Ghosts of sclerotina past haunt 2017

PORTAGE LA PRAIRIE, Man. — The Catch 22 of a healthy-looking canola crop with a thick canopy is that it’s not necessarily a healthy crop. Rather, this moisture trap is a breeding ground for sclerotinia.

Last year broke all sclerotinia records. The disease rate was 93 percent in Manitoba, 92 percent in Saskatchewan and 80 percent in Alberta, according to prairie agriculture ministries.

Heavy disease pressure in 2016 was followed by more unwanted rain last fall, so we certainly have excess soil moisture right now.

The good news is the moisture has the potential to foster a high yielding crop by establishing that much-desired healthy crop with a thick canopy.

The obvious bad news is that disease inoculum in the soil is waiting to infect that lush canola canopy.

As well, sclerotinia lives up to five years in the soil, surviving as sclerotia, and sclerotia is it’s own boss. It does whatever it wants to do, whenever it wants to do it, according to Canola Council of Canada agronomist Justine Cornelsen.

“The sclerotinia fungus can germinate whenever it wants to. It really just depends on environmental conditions. So, for growers, it’s something that’s always on the back of their minds,” says Cornelson, emphasizing pre-emptive action.

“You’ve got to get your fungicide application on before you see symptoms.

“First, growers need to get out into the field to scout. Boots in the field is one of the best things they can do. Next, one of the best management practices is to apply an early-season fungicide.”

BASF canola specialist Sydney Marlow told growers at a producer meeting in Portage la Prairie that they should be thinking right now about how they’re going to manage sclerotinia this year, and they should be thinking about their fungicide choices.

“This moisture is a virtual guarantee the plants will get a good start this spring,” Marlow said.

“But as we know, a thick canopy is going to trap moisture and keep humidity levels high. The better the crop looks, the higher the potential for sclerotinia if moisture remains plentiful.

“We use all these expensive inputs in the spring. Now we have to protect that investment right through to harvest.”

BASF representative Glen Forster said in a telephone interview that sclerotinia isn’t just in canola fields; it’s all around us.

“It’s scary because a lot of the broadleaf crops we grow in Western Canada serve as a host to sclerotinia,” he said.

“This isn’t just a canola problem. It’s in your lentils, your pulse crops, your soybeans, they’re all carriers. A field adjacent to your canola might be a carrier.”

Sclerotinia can break out anywhere if the conditions are right, he added.

“The best you can do is follow your local weather conditions closely and then get out in the field to monitor for signs as soon as your canopy starts forming,” he said.

“If you think you’re at risk, there are plenty of tools available to help you on the canola council website.”

Forster said seed treatments are not effective in preventing scler-otinia. The only option is to check the crop as it approaches the 20 percent flower stage. Fungicides are the only tools once the crop is growing.

“For sclerotinia, there are many fungicides with many modes of action. There are plenty to choose from,” Forster said.

“In Western Canada, fungicide immunity and fungicide resistance isn’t a problem yet. It’s not like ascocyta in chickpeas, which have a really high level of resistance.

“But just because our risk of fungicide resistance is relatively low today, it doesn’t mean we can ignore the threat. It’s always good to rotate your fungicides, especially if you grow a variety of sclerotinia host crops like lentils and peas.

The other smart option is to use a fungicide that has two modes of action.

“We typically recommend just one application at the early 20 percent to 30 percent flower stage. If you protect the crop at that point, that’s where you get the biggest bang for your buck. Fungicides work for 10 to 14 days, so you’ll get adequate protection at early 20 percent to 30 percent flowering.”

Agronomists are unanimous that producers must treat sclerotinia before they see it. But if their timing is off because of weather or other obstacles, then what?

“There’s still a benefit if you spray at the 30 percent to 50 percent flowering stage, but you’re better off starting a little early than late,” Forster said.

“Based on what we know about the biology of the disease, you want the chemical on prior to any of the petal drop.

“Sclerotinia needs a food source in order to infect the plant. It depends on the canola petals that fall. Sclerotinia uses those petals as a food source to grow and infect the plant at the base of the leaf. That’s why an early spray is better than a late spray.”

Forster said a good-looking canola stand can often be its own worse enemy because the thick canopy is an ideal host. The best-looking crop with the highest potential for success will create its own conditions for disease.

“With trends toward tighter canola rotations and increased moisture during flowering, we’ve seen an increase in sclerotinia in Western Canada during the past few years. An unprotected crop can have yield losses greater than 50 percent.”

Cornelsen said applying a fungicide not only increases yields but also reduces dockage because of sclerotia contamination of the seed, which results in small, shrivelled seeds.

Marlow said BASF has released a new weapon aimed at sclerotinia in canola, peas, lentils, chickpeas, soybeans and dry beans.

Cotegra is a blend of two older well-known fungicides that have a good reputation as sclerotinia control agents: boscalid, a Group 7 fungicide used in BASF Lance, and prothioconazole, a Group 3 fungicide used in Bayer Proline.

“A lot of work went into discovering the optimal rate of both active agents,” Marlow said.

“We needed to establish high enough rates of both main ingredients to make sure we had the best possible disease management. And we had to very mindful of resistance because that’s a major concern for growers. We wanted to make sure we provided a product that’s a good resistance management tool.”

Marlow said Cotegra has two years of canola field tests, in two very different conditions: 2015 was a relatively dry year and 2016 was just the opposite.

Testing against two other fungicides, the competitors’ products produced an average yield of 49 bushels while Cotegra gave an average of 51 bu. Testing against non-treated canola, Cotegra produced a seven bu. benefit.

“Yield is the end result, but we also saw a reduction in disease severity,” Marlow said.

“Cotegra consistently had less disease than either of the competitor fungicides.”

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