Control Weevils with Pyrethrins
With as common a pantry pest as weevils are, you would think that there would be quite a number of pesticides that target them directly. Unfortunately, this is far from the case. The reason is simple: weevils live and breed in your food. Since you would like to eat that food, contaminating it with insecticides probably isn't the best idea. For this reason, you should probably just stick with pyrethrins. There are quite a few different pyrethrin sprays and aerosols available that are sold to be used indoors and in food handling areas. You should still avoid spraying the food directly. Once your pantry and cupboards are completely empty, spray them down. I would recommend you leave the cupboards empty and open for at least a few hours before filling them back up.
Remove contaminated food products. Sounds like a no-brainer, but this might be the single most important step in getting rid of weevils. Look through your ENTIRE pantry and every single cupboard for any food products that might be contaminated. If you find something that you aren't sure of, pitch it. There's no point in risking reinfestation. It could very well cost you more money in the long run. Once you have it all gathered up, take it outside to the trash immediately and move the can as far away from your house as possible.
Pull a Cinderella. Conduct the most thorough cleaning of your pantry and cupboards that you have ever done. Start by taking absolutely everything off the shelves and vacuuming them. Make sure to get all the cracks where flour or other food bits might be hiding. If you have contact paper lining the shelves, remove it (you can put new stuff on later). Use a rag and some hot sudsy water to do the rest of the cleaning.
Kill weevils with cold. To avoid future problems with weevils, it is advisable to freeze your food. You can do this to flour, oats, cookies, corn meal, grits, whatever. If you have the space in your freezer, you should just keep the stuff in there full time. If you have a small freezer and can't afford the space, set the freezer as cold as it gets and leave the food in there for at least four days. That will kill any eggs, larvae, or weevils.
Kill weevils with heat. If you don't feel like freezing everything, a little heat exposure will accomplish the same thing. Spread your food or seeds thinly on a baking sheet, preheat the oven to 120°F, and leave it in there for 1 hour. If you're impatient, you can do 130°F for ½ hour. If you want to use the microwave, spread the stuff on a glass dish or plate, and run it for 5 minutes. Keep in mind that if you are heating seeds for gardening, the heat may destroy the seed's chances for germination. Also, don't heat fine-grained things, like flour, in case of combustion.
Further weevil prevention. Start by cleaning the cupboards and pantry regularly. If you spill something, clean it up immediately and thoroughly. In the pantry and cupboards, you may want to consider sealing any shelving cracks with caulk to keep food from getting trapped down there in the future. Buy your goods in smaller amounts that you can use quickly. Rotate your stock and don't mix new food with old. Finally, store all of your perishables in tight-lidded glass, tin, steel, or plastic containers.
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Graeme Stephens has been running the largest owned carpet cleaning company in new Zealand for 24 years. IICRC qualified "master restoration technician"