Ken R. Wilson, P.Ag. Orchard Hotline Report for the Georgian Bay Area - 2010, July 30, 2010.
I got an education the other day. I had an opportunity to work with Dr. Jason Deveau, OMAFRA Application Technology Specialist. What I learned would scare you. The orchard air blast spray is about 10-15 percent efficient in applying pesticides to the target. The rest of the spray volume is lost to the environment, falling to the ground or evaporated by the sun. This makes a conventional air blast orchard sprayer a very inefficient tool. Since this machine is so inherently inefficient we need to do all we can to improve its performance.
I had forgotten that our trees have grown under ideal conditions and now have a thick and full leaf volume. That canopy is so thick that sprayer coverage is compromised.
We are not getting the coverage we think we are. Using water sensitive paper I witnessed appalling coverage on leaves that to the casual observer looking at the spraying you would have said got adequately sprayed. When the forward travel speed was reduced, the water volume increased and the nozzle arrangement changed to direct the spray to the denser parts of the tree the spray coverage was greatly improved.
I believe coverage to be the number one issue that we have with poor miticide performance this year. We are spraying the outside of the trees but leaving too many survivors in the interior of the trees to restart the population building immediately. As a result the miticides last 4 weeks instead of 6-8 weeks expected. The extra water volume we talk about to improve coverage is only half the story. Unless the tree is opened up and the sprayer slowed down there is no possibility that adequate pesticide will get into the tree and do the job you paid for.