Sclerotinia Stem Rot in Canola

Every year, the presence of sclerotinia stem rot is a possibility. In the past, I have seen losses of yield in canola crops over the 50% mark. This can represent over a 30 bushel per acre loss potential. With the price of canola, this loss potential makes it important that canola growers understand what triggers the disease and what they can do about it. The key to dealing with this disease is to understand what causes the disease and whether it is appropriate to apply control measures. The disease is caused by spores produced by fungal bodies present in the soil that release spores in your air above your fields. Mushrooms form that produce these spores when the conditions are right. The mushrooms will form when the soil is warm enough and when there is moisture present. Crop rotation and weed control play an important part in the risk associated with this stage of the disease. If a canola rotation is tight or susceptible weeds have been left to thrive in past years, the risk of the disease goes up. Environmental conditions at the time of spore release must also be considered. The sclerotia bodies in the ground will release spores that will land on the flower petals of the plants. If the petals will fall onto the other parts of the plants (surface of leaves and crotches of the stems) and rot into the plant tissue in this areas, the disease will result. For this to happen, the petal must be present on the plant tissue for 8 to 12 hours with adequate moisture. If the crop canopy is thin or the weather is warm and dry, the wetness required is not present and the disease will not happen. Timing of spraying with available fungicides is critical. The window for control with most fungicides is 10 to 14 days. If a field is sprayed too early, the days of disease protection are reduced. This will mean that any later infections of the spores can still do damage. If the fungicide is sprayed too late, control of the early disease present will be missed. One way to check to see if the spores are present on the petals of the canola flowers is to use a petal test kit. This kit will tell when the infected petals show up in your field. This information is critical for the best possible disease control. In general, the canola crop should be sprayed in the 30 to 50% bloom stage, usually at the earlier 30% range. Petal testing must begin at about the 10% bloom stage to be effective. Sclerotinia stem rot is a disease that can be managed in canola. The key to managing the disease is to understand what conditions create the high risk environments for the disease and understand the proper use of the tools to control the disease. For anyone that wants further information on what to look for, go to the Canola Council of Canada website or talk to your local agronomist.