Storing corn, whether shelled or on the cob, often presents a challenge due to stored grain pests. These insects can quickly contaminate and destroy a significant portion of a harvest or purchased supply, making preventative measures necessary for long-term preservation. The maize weevil (Sitophilus zeamais) is one of the most common culprits, establishing itself in the grain before or shortly after storage. This guide provides practical, non-chemical methods to prevent, eliminate, and manage infestations to keep stored corn secure.
Identifying the Corn Weevil and Signs of Infestation
The corn weevil is a small, dark reddish-brown beetle recognizable by its distinct, elongated snout. Adults typically measure about one-eighth of an inch in length, making them difficult to spot within a large volume of grain. Infestations often begin in the field when the female chews a hole into a kernel, deposits a single egg, and seals the opening.
The developing larva remains hidden inside the kernel, feeding until it matures into an adult. This internal feeding makes early detection challenging since there is no external evidence of the pest. The first noticeable sign is the emergence of the new adult, which chews an exit hole, leaving the kernel with a characteristic “shot-hole” appearance. Other indicators include a fine, powdery residue near the grain from the weevils’ feeding, or the discovery of the small, winged adults crawling on storage containers.
Immediate Treatment Methods for Newly Harvested or Purchased Corn
To prevent an infestation from growing, corn intended for storage should be treated immediately upon acquisition to kill any weevils or eggs already present. Temperature-based methods are highly effective and represent a non-chemical approach to disinfestation. Both extreme cold and extreme heat achieve complete mortality across all life stages of the weevil.
For cold treatment, placing the corn into a freezer set to 0°F (-18°C) or lower for a minimum duration of three days is sufficient to kill all life stages. The corn must be placed in a moisture-proof container or bag to prevent condensation when it is removed and begins to warm. Condensation introduces moisture, which encourages mold growth and re-infestation. After freezing, the corn should return slowly to room temperature while still sealed before being moved to long-term storage.
Alternatively, heat treatment is effective for small batches. Spread the corn in a thin layer on a baking sheet and expose it to 140°F (60°C) for 15 minutes to eliminate all weevils inside. While higher temperatures can reduce treatment time, prolonged exposure above 140°F may affect the corn’s viability, particularly if it is intended for use as seed.
Long-Term Strategies for Storage and Environmental Control
Successful long-term storage relies on creating an environment inhospitable to weevil survival and reproduction. Maintaining low temperature and moisture levels is the most effective way to inhibit weevil development, as weevils cannot develop at temperatures below 50°F (10°C). Storing corn at a moisture content of 11% or less is also recommended because high moisture provides an ideal environment for pests and mold.
Selecting the correct storage container is paramount, as weevils can chew through paper and plastic bags. Grain should be stored in rigid, air-tight containers made of metal, glass, or heavy-duty food-grade plastic. Hermetic storage utilizes specialized bags or sealed containers. This method works by allowing the natural respiration of the corn and any insects to deplete the oxygen supply and increase carbon dioxide levels, leading to the suffocation of the weevils.
Physical barriers can be incorporated directly with the corn to provide ongoing protection. Food-grade diatomaceous earth (DE) is a natural, non-toxic powder that kills insects mechanically by scratching their exoskeletons, causing them to dehydrate. The recommended application rate for long-term protection is approximately one to two teaspoons of DE for every pound of corn, or roughly one cup for every 50 pounds. The powder should be layered in with the corn as the container is filled, ensuring the grain is evenly coated, which provides a long-lasting protective barrier.
Another traditional deterrent involves placing bay leaves inside the storage containers. While scientific evidence is limited, the leaves contain the aromatic compound eucalyptol, which is thought to repel weevils. This method is a simple, non-toxic addition to an integrated storage plan, providing an extra layer of defense against potential invaders.
Remediation Steps Following Discovery of Weevil Activity
If an active weevil infestation is discovered, the immediate priority is containment and sanitation to prevent the spread of pests. First, isolate the affected container and thoroughly inspect all surrounding stored goods for signs of migration. Heavily infested corn that is riddled with weevils and damage should be safely disposed of by sealing it in a bag and discarding it outside the home.
For corn that is lightly affected or suspected of infestation, salvage methods can be used. The grain can be disinfested by subjecting it to a freezer at 0°F for three days or heat at 140°F for 15 minutes. After the corn has been treated and removed, the storage area itself must be meticulously cleaned.
Shelves, cupboards, and crevices should be emptied and vacuumed thoroughly to remove any spilled grain, weevils, and powdery residue, as insects can survive on even small amounts of debris. Once cleaned, the corn should only be returned to the storage area in new, air-tight containers to prevent a recurrence of the problem.