Integrated control of broad mites in ornamental plants under variable greenhouse conditions

Abstract: Broad mites are an important pest in ornamental crops. They cause substantial damage to flowers and leaves, which render the plants unmarketable. Although a number of good Integrated Pest Management (IPM) strategies for the control of broad mites exist, some farmers still experience difficulties in keeping damage below economic thresholds. As growers have adapted temperature regimes in greenhouses to minimize energy consumption, different climatic conditions may affect control effectiveness. We therefore investigated the effect of variable greenhouse conditions (relative humidity, temperature, light) on both the broad mite and its main natural enemy, a predatory mite. We aimed at increasing control efficacy through better monitoring strategies and better choice of control strategies and predator species. We found that broad mites disperse faster than expected if monitoring is limited to visual observation of damage. This necessitates an adaptation of monitoring strategies and local treatments. Furthermore, broad mites thrive in a different location on the plant under different conditions, limiting exposure to chemical treatment. In addition, we found that predatory mite species respond differently to varying greenhouse conditions. Most predatory mite species perform better when day and night temperatures differ, at lower temperatures (daily mean 15-25 °C) and less so above 25 °C, both for reproduction as in predation capacity (Vangansbeke et al., 2015). Depending on the climate, release rate and frequency of release should be adapted. Providing additional food (Artemia, Typha) in the greenhouse resulted in good broad mite control with fewer predatory mite introductions. The knowledge and practical experience we built over the past years has aided growers to control this pest adequately on the farm through integrated control strategies.