Implementation of spore trapping network technology combined with improved forecasting systems to manage Onion Leaf Blight at the regional scale

Project Code PRR07-190

Project Lead

Odile Carisse - Agriculture and Agri-Food Canada

Objective

To implement a network of airborne inoculum monitoring, adapt existing forecasting systems to optimize the efficacy of currently registered fungicides, and assess economic and environmental benefits of combining spore trapping with forecasting

Summary of Results

Background

Botrytis leaf blight (BLB), caused by the fungus Botrytis squamosa, is a major disease of onions in Canada. The economic impact of this disease is especially high in muck (organic) soils of eastern onion growing regions, including Ontario and Quebec where about 90% of Canadian onion crops are grown. Severe epidemics, especially during warm and moist seasons, can lead to significant reductions in bulb number and size. Typically, BLB is managed with numerous foliar applications of fungicides on a calendar schedule most often at 7 to 10 day intervals. Typically, this can result in 8-14 fungicide sprays per growing season in an onion crop. Routine applications of fungicides, however, raise concerns about human and environmental health risks, unnecessary production costs and risks for development of pathogen insensitivity to fungicides. Several forecasting systems have been developed to improve timing and efficacy of fungicide applications, but their complexity and lack of reliability has limited grower uptake and use of these decision support tools.

This project aimed to validate the use of a network of airborne inoculum monitoring as a tool to optimize the accuracy and uptake of existing forecasters, and to implement a reliable decision support system for growers. The project was conducted from 2007 to 2010 by Agriculture and Agri-Food Canada (AAFC) scientists in collaboration with University of Guelph researchers and Phytodata Inc. experts, and targeted the largest onion growing regions in Ontario and Quebec.

Approaches

The effect of including airborne spore counts on predictive accuracy, usefulness and reliability of existing forecasters was evaluated through an integrated decision making approach. This approach combined spore trapping technology, DNA-based quantification of airborne B. squamosa inoculum in the field, and sporulation risk index estimates from existing weather-based forecasters. Inoculum present in the field was assessed using rotating-arm spore samplers established in 18 commercial onion fields in the muck soil region across Ontario and Quebec in 2007 and 2008. Spore traps were periodically exposed (10:00-12:00, 2-3 times/week) starting in early June, then collected and analysed in the laboratory. Immediately after the results were available, spray recommendations were delivered to growers who had signed up for the service.

In each province, two decision support systems were evaluated for delivering disease risk warnings as well as recommendations for the timing of initial and consecutive fungicide sprays in comparison with the calendar spray schedule. In Ontario, sprays were based on the number of lesions/leaf, inoculum concentration and Disease Severity Value (DSV; as provided by the BOTCAST forecaster). In Quebec, sprays were based on the number of lesions/leaf, inoculum concentration and Sporulation Index (SI; as provided by the PREDICTOR forecaster). Disease severity was estimated weekly as the number of lesions per leaf in sample sizes ranging from 50 (ON) to 100 (QC) onion plants in the field.

Pesticide risk reduction was estimated by comparing the numbers of fungicide sprays in fields using inoculum monitoring with those in fields using calendar schedule. Pesticide risk values were also calculated, based on the Pesticide Risk Indicator for Quebec (IRPeQ). An economic assessment was conducted to evaluate the costs and benefits of using the recommended tools. A grower survey was also conducted to assess the status of current BLB management practices and the potential for grower adoption of the forecasting technology.

Results

In both years, BLB severity was much higher in Quebec than in Ontario. Overall, there were no significant differences between yields in fields where BLB was managed according to decision support tools and those where the calendar spray schedule was used. In Ontario, the number of fungicide sprays was reduced by 42-47% (e.g. 3.5 vs. 6 sprays) and better disease control was achieved in fields managed according to decision support recommendations compared to those using the calendar schedule. In 2007 in Quebec, under very severe disease conditions, the number of sprays was reduced by 27% (e.g. 11.2 vs. 15.4 sprays) in fields managed according to decision support recommendations, and disease control levels were similar in both fungicide treatments schemes. No significant differences in number of sprays or disease control levels were observed in Quebec in 2008.

This study demonstrated that a fungicide application regime based on the quantification of airborne inoculum present in the field can reduce the frequency of fungicide sprays in onion crops while improving disease control, thus decreasing overall fungicide use and production costs. Best disease risk estimations were obtained when a forecaster based on inoculum monitoring was combined with a weather-based forecaster such as SI or DSV. Maximal pesticide risk and cost reduction benefits from the improved forecasting model proposed in this study are expected under dry conditions (i.e. low to moderate disease severity). However, both the spore samplers and the forecasting model needed to be further validated in large scale field trials before the technology and delivery of such services could be made commercially available. Since project completion, this validation has taken place, the results were published and the service is now available for use by growers.

Survey results (24 respondents, all in Quebec) indicated that BLB is the most important disease affecting onion production, at least in Quebec, and that growers rely on regular fungicide applications to manage BLB. However, the majority of respondents felt that using integrated disease management tools such as inoculum monitoring and forecasting would help them reduce pesticide use and/or improve disease control. The majority of growers were aware of spore samplers and most of them were willing to use the technology and services when commercially available.

This project is part of Pesticide Risk Reduction Program’s support to address the BLB issue while helping growers have access to improved and reliable decision making tools for effective integrated disease management. For more information, contact Dr. Odile Carisse.

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