Combining applications of potassium silicate and Beauveria bassiana to four crops to control two spotted spider mite, Tetranychus urticae Koch

A possible synergy between the biological control agent Beauveria bassiana (Bb) and potassium silicate (KSil) for the control of two spotted spider mite (TSM) was investigated. Greenhouse experiments were carried out on cucumber, eggplant, bean and maize plants. Potassium silicate was added to nutrient solutions at 0.02, 0.04, 0.08 and 0.16% (v/v) (equivalent to 20, 40, 80, 160mg of pure Si per liter, respectively). Conidia of Bb (Isolate R444) were suspended in Break-thru (R) and sprayed onto plants 7d after TSM inoculation. Plants treated with KSil at higher concentrations, 0.08 and 0.16%, suffered less damage by TSM. However, KSil alone did not kill mites. Higher mortality of adult mites, as well as juveniles, were caused by Bb and this enhanced efficiency when the fungus was combined with KSil. These results indicate that the application of KSil as a plant nutrient may provide some protection of plants against TSM infestations in both monocotyledonous and dicotyledonous plants, and enhance the biocontrol efficacy of Bb.