Sclerotinia Mythbusters

There are several common beliefs about how and when to treat for sclerotinia, but you might be surprised to learn the background behind the myths and facts.

We asked growers from Alberta, Manitoba and Saskatchewan to relay some of their thoughts and concerns about the disease. We’ve worked with experts to address questions, unveil the truth, and ultimately help you make the best treatment decision for your operation.



Last year’s sclerotinia pressure was low. So this year will be low again.

Each field is different, and needs to be treated differently. When determining whether to spray, growers should consider a variety of factors including: Is everything else there for the disease to thrive? Does the crop have a good canopy? Does the crop have a high yield potential (which makes the return on investment easier)?

The right thing to do is to assess your field in that critical time frame prior to flowering, paying specific attention to the moisture and environment. External factors like these can turn pretty quickly, so if you’ve seen sclerotinia out in the field in previous years that should be your first warning sign. With this disease, even if you can’t see it building but you know it’s there, you should plan for it every season.

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Sclerotinia in your area but not on your farm is not a problem.

Growers are equally exposed to sclerotinia over the longer term. Spores move and can infect adjacent fields. Even if it’s not this year, it’s recommended to begin a scouting process and get a sense of the levels of infection growers have seen in their field to give a better indication for the future. It’s always recommended that growers have a proactive plan. If you do feel there is an increased risk or you have sclerotinia and want to correct it, there is no doubt that the use of a fungicide is part of the solution in managing the disease, especially during those really damaging years. Remember, an application over a longer term strategy and dollar/cost over a longer term is still warranted.

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It’s better to apply fungicide before optimal spray timing than after.

We recommend that growers spray earlier in that window – more in the 20-30% flower range – even if the stand is a little less consistent. The reason behind this is that the main stem will be flowering, which is the biggest contributor to yield success. If you have success in the main stem you’ll have a better yield overall. If you get early infection, the damage is more severe as it often is on the main stem which can kill the entire plant. If infection comes later, it tends to just be a branch infection, which will impact yield but not as significantly.

Learn more about canola bloom stages »

Tighter canola rotations mean you don’t have to worry more about sclerotinia.

There are so many bridge crops for sclerotinia, so depending on what type of rotations growers are using, sclerotinia can really build up in the soil. Anything in a four-year rotation where one crop is the only one susceptible to the disease is ideal.

Spraying for sclerotinia this year doesn’t reduce the risk in future years.

Looking at the weather when approaching the time to spray is a good indicator of what might be happening in the field. You can see the benefits of it—what’s done is done at that point in time, but leaving a little untreated area of the field will give you a pretty good assessment. If there has been an untreated or susceptible spot in the field, growers will be able to spot the dying plant material in the field.

Sclerotinia bodies can survive in the soil for three or more years.

Sclerotinia can remain inactive in the soil for lengthy periods of time and overwinter. If you identify sclerotinia in your field one year, it’s something you’ll have to keep in mind for seasons to come and ensure to protect your crop.

Quickly reacting to sclerotinia is better than spraying in advance.

Once you see sclerotinia in your field, it’s already too late. Spray between 20% and 50% bloom to ensure you’re proactively protecting your crop.

Learn more about optimal spray timing »

Ascospores of sclerotinia don’t travel more than 15-20 metres.

Most travel between 100-150 metres of their launch site and have been known to travel several kilometres in stronger winds.

Yield loss from sclerotinia is generally half the infection level.

Here is a quick way to estimate your potential yield loss:

How to quantify your yield loss potential


Growers should expect about 5% yield loss from sclerotinia infections.

Yield loss from sclerotinia can actually range from 5% to 100% in extreme cases, where the disease could cost you your entire crop.

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