Implementation of a new biofungicide to reduce apple scab inoculum, opening the way to the use of newly developed tools

Project Code : BPI06-030

Project Lead

Odile Carisse - Agriculture and Agri-Food Canada

Objective

To develop an apple scab management plan that integrates a newly developed microbial biocontrol agent Microsphaeropsis ochracea.

Summary of Results

Apple scab is an endemic disease that requires up to 14 fungicide sprays throughout the season, raising concerns for the health of growers, workers and consumers. Because the economic threshold is low (1-2% fruit scabbed) it is practically impossible to produce apple without protection against apple scab. Several fungicides used to manage apple scab have a high environmental impact while those with smaller impact are subject to resistance in the population of the pathogen and must be used carefully. Despite the availability of several management tools, it is very difficult to reduce the number of fungicide sprays.

Over the last 6 years, Dr. Carisse and her research team developed a new microbial pest control agent, Microsphaeropsis ochracea. This microorganism clearly demonstrated its potential to reduce primary inoculum of apple scab. By reducing the amount of initial inoculum, it would be possible to significantly reduce the risk of disease and hence allow a reduction in fungicide usage. However its use must be integrated in a global apple scab management scheme.

As part of a research program with the Quebec apple growers, Dr Carisse and her team developed a simple approach for apple scab management based on monitoring of apple leaf emergence, ascospore availability and risk of infection. Using this approach it is possible to determine if the entire foliage has been protected and hence if a new fungicide application is required. Therefore, it is proposed to integrate the use of the microbial pest control agent Microsphaeropsis ochracea) into this new approach to apple scab management to ensure a low amount of inoculum in the orchard and open the door to less intensive fungicide programs, reducing at the same time risk to growers and consumers while keeping good disease control.

During the 2007 growing season, an Integrated Disease Management (IDM) scheme was evaluated in commercial and experimental orchards located in Ontario and Quebec. The IDM scheme was based on the integration of three management and decision tools. First, in the fall of 2006, a post-harvest treatment of the biological control agent (Microsphaeropsis ochracea) was applied to reduce the potential ascospore dose the next spring. Secondly, the fungicide sprays against the primary infections were applied based on risk derived from leaf emergence, ascospore maturity, and infection conditions. Thirdly, the summer fungicide sprays were applied based on evaluation of scab incidence using a sequential classification plan.

At the sites located in Ontario and at Magog (in Quebec) there were no differences in incidence of apple scab and in the amount of fungicide used in plots managed with the grower's schedule and the integrated disease management scheme. However, at the other two sites located in Quebec (St-Gregoire and Frelighsburg), they was significantly less scab and less fungicide applied in plots sprayed based on the IDM scheme.

The use of the sequential classification plan allowed a pesticide use reduction of 24% and 45% as compared to the grower's standard practice. The impact of the IDM scheme on pesticide reduction was not significant at the site in Ontario and at Magog in Quebec, but it was significant at the other two sites in Quebec. An evaluation over a longer period of time will be needed to evaluate the long term impact of such management program on pesticide risk reduction.

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