Swarms of insects can ruin garden plants and make working in your garden an unpleasant, skin-crawling experience. Powdered insecticides like diatomaceous earth and boric acid are an effective answer to invading insects when applied correctly. These powders are most effective outdoors when they are used in a dry environment. Removing garden features that attracted pests to your garden increases the effectiveness of these insecticides and discourages their return.
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The fossilized remains of aquatic diatoms make up deposits of silica near open bodies of water that are used to create diatomaceous earth. The active ingredient in diatomaceous earth is silicon dioxide, a naturally occurring substance that kills insects on contact. Once the powder sticks to an insect's body, it absorbs oils and fats from its exoskeleton, drying the insect out and killing it. Although diatomaceous earth is not effective at killing at insects while it is wet, its insecticidal properties are restored when it dries out again. Although diatomaceous earth is nontoxic, it is irritating when inhaled or if it comes in contact with skin or eyes.
Using Diatomaceous Earth
Diatomaceous earth is effective at killing insects until it gets wet. This power works best outdoors for short-term control during periods of dry weather. Diatomaceous earth is nontoxic and safe to use on and around plants. The best place to spread the dust is on and around the areas where you have seen the insects. You can also use diatomaceous earth to clear out nests of burrowing insects by mixing the powder with water and pouring it down the hole leading to the nest. Duster bulbs are also an effective method for applying diatomaceous earth into cracks and other difficult-to-reach areas.
Boric acid is a poison which kills insects that eat it within roughly five days. Boric acid is only mildly toxic to humans but can cause serious eye irritation or damage depending on its concentration. Wearing gloves and protective goggles when applying boric acid and washing your hands with soap and water afterward help reduce the chance of accidental contact. Never wipe your eyes while handling a product with the active ingredient sodium tetraborate decahydrate -- commonly known as borax.
Applying Boric Acid
Boric acid powders are also vulnerable to getting wet but do not regain their efficacy after they dry out. Boric acid works best in dry areas when sprinkled in a fine layer over the areas frequently visited by the target insects. Boric acid can damage plants, so avoid spreading dry powder on their foliage or using large amounts that could increase the amount of boron in the soil to a toxic level. An effective dusting of boric acid is a layer so fine that it is barely noticeable. Insects will avoid heavy piles of the material, and overuse in the garden may cause complications.