2006-07-21
Author: 800 CHAB News
With the staggering number of decisions farmers make about their spraying operations, many questions arise. The sprayer research at the AgTech Centre in Lethbridge, Alberta focuses on finding answers to these questions. One of the most common questions posed to the Centre is "Which nozzle do I use?"

Several new broadcast spraying technologies are on the market and they all have a common denominator: use of air, says Brian Storozynsky, sprayer technology specialist at the AgTech Centre. "Air can be used for atomization, as a carrier, or induced into spray droplets. Many nozzle technologies are used together; currently, twin nozzles and spraying angles are the topic of many questions."

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 standards for commercial scale spraying equipment operating at field speeds and nozzle sizes.

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."

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.

Growers have also questioned water rates for many years considering some sprayers and aerial applications have been using less than 56 L/ha (5 gpa). Industry generally believes high water rates provide the proper coverage and penetration needed for most applications. "But farmers would like to use lower water rates for economic and practical reasons," says Storozynsky.

Several years of testing foliar fungicides on dry beans, herbicides on field peas and canola and also desiccants on potatoes with a range of water rates show no significant differences in chemical efficacy as the water rates changed. Only one year of a five-year study using a contact herbicide in a canola crop showed applying 5 gpa (56 L/ha) had less weed control than at 10 gpa (112 L/ha). "This may be attributed to moisture conditions and weed populations being abnormally high that spring," says Storozynsky. All nozzles used in these studies were operated at manufacturers recommendations.

Most spraying technologies performed similar at low and high water rates when appropriate nozzles were selected and used as recommended. Herbicide efficacy depended more on herbicide rate, weed growth stage, population and growing conditions rather than water rates. "The take-home message is to follow the manufacturer recommendations for the nozzle you are using," says Storozynsky.

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.

To learn more about this research at the AgTech Centre, see the articles on the Canada Sprayer Guide Web site at www.CanadaSprayerGuide.com. Canada Sprayer Guide is developed by Meristem Information Resources Ltd. in cooperation with industry partners interested in providing producers with high quality information.