Sustainable management of the soybean aphid with biological control agents and reduced risk - and bio-pesticides

Project Code PRR07-490

Project Lead

Art Schaafsma / Rebecca Hallett - University of Guelph

Objective

To assess impacts of naturally occurring enemies of soybean aphid, recommend action thresholds based on natural enemy counts, evaluate the efficacy of reduced risk control products, and educate growers and crop consultants on recommended tools and products

Summary of Results

Background

The soybean aphid (SBA), Aphis glycines, is native to Asia. It has become a major pest of soybean since its discovery in North America in 2000. Conventional soybean producers have only two products available for aphid control, lambda-cyhalothrin and dimethoate, both of which are relatively old chemistries with undesirable impacts on natural enemies. Prior to conducting this project, recommended spray action thresholds for SBA did not incorporate data on natural enemy numbers, although natural enemies of SBA are widespread in Ontario in both conventional and organic production systems, playing an important role in regulating and suppressing soybean aphid populations. The main natural enemies of SBA found in Ontario soybean fields are multicoloured Asian lady beetles, seven-spotted lady beetles, Aphelinus certus, Orius insidiosus, Aphidoletes, lacewings and syrphids. Aphelinus certus, a soybean aphid parasitoid native to Asia, was also found in commercial soybean fields in Ontario, the first record of this species occurrence in North America. The main objectives of this project were to develop recommendations for incorporation of natural enemy counts into action thresholds for SBA and to evaluate the efficacy and compatibility with the natural enemies of reduced risk control products, including biopesticides, for SBA management.

Approach

Population dynamics of SBA and natural enemies in Ontario fields was investigated during 2007 and 2008 seasons. Predation and parasitism rates of the main natural enemies against Soybean Aphid were determined in the laboratory, which resulted in the development of a new measure, the Natural Enemy Unit (NEU). The NEU represents the natural enemy number which can kill 100 SBA in one day, and was developed to standardize the influence of natural enemies on SBA in 2008. A dynamic action threshold (DAT) calculation method, incorporating natural enemy counts was developed to aid in making soybean aphid management decisions. The DAT approach utilizes pest and natural enemy numbers, as well as expected population growth rates, so that an insecticide application is triggered only if natural enemy numbers are not sufficient to keep pest populations in check.

Field efficacy trials and laboratory bioassays were conducted in 2008-2009 with four reduced risk insecticides: spirotetramat, flonicamid, Beauveria bassiana and mineral oil.

Results

A hand-held disk-style calculator was designed which helps growers easily determine the DAT and decide if and when insecticide applications are necessary. In addition to DAT validation experiments, on-farm implementation of the DAT was conducted in collaboration with growers on 4 commercial soybean fields, two in Eastern Ontario, and two in Southwestern Ontario in 2009. These on-farm assessments of the DAT showed that yields equivalent to those in conventional production systems could be obtained, even in absence of an insecticide application, saving growers $20-30 per acre in insecticide costs, and reducing pesticide load to the environment. Grower co-operators in both Eastern and Southwestern Ontario indicated that as a result of having access to and using the DAT calculator disk, they did not apply any insecticides on their fields or those under their management. Without access to the disk, they indicated that they likely would have sprayed those fields with insecticides; thus a 100% reduction in insecticide use was achieved in those fields during this study. The DAT calculator is currently being developed into a smartphone application (app) that will be available for use in mid-July 2011, with support from the Ontario Ministery of Agriculture and Food and Rural Affairs -University of Guelph Partnership’s agreement on Knowledge Translation and Transfer (KTT) program.

Spirotetramat and flonicamid show promise as reduced-risk products for SBA control while Beauveria bassiana and mineral oil had only limited efficacy and low selectivity of the pest as compared with natural enemies. Dimethoate was very harmful to all natural enemies tested in laboratory assays. Lambda cyhalothrin was very harmful to Orius, but only moderately harmful to Harmonia and Aphelinus. The remaining pesticides were harmless to Harmonia and Aphelinus, but spirotetramat and flonicamid were moderately harmful, and mineral oil and Beauveria bassiana were harmful to Orius.

The knowledge generated in these studies was demonstrated and transferred to growers and consultants in Ontario through Demonstration Days, as well as via participation in the Southwest Diagnostic Days, Southwest Agricultural Conference, Canada’s Outdoor Farm Show and newsletters. Such information has also been transferred to Quebec soybean growers through collaboration with provincial crop specialists. Results of this project were also published in a number of scientific peer reviewed journals.

With the implementation of the results of this project, growers will be able to save money and reduce pesticide use associated with soybean aphid management, while still safe-guarding their crops. In addition, products with efficacy against SBA, and which are not harmful to SBA’s natural enemies have been identified for possible future registration in Canada. The registration of alternative products (such as the recent registration of spirotetramat) will benefit pesticide resistance management efforts, and provide soybean growers with more choices for soybean aphid management.

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