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Improving sclerotinia forecasting

A new, four-year pilot project launched in Western Canada will help improve disease forecasting and management of sclerotinia stem rot in canola. Developed in Denmark several years ago by Dr. Lone Buchwaldt, currently a researcher with Agriculture and Agri-Food Canada (AAFC) in Saskatoon, Sask., the sclerotia-depot method will be tested for the first time in Canada in the 2014 growing season.

“The sclerotia-depot method was used successfully in Denmark for many years and proved to be very reliable for forecasting sclerotia germination,” explains Buchwaldt. “We want to evaluate the usefulness of this method in Canada, either as a stand-alone risk assessment tool or in combination with the existing sclerotinia stem rot checklist available from the Canola Council of Canada. The project will continue to the end of 2017 and will be tested across Western Canada.”

For the 2014 growing season, a total of 37 volunteers have established 67 sclerotia-depots in Saskatchewan. A depot is made from two layers of nylon mesh heat-sealed together to produce 50 compartments of 5 x 10 rows. Each compartment contains a sclerotium, which is a resting body of the fungus Sclerotinia sclerotiorum that can germinate with spore-bearing apothecia under the right weather conditions. These spores typically colonize petals lodged on the plant, causing stem rot in canola. The depots were put into the ground for overwintering in the fall, and in the spring they were placed in selected canola fields where they are now being monitored. Sclerotia-depots are managed by volunteers primarily involved with extension work in the public or private sectors and a number of canola growers. They monitor the depots and report per cent sclerotia germination via the Internet using a mobile device or personal computer.

“We ask volunteers to go out once a week before the canola crop begins to bloom to observe and submit per cent sclerotia germination,” explains Buchwaldt. “Once the crop begins to bloom, we ask volunteers to go out every two or three days, particularly if apothecia are forming. The sclerotia will germinate with spore-bearing apothecia once the canola canopy shades the soil surface and only under cool, wet weather conditions. If apothecia begin to form, we need to have as up-to-date reports as possible. Our staff at AAFC are updating the data daily during the week, so that real time sclerotia germination data is available across the province.”

The data from all sclerotia-depots are available from June to July, or as long as canola is flowering, through SaskCanola’s website www.saskcanola.com (go to the Research page and select Sclerotinia risk assessment) and is shown on the per cent sclerotia germination map. The timing and rate of sclerotia germination in a depot is assumed to be correlated with natural sclerotia germination in the surrounding canola fields. Since weather conditions vary over short distances, a 10-kilometre (six mile) radius from a depot is tentatively set as a cut-off for this correlation.

The sclerotia germination data can be used with the sclerotinia stem rot checklist to calculate the risk at a field-specific level and make decisions as to whether or not a fungicide application is warranted. A new, interactive sclerotinia stem rot checklist is available on the SaskCanola website and is a modified version of the original checklist with the regional risk for apothecia development modified to per cent sclerotia germination in a local sclerotia-depot.

“This last question on the checklist relates to apothecia germination, and can be difficult to determine,” explains Buchwaldt. “The sclerotia-depot method should result in a more accurate number for the risk calculation. The total risk point for the six risk factors on the checklist is calculated automatically, with 40 risk points, as suggested in the original checklist, still the recommended threshold for applying a fungicide. We encourage growers to continue using the checklist along with the depot tool for the best overall assessment for their fields.”

As part of the evaluation of the sclerotia-depot method, Buchwaldt will be collecting data from fungicide trials and demonstration sites. Sclerotinia severity and yield data from sprayed and un-sprayed areas will be used to compare the relationship between yield loss and per cent infected plants, as well as the actual yield gain from a fungicide application. “We would like to improve the economic threshold estimate and will be developing another interactive calculator that will help growers determine a specific economic threshold based on factors such as per cent infection, cost of fungicide and application and the price of canola,” adds Buchwaldt. “All of these tools together should improve early forecasting and risk assessment, and the recommended threshold for applying a fungicide.”

Buchwaldt is seeking volunteers from across Western Canada to manage a depot in canola for the 2015 growing season. “We ask volunteers to contact us as soon as possible, as we would like to make arrangements to have all of the depots sent out and in place by October before frost. We are also asking volunteers if they can provide data from nearby sclerotinia fungicide trials as well.”

For more information about volunteering contact: sclerotia.depot@agr.gc.ca.

One additional aspect of the research project is a collaboration between AAFC and Weather INnovations Consulting LP (WIN), a private company involved in weather-based modelling of disease risk in various crops and decision support systems. “WIN has established weather data stations across Canada, with about 300 stations in Saskatchewan for example,” says Buchwaldt. “We will pick the stations closest to the sclerotia-depots and model the relationship between the weather data and the sclerotia germination data.”

With the data collected over the next three growing seasons, the objective is to develop a predictive computer model for the germination stage of the pathogen lifecycle. The model will be tested against actual field data to confirm the accuracy.

Buchwaldt adds they also plan to test another model developed in Germany that can predict infection hours. “Once the spores have landed on the plant or petals, the model uses climate data to determine whether or not the conditions are right for infection of the stem by sclerotinia spores. We hope by the end of the project to have better prediction capability for growers for sclerotinia in canola. The combination of real-time sclerotia-depot data and computer forecasting tools should help growers make more accurate risk assessments and better economic decisions for fungicide application.”

 


September 5, 2014
By Donna Fleury

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A sclerotia-depot buried at 2 cm soil depth with the nylon lip barely visible. A new

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