Review of status of management issues surrounding propagative pests in Canadian greenhouse floriculture industry

Project Code PRR11-040

Project Lead

Wendy Romero  University of Guelph

Objective

Conduct a thorough review of the management issues surrounding key pests of concern on propagative stock in the Canadian greenhouse floriculture industry to identify existing knowledge and technology gaps and reduced risk options for controlling these pests before they become established in the greenhouse

Summary of Results

Background

Through previous work with Canadian floriculture stakeholders, a pest management strategy aimed at reducing risks from pesticides in greenhouse floriculture was initiated. Within this strategy, the industry identified pests entering the greenhouse on propagative stock (cuttings) as a key concern threatening the competiveness of the Canadian floriculture industry.

Canadian growers routinely bring propagative material (e.g. cuttings, seedlings) into their greenhouses from North America, Central America, Europe, Africa, the Middle-east and Asia.

Insect pests can be introduced to the greenhouse from these materials, and once established keeping them under control then requires systematic application of pesticides throughout the crop production cycle. It is anticipated that preventing the entry and establishment of pests would significantly reduce the need for pesticide use in the greenhouse. Previous studies have already examined reduced risk techniques for the control of two pests (thrips and whitefly) commonly found on cuttings of two greenhouse ornamental crops (chrysanthemums and poinsettia, respectively). In order to carry this work forward more information is needed on other priority pests and potential techniques for controlling these pests at the propagative stage of ornamental crops. Through consultations with floriculture industry stakeholders and experts, the following list of priority pests to be targeted in this review was identified: thrips, mites, aphids, whitefly, mealybug, moths and scales. Through this project, reduced risk options appropriate for future investigation were identified.

Approaches

To obtain information for this report a variety of resources were consulted, including: industry professionals, factsheets, industry publications and published literature. From these sources information on technologies for disinfestation of quarantine pests on post-harvest commodities was found, however, there was limited published data on the implementation of control methods for incoming arthropod pests on propagative material. While there are multiple routes of entry for arthropod pests the primary focus for this project was on the potential techniques for pests introduced directly on propagative plant material.

Techniques investigated for potential use for treatment of pests on greenhouse propagative material included: hot water immersion, irradiation, controlled atmosphere, vacuum and controlled atmosphere, vapor heat, high-pressure water jets and hot water pre-treatment, and high-temperature controlled atmosphere.

Results

A review of the available literature revealed several practices which can minimize the likelihood in introduction or spread of propagative pests. The type of treatment to be used would depend on the plant material, target pests, and affordability.

Heat treatments were identified as having potential for success for a wide variety of insect pests. They present the advantage of low exposure risk to greenhouse employees, no residual impact on biological control agents already established in the greenhouse, and insects being unlikely to develop resistance to them. When using hot water immersion treatments, special attention would have to be paid to maintaining a precise and uniform temperature with narrow limits throughout the immersion period. There could be concerns regarding the potential for transmission of diseases when plant material is submerged, though this risk would need to be further investigated.

Immersion of propagative material in reduced risk pesticides or biopesticides is a technique with demonstrated efficacy. Insecticidal soap, horticultural oil, and Beauveria bassiana are products with great potential to be registered as immersion treatments for use in Canadian greenhouses and more trials to determine the efficacy of these products on other insect pests could be considered. As well other reduced risk pesticide formulations and biopesticides could be evaluated using the same immersion technique.

It was found through the literature search that in the ideal scenario a separated portion of the greenhouse would be used solely for the treatment of propagative material, which then could be transferred to the misting chamber of the greenhouse.

The main limiting factor on the use of any of the technologies reviewed through this project is the potential for phytotoxicity. While, ideally, research would be conducted on the phytotoxicity of these control treatments on different crops, Canadian greenhouse floriculture growers produce thousands of different varieties and species of plants, making trials for each one impractical.

Next Steps

Non-chemical technologies such as hot water immersion and the use of reduced risk or biopesticides as immersions are approaches with great potential for controlling insect pests on propagative material. While greenhouse pest management specialists affirm that growers have been practicing a variety of methods to disinfest propagative material, the efficacy of such methods is not often scientifically tested and results are not available.

There is still some scientific research to be conducted, and federal/provincial engagement is necessary to facilitate the registration and adoption of these technologies. More trials of reduced risk methods on more species of plants followed by communication of results to Integrated Pest Management specialists are valuable in finding solutions to this pervasive issue facing greenhouse growers.

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