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Sclerotinia myths and facts

By Tim Gardner, Senior Market Development Specialist

May 16, 2016 - In an integrated pest management (IPM) system, there are few diseases that are more troubling to Canadian canola growers than sclerotinia. How can growers effectively prevent, manage or treat the fungal pathogen, Sclerotinia sclerotiorum, which is so difficult to predict until it has already infected their canola?

There are several common beliefs across the country about how and when to treat for sclerotinia, but you might be surprised to learn the background behind these myths and facts. To do so, Bayer asked growers from Alberta, Manitoba and Saskatchewan to relay some of their thoughts and concerns about the disease. We've worked to address their questions, unveil the truth, and empower growers to make the best treatment decision for their operation.

Myth: If weather conditions aren't favourable to sclerotinia, there's no reason to spray.
Fact: It's unfortunately more complicated than that. Moisture doesn't have to be constant to promote sclerotinia, and external factors can change very quickly. More important considerations should be the local factors, like history of sclerotinia, crop canopy and yield potential.

With this particular disease, whether or not to spray should be more about a calculation of return on investment than a gamble with nature. Growers need to consider a long-term strategy of treatment rather than just the current growing season. Even if you might just break even this year, how will spraying for sclerotinia impact your ROI next year?

Myth: There's only a 50/50 chance that spraying for sclerotinia will work.
Fact: Fungicides intended to treat sclerotinia, like Proline, have been proven effective, but this myth is actually merging two separate issues. The question isn't whether or not it will work, but whether or not it's worth it to spray. Unlike other disease pressures, spraying for sclerotinia isn't always black and white.

An IPM approach would need to take into account several variables to assess field risk levels, including the current growing conditions and the past field conditions. Since sclerotinia survives so well in the soil and has so many bridge crops, with tight rotations a history of infection can greatly impact a future decision to spray.

Myth: It's better to spray too late than too early.
Fact: With Proline, for example, we recommend that growers err on the side of earlier spray timing. At 20-30 per cent flower range, the main stem will be flowering, which is the biggest contributor to the plant's success. If the main stem becomes infected, you could lose an entire plant, but if infection comes later, it tends to be a branch infection, which impacts yield but not nearly as much.

Many of these myths are based on the misconception that sclerotinia presents the same threat for every grower. In fact, it's so dependent on field-specific conditions that it's difficult to make blanket statements about whether or not growers should spray in a given season.

The bottom line is to focus on your bottom line, and use the right tool for the right job at the right time. Not just for this harvest, but for all the foreseeable harvests to come.

 

 


May 16, 2016
By Bayer CropScience

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