Effect of powdery mildew on the interaction between two-spotted spider miteand a predatory mite in strawberry

Abstract: Strawberry production in high plastic tunnels is becoming popular for the advantagesof extended production and reduced disease problems. However, this production system createsfavorable conditions for several pests, including the two-spotted spider mite (Tetranychusurticae) and for some diseases, of which powdery mildew (Podosphaera aphanis) is the mostimportant. Preliminary laboratory experiments were conducted to study: (1) the preference ofT. urticae to mildew infected vs. healthy strawberry leaves, and (2) the impact of powderymildew on T. urticae egg production and predation of the predatory mite Phytoseiulus persimilis.Five days after the mite release, the total number of T. urticae eggs and nymphs found on healthyleaf discs were two times higher than on leaf discs with powdery mildew, predatory mites orboth. In the preference experiment, a significant number of T. urticae moved to healthystrawberry leaf discs and settled there for the whole period of the experiment. The resultsindicated that T. urticae did not thrive on strawberry leaves heavily infested with powderymildew, and that powdery mildew seemed to reduce the predation efficiency of P. persimilis.Therefore, it may be economical and efficient to control powdery mildew before releasingP. persimilis to control the spider mites.