An analysis of weather data and the top zone (0 to 4 inch) soil moisture for the canola producing areas of North Dakota and Minnesota for the 10 day period ending June 17th 2007, indicates that there is a projected moderate risk of sclerotinia over much of North Dakota and Minnesota, as indicated in the risk map and some small areas show high risk as a result of recent heavy precipitation. The risk is increasing in Southwest North Dakota and the Southwestern area of Minnesota due to recent precipitation. This is a projected risk only as the majority of the canola is in the rosette and early bud stages as indicated in the GDD map. However individual fields within all areas may be in a further advanced stage because of an earlier seeding date then the average seeding dates used to prepare the GDD map.

Canola is not susceptible to sclerotinia until it is in the blossom stages but some early seeded canola has reached this stage. Images of canola blossom stages can be viewed at:

http://www.ext.nodak.edu/extpubs/plantsci/crops/a1208w.htm  

Fungicide applications are most effective when applied between the 10% to 50% blossom stages depending on product used. Endura, Quadris, Ronilan, Topsin and Thiophanate Methyl are registered for sclerotinia stem rot. For more information see the North Dakota 2007 Field Crop Fungicide Guide online at the following site:

http://www.ag.ndsu.edu/pubs/plantsci/pests/pp622/pp622.pdf  

The top zone soil moisture map indicates that the top 4 inches of soil over most of North Dakota and the area of Minnesota included in the forecast is over 100% of field capacity except for portions of Southwestern North Dakota where the top zone soil moisture is in the range of 90 to 100% of field capacity. If upper soil conditions remain moist for the next 10 days, apothecia are likely to be found in the last week of June. The germination of sclerotinia sclerotia requires about 10 days of moist soil to germinate. When they germinate, sclerotia produce the spore bearing structures called apothecia that release spores, which attack canola and cause stem rot. Spores are released by the apothecia at about the same time as canola comes into flower. Local weather, soil and crop conditions may result in a more favorable condition for germination of the sclerotia than is indicated in this report.

In assessing the risk for individual fields and the weather conditions the following points should be considered:

• Crop rotation. Other crops susceptible to sclerotinia include sunflower, and pulse crops such as field bean, field pea, and lentil. Although crop rotation is important, environmental conditions are the main determining factor in the development of sclerotinia in canola.
• Has sclerotinia been a problem in the immediate area on canola or other crops in recent years? Sclerotinia sclerotia can remain viable in the soil for up to four years.
• Is there a high yield outlook for the field based on fertilizer application and heavy crop stand? The higher the target yield, the greater the chance of sclerotinia occurrence.

The next sclerotinia risk forecast, is scheduled for June 21, 2007. If this information is of interest to you, future sclerotinia forecast maps and interpretations can be accessed at: