The active ingredient in cayenne peppers, a chemical called capsaicin, not only makes peppers taste hot on the human tongue, but this natural chemical is also toxic to many insects. Capsaicin disrupts nerve signals, as well as damages membranes in insects bodies. This makes cayenne peppers a common ingredient in many natural sprays for garden pests such as spiders, aphids, beetles and mosquitoes.
General Insect Control Spray
To make an all-natural organic spray to control garden pests, first blend one medium-sized garlic bulb and one onion. Add 1 tsp. ground cayenne pepper to the onion and garlic, then steep in 1 qt. warm water for at least four hours. Strain and pour into a spray bottle. You can also mix in 1 tsp. of liquid dishwashing detergent for added bug-killing power. Spray on the undersides of leaves and stems where bugs like to gather.
Whole cayenne peppers can also be used in a bug-killing spray for garden pests. For gardeners who like to use cayenne pepper bug spray, they can grow their own peppers in the garden. To make an insecticidal spray with whole peppers, use about six whole, mature cayenne peppers. Dry in the sun and then blend in a food processor. Soak crushed peppers in hot water for at least 12 hours to allow the capsaicin to permeate the water, then strain and use as an insect control spray in the garden. You can also add garlic in equal parts with the whole peppers.
Barriers to Garden Pests
Powdered cayenne peppers can also be sprinkled around plants to create a barrier for hard-bodied insects like caterpillars. The insects crawl over the pepper and get it on their bodies, which can kill or repel them. You can sprinkle powdered cayenne pepper around individual plants or around the garden plot, and you can also mix cayenne pepper with other powdered insect repellents like diatomaceous earth.
Cayenne pepper can also be burned like an incense to fumigate areas where pests have gathered, such as dog kennels or areas where pets my have brought in pests like fleas. Before fumigating for garden pests, always remove all pets or children from the area because pepper smoke can irritate eyes and nasal passages. To fumigate an area with cayenne, burn 1 oz. of powdered peppers on a small stove or briquette in a sealed room, and wait 24 hours before bringing pets back into the room.