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
- Soil under the canopy as grubs leave dropped fruit; results vary with soil
Pest
Plum curculio
Conotrachelus nenuphar
The short answer
A dark brown snout weevil, about 1/4 inch long with four humps on its back, a key fruit pest in eastern North America. In spring the female cuts a small crescent-shaped slit beside each egg she lays in young fruit. The scar is mostly cosmetic, but the legless white grub feeds inside, and infested fruit tends to drop early. It attacks apple, pear, peach, plum, cherry and blueberry. Control is timed to petal fall and the weeks after it, and picking up the dropped fruit breaks the cycle.
hero macro · adult weevil beside a crescent scar on a fruitlet
Adult Conotrachelus nenuphar on a young apple with a fresh crescent-shaped egg scar. Photo: pending.
Identification
The adult is a typical snout beetle about 1/4 inch (6.5 mm) long. It is dark brown to grey-brown and warty, with patches of white or grey, and it has four humps on the wing covers, two on each side. The curved snout is a quarter to a third of the body length (University of Kentucky and NC State differ slightly), with the chewing mouthparts at its tip.
The larva is a legless, white grub with a brown head, up to about 1/3 inch long, found in the flesh of young fruit. It leaves the fruit through a clean exit hole, with no frass or webbing, and goes into the soil to pupate.
Easily confused with
- Codling moth larvaAlso a pestA codling moth larva is a caterpillar, white to light pink with a dark brown head, and its entry hole is marked by reddish-brown frass; a plum curculio grub is legless and leaves a clean exit hole with no frass or webbing.
- Apple maggotAlso a pestApple maggot damage starts in midsummer as small pinpricks and dimples with brown threadlike trails in the flesh; plum curculio leaves crescent-shaped scars on fruitlets in the weeks after petal fall.
- Apple curculioAlso a pestA related snout weevil of apples. Its larvae pupate inside the fallen apple, whereas plum curculio grubs leave the dropped fruit and pupate in the soil.
Damage symptoms
The damage comes in two waves. In spring, egg-laying females cut crescent-shaped slits in young fruit, and the grubs feeding inside make infested fruit drop early. On apples that stay on the tree, the healed scar is often only cosmetic: University of Minnesota calls scarred fruit safe to eat, though it looks worse and may be dimpled or deformed. In late summer the new adults feed on ripening fruit and leave round punctures that can let rot in.
- Crescent-shaped scars about 1/8 inch across on young fruit
- Knotty, dimpled or cat-faced fruit where egg-laying scars healed as the fruit grew
- Young fruit dropping early, with a white legless grub inside
- Clean round exit holes in dropped fruit, with no frass
- Late in the season, round feeding punctures about 1/4 inch deep in ripening fruit, sometimes with rot
Lifecycle & degree days
Adults spend the winter in leaf litter and debris, often in woodland edges outside the orchard, and move into fruit trees around bloom and petal fall once the weather warms. University of Minnesota gives consistently above 60 °F; NC State says daily highs above 70 °F. Females lay into fruit as soon as it reaches about 5 mm, over two weeks in warm weather or four to six weeks in cool weather. In apples, the grubs complete their development only in dropped fruit, then leave it to pupate in the soil. New adults emerge about 8–10 weeks after the eggs were laid. Kentucky has a single generation; most of the Southeast has two, except at high elevation in the southern Appalachians, which has one.
- Egg to hatch
- About 5 days
- Egg to new adult
- About 8–10 weeks
- Risk window
- Petal fall until ~308–340 degree days °F (base 50 °F)
- Generations / yr
- 1 in Kentucky; usually 2 in the Southeast
- Overwinters
- Adults, in leaf litter and woodland edges
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Host crops
Apple, pear, peach, plum, cherry and other stone fruit, plus blueberry. The adults spend the winter in woodland edges, so University of Minnesota advises scouting the perimeter rows first, and removing wild fruit trees, such as wild plum, near orchard woodlands.
Monitoring & action thresholds
Action threshold
No home-garden threshold
Extension sources give none for home trees. University of Kentucky and NC State time protection by growth stage instead: petal fall and first cover on apple, shuck split and first cover on stone fruit. NC State advises checking fruit twice a week after bloom for new scars, and treating again if fresh damage appears when the second generation emerges in the South (late June–July). Minnesota growers carry protection to about 308–340 degree days (base 50 °F) after petal fall.
From petal fall, look over the fruitlets twice a week for fresh crescent-shaped slits, starting with the trees nearest woodland. To see the adults, spread a pale sheet or beating tray under a branch and tap it sharply, then look for the weevils that fall. University of Minnesota notes that circle trunk traps and pyramid traps detect the weevils but do not control them.
Beneficial
Biological control
No beneficial on this site reliably controls the adults in the tree: in Quebec, foliar sprays of S. carpocapsae cut damage in border-row trials but had no effect as broadcast sprays (Bélair et al. 1998). The stage that can be reached is the grub or pupa in the soil under the canopy. In New England apple orchards, Steinernema riobrave consistently reduced the number of adults emerging from the soil, and Steinernema carpocapsae did about as well in the one year the two were compared (Piñero et al. 2020). The results elsewhere are less consistent. In Michigan cherry and apple orchards, S. riobrave worked only in the sandiest soils and S. carpocapsae did less well (Pereault et al. 2009). In New Jersey highbush blueberry fields (Rutgers), S. riobrave gave 90% suppression, significantly more than the other nematodes tested. S. riobrave has no page here. Nematodes are a supplement to picking up drops, not a replacement for protecting the fruit at petal fall.
Cultural controls
In a home orchard, removing dropped fruit and knocking the adults out of the tree are the non-spray tools. Neither is complete on its own, and extension sources still time any spray to petal fall.
- Pick up and destroy dropped fruit promptly in late spring and early summer, before the grubs leave it for the soil
- Spread a sheet under small trees and shake or tap the branches daily in the weeks after petal fall; collect and destroy the weevils that drop
- Coat the fruitlets with kaolin clay before egg-laying starts, and reapply after rain
- Remove wild plums and abandoned fruit trees near the orchard edge, where they can be removed
- Keep sprays off open blossoms; the extension timing starts at petal fall
Chemical, last resort
Spray timing is petal fall and first cover. Never spray open blossoms or let either product drift onto flowering plants (UC IPM bee rating I), and pyrethroids also kill predatory mitesCheck any product before it goes on. Open the compatibility matrix →
- EsfenvalerateREI 12 h
- PhosmetREI 7 d
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
University of Kentucky ENTFACT-202, Plum Curculio (Bessin, rev. 2026)
University of Kentucky ENTFACT-201, Controlling Apple Pests (Bessin, rev. 2026)
NC State Extension, Plum Curculio (Walgenbach, 2015)
University of Minnesota Extension, Preparing for plum curculio in apple orchards (Wimmer, 2026)
Piñero et al., Attract-and-kill with entomopathogenic nematodes for plum curculio, Insects 2020
Pereault, Whalon & Alston, Fungi and nematodes against plum curculio, Environ. Entomol. 2009
Sousa et al., Entomopathogenic nematodes for plum curculio in highbush blueberry, Biology 2021
Bélair, Vincent & Chouinard, Foliar sprays with Steinernema carpocapsae against apple pests, J. Nematol. 1998
UC IPM, Relative Toxicities of Insecticides Used in Apples to Natural Enemies (2015)
UC IPM Pest Management Guidelines: Peach — Oriental Fruit Moth (treatment table)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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