Sage advice on battling sclerotinia in canola

Canola growers have their hands full in protecting their crops from sclerotinia stem rot. With a lifecycle that includes airborne spores that can fly up to 1 km and fungal storage bodies with staying power, it’s one of the most economically devastating canola diseases.

Last year, over 20 million acres of canola was grown in Canada. That’s a lot of host crop — not to mention the acres of soybeans, mustard, peas, beans, lentils, sunflowers and potatoes, or the broadleaf weeds that the sclerotinia fungus also tends to like. When it comes to the disease triangle, sclerotinia stem rot seems to have the “host” corner nailed.

Given all that, should you simply assume that the sclerotinia pathogen is in every field and just be prepared to spray if the other two corners of the triangle (presence of the pathogen, and the right environmental conditions) bear out? Or is that just unnecessary worry? Farm Forum asked five canola agronomists across Canada what they thought.

The five are: Greg Sekulic, agronomy specialist, Peace country, Canola Council of Canada, Grand Prairie, AB; Autumn Holmes-Saltzman, agronomy specialist, southern Alberta, Canola Council of Canada, Lethbridge, AB; Clint Jurke, agronomy specialist, western Saskatchewan, Canola Council of Canada, Lloydminster, SK; Kristen Phillips, regional agronomist, Manitoba, Canola Council of Canada, Brandon, MB; and Brian Hall, canola and bean specialist, Ontario Ministry of Agriculture and Food, Stratford, ON. From west to east, here’s what they had to say:

1. Should producers in your area assume that sclerotinia is in every field?

Greg/AB: Yes, they should. Sclerotinia is ubiquitous and affects every broadleaf crop we grow. One should assume the spores will be in the air.

Autumn/AB: Yes, because of the wide range of host crops and the fact that it can move into any field from an adjacent field, we should always assume there is some sclerotinia risk and be prepared to manage it.

Clint/SK: Yes. And that’s nothing to do with increased acreage and everything to do with yield expectations — plus some bad luck with weather. When you’re targeting 35 to 40 bushels per acre, you should just plan to use a fungicide because under the crop canopy you’re creating a micro-climate that is ideal for sclerotinia.

Kristen/MB: Yes. In Manitoba, we have a high level of inoculum in our soil so we assume the disease will be present given the right conditions.

Brian/ON:
I would say no, but that doesn’t mean growers shouldn’t pay attention. Canola rotations aren’t very short here in southern Ontario, and we tend to be quite hot and dry during flowering. It’s different in northern Ontario where it’s cooler and heavy overnight dews are a bigger factor.

2. What was the disease level like in your area in 2012?

Greg/AB: Extremely varied. In the southeast corner of the Peace region there was a lot of moisture and a good expression of the disease. The central area was quite dry, almost a drought in some places, so it wasn’t so bad. Further north, around Fairview, AB, we did a bit of spraying, while the north Peace was so dry, there was almost no disease to speak of.

Autumn/AB: Since I just joined the Canola Council in February, I consulted Mike Harding with Alberta Agriculture in Brooks, AB, for some local information. He says sclerotinia was found all over southern Alberta last year and, according to provincial disease surveys, the average incidence of infection in the south was higher than the provincial average.

Clint/SK: Awful. Hideous. I saw some fields that were 80 per cent infected. Still, I could drive two miles away and there was no sclerotinia at all, but the yield potential was only 20 bu/ac. In general in west Saskatchewan, the further north you went, the worse it was.

Kristen/MB: Our provincial disease survey showed the prevalence of sclerotinia-infested crops ranging from a high of 75 per cent in the northwest region, to 51 per cent in the central region, with a provincial mean of 65 per cent. Throughout the province, the mean severity of sclerotinia stem rot was low, but both the prevalence and incidence were higher than in 2011.

Brian/ON: Very hot and dry weather meant we had very low infection levels last year. Plus, the canopies just weren’t there. It was the same the year before.

3. What disease levels do you anticipate this season?

Greg/AB: I think it will be the same as usual — it doesn’t take a lot of pressure to get the disease to express itself. All we’re waiting for are the right conditions for it to get going.

Autumn/AB: Well, it will depend on the weather, of course. We do know that 2012 crops produced plenty of inoculum, so there’s potential for it this year, especially if we get cool, wet weather while canola is flowering.

Clint/SK: If we have a wet start, it’s safe to assume we’ll have some high levels of infection again. Growers should budget for fungicide.

Kristen/MB: Like other fungal diseases, it will depend on the weather. We know the inoculum is present, so if conditions are right at the ideal time, then there is high potential for sclerotinia.

Brian/ON: That’s difficult, because you can’t use last year’s history as a good predictor here. We’ve tried to use the sclerotinia prediction model from the west, but the humidity here throws it off. Long rotations mean that sclerotinia in the soil is not as much of a concern as the environmental factors. I would say that for fields with a history of sclerotinia infection, growers should be vigilant. Then again, I’ve seen infection develop in fields where canola was never cropped before.

