Slow and steady is the better bet when spraying, says a sprayer specialist.
“When you have to cover each acre five times per year, you may be very tempted to travel fast,” said AgriMetrix’s Tom Wolf at the recent Cereal Disease Conference.
“I’m going to try to convince people to go slower. I know it’s a losing battle, but I’ll go down fighting.”
Manufacturers are pouring research dollars into developing faster sprayers, but higher travel speeds can cause uneven spray distribution on the plant, reducing the overall effectiveness of the spray, he said.
In most cases, spray droplets fall “more vertically” at higher speeds, landing mainly on the forward side of the plant, and the challenge is “getting it to deposit on the side facing away.”
“The faster you go with a vertical target, the more deposition you get on the forward-facing side.”
Nozzles are also “aerodynamically non-porous” — which means some air moves through the nozzles, but most of the air moves around them, a problem that becomes more pronounced at faster speeds.
“(Nozzles) essentially behave like pieces of plywood hanging off your boom,” said Wolf. “They’re aerodynamic walls.”
Forcing air to go around nozzles creates negative pressure, which draws any small droplets out and disperses them.
“When we go fast, we lose control over the droplets,” he said. “You lose an increasing proportion of your small droplets, and you lose control over whether they go into the canopy.”
Producers improve spray distribution by moving to an asymmetric nozzle that varies fan angles and flow rates.
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“It’s very difficult to get the same amount of spray on both sides of the head when you have the same fan angles and the same flow rates,” said Wolf.
But one recent study suggests that producers can achieve a better spray distribution with the right nozzle, regardless of sprayer travel speeds.
Using an asymmetric nozzle design with an air-induction tip, Wolf had “terrific results” at five miles per hour. At 10 miles per hour, the deposit became “less uniform,” but the sprayer did a “reasonably consistent job over a range of travel speeds.”
“We found the same basic deposition at all speeds. That was good news,” said Wolf, who will be conducting more research on travel speeds over the next three years as part of a research project with Agriculture and Agri-Food Canada.
But in the meantime, producers can increase their productivity without increasing their speed, said Wolf. Using a bigger tank, a wider boom, and a faster fill speed can double the rate of application — without the risks that come at higher speeds.
“We don’t have to go fast to be more productive.”