This year has certainly been challenging for canola production and, as a result, crop staging is wide ranging in some fields. Should a fungicide be applied now when the oldest plants flower or later with the later-flowering plants? Each field should be assessed individually for risk of infection from sclerotinia stem rot. A few things to keep in mind:
- Thin plant stands are more open and will dry out more readily during the day. Infection risk will be lower unless regular showers or high relative humidity with heavy dews keep the canopy damp.
- Recent rains do not necessarily mean increased risk of infection. Sclerotia require good soil moisture (one to two inches of rain in one to two week period) to germinate into apothecia and produce spores for infection. Surface soil moisture has certainly been limited recently in many parts of western Manitoba, southwestern Saskatchewan and Alberta. With recent rains it may take about a week for sclerotia to germinate into apothecia and release spores that cause infection. Canola staging may advance enough that this late release of spores is too late to cause significant disease development in earlier maturing fields.
- Scout for apothecia (small golf tee shaped mushrooms that produce the spores) in fields where susceptible crops, such as canola, pulses and sunflowers, were grown last year. The more you find the greater the potential for spore production.
- Generally earliest infections cause the greatest yield loss. If you are making one application, scout fields well to determine when the majority of plants (that are the biggest yield contributors) are at the appropriate stage for fungicide application.
- If the crop staging (and ultimately flowering) is variable, consider a split application. The first application can be made when the first plants reach recommended staging. If necessary, a second application can be made when the remaining plants are ready to be sprayed. In Manitoba, fungicides are being sprayed on portions of a field because of the variable staging. This too may be an option. Refer to current crop protection guides to determine which products are registered for split application and recommended rates of application: http://www.gov.mb.ca/agriculture/crops/cropproduction/gaa01d01.html
- Consider the lateness of the season and frost-free days remaining. Be realistic with yield goals. If the crop is flowering late, is there enough time to gain a return on the fungicide investment?
- Bayer Weather Command Centre produces a risk map daily for sclerotinia infection based on weather data (temperature and relative humidity) collected from Weatherbug stations located throughout western Canada. If interested in viewing the risk map, visit the following link http://www.bayerweather.ca/ and login into the site with Canola as the ‘username’ and Grower as the ‘password’. Please take note that the login information must be typed with capital and lower case letters exactly as shown. The sclerotinia risk map is located under the risk analysis tab. Access to this site will be for a limited time only and anyone interested in long term access can email email@example.com.
The following link has good photos of a canola field progressing through flowering stages (10% to full bloom):http://www.ag.ndsu.edu/pubs/plantsci/crops/pp1410.pdf