Diatomaceous earth (DE) is a naturally occurring powder created from the fossilized remains of diatoms, which are tiny, single-celled aquatic organisms. The skeletons of these organisms are primarily composed of amorphous silica, resulting in a fine, abrasive material. This silica-based powder is frequently used for pest control and can be mixed with water to create a slurry for application. This liquid method is often preferred for treating surfaces where dry dusting is impractical or less effective.
The Mechanism of Diatomaceous Earth
Diatomaceous earth functions as a physical, rather than a chemical, deterrent against many insects. The microscopic structure of the fossilized diatom shells is abrasive and highly porous. When an insect crawls across the fine powder, the sharp edges of the silica particles cut into the insect’s protective outer layer, which is known as the exoskeleton.
This mechanical action damages the waxy, oily coating that helps the insect retain essential moisture. The porous nature of the DE then absorbs the insect’s internal lipids and moisture through these microscopic abrasions. This process leads to the rapid desiccation, or drying out, of the pest.
When DE is mixed with water, the water acts solely as a carrier to transport the powder to the target area. The silica particles themselves do not dissolve in the water, which means the mechanical mechanism remains intact. The efficacy of the DE is only activated once the water evaporates completely, leaving the dry, sharp powder behind.
Practical Applications of the Water Mixture
Applying diatomaceous earth as a slurry offers distinct advantages over dry dusting, especially when treating specific environments. A liquid mixture allows the DE to adhere to vertical or inverted surfaces that a dry powder would simply fall off of, such as baseboards, walls, and the undersides of leaves. This capability makes it an ideal choice for treating hard-to-reach areas and crevices where pests often hide.
Using the water mixture as a foliar spray is beneficial in gardening, as it provides a more uniform coating over plant surfaces. The liquid application helps the DE stick to the stems and leaves, improving overall coverage. Additionally, the wet application significantly reduces airborne dust, minimizing the risk of inhalation.
Applying DE in a liquid form is also effective for covering large areas quickly, such as expansive garden beds or lawns. Once the water dries, the resulting fine film of DE is left behind, ready to contact any passing pests. This method ensures the powder is placed precisely where it is needed without scattering in the wind.
Mixing Techniques and Application Tips
Achieving a usable slurry requires careful attention to the mixing ratio and technique to ensure an effective application that will not clog equipment. A common and effective ratio is approximately two to four tablespoons of food-grade diatomaceous earth mixed into one gallon of water. It is important to always use food-grade DE for applications around homes and gardens.
Before mixing, sifting the DE powder through a fine screen helps remove clumps or larger particulates that might block the sprayer nozzle. Because the silica particles do not dissolve, the DE settles at the bottom of the container almost immediately. The mixture must be continuously agitated or shaken throughout the application process to keep the DE evenly dispersed and prevent clogging.
A pump sprayer equipped with a wide nozzle is the most effective tool for applying the slurry. When spraying plants, apply the mixture until it just begins to run off the surface, ensuring the leaves and stems are thoroughly coated. Applying the spray in the early morning or late evening prevents the mixture from drying too quickly, which could cause sun scorching in high heat.
Maintaining Efficacy After Application
The desiccating action of diatomaceous earth is entirely dependent on the powder being dry. Therefore, the DE slurry only becomes active once the water carrier has completely evaporated from the treated surface. Once dry, the mixture leaves a barely visible, fine, powdery residue that is ready to act against insects.
Drying time varies based on temperature, humidity, and application thickness, but the residue must be completely dry to be fully effective. The resulting residue must remain dry to maintain its sharp, abrasive properties and its ability to absorb lipids. Any form of moisture, including rain, heavy dew, or overhead irrigation, will saturate the residue and negate its effectiveness.
If the treated area is exposed to moisture, the DE will clump, requiring reapplication to restore the dry, desiccating layer. Sticking to surfaces is a benefit of the wet application, but the residue’s longevity is contingent on dry conditions following the initial application. Reapplication frequency is dictated more by environmental moisture than by a set time frame.