Evaluation of acaricide-treated string curtains for control of two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) on greenhouse roses and impact of the string curtain on the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae)

Foliar sprays of pesticides are frequently used to control two-spotted mites on rose flowers, but these also destroy predatory mites and pose a high risk of contamination for humans and the environment. Using a novel approach to avoid spray applications on rose plants, modified acaricide-treated string curtains were adapted to control the pest. Two main aims of this study were: (i) to identify the lethal concentration of string curtains treated with propargite, dicofol, flufenoxuron, acrinathrin or tau-fluvalinate (τ-fluvalinate) on Tetranychus urticae, and (ii) to test the design (feasibility) and efficiency of the string curtains to trap the phytophagous mites on the plants during their circadian migration. Bioassay results in the lab confirmed T. urticae circadian migration, toxicity of the five kinds of treated string curtains and a concentration-dependent repellent effect of each chemical on T. urticae females. Of the two products tested in the field, dicofol was more effective than acrinathrin in controlling T. urticae compared to an acaricidal spray of the same products. The effect of acaricide-treated string curtain use on Phytoseiulus persimilis did not differ significantly from the control. The string curtain technique proved to be effective, but because of some biotic and abiotic constraints and the low economic threshold of mites, even for the commercialized high canopy stem roses, the present device could be more appropriate for another horticultural crop, e.g. tomato. •Tetranychus urticae has a circadian migratory behaviour.•An acaricide-treated string curtain was efficient in controlling T. urticae.•The lethal concentration of treated material differed between products.•The treated string curtain could be combined with predator release.•The treated string curtain is a concept that can be adapted to a range of vegetable crops.