Sprayer Technology Research Sheds Light on System Performance

With the battery of pesticides available today, effective control of crop pests sounds simple, but it is a complex issue, says Brian Storozynsky, sprayer technology specialist at the AgTech Centre. Aside from selecting the actual pesticide, producers face an ever-expanding lineup of application equipment and nozzles.

Equipment choices
While far from obsolete, the pull-type sprayer equipped with model 8002 flat fan nozzles is no longer the benchmark sprayer system. That type of equipment has served the industry for decades. Today however, sprayers include conventional pull-types, self-propelled high clearance units, hybrid combinations of pull-type, high clearance sprayers and sprayers equipped with updated and improved air assist and electrostatic sprayer accessories.

The standard flat fan nozzle is now just one of a host of nozzle types, designs and capacities made by more than a dozen manufacturers. Options include the standard nozzles, extended range nozzles, pre-orifice, combo jets and air induction nozzles with a range of models within each type.

Along with equipment, producers also have to weigh the sometimes conflicting and controversial claims that use of specific sprayer and nozzle technology makes it possible to reduce both chemical and water rates while achieving as good as or better weed and disease control. The offer to treat more with less, and maintain product efficacy has huge appeal in helping reduce crop input costs, but does it work?

"Producers really want to know what is the most effective nozzle providing the best balance between coverage and reduced drift," says Storozynsky. "What’s the best system? And there are really no simple answers."

Extensive research
AgTech lab and field research have addressed several key issues. Using both wind tunnel simulation along with extensive field-scale testing in grain, oilseed and some special crops, Storozynsky has evaluated key sprayer technologies for effectiveness in spray coverage, herbicide efficacy and reducing spray drift in typical in-crop weed, disease control and desiccant treatments. The latest nozzle technologies, along with several air assisted technologies were tested at conventional pull-type and high clearance spraying speeds and setups. Each of the six technologies tested represented one of the ASAE Standard S-572 droplet size classifications. "We’re finding some of the answers, but there are many more issues to be addressed," he says.

Reducing drift
Nozzle research with specially designed field-scale sprayer equipment that represents various sprayer types has generated some interesting results in the bid to reduce airborne spray drift. Key points include:

• Pre-orifice nozzles, such as Turbo TeeJet and DriftGuard, reduced drift by as much as 50 percent over extended range nozzles.
• Low-pressure venturi nozzles, such as the Air Bubble Jet and Airmix, reduced drift by 35 to 60 percent compared to pre-orifice (low drift) nozzles. For best results these nozzles should be operated between 25 and 60 pounds per square inch (psi), averaging around 40 psi, but regardless of manufacturer recommendations, not lower than 25 psi.
• High-pressure venturi nozzles, such as the TurboDrop and AI TeeJet, reduced drift by 60 to 90 percent compared to pre-orifice nozzles. They can be operated at 40 to 120 psi with an average of 75 psi, but regardless of manufacturer recommendations, not lower than 40 psi.
• High-pressure venturi nozzles are best suited for high clearance sprayers if drift is the primary concern. The nozzles produce a coarser droplet size, which has a lower risk of drift when higher spray booms are used. Low-pressure venturi nozzles are sufficient for pull-type equipment.
• Shrouds are still needed. The combination of a conventional sprayer equipped with low drift or venturi nozzles and a shroud produces optimum drift reduction at higher wind speeds.

• Recommended pesticide label rates worked in most cases. No matter which sprayer or nozzle type was used, the recommended rates for water and chemical, in most situations, achieved at least 85 percent weed control. That wasn’t always the case in research using reduced water and herbicide rates. In some trials with herbicides such as Roundup Transorb, Odyssey, Liberty, Everest/Buctril M, Puma Super/Refine Extra/MCPA and Everest/Thumper, there was reduced weed control at lower herbicide rates. For research purposes, herbicide rates were reduced by as much as 50 percent to aid in understanding the effectiveness of different spray coverage and droplet size.
• There was little or no difference among sprayer types as far as effectiveness in weed control. At maximum ground speed of 12 miles per hour, conventional pull-type, high clearance and air assist sprayers were about equal in their performance whether applying a systemic or contact-type herbicide. Air assist and electrostatic sprayers with fine to very fine spray droplets appeared to be more effective in fungicide application on field bean crops.
• Air-induction venturi nozzles, which deliver a coarser spray, provided as effective weed control as other nozzle types most years. It has long been viewed that a finer droplet size provided better coverage and therefore improved herbicide efficacy. But research showed venturi nozzles were just as effective, four out of five years, as nozzles producing a finer spray. The exception was reduced control in plots with a dense population of grassy weeds, and especially at reduced herbicide rates.

"To date we’ve primarily looked at how these systems worked in post-emergent or in-crop treatments in grain crops," he says."And with our research sprayers, the maximum practical ground speed is 12 miles per hour. We plan to continue research to measure performance of sprayers at grounds speeds up to 17 and 20 miles per hour and under a wider range of crop and spraying conditions."

While improved sprayer technology has helped reduce spray drift dramatically in recent years, Storozynsky wonders if more gains can be made. With the recent introduction of venturi nozzles, spray drift has been reduced to about three percent. That’s down from about 7.5 percent in the mid-’90s and as much as 15 percent in the mid-’80s. (See Figure 1 , which illustrates spray drift trends over the past 25 years.)

Drift and efficacy questions
Minimizing drift is important from crop safety, legal liability and environmental aspects. "The more we can use sprayer technology to keep pesticides where they are intended, the better," says Storozynsky. "Low pressure venturi nozzles, for example, potentially produce more drift than high-pressure venturi nozzles, but adding shrouds on ground sprayers may make it possible to operate under higher wind conditions and still maintain low drift levels."

Herbicide efficacy is another key aspect of sprayer technology research. Along with in-crop treatments in cereals, Storozynsky plans to evaluate how equipment works in a wider range of field conditions.

"Our research to date shows most equipment worked equally well in applying a post emergent herbicide," says Storozynsky. "But my personal theory is the crop also played a role in controlling weeds. The herbicide was effective, but the crop provided competition, which further helped control weeds that were partially stunted by the herbicide. So the question is, how well does the sprayer technology work under different conditions."

Future issues
While time and money are always limiting factors, Storozynsky says there is a growing list of research needed to answer sprayer technology questions. Future projects will:

• Evaluate equipment performance and herbicide efficacy for different applications ranging from a pre-seeding burn-off to pre-harvest treatments.
• Evaluate herbicide efficacy with new sprayer technologies and ultra low water rates.
• Evaluate sprayer equipment and herbicide efficacy at faster ground speeds, up to 20 miles per hour, to better reflect on-farm application.
• Evaluate nozzle location and orientation on the spray boom. Is there improved coverage and herbicide efficacy if nozzles are angle-mounted to spray forward and/or backward into the crop canopy?
• Evaluate the effect of water quality. For example, does pure or mineral-free water affect the efficacy of herbicides?