The window for fungicide application closes after 50 per cent flower – which is when the field is at its most yellow. Once this “full bloom” starts to wane, spraying must stop.
Sclerotinia: Does fungicide at 50% flower make sense?
In general, late applications are not as effective as applications at 20 per cent flower because early infection tends to cause the most yield loss. But fungicide applied late in the window can provide valuable protection from sclerotinia stem rot if flowering is extended or if conditions become more conducive to disease.
Give the plants a mid-season root check
While scouting canola fields at flowering and podding stages, dig up a few plants in each field and look at the crown and primary root. If the crop has above-ground symptoms, compare the roots of healthy and unhealthy plants. That might help you discover the problem.
Top 10 sclerotinia stem rot questions
What is 20 per cent flower? When to spray an uneven crop? What is the right amount of moisture for disease? And more…
QUIZ – Sclerotinia stem rot risk
These three questions will help canola farmers and agronomists assess the sclerotinia stem rot risk in their areas.
Factors in the sclerotinia spray decision
The decision to apply a fungicide to prevent sclerotinia stem rot may be generalized by answering these four questions: (1) Have environmental conditions prior to flowering been wet enough for apothecia development and survival? (2) Is the canola crop canopy dense and is yield potential high? (3) Does the weather forecast predict precipitation and/or humidity during the flowering period? (4) Is the pathogen present in sufficient quantities?
Sclerotinia stem rot: Timeline for infection
Once petals drop and start to decay, infection proceeds very quickly with lesions being visible in as little as 24 hours.
Sclerotinia fungicide: Timing and performance tips
Timing and coverage are keys. For most fungicides, the recommended window for application falls between 20 and 50 per cent bloom, with optimum timing typically around 30 per cent bloom.
Sclerotinia risk with hot weather
Hot, dry weather reduces infection rates and the progression of sclerotinia within the plant. The disease risk is limited when current conditions are dry, max daily temps are 30°C or more, and forecast is for this to continue for seven to 14 days. Hot weather can also increase flower and pod abortion, which could reduce overall yield potential. Return on …
Last chance for blackleg control
Fungicide is probably not necessary in a field with at least a two-year break between canola crops, blackleg-resistant varieties and rotation of genetics. But if factors suggest a fungicide ROI, it has to be applied before the four-leaf stage.