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Four Tips For Managing Sclerotinia In Canola

Sclerotinia is one of the most widespread diseases in canola. Farmers need to use a number of strategies to mitigate its impact. Management starts with cultural controls such as rotation and includes the use of fungicides, biological controls and the use of partially resistant varieties. Not all options are terribly effective and need to be combined for maximum effectiveness.

Management begins with understanding why sclerotinia is so widespread in the first place. It has a wide host range, with many broadleaf plants and crops being susceptible to it including canola, mustard, pulse crops, soybeans, carrots, sunflowers and even weeds like wild mustard, shepherd’s purse, stinkweed and thistles.

Secondly, when we look at the life cycle of sclerotinia, illustrated in Figure 1, we see that the spread of sclerotinia in canola is from many, many spores that originate on the soil surface and land on the petals of the canola. These infected petals then fall off the flower and land in the leaf axils of the plant (where the leaf joins to the stem). The spores use the petals as their initial food source and that’s when they infect the plant.

ROTATION

This is why when we look at one of the potential cultural controls such as rotation, its impact on the incidence of sclerotinia in canola is quite low. Even though we may have a good break between consecutive canola crops in any given field, the widespread use of other susceptible broadleaf crops in rotation and weeds both within our own fields and also adjacent fields mean that there is usually a generous supply of inoculum available to infect our canola fields when the conditions are right. Therefore, even though rotation is often mentioned as a control measure for sclerotinia in canola, its role is usually relatively minor in the traditional canola areas of Western Canada.

SCLEROTINIA PREDATOR

A second potential control measure is with the use of a biological control such as Contans. Contans, distributed by UAP Canada, is the commercial name of a biological control product that contains a fungus called Coniothyrium minitans.This fungus destroys the resting sclerotia bodies present in the soil. This product has been used for many years in Europe and has been shown to reduce the level of sclerotia bodies in the soil and therefore reduce the level of sclerotinia infection that occurs within the field that it is applied in.

There are however several concerns with its application methods and potential effectiveness. First, according to the label, the product should be applied approximately three months before the infection is going to occur. That means, practically speaking, that for most of Western Canada, that the product will need to be applied in the previous fall. Second, the product requires some incorporation within the top five to 10 cm of soil. That means, in most cases, using tillage, which will not be a popular option for those practising zero tillage. And although the product may end up significantly reducing the sclerotinia infection within the field that it is applied in, it will not control the spores that are produced from neighbouring fields, especially those that are situated upwind. So it’s a tool that can reduce the level of infection within a field, but will not reduce the risk from neighbouring fields.

 

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