Their habit of turning thousands of different plants into meals isn't what has earned mealybugs their name. That comes from their ability to bury themselves -- almost from birth -- in layers of mealy, white wax. This waterproof barrier protects the insects from dehydration and predators. The difficulty for plant lovers is that it also repels most contact insecticides. A homemade spray of rubbing alcohol and dish soap, however, solves that problem.
How It Works
Separately and together, the alcohol and soap dissolve mealybug wax. Without their covering, the insects soon die from fluid loss. By acting as a spreader-sticker, the dish soap also helps the spray adhere to the plants evenly. The trouble is that the combination kills only on contact and while wet.
According to Dr. Paul Johnson of South Dakota State University's Insect Research Collection, mixing an alcohol-soap spray to control mealybugs isn't an exact science. Don't despair if your first attempt isn't quite right; with the household ingredients involved, tweaking their amounts to find what works is easy and inexpensive.
Measure 3 cups of the rubbing alcohol and pour it into the spray bottle.
Add 3 cups of water to the bottle.
Add 1 teaspoon of dish soap to the alcohol-water solution.
Top the mixture off with 1 teaspoon of mineral oil, if desired. It suffocates the mealybug by clogging their breathing holes.
Testing the Spray
Always test your plants for sensitivity before treating them with the alcohol-soap mixture. Wait for their new growth to harden off and water them well before testing. Spray one or two leaves and flowers. Wait 48 hours and check for brown or yellow leaf spots and edges, or dried, darkening petals.
If the sprayed tissue remains healthy, repeat the test on different flowers and leaves. Treat the mealybugs only if the plant passes the tests.
Using the Spray
If you're spraying indoors, move the infested plant to a dimly lit area and cover the surrounding surfaces to protect them from the overspray. To slow the mixture's evaporation rate, treat outdoor plants in early morning, before the temperature rises.
Spray until the solution covers all the plant's surface, including both sides of the leaves, and penetrates the protected areas, such as leaf sheaths or branch crotches.