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Saturday April 19, 2014

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Guenther: Critical period now in sclerotinia cycle

Use experience in 2012 to help decide whether to spray: CCC

Last year's sclerotinia pressure on the Prairies means farmers should be prepared to spray again if conditions are right, and the economics and yield potential warrant it.

Canola farmers in Alberta and Saskatchewan saw what was probably the highest sclerotinia pressure ever last year, says Todd Friday, pulse and oilseeds market segment manager with DuPont.

Fungicides are meant to prevent, not treat, sclerotinia, so if farmers are going to spray, they need to do so before symptoms appear. But whether or not to spray for sclerotinia is not always a clear-cut decision.

"The trouble with sclerotinia, it's more of an art than a science in a lot of ways. And that feel goes into a lot of the decision-making process," says Clint Jurke, the Canola Council of Canada's agronomist for western Saskatchewan at Lloydminster.

Jurke says growers should use their experience in 2012 to help decide whether to spray this year.

To spray or not to spray?

Right now is a critical period in the disease cycle, says Jurke.

"From seeding time right up until probably about the five-leaf stage, if we've had fairly good soil moisture, that's what's required to get the sclerotia producing those apothecia," says Jurke. Apothecia release sclerotinia ascospores, which land on canola petals and cause the disease.

"Those apothecia are not going to emerge for another month, which happens to coincide with the flowering period," Jurke says.

The Canola Council has a checklist to help canola growers decide whether to spray for sclerotinia. The checklist includes factors such as rotation length, disease incidence in host crops, crop density, recent rain, the weather forecast and apothecia development.

But Jurke says farmers should keep in mind the checklist was developed in Sweden. He says apothecia, previous disease levels and rotation are given too much weight for Western Canada. For example, he points out first-time canola growers in southwestern Saskatchewan ran into sclerotinia last year. "So crop rotation is not an answer for this disease, unfortunately.

"It really comes down to how thick is that canopy, what is the yield potential, and how wet is that canopy, in the decision-making process."

Friday says that even if the temperature and climate don't suggest spraying will be necessary, new canola hybrids can create a moist microclimate in the bottom foot that fosters sclerotinia.

The new hybrids cover the ground, have larger plants and seeds, and develop thick canopies, which contribute to the microclimate, he says.

He observed this microclimate while walking through canola fields in the afternoon last July, when the fields seemed like they should be dry. "You wouldn't have to walk very far and you were soaked from the knee down."

Jurke agrees a crop with high yield potential is likely to have a microclimate conducive to disease development. "The disease doesn't need sopping wet conditions. What it requires is high humidity within the canopy to grow."

Many products need to be applied when the crop at 20 to 50 per cent bloom and a few are registered for 20 to 30 per cent bloom.

The short application window means farmers will have to move fast once canola starts flowering, especially if they have many canola acres that were seeded at the same time, says Friday. He suggests having product on hand if there's a good chance spraying will be necessary.

Split applications

If the climate is right for an early or persistent sclerotinia flush, and the economics and yield potential add up, farmers may want to apply fungicide twice, says Friday.

"I would be scouting as soon as those flowers start to emerge, looking at how wet the conditions are," says Jurke of split applications.

Generally the first application is done at 20 per cent, and the second at 50 per cent. Friday points out the crop can go from 20 per cent to 50 per cent bloom in four to seven days, so farmers considering a split application will need to act quickly.

Farmers should also follow the label rates for both applications, as Friday says cutting rates could drop effectiveness radically.

"From a stewardship perspective, we recommend if producers are going to do a second application, and this year there would be more producers that would be looking at that, we would recommend switching to a (different) group" to prevent fungicide resistance, says Friday.

-- Lisa Guenther is a field editor for Grainews at Livelong, Sask. Follow her @LtoG on Twitter.


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