Brad Edwards and I were looking in a field treated with Safari last July to look at scale control. Long story short, the Safari worked well. I'd estimate 99% control. But what really caught our attention was what was going on under the trees. There was an almost continuous carpet of purple deadnettle that was starting to bloom. And it was full of bees! Most had pollen sacs full of red pollen.
This field was at just under 3,000 feet in elevation and southern exposure. The high was only 51 oF in Jefferson today. They say bees don't get out and start working until it's 55 oF. Obviously the bees don't read too well.
In any case, if you need to apply an insecticide, it's important to look and see if bees are in your trees. Pick a warm day at mid-day and look for bees. If you can spray at night, you should be OK. But if you have to spray in the day, clean up the field of flowers by using Roundup at suppression rates a week or so before treatment. Know if you have bee hives close by, and if you do, tell the bee keeper what you plan on doing. They may want to shut up the hive while you are spraying so the bees aren't exposed.
For more information about how to protect bees in trees see: FRASER FIR PEST CONTROL PORTAL: Tips for Keeping Bees Safe.