Integrated pest management of two-spotted mite Tetranychus urticae on greenhouse roses using petroleum spray oil and the predatory mite Phytoseiulus persimilis

From 1995 to 1999, four experiments were conducted on greenhouse roses to a ssess the effectiveness of the nC24 petroleum spray oil (PSO), D-C-Tron Plu s, against two-spotted mite, Tetranychus urticae Koch (Acarina: Tetranychid ae), and to determine how the oil could be most efficiently and effectively used in combination with the predatory mite Phytoseiulus persimilis Athias -Henriot (Acarina: Phytoseiidae) in an integrated pest management program. The results showed that 0.5% PSO applied fortnightly to roses gave excellen t protection from T. urticae infestation when the mite population was not a lready established. However, PSO applied after roses were infested with T. urticae above the economic threshold only stabilised populations without re ducing them below that threshold. Populations of P. persimilis in the upper and lower canopies were unchanged after two sprays of PSO at 7-day interva ls, and application of PSO to the upper canopy was as effective in controll ing T. urticae in the presence of P. persimilis as spraying the entire plan t. Combining PSO with P. persimilis gave better control of T. urticae than using P. persimilis alone. The most cost-effective use of PSO in the presen ce of P. persimilis is, therefore, to apply spray only to the upper canopy. This will not affect control of powdery mildew with PSO. Comparison of a c ontrol program for T. urticae based on the monitored use of synthetic mitic ides with that based on calendar application of PSO revealed that both gave equally effective control. The benefits of combining PSO and P. persimilis in an integrated pest management program for T. urticae on roses over a pr ogram based on synthetic fungicides are discussed.