Considerations and combinations to improve control of pupating western flower thrips in chrysanthemums


Abstract: Western flower thrips (WFT) are a major impediment in greenhouse floriculture. They are pests of global significance, resistant to many conventional insecticides and in Canada today, there is only one registered product that will successfully control this insect. Biological control is the only viable option available to Canadian growers. The thrips life cycle provides two distinct environments and life stages that can be targeted with different natural enemies. Nematodes, primarily Steinernema feltiae (e.g., Nemasys®), applied as a drench treatment, are widely used against soil-dwelling stages (pro-pupae and pupae). Metarhizium brunneum (formerly anisopliae; Met52® granular biopesticide) is registered for thrips control in Canada. The fungus is incorporated into potting media and will infect and kill thrips entering the soil to pupate. The purpose of the current trial was to define efficient use practices for these biocontrol agents and confirm their compatibility. We investigated effects of plant growth stage on nematode deposition onto the soil, nematode-Met52compatibility, and the relative efficacy of individual and combined, i.e. Nemasys + Met52, treatments against WFT. As chrysanthemums grew and the density of the plant canopy increased, fewer nematodes reached the soil after each spray which may affect efficacy. Overall, Met52 appears to be compatible with S. feltiae. Individual nematode and fungus treatments had a measurable suppressive effect on thrips, but the combined nematode/fungus treatment provided superior control. WFT populations were consistently lower on plants receiving the combined treatment; at the conclusion of the trial (8 weeks) < 10 WFT/pot were recovered. Opportunities therefore exist to enhance the reliability and cost-effectiveness of thrips biocontrol agents by taking an integrated approach to their deployment.

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