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Apr 27, 2023

Slow down, up the volume, reduce the pressure

Published: May 25, 2023 Crops Δ gform.initializeOnLoaded( function()

Published: May 25, 2023

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A spraying specialist weighs in on how producers can achieve effective deep canopy coverage while applying fungicides

Slow down, lower your booms and increase your water volumes.

That, in a nutshell, is the key to achieving good canopy penetration when applying fungicides to control mycosphaerella blight (ascocyhta blight) in field peas.

"The real powerful way to get through a thick pea canopy is with water volume," said Tom Wolf, a spray application specialist and researcher with Agrimetrix Research and Training in Saskatoon.

"In our studies using fungicides… we found that water volume was by far the most powerful way to get better penetration, deeper down (in the canopy)."

In a recent interview, Wolf offered a variety of tips to improve fungicide spray coverage in pulse crops.

He also dispelled common myths.

According to Wolf, many growers believe that increasing spray pressure is an effective way to force the spray deeper into a thick pulse canopy but that's not true.

Increasing spray pressure might provide some benefit when used in combination with lower boom heights and slower ground speeds. But when boom heights are 20 to 30 inches above the canopy, any benefits derived from higher spray pressure will be negligible, at best, he said.

At higher boom heights, the pressure dissipates before reaching its target.

"We just can't retain that spray velocity for any length of time," Wolf said.

"It's like throwing a feather. You can really wind up and throw that feather super-hard, but it won't go anywhere. It will go back to its normal slow velocity within a few inches."

Instead of focusing on spray pressure, growers should increase water volume.

In Agrimetrix research conducted in chickpeas and field peas, water volume was the most important factor associated with good canopy penetration.

In field peas specifically, increasing the water volume from five gallons per acre to 10 gallons per acre showed significant improvement in canopy penetration.

The benefits were especially evident in the lower canopy, where mycosphaerella symptoms are typically the most evident.

Further improvements in spray coverage and canopy penetration were observed when water volume was increased to 15 gallons per acre.

Lower boom heights and slower ground speeds are conducive to improved canopy penetration, particularly when used in combination with higher water volume.

"It's all about distance," said Wolf.

"Droplets slow down the further they get from the nozzle, so the lower you can get your booms… the more likely you’re going to be to be able to "force" that spray into the canopy."

Slower ground speeds will allow applicators to lower booms and reduce boom sway.

Reduced travel speeds also are associated with better crop penetration.

In research trials, Agrimetrix compared two techniques to see which approach was more effective:

"When we slowed down, we had a greater response to water volume," Wolf said.

Droplet size is a factor worth thinking about, but it may not be as important as you think for field pea canopy penetration, Wolf added.

"We need small droplets for good coverage … but there's a limit," he said.

"And making the spray too fine doesn't serve anyone's purposes."

If spray droplets are too small, the risk of evaporation or spray drift increases. This is particularly true with fungicides, which are typically applied during the hottest part of the growing season.

"We want to keep some of those droplets a bit larger, just to prevent that evaporation from happening."

For fungicide applications, traditional low-pressure air induction tips should provide effective coverage.

"I would probably increase the pressure a bit but you don't necessarily need a special tip (for fungicide applications in peas)," Wolf said.

"We think a traditional low drift tip is quite OK."

And most importantly, a grower's priority should be proper timing.

"When it comes time to spray, don't fuss too much about how you’re going to do it. Of course, it's important to try to do things right, but it's probably more important to do it at the right time."

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