Efficacy of biorational insecticides against chilli thrips, Scirtothrips dorsalis (Thysanoptera: Thripidae), infesting roses under nursery conditions

We evaluated biopesticides based on entomopathogenic fungi, azadirachtin and horticultural oils for the management of the chilli thrips, Scirtothrips dorsalis Hood, an economically significant invasive pest in the United States. Insecticides were applied four times at 7- to 10-day intervals against established S. dorsalis infestations on shrub roses KnockOut®, Rosa x ‘Radrazz’ under simulated nursery conditions. When applied as stand-alone treatments, Beauveria bassiana GHA (BotaniGard® ES), Metarhizium brunneum F52 (Met-52 EC), a horticultural oil (SuffOil-X®) and azadirachtin (Molt-X®) at label rates provided significant control, reducing populations of S. dorsalis by 48–71% compared with control over 4–6 weeks. Similar results were observed when the biopesticides were applied in rotation with each other. A conventional standard, spinosad (Conserve® SC), was consistently the most effective treatment in these studies, reducing thrips populations by >95% overall. In another study, more effective control (87%–92%) was achieved in biopesticide rotation programmes that included spinosad, when compared with those that did not. Results also showed that these biopesticides can be tank-mixed. However, there was no evidence that B. bassiana or M. brunneum combined with azadirachtin resulted in additive or synergistic control, as neither tank-mix treatment improved control compared with azadirachtin alone. These findings highlight the potential use of biopesticides in rotation programmes with conventional insecticides to manage S. dorsalis on roses. Biopesticides evaluated in this study can be incorporated into an IPM programme for roses.