If it is dead calm, a windblast orchard sprayer can create a uniform 50'-60' fog easily. But they need an air velocity in the nozzle impingement stream of 100+ mph so it's a job for a 50hp high-pressure fan - serious machinery.
Getting rid of pest populations in trees is a tricky business. A good first step (if you haven't done so already) is to get with your local Ag Extension Service to see whether they are already tracking the situation. In my area, the entymology dept at UMass is a great resource. Out your way, there's a NY state Experiment Station at Geneva I think. You might find out that the pest population has peaked and is about to crash by itself anyway (they do that). Sometimes the solution can be something like spraying a light oil so the eggs don't hatch - timing is important - the bug guys know what's possible, and when to do it. In most situations a lot of time and money can be saved and the unwanted side effects minimized.
If a spraying program is in order, I would recommend contacting a commercial applicator. In many states a license is required, even for private spraying. Following Fredex's idea above a little further, if you have any orchards in your area, talk to them about possibly doing your place with their rig. They will already know about callibration, tractor cab isolation, operator respirators and maybe even the right pesticides to use. Ideally they'll have a commercial applicator's license for the type of pesticide, and they'll be able to buy it in the concentration appropriate to their sprayer. They may have liability insurance too.
Like everything else in life these days, tree spraying has gotten much more complicated in recent years. Good luck, and be safe. Take care, Dick B
