Keep in mind that before planes/helicopters had gps guidance, they used mechanical flagMAN. Started in late '60s. Pilot shot a piece of cardboard from wing-mounted container that had paper similar to toilet paper at the end of a pass. He could make a visual on it while banking around and pick up his next pass.

Prior to that the flagMAN was just that....a man with a flag. He stood with a flag and marked the pass for the plane. Plane flew overhead & started dispensing. Normally flagman was encouraged to wear rain gear. I know that didn't happen when it was 95 degrees out. Did they get sprayed? What do you think?

I personally know 2 farmers that acted as human flagman. They both have passed away. Neither from cancer.

Did/do some people that handle pesticides deal with cancer? 
Did/do some people that spend 60 years as the local librarian deal with cancer? Of course.