Posted: June 30, 2006
Research targets practical nozzle information to help farmers make informed decisions.
The number of decisions farmers need to make regarding their spraying system is staggering. What nozzle, what sprayer type, can or should chemical rates or water rates be reduced, how fast to drive the sprayer, what is the target spray droplet size, is spray drift a concern, is spray coverage a concern? Those are the kinds of questions farmers are asking the AgTech Centre in Lethbridge, Alberta. They want answers regarding spraying technologies, reduced rates and spraying speeds.
Several new broadcast spraying technologies are on the market and they all have a common denominator: use of air. "Air can be used for atomization, as a carrier, or induced into spray droplets," says Brian Storozynsky, sprayer technology specialist at the AgTech Centre. "Many nozzle technologies are used together; currently, twin nozzles and spraying angles are the topic of many questions."
Manufacturers of new spraying technologies claim to improve spray droplet quality, penetration and deposition on its intended target. Over the past seven years, the AgTech Centre has tested sprayers and nozzles in several cereal, oilseed and special crops that included field peas, beans and potatoes.
"Producers really want to know the most effective nozzle that provides the best balance between coverage and reduced drift," says Storozynsky. "After many years of testing, some key findings will help applicators. Producers should not sweat the small differences in spray droplet size and deposition when selecting nozzles."
Sprayer and nozzle technologies are evaluated at the AgTech Centre based on the following three tests: spray drift, spray deposition and chemical efficacy. The Centre has built research sprayers equipped with several new spraying technologies. These sprayers are designed for scientific studies following standard for full size spraying equipment operating at field speed and nozzle sizes.
"Testing spray technologies in typical field conditions and operating speeds is key in AgTech research," says Storozynsky. "The detailed testing performed on nozzles uses specialized facilities such as a wind tunnel, spray table patternator and spray deposition track."
One project tested seven different types of nozzles used to apply a single application of a foliar fungicide on a bean crop in the summer of 2005. Two types of venturi nozzles, two types of twin nozzles, two air assist systems and an extended range nozzle were tested.
With just one application of the foliar fungicide, nozzles with better coverage and spray droplet size should have produced better results if, in fact, more coverage and appropriate droplet size always translate to better control. Although there was no significant difference in disease incidence among nozzle types, disease incidences tended to be lower in plots sprayed with air assisted flat fan nozzles, twin venturi nozzles and the high-pressure venturi nozzles. "This may suggest the air blast used to open the crop canopy and draw the spray in may be beneficial in applying foliar fungicides," says Storozynsky.
"Other field tests have shown similar results regarding spraying technology. Although some differences in weed control occurred among nozzle technologies, these differences were statistically insignificant."
Chemical rates were reduced to try and highlight differences among nozzle types. However, this is not a suggestion for growers to reduce chemical rates. Overall, wild oat control was reduced but weed control among nozzle technologies was not significantly different with one exception: high pressure venturis that produce very coarse droplets and fewest number of droplets per cm2 had less wild oat control than the other nozzles tested.
"This result indicates a limit exists on the size of spray droplets that can be used when applying herbicides and that an adequate coverage is required when using venturi nozzles," says Storozynsky.
Based on seven seasons with field scale studies, there were little to no effects of spraying technology on post-emergent spraying of cereal crops. Herbicide efficacy depended more on herbicide rate, weed growth stage, population and growing conditions rather than spraying technology. During extremely wet growing conditions or heavy weed populations, using recommended chemical rates, spraying at early stages and using higher nozzle pressures improved efficacy, especially for venturi-type nozzles.
Reprintable with credit. Available for reprint, with acknowledgement of Canada Sprayer Guide.
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