For most fungicides, the window for application is from 20 to 50 per cent flower, with optimum timing typically around 30 per cent flower. How to assess the bloom stage. Generally, it takes a crop four to five days to move from first flower to 20 per cent bloom.
The objective of the fungicide application is to cover as many petals as possible while ensuring that some chemical also penetrates into the canopy.
Fungicide applied at the beginning of the label window will coat the petals that are there, but also provide important coverage down in the canopy. Fungicide down in the canopy coats the key plant tissues where the most damaging infections occur. These targets include leaves, leaf bases, leaf axils and perhaps even leaf petioles where infested petals clump. That is why water rates are so important – to get that penetration and coverage into the canopy targets. Fungicide protection in these areas can last two weeks or more. That is why fungicide targeting is not just about the petals because flowers only have about a six-day life cycle. If you were to focus on applying fungicide on petals themselves you would need to repeatedly apply fungicide to coat each successive crop of newly emerged flower and petals.
As for early applications that target buds before they open to form flowers, that is probably not providing much benefit given the limited systemic action of the fungicides available for canola. They would not typically penetrate from the green sepal tissue into the petal tissue itself.
*Thanks to Kelly Turkington, plant pathologisit with AAFC, for help with this article.
Fungicides for sclerotinia stem rot in canola
Fungicide performance tips
- Timing is key. You want to be within the spray window of 20 to 50 per cent flowering (which is the window for most products) and going around 20 per cent flowering will usually provide a higher economic return if moisture conditions favour infection.
- As noted above, fungicide applied at the beginning of the label window will coat the petals that are there, but also provide a protective barrier for leaf and step tissue down in the canopy.
- Fungicide protection on tissues in the canopy areas can last two weeks or more. That is why fungicide targeting is not just about the petals because flowers only have about a six-day life cycle. If you were to focus on applying fungicide on petals themselves, you would need to repeatedly apply fungicide to coat each successive crop of newly emerged flower and petals.
- The actual length of fungicide protection will depend on the product and its persistence, as well as the quality of application and its penetration into the canopy. For second fungicide applications, the recommendation is to wait seven to 14 days after the first application.
- Most of the fungicides available for canola are locally systemic – they only penetrate into the outside layers of the plant tissue they are applied to. Some do move a bit more extensively, such as from one side of a leaf to another, or even from the centre of a leaf to the tip. (See the illustration at the bottom.) Another note is that some fungicides are more lipophylic than others. This “love of fats” might be more advantageous than systemic activity. Lipophylic fungicides will bind to the waxy cuticle which might be good since it will keep the active ingredient on the leaves which is where they need to fight the disease.
- Earlier applications that target buds before they open to form flowers would probably not provide much benefit given the limited systemic action of the fungicides available for canola. They would not typically penetrate from the green sepal tissue into the petal tissue itself.
- In its article Fungicide application basics, Sprayers 101 says the two top considerations for effective fungicide applications, in general, are timing and water volume.
- For fungicides applied to protect canola from sclerotinia stem rot, water volume at recommended amounts will improve coverage of flower petals and penetration down into the canopy.
- For growers without the equipment to spray fungicide on a flowering canola crop, book a custom applicator as early as possible.
- Nozzle choice is less important. Research at AAFC Saskatoon compared five methods of fungicide application over three years to determine the effect of nozzle type and pressure on sclerotinia stem rot infection of canola and crop yield. Variation in product performance among years indicated that environmental conditions had a major effect on crop development, sclerotinia stem rot infection, the effect of fungicides and subsequent yield. Overall, conventional flat fan nozzles (TeeJet XR), low-drift venturi nozzles (CFFC TurboDrop) and hollow cone nozzles (TeeJet TXVS-8) were all effective at reducing disease symptoms. Both 275 and 550 kPa (40 and 80 psi) provided similar performance although increasing the venturi nozzle pressure to 550 kPa (80 psi) improved disease control slightly. These results indicate that venturi nozzle technology is appropriate for use with foliar fungicides for sclerotinia control in canola provided pressures are adjusted to optimize nozzle performance.
- Research shows minimal effect from droplet size. Sprayers 101 makes this statement: “Work at AAFC in Melfort compared conventional and low-drift sprays at two pressures, and showed that droplet size had no effect on disease control. In fact, the fine spray produced by hollow cone nozzles at high pressure did not significantly improve sclerotinia control compared to a venturi nozzle at its recommended pressure of about 60 psi.”
- Hot conditions can increase evaporation of the spray, reducing its performance. Some companies say to avoid spraying in temperatures above 25-27°C. A tip is to keep the water volumes at a minimum of 10 gallons per acre. Coarse spray droplets, in this case, will help to reduce rapid droplet evaporation while still maintaining very good target coverage. Rainfastness varies by product. Some can be applied as little as 30 minutes before a rain. Others are recommended to have at least three hours before a rain. Also use the appropriate nozzle filter screens to improve fungicide performance. Ask the retail or check labels for specific notes on filter screens.
- Many fungicides allow for aerial application. Sprayers 101 notes that an aircraft’s chief advantage is to cover large areas with no crop trampling, and can do so even in wet conditions. As a result, they offer the timing advantage that is so important. Sprayers 101 expands on the aerial option: A producer hiring an aircraft for spraying ought to have a conversation with the pilot and discuss water volume and droplet size. Aircraft, out of practical necessity, apply less water and distribute it in finer sprays to offer the required coverage. Although this has been shown to be effective, it creates drift and evaporation potential. It is worthwhile to ask for higher water volumes if it means that the spray can be applied somewhat coarser, creating less drift. The rotary atomizers on many aircraft produce fairly uniform droplet sizes and do a good job of eliminating the larger droplets. This makes even more droplets available for coverage. However, even with this technology spray drift still matters and all steps to prevent it should be taken. This means using larger average droplet sizes and increasing water volumes accordingly to their label recommendations.