With any disease that affects our crops, the first step to controlling the disease is to understand it. Sclerotinia stem rot can be a devastating disease with canola. Last year in the Meadow Lake area we say upwards of 50% of the plants in some fields infected. This significantly reduced the yield of the canola. We have some beautiful looking canola crops in the area that are worth protecting from this disease.
The first consideration with sclerotinia disease pressure is whether the fungus will be present in your fields. There are sclerotia bodies (the dormant stage of the disease) in pretty much all of the soils in the area. The conditions that are required to these sclerotia bodies to germinate have been present in our soils over the last couple of weeks. The soils must be in the 11 to 15 degree Celsius range and they must be moist for two to three weeks. These conditions have been both present in our area.
Once the sclerotinia bodies form mushrooms, spore production will start. Spores usually move 100 to 150 meters in a field but wind can carry them great distances. This means that the adjacent field as well as the field that the canola is in can be the source of the infection. If the spores land on a flower petal, the potential for infection process of the canola plant can begin.
When the flower petals of the canola plant fall off, they can land on the plant. Extended warm periods with high humidity increase the likelihood of disease. If a dry period occurs in the weather, the likelihood of the disease is lessoned. A standard rule of thumb that I use is that if you walk into a field after dinner and your pants are wet from the moisture in the crop canopy, the disease risk is significant. This can be common in a thick canola stand.
Making a decision as to whether to apply control measures for this disease is always a tough one. At Cavalier Agrow, we check petals for the presence of the spores in specific fields. This is the first indicator that the disease potential exists. If the crop canopy is thick, the disease risk is higher. If the crop canopy stays wet throughout the day, sclerotinia risk increases. If the rotation in a specific field has been tight, the risk for the disease is higher. Finally, if there is rain in the forecast, this significantly increases the risk of disease development. A checklist for evaluating the disease potential can be found in the Canola Production Guide at the Canola Council of Canada website.
Disease management is essential when growing any crop. Sclerotinia stem rot can be a devastating disease. Understanding the disease and making sound decisions as to whether control measures should be applied is all part of growing more bushels.
By Dave Cubbon, P Ag