While the WSU-DAS system focuses on using pest and disease phenology to properly time pesticide sprays, it is critical that the properly-timed sprays are applied correctly. Without proper coverage, sprays will not serve their intended purpose, and growers may waste material, labor, and money, without getting the anticipated control.

One of the most important ways to make sure you are getting the proper control out of your sprays is to ensure your sprayer is calibrated and remains calibrated correctly throughout the season and to apply enough water to get good coverage.

Here are a few basic things to consider to ensure proper calibration:

• Operators should make sure all hoses, pressure gauges, pumps and agitators are working properly.
• The speed of the tractor should be measured using either a manual calculation or GPS application (speedometers on tractors are notoriously unreliable).  Speeds should generally not be significantly greater than 2.5 mph.
• Adjust the direction of the air into the canopies of the trees, and consider turning off any nozzles that are not pointed into the canopies. This will likely change if you have multiple canopy shapes present in the orchard.
• Make sure to match the air volume to the canopy density and adjust this throughout the season as canopy densities change.
• Calculate the expected nozzle output and record the actual nozzle output.
• Verify the coverage actually occurring in your orchard using water sensitive paper. Apply the paper both at the top and middle of the canopy as well as the outside of the canopy to ensure that you have the coverage throughout the tree!
• The volume needed for good coverage varies by tree height and canopy density; however, typical values would be 100-400 gpa depending on the tree size and sprayers. If you have gotten bad results for codling moth control using oils, make sure you are getting complete coverage and the gallonage should be at least 1-200 gpa for good control.

For more detailed information visit: http://treefruit.wsu.edu/web-article/six-steps-to-calibrate-and-optimize-airblast-sprayers/