Steinernema carpocapsae
Entomopathogenic nematode- Rate
- 250k–500k /m² (≈1 billion per acre at the low end)
- Temp
- 14–34 °C; best 19–31 °C
- Best for
- Drench at the trunk base or inject into tunnels; >80% control in USDA trials
Pest
Peachtree borer
Synanthedon exitiosa
The short answer
The larva of a clearwing moth that bores under the bark at the base of peach, nectarine, cherry, plum, apricot and ornamental Prunus. It feeds on the living inner bark from a few inches below the soil to about a foot above it, and the tree bleeds gum mixed with frass and sawdust. Pacific Northwest guides warn that a single larva can girdle a newly planted tree; established trees are weakened. There is one generation a year. Beneficial nematodes (Steinernema carpocapsae) gave over 80% control of existing larvae in USDA peach-orchard trials, and they are the realistic biological option for a backyard tree. Commercial mating disruption dispensers are rated per acre and are not a home-garden tool.
hero · gum and frass mass at the base of a peach trunk
Gum and frass at the soil line of a peach trunk, the classic sign of Synanthedon exitiosa. Photo: pending.
Identification
The adults look like wasps, not moths, and fly by day, mostly from late morning to early afternoon. The female is dark metallic blue with a broad orange band round the abdomen (NC State describes two) and opaque front wings; wingspan is 1⅓–1½ inches (33–38 mm). The male is smaller, 1–1¼ inches, with clear wings and narrow yellow bands on the abdomen.
The larva is the stage you find: cream to pinkish white with a brown head, up to 1–1½ inches long, in a tunnel under the bark at or below the soil line. Empty brown pupal cases, about ½–¾ inch long, may stick out of the bark or soil after the moths emerge. The lesser peachtree borer is a related species that attacks the trunk above ground and the scaffold limbs and branches, and has two generations a year.
Easily confused with
- WaspsHarmlessThe day-flying adults pass for wasps. UC IPM’s tell for clearwing moths is a moth’s thick waist, not the narrow waist of a wasp.
- Lesser peachtree borerAlso a pestAttacks the trunk above ground and the scaffold limbs, and has two generations a year. Peachtree borer gum and frass sit at the trunk base, from just below the soil to about a foot up.
- Beetle borersAlso a pestFlatheaded and roundheaded borers leave wet spots, dark stains and D- or O-shaped exit holes. Clearwing borers leave larger open tunnels filled with sawdust-like frass.
Damage symptoms
Because the larvae feed out of sight under the bark, the gum is the first sign most people see. Penn State describes it as a mass of gum around the base of the trunk, from about 3 inches below to 12 inches above the soil, containing bits of sawdust and frass. The frass mixed into the gum is what points to a borer.
- A mass of gum at the trunk base, mixed with brown frass and sawdust
- Tunnels under the bark at or just below the soil line when the gum is scraped back
- Twig and branch dieback
- Young trees that decline or die after being girdled
- Empty pupal cases sticking out of the bark or soil in summer
Lifecycle & degree days
There is one generation a year. Larvae of various sizes overwinter under the bark, usually below the soil surface, and resume feeding in spring once temperatures pass about 50 °F. They pupate at the trunk base in late spring and summer, and the moths fly from late spring into early autumn, depending on region. Females lay eggs on the lower trunk and nearby soil, and the new larvae bore straight in.
- Generations / yr
- One
- Moth flight
- May–September in California; late June–early September in Pennsylvania; June–September in the Pacific Northwest
- Egg to hatch
- 7–10 days
- Pupal stage
- 18–30 days (about 3 weeks)
- Overwinters
- Larvae under the bark, usually below the soil line
J
F
M
A
M
J
J
A
S
O
N
D
Host crops
Prunus hosts: peach, nectarine, cherry, plum and apricot, plus ornamentals such as purple leaf sand cherry, cherry laurel, purple-leaf cherry plum and wild black cherry. Penn State says it typically attacks trees more than 2 inches in diameter, and Pacific Northwest guides that one larva can girdle a newly planted tree.
Monitoring & action thresholds
Action threshold
Any gum with frass at the soil line
No numeric threshold exists for home trees. Because a few larvae can girdle a young tree, extension sources treat any sign of frass-filled gum at the base as a reason to act, and commercial programmes prevent it each year rather than waiting for damage.
Pull back mulch and weeds so you can see the bark at the soil line, and check it for fresh gum and frass; UC IPM advises inspecting damaged bark weekly from before the moths are due to emerge. Pheromone traps for peachtree borer show when the moths are flying: Penn State hangs them near the trees in early June, UC IPM hangs them about shoulder high and checks weekly. Any trunk spray is timed from the first male caught — Penn State says 7–10 days later, NC State 8–16 days, UC IPM 10–14.
Beneficial
Biological control
Steinernema carpocapsae is the one biological control with field evidence. In a Georgia trial, it gave 88% control of peachtree borer larvae at 300,000 infective juveniles per tree (Cottrell & Shapiro-Ilan 2006). In spring trials on established infestations, about 1 million per tree gave more than 80% corrected control with a handgun sprayer, while chlorpyrifos failed (Shapiro-Ilan et al. 2016); earlier autumn applications reduced infestations by 77–100%. UC IPM also describes squirting nematodes into each tunnel. Penn State notes wild egg, larval and pupal parasitoids, but no source quantifies them.
Cultural controls
In a backyard, the tree's own vigour and a clear trunk base do a lot of the work, and physical removal is still an option for a few trees.
- Keep mulch, weeds and grass pulled back from the base of the trunk, and remove suckers
- Avoid wounding the bark, and keep trees well watered
- "Worm" the tree: in spring, dig out larvae with a pocketknife or push a wire into the tunnels, taking care not to do more damage than the borers
- Fit a plastic or metal cone round the trunk base, pushed 1–2 inches into the soil, before egg-laying begins (Pacific Northwest guide)
- Remove and destroy badly infested trees rather than leaving them as a source
Chemical, last resort
Trunk sprays only stop newly hatched larvae — time them to the moth flight. Both are highly toxic to bees and fishCheck any product before it goes on. Open the compatibility matrix →
- EsfenvalerateREI 12 h
- PermethrinREI 12 h
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
Penn State Extension, Peachtree Borer (Skvarla, updated 07/2024)
NC State Extension, Peachtree Borer (Walgenbach, 2015)
UC IPM Pest Notes 7477, Clearwing Moths (Karlik, Tjosvold & Dreistadt, 12/2013)
UC IPM Pest Management Guidelines: Peach — Peachtree Borer (UC ANR 3454, text 09/15)
Pacific Northwest Insect Management Handbook, Peach and nectarine — Peachtree borer
Univ. of Kentucky ENTFACT-213, Lesser Peachtree Borer (Bessin, rev. 1/26)
Cottrell & Shapiro-Ilan, J. Invertebr. Pathol. 92:85–88 (2006)
Shapiro-Ilan et al., Curative Control of the Peachtree Borer Using EPNs, J. Nematol. 48:170 (2016)
UC IPM, Relative Toxicities of Insecticides Used in Peaches to Natural Enemies (09/15)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →Peachtree borer by crop
The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.