The acorn weevil, a small beetle known scientifically as Curculio glandium, poses a significant challenge for anyone collecting and storing acorns. This insect begins its life cycle by infesting the nut while it is still on the oak tree. The damage is caused by the weevil’s larva, which consumes the nutmeat inside the shell. This guide provides practical, step-by-step methods for removing these pests from already collected acorns and implementing long-term strategies to keep your future harvests weevil-free.
Identifying Acorn Weevils
Recognizing the signs of infestation is the first step toward effective removal. The adult acorn weevil is a small, brownish beetle, typically reaching about 3/8 of an inch in length, distinguished by an extremely long, slender snout called a rostrum. Females use this rostrum to bore a tiny hole into the developing acorn to deposit their eggs inside the nut.
The developing larvae, or grubs, are legless, creamy white, and curved, growing up to 3/8 of an inch long as they feed on the interior of the nut. Once the acorn falls, the mature larva chews a distinct, circular exit hole, often about 1/8 inch in diameter, through the shell to escape and burrow into the soil. Acorns that feel noticeably lightweight or have a squishy texture indicate that the internal material has been consumed.
Immediate Methods for Eradication
Once collected, the first step is to separate infested acorns from sound ones using the float test. Place the acorns into a bucket of water and allow them to soak for six to eight hours. This soaking rehydrates the nuts and causes those with internal damage or a developing larva to float.
The air pockets created by the feeding grub and the lower density of the damaged kernel cause the infested nuts to lose weight and buoyancy. Acorns that sink are generally healthy and should be removed promptly, while the floating nuts are highly likely to contain weevils and should be discarded.
For the sound acorns, two non-chemical methods are effective at killing any remaining weevil larvae. The first method is freezing. Placing the acorns in a sealed container or bag and storing them in a freezer for a minimum of 48 to 72 hours will kill any weevil eggs or larvae inside.
Another option is low-temperature heat treatment, useful if you intend to use the acorns for planting or consumption soon after treatment. Soaking the acorns in hot water maintained at 120° Fahrenheit for 20 minutes kills the grubs. Alternatively, baking the acorns in an oven at a low temperature, such as 200°F for about one hour, also eradicates the pests. Monitor the nuts during this process to ensure the heat does not damage the nutmeat or shell.
Preventing Future Infestations
Long-term management begins with careful harvesting practices. The window for collecting acorns before weevils emerge is narrow, so gather them as soon as possible after they fall, ideally within one to three days. Rapid collection prevents mature larvae from boring exit holes and escaping into the soil, which helps break the pest’s life cycle.
When collecting, visually inspect each acorn and immediately discard any that show obvious signs of damage, such as small, round exit holes. Only bring home acorns that appear sound and intact, which reduces the number of weevils requiring treatment later.
After you have successfully treated your collected acorns using the freezing or heating methods, proper storage is necessary to prevent re-infestation. Acorns should be stored in a cool, dry environment, as warmth and moisture can encourage the development of any surviving pests or mold.
Store the cleaned, dried acorns in a sealed container or bag. Using an airtight container ensures that adult weevils cannot re-enter the nuts or lay new eggs. For long-term storage, refrigeration is the best choice, as the consistently cool temperature keeps the acorns fresh and discourages pest activity.