Use of trap plants as a risk reduction control option for thrips on greenhouses ornamentals

Project Code : MUR06-090

Project Lead

Les Shipp - Agriculture and Agri-Food Canada

Objective

To investigate the use of trap plants treated with and without the application of a pesticide (Spinosad) for control of Western flower thrips (WFT) on potted chrysanthemum

Summary of Results

Western flower thrips (WFT), Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), are a major pest of greenhouse ornamentals. Chemical pesticides are the main control measure used for WFT control on ornamentals and their use impedes the implementation of biological control. Indeed, in potted chrysanthemum production, 68% of all insecticide treatments were for control of WFT. The use of trap plants (i.e. plants more attractive to a pest than the crop) is new in greenhouse production and can be a useful addition to ornamental IPM and risk reduction strategies.

In this project, several aspects that can influence the efficacy of the trap plant strategy were investigated. In choice trials, yellow flowering chrysanthemums were more attractive to adult WFT than gerbera or eggplants. WFT preferred flowering chrysanthemums as compared to vegetative, bud or crack-bud chrysanthemum stages, which means that they can be used as trap plants in chrysanthemum production for almost the whole crop production cycle. Trap plants were most effective to attract dispersing thrips. Thrips that were already on a plant were less likely to move to the trap plants. Thus, it is important to place trap plants in sites where thrips are dispersing or moving around the greenhouse such as vents and doorways or between flowering and non-flowering crops. Large cage greenhouse trials demonstrated that flowering chrysanthemums as trap plants can suppress populations of WFT in a vegetative chrysanthemum crop and reduce crop damage. A commercial trial in potted chrysanthemum showed that trap plants reduced thrips populations under commercial growing practices and natural thrips infestations. Treating the trap plants with a reduced-risk insecticide like spinosad (Success) did not improve their efficacy as compared to replacing the trap plants every week. These findings suggest that thrips stay on the trap plants and do not move back into the crop. Another aspect of the project looked at combining the trap plant strategy with application of biological control agents (the entomopathogenic fungus Beauveria bassiana or the predatory mite Amblyseius swirskii). These experiments were not conclusive, however, and further investigation will be required.

Results of the project indicate that whole greenhouse sprays of insecticides against WFT can potentially be reduced by 85-100% in ornamentals production by employing a trap plant strategy. Elimination of these chemical sprays will enable growers to make use of more biological control agents against other greenhouse pests, resulting in a further reduction in the amount of chemical pest control required to product the crop. Results of this study have been published in the industry magazine "Greenhouse Canada", and in the scientific journal Environmental Entomology.

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