Peach tree borer
The peach tree borer (Synanthedon exitiosa) kills more young peach trees in the eastern US than any disease. It attacks the trunk at and below the soil line -- exactly the area least likely to be inspected -- where larvae feed on the bark and cambium tissue, girdling the trunk over one or two.
—- title: "Peach tree borer" slug: peach-tree-borer hub: problems category: "Disease-by-host" description: "Peach tree borer larvae kill young peach trees by girdling the crown. Identify the gummy, glistening mass at the trunk base, understand the pheromone trap monitoring approach, and apply insecticide at the right summer timing." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-
The peach tree borer (Synanthedon exitiosa) kills more young peach trees in the eastern US than any disease. It attacks the trunk at and below the soil line — exactly the area least likely to be inspected — where larvae feed on the bark and cambium tissue, girdling the trunk over one or two seasons. A young tree that seems to be declining without obvious cause often has a peach tree borer infestation at the base that has been active for months.
I don't grow peaches at my Long Island property, so this guide draws on Penn State Extension, Cornell Cooperative Extension, and Clemson HGIC research.
The pest
The peach tree borer (Synanthedon exitiosa) is a clearwing moth (Sesiidae). Per Penn State Extension, adults:
- Are wasp-mimics with clear wings (wing scales are shed on emergence) and banded abdomens; females are metallic blue-black with an orange band on the abdomen; males are smaller and have yellow-and-black banded abdomens
- Are active in late summer (July–September in most of the mid-Atlantic and Northeast)
- Lay eggs on the trunk base and in bark crevices near the soil line
Per Cornell Cooperative Extension, the larvae:
- Hatch and bore into the bark and cambium at and just below the soil line
- Feed through the fall, overwinter as larvae in the feeding gallery, and resume feeding in spring
- Complete development by late spring–early summer of the following year; mature larvae are 1–1.25 inches, cream-colored with a brown head
The species infests peach, nectarine, plum, cherry, and occasionally apricot and ornamental Prunus.
Identification
The gum-and-frass mass
Per Clemson HGIC, the primary diagnostic sign is:
- A glistening, gummy mass mixed with brown frass at the base of the trunk, at or just below the soil line
- The gum-frass mixture is amber to brown, sometimes quite large (1–3 inches across) in established infestations
- A hand trowel used to scrape soil from the trunk base reveals the feeding area and, often, one or more larvae
Per Penn State Extension, the gum mass at the trunk base is the most reliable sign and should be checked every spring and late summer by clearing soil from the base.
The lesser peach tree borer
Per Clemson HGIC, the lesser peach tree borer (Synanthedon pictipes) attacks the upper trunk and scaffold branches of peaches, not the base. Its presence (gum mass on upper trunk or branches) is different from the crown-level attack of the peach tree borer.
Tree decline pattern
Per Penn State Extension, infested trees show:
- Reduced vigor and growth compared to uninfested trees
- Gum masses at the trunk base (see above)
- In severe infestations: wilting of branches above the infestation in summer
- Sudden tree death in young trees (1–3 years old) when the trunk is completely girdled
Young trees (1–5 years old) are at greatest risk; older trees can tolerate some borer activity but remain susceptible.
Timing: when adults are active
Per Penn State Extension, adult flight period varies by latitude:
- Mid-Atlantic and Northeast: late July through September; peak flight typically mid-August
- South: may begin in late June
Pheromone traps designed for S. exitiosa (available from commercial suppliers) are the most accurate tool for tracking adult flight in your specific location. Per Cornell Cooperative Extension, trap catches of 5+ males per week indicate active flight and the beginning of the insecticide application window.
Management
Pheromone trap monitoring
Per Penn State Extension, place pheromone traps 2–3 feet above ground near peach trees in mid-July. Monitor weekly. Begin insecticide application when trap catches indicate active adult flight or per a fixed calendar date recommendation for your region.
Trunk insecticide at adult flight
Per Clemson HGIC, preventive insecticide applied to the trunk base during adult flight is the most effective management approach. Apply from the soil line up to 18 inches on the trunk:
- Permethrin — widely labeled for peach tree borer on fruit trees; apply thorough coverage to lower trunk; repeat 3 weeks after first application during the extended flight period
- Kaolin clay — applied to the trunk as a barrier slurry; physical deterrent to egg-laying; OMRI-listed; reapply after rain
Per Cornell Cooperative Extension, insecticides must be applied to the trunk base (soil line to 18 inches) where eggs are laid and larvae enter — not to the canopy or as a soil drench.
Remove existing larvae
Per Penn State Extension, larvae found in the gum-frass mass can be physically removed with a thin wire probe or a sharp knife. This direct removal kills the larvae without insecticide and is appropriate for young trees with a small number of borers. Be careful not to damage the cambium beyond what the larvae have already injured.
Mulch management
Per Clemson HGIC, do not mound mulch against the trunk — this retains moisture, encourages borer access, and makes inspection difficult. Keep mulch pulled 6 inches away from the trunk base.
Common problems table
| Symptom | Likely cause | Action |
|---|---|---|
| Gum-frass mass at trunk base, below soil line | Peach tree borer larvae | Probe for larvae; apply trunk insecticide at adult flight |
| Gum mass on upper scaffold branches | Lesser peach tree borer | Different pest; same management approach at upper trunk |
| Young tree sudden wilt in summer | Severe crown girdling from borer | Dig crown; assess girdling extent; may not be recoverable |
| Tree decline without obvious above-ground symptoms | Borer activity at crown | Scrape soil from base; look for gum-frass mass |
Frequently Asked Questions
How do I know if my peach tree has peach tree borer?
Per Penn State Extension, use a hand trowel or cultivating fork to carefully clear soil from the trunk base each spring (April) and late summer (August). Examine the bark for gum mixed with brown frass — this is the diagnostic sign. Any healthy peach should be inspected annually.
Can a tree recover from peach tree borer infestation?
Per Clemson HGIC, established trees (5+ years old) can recover from moderate infestations if the borers are managed and the trunk is not completely girdled. Young trees with severe girdling often die. Removing larvae and applying trunk insecticide the following season gives recovering trees the best chance.
Does peach tree borer affect cherry trees?
Per Penn State Extension, yes — both sweet and sour cherry are susceptible. The same management approach applies. Plum and nectarine are also infested.
Is there a way to prevent peach tree borer without insecticide?
Per Cornell Cooperative Extension, kaolin clay trunk applications provide some deterrence without synthetic insecticide. Physical inspection and larval removal are labor-intensive but chemical-free. No approach provides complete protection without active management.
—-
Sources
- Penn State Extension — Peach Tree Borer
- Clemson HGIC — Peach Tree Borer
- Cornell Cooperative Extension — Peach Pest Management