Shift in weather complicates sclerotinia decisions

Canola is starting to flower and the canopy is wet, usually a recipe for sclerotinia, but perhaps not this year

Parts of Manitoba have taken a sharp turn from bone dry to very wet since the start of June, and that’s impacting the discussion around sclerotinia.

“Because parts of the province have had lots of moisture and lots of humidity, we’re gearing up that it could be a bad sclerotinia season,” Justine Cornelsen of the Canola Council of Canada said. “but typically you need a really wet canopy going into flowering.”

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Heat and wind would have served to dry out that critical shallow topsoil layer, she noted.

Environment and Climate Change Canada meteorologists claimed this spring as the windiest period from mid-May to mid-June since 1990. Areas in central Manitoba saw maximum wind gusts of 120 kilometres an hour, with several days where gusts grew past 70 kilometres an hour. The Manitoba Agricultural Services Corporation noted wind as one of the main factors for their uptick in reseed claims this spring.

And while both eastern and western parts of the province have had dry spells earlier this year, both have now seen significant moisture thanks to storms.

Eastern Manitoba went from dry in May to 188 per cent of normal moisture as of June 24 thanks to mid-June storms which led to flooding in the R.M. of  Stuartburn. Western Manitoba north of Brandon, meanwhile, saw a multiple storms June 28 through the first week of July, storms that had dropped up to 214 millimetres, according to provincial ag weather data, and led to evacuations, widespread flooding, and multiple states of emergency.

Outside of that patch, most of the Parkland and central Manitoba ranged from 20 to 80 millimetres of rain from June 28 to July 1, the province said, while much of the southern Interlake was still significantly dry.

Manitoba Agriculture suggests soil needs to be near saturated for seven to eight days for apothecia to appear.
photo: Greg Berg

The Canola Council of Canada points to either regular rains or high humidity in the period leading up to and during flowering, factors which provide the moisture required for sclerotia to germinate into spore producing apothecia (small, golf tee-like mushrooms).

Producers will be familiar with the “wet pants” test, the idea that if walking through the fields in the afternoon dampens pant legs, then the environment under the canopy is likely ripe for sclerotinia.

Manitoba Agriculture and Resource Development suggests that soil needs to be near saturated for seven to eight days for apothecia to appear.

“It’ll be very different across the province, depending on the conditions,” Cornelsen said June 30. “As of two days ago, the western half was extremely dry.”

Stands in eastern Manitoba are further along in flower, Cornelsen noted, while stands in the west were likely a week away from the 20 to 50 per cent bloom window for foliar fungicide.

“Is that week of saturated soil enough to get the sclerotia bodies to germinate and create an apothecia? It’s really tough to say,” she said. “and, you know, if we have a few dry or really windy conditions again, that will take that risk off. It really comes back to a field-to-field situation.”

The last few years might also offer some buffer, Dane Froese, oilseeds specialist with the province, said, since sclerotinia is overwintered as sclerotia from a previous infected crop.

Those sclerotia might be thin on the ground this year, however, after several consecutive years of dry conditions, Froese noted.

“We’ve had two dry summers with very, very low sclerotinia infection incidences,” he said, noting that might tamp down on disease pressure this year.

In 2019, the province’s canola disease survey found sclerotinia in 25 per cent of the 165 fields surveyed. In 2018, 36 per cent out of 180 fields showed evidence of the disease.

Both years, however, were a significant drop from 2017, when 73 per cent of the 162 surveyed fields were infected and even lower than 2016, when 93 per cent of fields showed evidence of sclerotinia.

“Overall, we would expect to see less sclerotia bodies return to the soil, causing infections for future years,” Froese said. “Not to say that they can’t be there, but they are generally fairly short lived. They don’t live longer than a couple of years.”

At the same time, he cautioned, microclimates might vary hugely from field to field, which would impact risk.

For producers still on the fence on spraying, Cornelsen pointed them to tools such as petal tests, which confirms sclerotinia DNA on collected petals.

“Sclerotinia is always a really tough one,” she said. “It’s never an easy decision to decide to spray or not.”

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@AlexisStockford

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Alexis Stockford

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.

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