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Moisture top sclerotinia risk factor

June 28, 2013 - The Canola Council of Canada is reminding growers who have high risk conditions for sclerotinia stem rot that they may want to get their management plan in place.

The following factors will determine the level of risk:

1. Moisture
Moisture is the key factor in sclerotinia stem rot risk. Good soil moisture and a few rains in the period starting two weeks before flowering and carrying through to infection after flowering will greatly increase the sclerotinia stem rot risk. Moisture can come from rain, relative humidity in the high 80s or morning dew.

2. Temperature
Moisture has a much larger influence than temperature, however temperature can influence severity. Night and morning lows of 15 degrees C are ideal for sclerotinia, especially with heavy dew. Infection may not advance during the heat of the day, but it will grow at night.

3. Canopy conditions
Sclerotinia disease level is highly dependent on the microclimate within the field:

• Higher disease levels will occur in varieties that have more leaf area, tall stature and/or poor standability;
• Higher nitrogen rates or the addition of manure results in heavier, more dense and thick canopies, which tend to increase humidity in the canopy;
• Lodged crops tend not to dry out quickly, and increased direct plant-to-plant contact will increase disease spread from infected to healthy tissue;
• Neighbouring canola fields with different seeding dates and maturities may have different levels of sclerotinia damage depending on how their flowering stages coincided with weather conditions conducive to disease infection and development;
• Dense stands are good for competition with weeds and earlier, more uniform maturity, but they tend to result in moist canopies. In addition, higher plant populations usually result in plants with smaller, weaker stems that are more prone to lodging.

4. Rotation
Because environment is such a large factor in sclerotinia infection rates, and with so many acres of host crops (e.g. canola, beans, lentils, sunflowers) across the Prairies, rotation on any one field does little to reduce the sclerotinia stem rot risk.

The Canola Council of Canada suggests booking fungicide may be worthwhile if you have a preferred product. This is pre-planning only. Fungicide applications must target flowers to be effective, so do not spray until a field reaches at least 20 per cent flowering.

Visit http://www.canolawatch.org/2013/01/09/sclerotinia-stem-rot-management/ for detailed sclerotinia stem rot management.

June 28, 2013  By Top Crop Manager