Chestnut Weevil
Curculio sayi, C. caryatrypes
The main insect pests of chestnuts, two native long-snouted weevils whose grubs develop hidden inside the nuts. Infested nuts look fine at harvest but soon show exit holes as cream-colored larvae chew their way out, ruining the crop for eating and storage.
🔎 How to spot it
Adults are brown to tan weevils mottled or striped with lighter scales, with a remarkable long curved snout. The lesser chestnut weevil is about a quarter inch long with a snout as long as or longer than its body, while the large chestnut weevil is bigger, roughly three eighths of an inch, with an even longer snout. The legless, cream-colored, C-shaped grubs are found inside the nuts, and round exit holes appear in the shells.
🥀 Damage it causes
The larvae feed inside the developing kernel, tunneling it full of frass and making the nuts inedible and unstorable. A single nut can hold several grubs, and where weevils are unchecked they can infest and destroy the majority of a crop. Damage often goes unnoticed until larvae chew their exit holes and emerge from harvested nuts.
🛡️ Prevent it
Sanitation is the foundation: collect fallen nuts promptly and often, at least every day or two during the drop, and destroy infested and leftover nuts so larvae cannot complete development in the soil beneath the trees. Removing dropped nuts each season steadily lowers the local weevil population. Wild and abandoned chestnut and chinquapin nearby can reseed the problem.
🧯 If it is already here
A practical home treatment for harvested nuts is a hot-water dip: holding sound-looking nuts in water kept near 120 F (about 49 C) for roughly twenty minutes kills the grubs developing inside, after which the nuts are cooled and dried. Promptly refrigerating clean nuts also stops larval development. Where pressure is high, well-timed insecticide sprays target adults as they emerge and feed before egg-laying, but timing is critical and sanitation remains essential.
💡 Good to know
The weevils are host-specific to chestnut and chinquapin (genus Castanea). Adults emerge over an extended period, often in spring around bloom and again in late summer or early fall as the burrs open. The lesser chestnut weevil has a long life cycle, with larvae dropping to the soil and pupating over two to three years, so control must be sustained across seasons rather than expected to work in a single year.
🌱 Plants it attacks
2 plants in the library can be attacked by this pest
For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.