Abstract

In an attempt to control pathogens and insect pests affecting greenhouse tomatoes, we evaluated an electric field screen to create an airy greenhouse condition that successfully excluded insect vectors (whiteflies, green peach aphids, western flower thrips and shore flies) of pathogens and airborne conidia of tomato powdery mildew. The screen consisted of three parts: 1) insulated conductor wires (ICWs) arrayed in parallel at 5-mm intervals, 2) two stainless-steel nets that were grounded and placed on both sides of the ICWs, and 3) a direct current (DC) voltage generator to negatively charge the ICWs. An electric field formed between the negative surface charge of the ICWs and the positive charge on the ICW-side surface of the grounded net. The ICWs captured insects and airborne conidia that entered the field. Insects that contacted the outer surface of the screen net avoided the electric field and flew away from the screen. During continuous 3-month greenhouse operation, the screen was durable and functional in exerting stable pest exclusion and good air penetration for ventilation under changing greenhouse climate conditions. In three experiments examining the occurrence of powdery mildew in hydroponically cultured tomato plants on either side of a greenhouse partition, the screen-guarded plants remained germ free throughout the culture period (1 month), whereas powdery mildew was present on the leaves of almost all unguarded tomato plants. Thus, our electric field screen provided an airy condition for tomatoes in an open-window greenhouse that successfully excluded airborne pathogens and flying insect pests.

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