Diatomaceous Earth (DE) is a natural pest management method utilizing the finely milled fossilized remains of diatoms to dehydrate insects. While powder is the most common form, applying DE as a liquid spray, or slurry, allows it to reach areas difficult to dust, such as high walls, vertical surfaces, and the undersides of plant leaves. A liquid application is useful when dry conditions are not possible or when wind would blow away a fine dusting. The water acts as a carrier, allowing the microscopic DE particles to adhere to the surface, becoming active only once the water evaporates.
Preparing the Diatomaceous Earth Slurry
Preparing the slurry requires selecting food-grade diatomaceous earth, which is safe for pest control applications around humans and pets. Industrial-grade DE is treated differently and should not be used. Since DE does not dissolve, you must suspend the powder in water. A common ratio for general application is four tablespoons of DE powder per gallon of water, aiming for a consistency thin enough to spray but concentrated enough to leave a visible film once dry.
A more concentrated mix, such as one cup of DE for every four cups of water, is an option for a thicker solution. Because DE particles are heavier than water, they quickly settle, requiring constant agitation during mixing and application. To enhance the slurry’s ability to stick to surfaces, incorporate a few drops of mild dish soap or a non-ionic surfactant. The soap acts as an adhesive agent, preventing the DE from running off the surface as it dries.
Choosing the Right Sprayer
Diatomaceous earth’s abrasive nature and fine particle size challenge standard garden sprayers, which are prone to immediate clogging. Sprayers designed for fine-mist applications should be avoided entirely. The most appropriate tool is a pump sprayer or compressed air sprayer equipped with a wide-bore nozzle, designed to handle particulate-heavy liquids.
The nozzle opening is the most important factor; set it to the widest possible fan pattern or stream to allow suspended particles to pass through easily. Even with the right equipment, the DE will settle in the tank, so the sprayer must be shaken frequently, or continuously, during application. Maintaining adequate pressure in the pump sprayer helps force the slurry through the nozzle, reducing clogs and ensuring consistent flow.
Effective Application Techniques
The objective of spraying is to lay down a uniform, thin, visible film that becomes the active powder layer upon drying, not to soak the target area. This technique effectively reaches cracks, crevices, and small entry points where crawling pests hide or travel. When treating plants, focus the spray on the undersides of leaves, where many soft-bodied pests congregate.
Apply the slurry in a steady, sweeping motion, ensuring the surface is fully coated with the milky white film without excessive runoff. DE is a mechanical insecticide that kills by physical abrasion and absorbing the waxy outer layer of an insect’s exoskeleton, causing fatal dehydration. This effect occurs only after the water has fully evaporated, leaving behind the dry, desiccating powder residue. If the treated area is exposed to rain or heavy watering, the DE will wash away, and the application must be repeated to maintain the protective barrier.
Safety and Post-Spray Cleanup
While food-grade DE is non-toxic, the fine dust particles can irritate the eyes and respiratory system if inhaled. Wearing a dust mask or respirator and protective eyewear is necessary during the mixing and spraying process. The slurry must be given sufficient time to dry completely, as the material is only effective as a pest control agent in its dry, powdered state.
Immediately following application, the sprayer must be thoroughly cleaned to prevent DE particles from hardening inside the components. Residual DE can dry and cement within the pump, hoses, and nozzle, leading to clogs and damage. Flushing the sprayer several times with clean water is necessary to remove all traces of the slurry and ensure the equipment remains functional.