Sclerotinia meets its match with natural soil fungus

Significant sclerotinia pressure was evident in many prairie crops this summer, spurred on by excess moisture.

“Sclerotinia is one of those diseases we are going to see higher incidence when conditions are more conducive,” says Barbara Ziesman, a plant disease specialist with Saskatchewan Agriculture.

“Unfortunately, this year had very favourable conditions throughout the province.”

Sclerotinia inoculant levels are now high in many prairie fields, so disease management could be critical in the coming year.

Growing crops that are not susceptible to sclerotinia in the crop rotation, as well as a comprehensive foliar fungicide program, remain the go-to management techniques for sclerotinia.

However, producers who want to get a jump on their sclerotinia management this fall have another option.

Contans is a soil applied biological fungicide that helps to break the cycle of sclerotinia disease, and it can be applied in the fall.

“It’s an antagonistic fungus, and the fungus actually attacks the sclerotia,” said Ziesman.

“What Contans will do is it will reduce the amount of asper spores that are produced so it will reduce the inoculums from the field.”

Dale Ziprick, manager of agronomic services at United Agri Products, said Contans is a natural parasite of sclerotinia.

“So all we’re doing is we are building the natural population that is within the soil already to a level that allows for that control/suppression of sclerotinia to occur.”

Ziprick said after harvest is the preferred time to applied Contans because it gives the helpful fungus enough time to become established and deplete sclerotia bodies.

“You need time, you need temperature and you need moisture conditions for the product to work,” Ziprick said. “The key thing being time. We see the data supplied by the manufacturer show that you do get an improvement in efficacy the longer Contans has to work.”

Contans is also regularly applied before seeding.

The active ingredient is a natural soil fungus called Coniothyrium minitans, which remains active between soil temperatures of five to 30 C. Contans stops its activity when temperatures drop below freezing and waits for warmer temperatures.

“It takes about six weeks to completely destroy sclerotia bodies upon infection,” Ziprick said.

“Being a fungus, again, we know warmer temperatures will help to speed that up.”

Incorporating Contans into the soil is recommended with a heavy harrow or light cultivation. Tillage depth should be no deeper than five centimetres because sclerotia bodies generally do not germinate below that point.

“You do want the Contans to be given the best opportunity to get in touch with the sclerotia bodies.”

Growers can use irrigation to help wash Contans into the soil, and many growers time application with a rain to get better results.

“That ability to wash it off the plant residues and the harvest residues and into the soil is an effective means to make sure that product gets into that layer where we want it, which is in that one to two inches (2.5 to five cm) of the top level of the soil profile where the sclerotia bodies that have the highest opportunity or highest percentage of germination would occur,” Ziprick said.

Rain within two weeks of application is best when relying on it to wash in the product because Contans is subject to photo degradation.

The product can be tank mixed with some chemicals, including glyphosate. However, the fungus is sensitive to chemicals and should be applied within four hours of mixing. UAP advises farmers to consult it for its latest compatibility chart before mixing any chemicals with Contans.

Ziesman said Contans can re-duce the selection pressure placed on fungicides, but the product won’t eliminate the risk of sclero-tinia by itself.

“You’re still going to want to be paying attention and looking for favourable conditions (for scler-otinia) because you can still get spores coming in from neighbour-ing fields as well.”

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