Soapy water sprays control insect pests such as aphids, mealybugs, psyllids and spider mites. They act as contact insecticides with no residual effect once the soapy water dried on plant’s surfaces. Soapy water spray is made from dishwashing liquid or commercially available insecticidal soap. Homemade soap sprays from dishwashing liquid are far less expensive but increase the possibly of plant injury. Commercial soap products are targeted to specific pest insects and do not injure plants.
How It Works
Soapy water spray solutions must contain 2 percent soap to be effective and are sprayed to cover the entire targeted insect colony. The chemicals in soap disrupt cell membranes on some insects and dissolve the protective wax coating on others. Insects may die from asphyxiation or from water loss. Soapy water spray must cover the insects completely to be effective and any residual soap is harmless. Wash plant leaves with clean water within several hours of using a soapy water insecticide. Leaf injury may accumulate with repeated applications.
Psyllids, also known as jumping plant lice, suck plant juice and exude a white, waxy substance that is a medium for sooty mold. Aphids have a similar effect on plants and are more common. Aphid communities develop on new green growth in spring, gathering underneath leaves and on plant stems. Aim soapy water spray directly and thoroughly over the entire aphid or psyllid colony. A white, fuzzy substance on plants indicates mealybugs, which also suck sap and destroy a plant’s vitality. Ants protect mealybugs. Spider mite plant damage includes leaf discoloration or speckling.
A 2 percent soapy water spray is made by using 5 tbsp. of liquid dishwashing soap per gallon of water, or 2 tbsp. per pint. Stir it carefully to avoid excessive bubbling, place in a hand-held or hose nozzle sprayer and spray the infested plant areas. Spraying in early morning allows time for the insects to die and the plant to be washed. The sun dries the plant before cooler evening temperatures create disease susceptibility on a wet plant surface. Repeat the application of soapy water spray in four to seven day intervals until insects are controlled.
Leafminers are chewing insect plant pests that are more effectively controlled with neem oil than soapy water spray. Neem oil is a botanical insecticide derived from a tree native to the Middle East. Neem oil works more slowly than other insecticides and is less effective in cooler weather. As with soapy sprays, neem oil does not persist in the environment and has low toxicity. Insects on plants are also controlled by companion planting. Aphids are repelled by garlic, onions, petunias and radish.
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