Control of the poultry red mite Dermanyssus gallinae is a challenge for organic as well as conventional egg producers. In organic agriculture, control should be attempted by mechanically acting substances (e.g. oils or diatomaceous earth), before acaricides are applied. Diatomaceous earth (DE) without acaricides was at least as effective as DE supplemented with pyrethrum or essential oils and a liquid formulation of silica in vitro. In on farm experiments, DE was effective during a limited period only, whereas the liquid formulation had a very good residual effect over several weeks
