Effects of Ultraviolet-B irradiation used in combination with phytoseiid mites on the control of the two-spotted spider mite Tetranychus urticae Koch in high-bench strawberry cultivation

Abstract

Recently, a new method to control the two-spotted spider mite Tetranychus urticae Koch with ultraviolet-B (UVB) irradiation has been established. Here, we employed UVB irradiation in combination with phytoseiid mites to control the two-spotted mite in high-bench strawberry cultivation in a commercial greenhouse for two years. We did not observe any adverse effects on the phytoseiid mites exposed to UVB at 26–79 mW/m² intensity at the top of strawberry plants for 2–3 h every night. Irrespective of the presence or absence of sheets to reflect UVB on the leaf surface, the combination of UVB irradiation and phytoseiid mites suppressed the two-spotted spider mite to a level below the control threshold from October to early April.