If soybean diseases had a contest, it’d be easy to think of third or fourth place as something of a win, especially with soybean cyst nematode (SCN) and sudden death syndrome (SDS) holding firmly on to first and second. Yet for growers in eastern Ontario and western Quebec, white mould’s less-than-prominent status is hardly a consolation — it’s a yield-robber and if not a perennial issue, it’s very close.
Disease management has greatly improved in the past 10 to 15 years. One reason is the enhanced genetics, along with efforts to screen out seed lines showing susceptibility to specific diseases. Another is learning how to use newer fungicides — growers have certainly “upped their game” with help from agronomists and advisors. Finally, there’s a better understanding of the physiology of diseases and the relationship between pathogen, host and environment, and how if one “corner” of that triangle is missing, there can be no infection.
Yet white mould is that constantly nagging issue for many growers in eastern Ontario and into Quebec, almost to the point where it’s a greater concern than SCN or SDS. According to data from the Crop Protection Network (cropprotectionnetwork.org), 2021 saw an estimated 1.21-million-bushel loss due to white mould in Ontario, making it the third-highest yield-robber behind SCN and SDS.
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Sheila Murphy says affected growers have learned to rely on best management practices to reduce infection and protect their yields.
“The fungus Sclerotinia sclerotiorum is endemic to Eastern Canada and overwinters here, so the inoculum is present,” says Murphy, Corteva Agriscience seed product agronomist for Eastern Canada. “We know in eastern Ontario and western Quebec there’s a continued concern about white mould, whereas in southwestern Ontario, it’s not as concerning, and I think that’s largely attributed to the climate.”
Historically, crop advisors in parts of southern Ontario have encountered pockets of white mould, often in dairy operations. The addition of manure provides the moister environment to help white mould flourish. But the disease’s impact is much less in that region compared to SCN, SDS and a few others that can pop up from time to time.
The focus on white mould comes with the launch of Pioneer’s A-Series Enlist E3 soybeans, with 21 varieties available in a range of maturities for Eastern Canada. The A-Series offers a suite of enhanced traits that are expected to help with resistance to SCN, SDS, Phytophthora root rot and white mould.
Murphy says the Enlist E3 and A-Series bring together the strong agronomics of the A-Series, “Plus there’s the Enlist E3 tolerance which allows growers to use the E3 program with stronger products.”
Likes it cooler
For eastern Ontario, the environment is arguably the key. Although there are more dairy operations, it’s the tendency for air temperatures below 28 C that seems to be the key. According to resources from the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), “White mould prefers temperatures below 28 C, moist soils and high humidity.”
For Darren McColm, that reflects conditions in eastern Ontario.
“There are instances of white mould in almost every county in Ontario,” says McColm, agronomy lead (east) for WinField United Canada. “However, parts of eastern Ontario see those moderate temperatures increasing the potential for the disease. White mould instances can vary from farm to farm depending on rotation, cultural practices and even soil types.”
Like Murphy, McColm believes agronomic practices can make a bigger difference, including wider rows, longer rotations and paying attention to high-fertility field conditions. Higher fertility increases vegetative growth that traps moisture in the canopy and provides an optimal environment for white mould. He also stresses row width and plant populations as key agronomic factors to combat the disease.
“You can also plant a variety with high tolerance,” says McColm. “No variety is a silver bullet but if you have bad white mould in the past, you can mitigate risk with a variety that’s rated for high tolerance.”
Murphy also cites the “silver bullet” reference, adding there is no complete resistance factor for the disease, meaning there’s no “easy button” other than best management practices. As much as breeders can work to impart characteristics that battle stresses, there is only one real metric that interests growers: yield.
“With any crop that we’re breeding, we have to balance all of those desired traits, whether it be yield, disease resistance or drought tolerance,” says Murphy. “Mother Nature throws everything at us, but for our growers, white mould is a concern, and it’s a very large part of what we do in the breeding programs — continuing to breed for yield, SCN and SDS resistance. But white mould is something we’re actively engaged in bringing tolerant varieties to the marketplace.”
The right tools
In the absence of any “total package” soybean variety, growers must manage using agronomic practices but they also have a good selection of fungicides. McColm mentions products from Groups 3, 7 and 11, yet notes growers aren’t using them as “insurance” or an annual measure. He also hasn’t seen any growers opt out of needed fungicide applications as a cost-cutting measure in the wake of higher fertilizer or fuel costs: when crops need a fungicide, growers protect that investment.
“There are tank mixes and some multi-mode-of-action products that are premixed that work great,” says McColm. “Fungicides are a tool that can be used, although very few use them as ‘automatic.’ Some growers will plan to use a fungicide application if environmental conditions favour that application and they have had issues in the past.”
Ultimately, growers have to pay stricter attention to avoid white mould. Environmental conditions and varietal selection are important. McColm says a variety with high tolerance doesn’t guarantee the disease won’t be a problem. Growers must be mindful of environmental conditions, and use a fungicide if conditions are favourable.
