Trying to hit a moving target is one problem. Trying to hit thousands of unseen moving targets all at once is something entirely different. Yet countless gardeners and indoor plant enthusiasts face this challenge each day when the first signs of spider mites appear on their plants.
Whether it's the impossibly fine webs they spin on their host plants, or the stippled leaves they wreck with their feeding, the mites' obvious damage is a call to immediate action. Chemical miticides are plentiful, but they often defeat their own purpose by killing the pests' natural predators. For an unproven but recommended alternative, consider controlling them with diluted, food-grade, 35-percent hydrogen peroxide.
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Hydrogen Peroxide as a Pesticide
Although food-grade hydrogen peroxide has been registered by the U.S. Environmental Protection Agency as a plant-safe pesticide since 1998, the only pests it's registered for are disease-causing fungi and bacteria. Insects and mites aren't covered. Nevertheless, it's an environmentally safe product and, when diluted in water to a concentration of 5 percent or less, is harmless to people and animals.
No official research has been done to establish hydrogen peroxide's effectiveness against spider mites. The Central Vancouver Island Orchid Society, however, claims that a 5-percent solution is lethal to most insects and insect eggs. The major exceptions are hard-shelled armored scales, and even they eventually die after repeated spraying.
Dress in protective clothing and gear, including a long-sleeved shirt, long pants, socks, boots, a hat, chemicalproof gloves, safety goggles and a respiratory mask, before you handle the extremely corrosive, food-grade, 35-percent hydrogen peroxide. That hydrogen peroxide formula is available at hydroponics stores.
Measure 5/8 cup of the hydrogen peroxide. Pour it into a 1-liter spray bottle.
Add 4 teaspoons of 70-percent isopropyl rubbing alcohol to the spray bottle.
Add four drops of liquid, ammonia-free dish soap to the spray bottle. It will help the solution stick to plants.
Fill the remainder of the spray bottle with water. The hydrogen peroxide in the spray bottle is now diluted to 5 percent, and the bottle's solution should be safe to handle without protection.
Application on the Mites
Spray spider mite-affected plants with the spray bottle's solution until it covers the plants completely, including the backs of leaves, where spider mites often feed. When the hydrogen peroxide in the solution hits the plant's surface, it will "fizz," the way it does when poured into an open wound. The fizz is a reaction to the enzyme catalase found in spider mites and their eggs. Catalase breaks down hydrogen peroxide into water and oxygen.
Repeat the application as needed until the spider mite infestation subsides.