be set at the correct depth, avoiding excessively deep planting that can stress the root collar. Combining these cultural practices with annual monitoring provides comprehensive, long-term protection.