Rose (Rosa hybrida L.) is the most important ornamental crop in Kenya, with huge investments in pest management. We provide the first full-scale, replicated experiment comparing cost and yield of conventional two-spotted spider mite (Tetranychus urticae Koch) control with hot-spot applications
of the predatory mite Phytoseiulus persimilis (Acari: Phytoseidae) in large commercial rose greenhouses. Hot-spot treatments replaced acaricides except at high infestations and the two treatments were applied in seven greenhouses each. With the conventional treatment, acaricides were applied when T. urticae populations exceeded 250 motile individuals per plant based on scouting. Treatments with acaricides and P. persimilis were guided by weekly scouting and hot-spot treated greenhouses with infestations exceeding 1000 individuals m-2 (calculated as average mites/leaflet 9 average leaflets per plant) were first blanket-treated with an acaricide to decrease infestations. Roses subjected to the hot-spot treatment had significantly lower T. urticae infestations compared with conventionally treated roses. In addition, significantly fewer high spider mite infestations were recorded in roses with the hot-spot treatment. The cost of pest management was significantly lower in the hotspot- treated greenhouses than in the conventional treatment. However, there was no significant difference in the number of harvested stems from the two treatments. It can therefore be concluded that acaricides can be replaced by P. persimilis hot-spot treatments in commercial cut rose production, effectively reducing pest management costs with no loss in crop yield.