Sclerotinia

Sclerotinia has become a yearly concern for most Manitoba canola growers. Many pencil in the potential cost of a fungicide treatment with the assumption it is probably going to be another risky year. Why? Manitoba tends to have the right weather (moderate temperatures and good moisture during flowering) that favour infection and development, as well as other crops in rotation with canola (sunflowers, dry beans, soybeans, other canola) that also are affected and can provide inoculum to infect canola later on in the rotation.

Click link to use the Sclerotinia Treatment Decision Tool put out by Manitoba Agriculture Food and Rural Development.

In 2009, a canola disease survey was conducted in Manitoba by AAFC Brandon, MAFRI, Canola Council and supported by the Manitoba Canola Growers Association. The survey looked at 140 fields and visually assessed sclerotinia infection. From all the fields surveyed in the province, 91% had sclerotinia symptoms, which is similar to 2008 survey at 94%. These numbers are high, but only tell half of the story. Within each field not all plants were affected. The average for all the fields surveyed was only 18% of plants with infection.

The numbers tell us the end results, but what really happened and how can you use this information for your future crop? In 2009, the sclerotinia infection seemed to be more on the top branches, which prematurely ripened and shelled out. Yield losses may not have been high, since most of the plant was still healthy with good seed set, but it left farmers scratching their heads as to what had happened and if their fungicide control program was as good as in other years. A potential answer is at that the infection came in late and we had a really long flowering period (up to 6 weeks in some fields). For example, if a producer sprayed at the 20% bloom stage, they would have provided control for the sclerotinia at that time, but flowering kept on occurring for another 2 to 3 weeks and weather became warmer with more frequent rains. That meant better conditions and more opportunities for later infections.

So should spray plans change for 2010, based on 2009? Remember, successful sclerotinia infection and timing is very weather dependent. The recommendations for scouting, bloom staging and assessing the need for fungicide application, is based on a number of years with a wide range weather conditions. 2009 was a different year – we normally have warm early July weather and not 6 weeks of canola flowering. The ‘window’ for scouting, assessing risk and fungicide application timing of 20% (14-16 flowers open) to 50% (20+ flowers opened) bloom should still be your guide. The goal of the fungicide use is to coat as many petals as possible (which occurs between 20 – 50% bloom) to provide protection to potential infection sites as the petals drop.