4. Other than scouting and spraying, what advice do you have for producers in your area?

Greg/AB: Budget to make the application every year — include the cost in your winter planning. It’s easy to demonstrate yield returns of 10 to 15 per cent if conditions are right. Then make the decision not to spray only if it’s really dry. This way, if you need to spray, your decision has already been made.

Autumn/AB: Sclerotinia-tolerant varieties are now available to help manage the disease, but the biggest factor for infection is weather. Irrigation farmers can try to minimize irrigating during flowering, but the best advice I can give is to keep track of local weather conditions and be prepared to use a fungicide if you have to.

Clint/SK: Scouting and spraying are your two best defenses. Fungicide is still the best tool. Rotation isn’t going to help much. Data from Manitoba shows that regardless of the length of rotation, sclerotinia infection rates remain the same. There are so many good sclerotinia hosts around — any broadleaf plant is a potential host for the disease.

Kristen/MB: My No. 1 message is still to get out there and scout! You need to assess your canola on a yearly basis — hop off the swather and assess your plants for infection. If you need help identifying sclerotinia, reach out to the Canola Council, Manitoba Agriculture, Food and Rural Initiatives, or your agronomists — we’re all willing to help. Also, it’s important to scout the conditions to know if they’re right for infection at flowering. The “pant leg” test is always a good one — at what time in the day can you walk through your canola and come out with dry pant legs? The longer that morning dew lasts, the higher the risk of sclerotinia.

Brian/ON: I do like the “pant test.” I suggest growers walk through the canola around 10 in the morning, and if they come out soaking wet, they have the right conditions for disease. After two to three days of that, then you need to go.

5. What’s your No. 1 tip for effective scouting and spraying?

Greg/AB: If it’s been wet for a week or 10 days up to or during flowering, and the soils are at saturation levels, go for a walk through the crop — at 20 to 30 per cent flowering — in the morning and see if your pants are wet from the knees down. If they are, go again in the afternoon and if they’re still wet, it’s time to spray.

Autumn/AB: Spraying at the right time (20 to 50 per cent bloom) is critical. Once you see stem rot, it’s often too late to apply a fungicide. The Canola Council’s Sclerotinia Stem Rot Checklist is a great tool to use early in the season to assess your level of risk.

Clint/SK: If you have a wet spring, that will get the fungal apothecia (spore-producing structures) going. I wouldn’t bother to scout for apothecia, but spend time in the crop to get some sense of yield potential. Keep track of how much rain you’ve had, how wet the canopy is and what the weather forecast predicts over the flowering period.

Also, if you have to spray often for sclerotinia, make sure you’re mixing your fungicide groups from year to year so the disease doesn’t develop resistance to any one fungicide. To that end, make sure you have to use a fungicide before you apply it. It’s kind of a reverse logic: plan to use it, then convince yourself not to.

Kristen/MB: For scouting, use the Canola Disease Scouting and Risk Assessment Card (see below for link). Knowing your infection level from the prevoius canola crop is essential, so make sure you scout on a yearly basis. For spraying, application between 20 and 50 per cent bloom, is crucial. I especially stress the early timing for an application, at 20 to 30 per cent bloom, but definitely no later than 50 per cent — after that point it’s too late and you have missed the key infection period.

Brian/ON: You need to make the decision early; you can’t wait to see the disease. If you have the right weather and field conditions, spray with the two-week forecast in mind. Flowering timing is critical. I’ve seen canola take two weeks to flower some years, but three weeks in other years. If you spray too soon, you can miss a big window. I could see going later than 50 per cent flower in southern Ontario, if the conditions are right.

6. Is control worth the cost?

Greg/AB: Well, it’s pretty rare to hear someone complain about spraying. More often, you hear, “Geez, I wish I would have sprayed.”

Autumn/AB: Usually, yes. There may be exceptions in years when environmental or other factors affect how the crop responds to fungicide, but overall, fungicides are a valuable part of an integrated management plan, and should be used when necessary.

Clint/SK: Definitely. Some guys lost half their yield last year. If they’d sprayed they’d have made 12 times the cost of the fungicide. Last year, on a 50-bushel crop, you needed only 8 per cent of the plants showing infection for the fungicide to pay for itself.

Kristen/MB: If you have the right conditions, then YES! Many studies show that applying fungicide at the right time and under the right conditions can provide significant yield protection in high-risk situations.

Brian/ON: If scouting shows you have sclerotinia, then absolutely; losses can be very high. But in southern Ontario, we have not seen a consistent payback by spraying fungicides at flowering. It’s different in the north and western parts of Ontario, though. I’m very much of the philosophy that we should not apply a pesticide unless the risk is definitely present. You need to have a good, integrated pest management plan.

Canola Disease Scouting and Risk Assessment Card

Stem Rot Checklist

OMAF guide to sclerotinia in canola

OMAF Field Crop Protection Guide