Early sclerotinia forecasting
By Donna Fleury
Test of sclerotia germination in a depot under optimal conditions in a growth chamber. Each flag marks the first appearance of apothecia from the 50 buried sclerotia. Photo by AAFC Saskatoon.
A pilot project to improve sclerotinia risk assessment in canola was launched in 2014 using a sclerotia-depot method, which was developed by Lone Buchwaldt and successfully used in Denmark for many years. Buchwaldt, now a researcher with Agriculture and Agri-Food Canada (AAFC) in Saskatoon, set out to evaluate the usefulness of this method in Canada.
“We initiated this pilot project on a small scale in Saskatchewan to find out if extension specialists and growers were interested in helping with forecasting of sclerotia germination in commercial fields,” Buchwaldt explains. “Our objective was to evaluate the usefulness of this method in Western Canada in combination with the existing ‘sclerotinia stem rot checklist’ available from the Canola Council of Canada. This checklist is composed of six risk factors, one of which is the presence of apothecia.”
(An interactive version of the checklist can be found on SaskCanola’s website www.saskcanola.com; go to “Research,” select “Sclerotinia risk assessment” and select “Stem rot checklist.”)
A “depot” consists of sclerotia, inserted in small pockets made of white nylon mesh. “Visiting a depot buried in a commercial canola field is a convenient way to check if conditions are right for sclerotia germination in the surrounding fields,” Buchwaldt explains. She emphasizes it is important to use the checklist to determine the level of risk for each individual field. It is particularly important to note previous problems with sclerotinia and how often canola and other susceptible crops have been grown, since sclerotinia can be maintained by most non-cereal crops, many weed species and volunteer canola.
Sclerotia for the project have been collected from infected canola stems in different fields in Saskatchewan and sorted by size, so only the largest ones are used. “Sclerotia in nature are subjected to variable temperatures and wetness, so the sclerotia we used in 2014 were placed in the soil outside from October to April. However, this did not give us enough time to test their viability before they were sent to our volunteers in May,” Buchwaldt notes.
This step has been changed so now sclerotia receive several cycles of cold/wet treatments indoors, which allows enough time for a germination test in a growth chamber. “We know from the tests that the sclerotia are viable, because there was between 50 and 75 per cent germination success of the sclerotia used in 2015, as well as for those that will be used in the upcoming 2016 growing season.”
Buchwaldt says an excessive amount of rain in the spring of 2014 meant many depots were lost due to flooding, and warm dry conditions during flowering prevented sclerotia germination in other depots. In 2015, dry weather conditions leading up to and during canola flowering across much of Western Canada meant zero germination was reported, except in the Benito area (by Duck Mountain National Park) where six to eight per cent germination was reported. “The reports from volunteers typically included comments about drought conditions resulting in poor plant stands,” Buchwaldt notes. “Therefore it isn’t surprising we didn’t see germination.”
Canola disease surveys coordinated by the Saskatchewan Ministry of Agriculture indicate the majority of canola crops have some incidence of sclerotinia every year. However, Buchwaldt stresses yield is only affected when the main stem is completely colonized by sclerotinia, causing the typical whitish lesions with new sclerotia forming inside the stem. In 2014 and 2015 there were only a few records of fields with severe stem infection.
“Nevertheless, the surveys tell us that growers need to monitor weather conditions every year and use available forecasting tools to assess whether to apply a fungicide,” Buchwaldt says. “As a rule, the threshold for economical fungicide application is 15 per cent infected stems or higher. However, fungicides have to be applied
before symptoms appear and that is why risk assessment is so important.”
Pilot project gears up in 2016
In 2014, a total of 67 depots were established in Saskatchewan, managed by 37 volunteers. The project expanded in 2015 to 140 depots across Western Canada, with 67, 65 and eight depots in Alberta, Saskatchewan and Manitoba, respectively. The project is gearing up for the 2016 season, with 180 sclerotia-depots available for distribution.
“The sclerotia have undergone the necessary cold/wet treatment and are viable,” Buchwaldt says. “We welcome returning and new volunteers from across Western Canada and are hoping to see a greater number from Manitoba this year.”
Volunteers will receive depots by mail in early spring. Once the canola plants have germinated, the depots can be placed between the rows in the selected canola fields. Marking the depots with a stake helps in finding them during the growing season. Also, marking each germinating sclerotia with a toothpick makes counting easier.
Volunteers are asked to monitor the depots once per week during the vegetative growth stage and one or two times per week during flowering, particularly if apothecia are forming. Per cent sclerotia germination is submitted to a website using a cell phone or computer. Anyone interested in becoming a volunteer can email email@example.com.
During the growing season, the AAFC team in Saskatoon regularly updates the maps, making real-time sclerotia germination data available across Western Canada. The data are available until the end of flowering through SaskCanola’s website. The pilot project will finish with the growing season in 2017. Buchwaldt hopes that at that time, other people will be interested in taking over the sclerotia-depot idea.