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Identification of efficient sprayer application tools to maximize onion thrips control

Project Code: PRR07-350

Project Lead

Jennifer Allen - Ontario Ministry of Agriculture, Food and Rural Affairs


To develop and implement a plan for growers to reduce the number of sprays and amount of pesticide required to manage onion thrips in Ontario and Quebec onion production, and to make recommendations for reduced-risk control products to replace older chemistries

Summary of Results


Onion thrips, Thrips tabaci Lindeman, are economic pests of onion crops worldwide. During dry, hot months, crop loses could reach over 40%, forcing growers to make two to ten insecticide applications, depending on the season. Although individual thrips are easily killed with insecticides, problems are caused by heavily infested individual plants (local populations are able to grow exponentially in a very short period of time), rapid increases in field populations caused by pest immigration into fields, and the behaviour of the pests which tend to congregate deep within onion leaf axils. Studies have shown that only 1 to 5% of a given foliar insecticide reaches the intended target under field conditions.

The purpose of this study is to improve the delivery of currently registered products to the inner onion leaf axils, as this is essential to maximizing insecticide efficacy. This is especially important with reduced-risk pesticides which possess narrower activity spectrums. This project aimed to establish spray parameters to maximize the delivery of insecticides to the target site by identifying the most effective (1) carrier volume, (2) surfactant, and (3) nozzle angle. The project also evaluated reduced-risk pesticides as potential candidates for future data generation and registration. Access to newer pest control products is not only important for economic and environmental reasons; it also helps to manage resistance, which has been documented in onion trips populations in North America.


From 2007 to 2009, trials were conducted in organic soils of the Holland Marsh area of Ontario to evaluate different spray angles, surfactants, and water volumes for their ability to penetrate the crop canopy and cover the inner leaf axils. Two methods were used to assess spray coverage: water sensitive paper and an ultraviolet (UV) fluorescent dye. The water-sensitive paper was introduced to the plots before they were sprayed. Long paper rectangles were placed upright between the two youngest onion leaves of each plant and the fluorescent dye was dissolved in the spray tank. Plots were sprayed using a tractor-mounted sprayer with water volumes of 400, 500, and 600 litre (L) water per ha. Plots were sprayed with and without a surfactant (Sylgard 309) with nozzles at a 0° or 22° angle. Once dried, onions and water-sensitive paper were collected from each plot. The onions were photographed under a UV lamp and the papers were scanned. Images were then analysed using Assess (Image Analysis Software for Plant Disease Quantification) to determine the coverage percentage.


Analysis of the water-sensitive paper revealed that in all years, regardless of nozzle angle, more spray reached the target site (inner leaf axils) when the solution was applied in greater amounts of water (500 and 600 L/ha). On these paper rectangles there were no differences in spray coverage between Sylgard 309 and water (that is, with or without surfactant). When nozzle angle, water volume, and surfactant were considered in combination, the top treatment for each year was applied at a 22° angle. The most effective treatments were: Sylgard 309 at 600 L/ha (2007); water at 500 L/ha (2008); and water at 600 L/ha (2009).

Analysis of actual onion leaf coverage revealed that, regardless of nozzle angle, the surfactant Sylgard 309 provided better coverage than water. Additionally, using 500 or 600 L/ha provided better coverage than using 400 L/ha. When combinations were compared, the top treatment for each year was applied with Sylgard 309 at the 22° angle: 500 L/ha (2007); 600 L/ha (2008); and 600 L/ha (2009). These results demonstrate that all three factors (water volume, surfactant, and nozzle angle) affect spray coverage. The one factor that had the greatest impact was water volume.

Depending on local conditions, a grower may not always be able to modify all three factors. In cases in which adding a surfactant is not feasible, increasing the amount of water as a carrier can help to improve delivery of the product to the target site. Conversely, when limitations exist regarding water volume output, adding a surfactant can increase coverage even if water volume is low.

Spraying early in the morning or later in the evening (after sunset) is another helpful tip for maximizing thrips control. Dew in the morning will help the insecticide find its way into the leaf axils where thrips typically reside. Evening spraying, when temperatures have cooled down, helps to maximize efficacy of pyrethroid insecticides.

The project also evaluated registered and non-registered reduced-risk insecticides for their efficacy in controlling onion thrips. Active ingredients that were found to be effective (spinetoram, cyantraniliprole) are currently being pursued for registration under Pesticide Minor Use Pesticides of AAFC.

By maximizing the efficacy of insecticides, onion growers can reduce the number of applications per season and still maintain commercially acceptable levels of thrips control, benefiting growers (by reducing the cost of pest management activities), the environment, and human health - all of which are core goals of AAFC’s Risk Reduction.

The results of this project were communicated to growers and other target audiences through presentations in meetings during 2008 and 2009 (for example, Southwestern Agriculture Conference in Ridgetown, Ontario, in 2008; Scotia Horticulture Congress in Wolfville, Nova Scotia, in 2009; The Entomological Society of Canada and Manitoba Joint Annual Meeting in 2009), posters (for example, Ontario Fruit and Vegetable Convention, St. Catherines, Ontario, in 2008), reports, and publications. A factsheet to provide a more detailed account of results and recommendations is in preparation.

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