Plum Curculio: Crescent-Scar ID and Petal-Fall Timing

The crescent scar: how to identify plum curculio

The egg-laying wound is unmistakable once you know it. Penn State describes the characteristic injury as a crescent-shaped cut that partly surrounds the sunken egg; when the egg fails to develop, a half-moon scar remains on the growing fruit. The female makes this crescent deliberately, cutting a flap so the swelling fruit does not crush the egg beneath it.

The insect itself is easy to overlook. Penn State describes a quarter-inch weevil that is dark brown with whitish patches, with four humps on its wing covers and a protruding snout; Utah State calls it simply a small brown weevil (a beetle with a snout). It attacks both pome fruit (apples, pears) and stone fruit (plums, cherries, peaches, nectarines, apricots), and Utah notes wild plums are especially preferred, which is why nearby wild or neglected trees can seed a problem.

Clean up the drops

The weevil's life cycle has a weak point on the ground. Penn State explains that larvae develop primarily in dropped fruit, where they make large irregular cavities and feed for about 16 days before maturing and then pupate in the soil, and that larvae rarely complete development in fruit remaining on the tree. That means fruit the tree sheds is the nursery for next year's weevils.

So the home control is aggressive drop cleanup. Remove and destroy fallen fruit frequently during the early-drop period, ideally every few days, before larvae exit into the soil. Utah State likewise advises removing fallen fruit during the summer and, where practical, removing wild and ornamental fruit trees nearby that harbor populations. Consistent sanitation over a couple of seasons noticeably lowers pressure on a backyard tree.

Timing control at petal fall

Plum curculio activity is temperature-driven, and the danger window opens right after the flowers finish. Penn State notes adults emerge during bloom and are most active during the first warm period after petal fall, when the maximum temperature is 70F or higher, while cool, rainy weather below 70F suppresses them. The critical control period is those first few warm, humid days following petal fall.

If you use an insecticide, that is when it goes on, not before, because spraying open blossoms kills pollinators. Utah State times applications at petal fall and repeated in 7 to 10 days, with a possible third application if pressure is high. Penn State frames it in growing degree days, maintaining coverage for roughly 300-plus degree days (base 50F) after petal fall. Use the products and intervals your Extension lists; this fits into the broader backyard fruit tree spray schedule, which puts all insect sprays after bloom.

Sources

Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.

• Penn State Extension - Tree Fruit Insect Pest: Plum Curculio — A quarter-inch dark brown weevil with four humps and a snout attacks apples, cherries, nectarines, peaches, and plums; the injury is a crescent-shaped cut partly surrounding the sunken egg, leaving a half-moon scar; larvae develop primarily in dropped fruit, feeding about 16 days before maturing, and rarely complete development in fruit on the tree; adults emerge at bloom and are most active in the first warm period after petal fall when the max temperature is 70F or higher; the critical control window is the first few warm humid days after petal fall.
• Utah State University Extension - Plum Curculio — A small brown snout weevil, 1/4 inch, whose females make crescent-shaped slits leaving a darkened scab on the fruit; it attacks stone and pome fruits with wild plums most preferred; egg-laying begins at approximately petal fall and continues about 30 days; most infested fruit drops prematurely; remove fallen fruit during summer and nearby wild/ornamental hosts; insecticide is applied at petal fall and repeated in 7 to 10 days, with a possible third application.

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