Normally soil moisture may leave canola crops open to the risk of sclerotinia stem rot, but areas where the moisture is well past normal may in fact see less risk from the spores.
“With all this moisture, many growers and retailers have asked us if that means a higher sclerotinia stem rot risk,” the Canola Council of Canada noted in a grower newsletter this week. “It depends.”
The sclerotia that cause stem rot in infected crops don’t tolerate saturated soils, so “very wet” conditions could cut down apothecia germination and spore production from those fields, the council said.
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In areas with “good” moisture and “great” yield potential, however, canola may be at higher risk, the council said.
When flowering starts, growers will need to consider whether spraying against sclerotinia is warranted, the council said.
Where soil moisture is still at reasonable levels, stem rot risk rises along with the amount of rainfall in the previous two weeks; the disease incidence in the last host crop; the crop density; the level of risk for apothecia development in the region; and the probability of low pressure in the weather forecast.
The council’s disease scouting and risk assessment card also gives more “risk points” for sclerotinia to a field that has seen canola crops just one to two years apart. The risk points drop to zero on fields where canola crops are more than six years apart in the rotation.
Effective risk assessment calls for growers to scout for apothecia, the council noted, usually in nearby cereal crops following higher-risk crops such as canola, beans or sunflower in a rotation.
Apothecia are small fruiting structures that look like tiny mushrooms germinating from sclerotia. They release the spores which are the infectious agents for the fungus. Large numbers of apothecia emerging at or just before the early bloom stage point to higher risk of petal infection.
Research has also shown a connection between crop lodging and sclerotinia levels, the council said, pointing to a variety’s genetic susceptibility to lodging as a potential risk factor.
