Prevention is better than cure: Early-season intervention to control whitefly on poinsettia

Abstract: Historically, poinsettia cuttings shipped into Ontario from offshore production facilities have carried very low levels of immature Bemisia whiteflies. These have been successfully controlled by preventative releases of parasitoids (Encarsia formosa, Eretmocerus mundus). In 2012 though, cuttings arrived into Ontario carrying large numbers of Bemisia eggs and nymphs. Parasitoid releases proceeded as normal but failed to regulate whitefly populations; multiple pesticide treatments were required to provide effective control. Endemic whitefly resistance (owing to heavy pesticide use in production facilities) means that insecticides registered in Canada frequently have reduced efficacy. Furthermore, pesticide residues on imported material can have a detrimental effect on parasitoid survival and performance. To ensure greater sustainability in poinsettia production, new methods of control are required to mitigate incoming pests on cuttings and ensure that biological control systems can be maintained through the crop production cycle. Several reduced-risk products, biopesticides and combination treatments, applied to infested cuttings by dipping immediately prior to sticking, were therefore evaluated to determine their relative efficacy against whitefly, ensure compatibility with parasitoids and to assess possible phytotoxic effects. A combination of insecticidal soap and Beauveria bassiana (BotaniGard® WP; BioWorks Inc., Victor, NY) was the most effective treatment tested; phytotoxic effects were minimal (some variation across cultivars) and survival of Encarsia and Eretmocerus was not affected following release onto treated leaves. The project has allowed effective treatments to be identified that can be readily implemented on a commercial scale.