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Combining technology may improve spray performance.
Research often presents surprising results that conflict with conventional thinking, says Brian Storozynsky, sprayer technology specialist. Twenty-five years of sprayer technology experience and seven years of extensive field testing point to trends and conclusions not everyone agrees with.
Even though air-induction venturi nozzles, for example, deliver less coverage on the plant surface, herbicide efficacy doesn’t appear compromised, at least not in post-emergent chemical treatments. In most of the dozens of treatments involving both contact and systemic herbicide products were equally effective regardless of nozzle type.
Although coverage/droplet size varies depending on the nozzle, size and operating pressure range produced by different manufacturers, the research shows, in relative terms, that venturi nozzles, which deliver about 35 droplets of chemical per square centimeter (cm2), appeared to be as effective as nozzles that deliver much finer sprays. That contradicts conventional thinking, but the research results speak for themselves.
Extended range nozzles used in this research, produced fine to medium sprays, with coverage of about 125 to 150 droplets per cm².
Air assist and electrostatic systems are above 200 droplets per cm².
Turbo TeeJet nozzles on research equipment, produced medium to coarse sprays with a droplet density of about 75 to 100 droplets per cm².
Venturi nozzles produced coarse to extremely coarse sprays with a droplet density of about 20 to 50 droplets per cm².
"With the coarser droplets produced by venturi nozzles, drift is reduced," says Storozynsky. "Standard thinking is coarser droplets would reduce efficacy, but that wasn’t the case. Control with venturi nozzles was just as good as with nozzles producing finer droplets. That result surprises many people."
Fit for shrouds
Sprayers equipped with low-pressure venturi nozzles can produce more spray drift than high-pressure venturi nozzles.
That’s another contradiction, says Storozynsky. "In the past, high pressure has been associated with high drift, but not with the high-pressure venturi," he says. "When operated between 40 and 120 psi, drift is reduced."
To minimize drift with ground sprayers in higher wind speeds, shrouds should be considered, says Storozynsky. With the development of low drift nozzles, producers trended away from using shrouds, but shrouds may help increase the operating range of low pressure venturi nozzles.
"Shrouds were popular up until the mid-’90s, but dropped off with the introduction of newer nozzle technology," says Storozynsky.
While it’s an area of ongoing research, he suspects low drift levels can be maintained even under slightly higher wind conditions, if shrouds are used in conjunction with low pressure venturi nozzles.
Role for air assist
Expanding research treatments to include pre-emergent, pre-harvest herbicide and insecticide applications may better demonstrate the potential benefit of sprayers equipped with air assist and electrostatic technology, says Storozynsky.
The sprayer accessories, intended to boost the performance of spray penetration on high clearance sprayers, increase over-all sprayer costs and need more horsepower to operate. However, some manufacturers claim improved spray deposition and penetration increases efficiency, which means both herbicide and water rates can be reduced.
Storozynsky’s research under field conditions, showed air assist and electrostatic sprayers performed as well as standard pull type and high clearance sprayers for post-emergent applications at 5 and 10 gpa. Results may be different in a pre-seeding burn down where weeds have no crop cover, or in a pre-harvest herbicide treatment, which generally means higher and heavier crop canopy. |