It’s always been my experience/ understanding DE on the soil doesn’t work very well against fungus gnats. I was doing a little reading tonight, and I came across these two articles.
Curious everyone’s input on this.
The efficacy of DE primarily depends on the physical properties of its dust, and not on its chemical composition (Korunic, 1997). The dust is physically stable and will affect insects as long as it is dry and in sufficient concentration to ensure that insects will come in contact with enough diatom particles. Everything that reduces the ability of particles to absorb wax from insect cuticles directly reduces the efficacy of DE. An increase in moisture content of treated grain or air relative humidity (r.h.) will considerably reduce the efficacy of DE, especially if moisture content is more than 14% or relative humidity exceeds 70% (Korunic, 1994; Fields and Korunic 2000). It means that products with high moisture content should not be treated with DE or, having no other solu- tion, higher dosages should be applied. Increased temperature increases the efficacy of DE, an exception being spe- cies of the genus Tribolium (T. castaneum and Tribolium confusum Jacquelin du Val).
Effect of Diatomaceous Earth and Trichoderma harzianum T-22…
The dry and moist DE and sand treatments had no affect on fungus gnats in terms of inhibiting adult emergence or preventing egg laying by females. Adsorption of moisture by DE particles reduces the abrasive properties and thus effectiveness against arthropod pests that reside in the growing medium (Maceljski and Korunic 1971, Weinzierl 1998). In addition, during the course of the Þrst two experiments we observed that the DE dry treatments expanded, providing Þssures (or openings) that allowed the fungus gnats to pupate and females to lay eggs.
DE-insecticide.pdf (552.9 KB)