Canola disease survey shows changing disease pressure

Proper field management helps Field surveys show sclerotinia cases dropped 31 percent in Saskatchewan in 2013

Favourable canola growing conditions last year resulted in less conducive conditions for some plant diseases, says a plant disease specialist with Saskatchewan Agriculture.


“Actually, 2013 wasn’t a huge year for diseases,” Faye Dokken-Bouchard told Cropsphere in Saskatoon last week.


Dokken-Bouchard, who presented the findings from an annual canola disease survey that looked at 268 fields last year, said more canola fields, producers and agronomists are included in the survey every year.


Fields are either volunteered by growers or randomly selected. In each field, canola diseases are recorded as either present or absent on 100 plants. The final report is sent to the Canadian Plant Disease Survey at www.cps-scp.ca/cpds.shtml.


The results help show how major disease information changes under different conditions.


The survey found that 60 percent of crops had at least a trace of sclerotinia in 2013 compared to 91 percent in 2012.


Less moisture last year helped reduce the incidence of sclerotinia from 2012 and 2010.


“This is a disease that really prefers moist conditions,” she said.


“If we have a year with more excess moisture, we have more disease.”


Management practices such as scouting and proper application of fungicides also help the percentage.


Now in its 14th year, the survey has revealed a trend in which sclerotinia levels go up and down from year to year depending on moisture conditions.


“We have a rule of thumb where we take the incidence and we divide it by two to get the expected yield loss,” Dokken-Bouchard said.


“So if you had 40 percent incidence of sclerotinia in your field, you might expect a 20 percent yield loss.”


A sclerotinia check list on the Canola Council of Canada website helps producers determine if they should spray.


It factors in the number of years since the last host crop, disease incidence in the last host crop, crop density, rain in the last two weeks and the weather forecast.


Aster yellows is another major disease in the survey. Dokken-Bouchard said 2007 and 2012 were big years for the disease, but symptoms dropped off to normal levels in trace amounts last year.


“The issue with aster yellows is the insect factors that bring the phytoplasma into the canola fields, as well as other crops that are susceptible to this disease issue,” she said. 


The survey has found that blackleg numbers may be increasing. Resistant varieties are available, but the disease can have devastating effects on crops.


She said it was observed in 31 percent of the canola crop last year, but the overall severity was low.


“The important thing is to watch out for it because if we start to see it in increasing numbers, we might be concerned that the resistance that we have in the good varieties is breaking down,” she said.


Clubroot is the newest major plant disease in the survey and continues to be taken seriously because of the effects it has had in Alberta. 


The first potential positive in Sask-atchewan was confirmed in 2008 when the first DNA test was done on soil. The last survey collected soil samples from 110 fields, but the results are not yet confirmed.


“We haven’t seen any symptoms in the field with our survey thus far,” she said.


Farmers can send samples for any of the disease issues to Saskatchewan Agriculture’s crop protection lab in Regina. There are similar programs in other provinces


Producers may also participate by volunteering in the clubroot survey, which tests soil samples, and doing their own testing with private labs.