All by itself, water can be surprisingly effective against whiteflies or aphids. Turn your hose nozzle to a fine spray and blast the pests off the leaves, making sure to hit the undersides, too. For outdoor plants, knocking most of the pests off will often allow beneficial insects to move in and keep the remaining population in check.
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If water alone doesn't work, add soap. The natural fatty acids in soap dissolve the outer coating or shell of many insects, eventually killing them. So you just need to get the pests wet, not knock them head over teakettle (not that that isn't satisfying). Soap spray can help you manage a wide variety of garden pests, including aphids, scale, mites, and thrips.
A basic recipe: Put 1 teaspoon natural dish soap or liquid castile soap, such as Dr. Bronner's, into a one-quart spray bottle and top it off with water. Spray on insect-infested areas, remembering the undersides of leaves and stems. Repeat whenever live insects are present.
Sergeant Pepper's Revenge
Garlic and hot pepper are both great ways to ramp up the killing power of soap spray and make your plants temporarily taste less appealing to some pests.
- 1 small bulb garlic (about 6 cloves)
- 1 small hot pepper or 1 teaspoon hot sauce
- 1 teaspoon natural dish soap or liquid castile soap
Chop the garlic and pepper and put them in a blender with about a cup of water and puree until smooth. Let the mixture steep for at least an hour (or overnight in your refrigerator) and then strain it through a coffee filter to remove the solid bits, which will clog your spray bottle. Pour the resulting garlic-pepper juice into a one-quart spray bottle, add the soap, and top off with water.
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Spray your plants thoroughly, including leaf undersides. Store any leftover spray for up to a week in the refrigerator.