Spraying a fungicide requires considering the stage of plant a bit differently than when spraying a herbicide. At herbicide timing, the canopy of the crop is a lot shorter and less dense.
“For fungicides, we’re now talking about a taller canopy, a canopy that’s probably closed in, and a canopy that’s a little bit diverse in its structure, where the top half might look completely different from the bottom half,” says Tom Wolf of AgriMetrix and Sprayers 101, in this Wheat School episode.
With respect to targeting a disease, it’s good to understand where the disease develops and how it will travel through the canopy, in order to target it properly. Wolf says that the spray needs to land where the disease is, as most fungicides don’t translocate within a plant very well.
Water volumes in the tank mix plays into this by manipulating where the spray goes, especially deeper into the canopy — it’s the most powerful tool available when applying fungicides, says Wolf.
A wheat or cereal canopy has roughly three layers, or target zones. The top layer is the emerged head, for fusarium head blight timing, which is a relatively easy target with twin nozzles for a directed spray, says Wolf.
Getting deeper into the canopy to hit those bottom two layers, for tan spot, or other diseases that come up from residue, the only way to hit them is to increase water volume, to increase the droplet density, which Wolf says is the “currency of fungicide performance.” (Story continues below video)
“What I often recommend is to look down, and ask yourself the question what part of the plant canopy do I have to target, based on the disease and the mode of action, and can I see that plant part?” Wolf says, and if you can’t see the plant part, that’s where the water volume aids.
When it comes to temperature and spraying fungicides, the plant still needs to take that fungicide up, which is much more efficient when the droplet is still wet, and in hot, dry conditions, that droplet could dry before it’s absorbed by the plant.
Wolf suggests to look at the Delta T (which you can find more info on in this Wheat School episode), increase the water volume, and consider the droplet size.
For aerial spraying, practicality comes into play as an aircraft has a smaller hopper that puts down finer droplets, but they can’t spray on windier or hotter days.