Refining and making accessible to growers a validated dynamic action threshold for cereal aphid control in cereal crops
Project Code: PRR15-040
Tyler Wist and Erl Svendsen - Agriculture and Agri-Food Canada
To refine, validate and transfer a previously developed dynamic action threshold (DAT) model as a tool to help growers make spray decisions for aphid management in cereal crops
Summary of Results
Cereal aphids are a serious periodic threat to wheat, oats and barley in the Canadian prairies. Aphid infestations can build up quickly causing yield losses as high as 35-40%. With only broad-spectrum organophosphate-based insecticides available for aphid control in cereals, it is important to rationalize spray applications to preserve beneficial insects by applying only when aphid populations are predicted to exceed the economic threshold. The threshold triggering a spray action for aphid control in Western Canada is an average of 12-15 aphids per tiller, but this threshold does not account for aphid mortality due to natural enemies.
In 2011, a Pest Management Centre (PMC) led stakeholder working group identified cereal aphids as a priority pest issue to be addressed by the PMC’s pesticide risk reduction strategy for Foliar Insect Pests of Prairie Field Crops. A two-year project initiated under this strategy in 2012 led to the development of a Dynamic Action Threshold (DAT) model equation designed to account for the suppressive effects of key natural enemies present in the crop capable of keeping the cereal aphid population in check.
This follow-up project aimed to update, refine and field validate the new DAT model and turn it into an accessible tool for growers to use in making economically sound and environmentally conscious spray decisions for cereal aphid management in the Canadian prairies.
Field surveys were conducted in 2015, 2016 and 2017 across cereal (wheat, barley, and oat) fields in Saskatchewan (SK) and Manitoba (MB) to monitor population dynamics and interactions between aphids and their natural enemies. Weekly sampling included both net sweeps and actual counts of aphid and naturally occurring predator and parasitoid species per cereal tiller. Aphid mummies were also collected from the field and reared in the lab to determine actual parasitism levels. To complement the already published data, additional voracity studies were carried out to assess the rates of aphid consumption or parasitism by the key predators and parasitoids, respectively. The resulting information was incorporated into the existing DAT equation to refine its predictive function.
To validate the prediction accuracy and efficacy of the DAT equation against field observations, the fit of field gathered data and model generated predictions was assessed during 2017. The refined DAT equation was converted into an interactive platform as a smart phone application. The app allows growers to instantly access images and record counts of cereal aphids and beneficial insects, and will reliably generate a spray recommendation based on field specific data input by the user. Some 30 agrologists in SK and MB were asked to test the smartphone app for making spray decisions in the field in comparison to the conventional methods and to record the resulting data.
Two main species of aphid are typically present in cereal crops on the Canadian Prairies: the English grain aphid, Sitobion avenae Haliday and Bird-Cherry Oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Common natural enemies known to attack these aphids in cereal crops included predators, e.g. green lacewings (Chrysoperla carnea and oculata), ladybeetles (Coccinella septempunctata, Hippodamia tredecimpunctata), minute pirate bugs (Orius tristicolor) and Damsel bugs (Nabis americoferus) and parasitoids such as Aphidius avenaphis, A. ervi, A. colemani and Aphilinus varipes.
A refined and field validated computer-based DAT calculator for wheat and barley aphids which is responsive to changing numbers of aphids and their natural enemies was created. This DAT incorporates the life cycles of predators and aphids and predicts population growth of aphids and population control by natural enemies. The DAT will recommend an insecticidal treatment if the economic threshold will be exceeded, or no treatment with continued monitoring, if existing natural enemies are expected to supress aphid population growth below the threshold.
The Cereal Aphid Manager (CAM) smartphone application was built for iOS and Android platforms based on the DAT calculator and has been available to growers through free downloads from Google Play and Apple stores since March 2018. It allows growers to identify, quantify and record aphids and their natural enemies present in the field, it predicts aphid population growth and compares this with the standard economic thresholds as an in-field decision support tool. As such, the CAM is an important integrated pest management tool that supports effective scouting and informed management decision making, offering the potential to eliminate unnecessary use of pesticides.
Through extensive monitoring and field surveys across Saskatchewan and Manitoba, this project has contributed to an improved understanding of population dynamics and interactions between aphids and their natural enemies in cereal crops. It has also helped growers become more aware of the natural enemies of aphids and their important role, demonstrating the abundance of these species in cereal crops and their suppressive impacts on aphid populations. Minimizing the use of broad-spectrum insecticides as a result of adopting the CAM tool will help to conserve natural enemy populations, pollinators and other beneficial insects.
The project results were regularly communicated to scientific communities and growers, emphasizing the significant aphid control services that natural predators and parasitoids can provide when present. Recommendations were also conveyed on how growers can actively encourage increased populations of natural enemies of aphids and enhance their benefits and performance.
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