Below are 12 practical tips to complement the recent Canola Watch Information (posted July 2, 2020 in Issue 16).
Tweeted 25 June 2019 by @PCDMN
Factors related TO THE HOST…
1. Canopy closure: Closure promotes soil moisture favourable to germination of sclerotia and production of apothecia when rainfall occurs.
2. Flowering date and period: Does flowering coincide with favourable weather conditions, i.e. moderate temps and rainfall/high relative humidity?
3. Lodging potential: Varieties with a greater lodging risk or where fertility levels (N) are high may have an increased risk of stem rot.
4. Yield potential:
* Impacts canopy density, which is also influenced by N fertility.
* Limited risk and need for fungicide when yield <30 bu/acre.
5. Commodity price:
* Impacts cost/benefit of using a fungicide.
* Low commodity price = tough decision.
* High commodity price = easier decision.
Factors related TO THE PATHOGEN…
6. History of sclerotinia in field or area AND Presence of apothecia:
* In field or adjacent fields
* Easy to find within 20-30 minutes
7. Moderate-high – levels of petal infestation with the stem rot fungus and/or ascospore load in the air: Can change over the flowering period
8. Increased risk when: History of stem rot and/or ample inoculum at flowering coincides with frequent rainfall, and ↑ed yield potential.
9. Reduced risk when: Limited history of stem rot and lack of inoculum at flowering coincides with dry conditions and temperatures of >30 °C.
Factors related TO THE ENVIRONMENT….
10. June rainfall:
* Sufficient to maintain soil near field capacity
* Plus a well-developed canopy will promote sclerotial germination
11. July conditions:
* Rainfall (at least 5-10 mm) on > than 2 days per week and/or RH >80-90%
* Humidity promotes sticking of petals to canopy
12. July conditions:
* Crop canopy is wet throughout most to all of the day
* Irrigation may ↑ risk, but high temps (>30C) will ↓ risk