Hello 4ero,
I have done some crop spraying (not enough, I should say...lot of fun !) all on Alouette 2.
The technique I was taught in this time, was to avoid as much as possible these vertical torque turn, but rather to privilege torque flat turns....It can be done without stressing the airframe too much if you play with the torque when you reduce power for speed reduction and initiate a right turn, you have the feeling to turn around your boom tip.
For vertical turns, I wasn't reducing speed (50 Kts was the normal spraying speed) and at the top the climb, I was adding some more pitch to turn left, a bit as a fixed wing stall turn ( I also had the feeling to increase the coning angle, for clearance with the tail boom purpose)....It was becoming a bit tricky at heavy weights and/ or in gusty winds....sometimes earth was looking a bit close and the strengh of gravity a bit high.
But we had no school nor real training for that, only casual chats with other pilots.
It wasn't in (french)army or air force training program anyway.
But I assume that all helicopters and pilots have different techniques.....
I believe that a proper course exists in some countries where standard practices are set up.
.....If I could do a living wiith this type of flying, I wouldn't mind to give up my off-shore on almost fully automatic helicopters (here passengers don't find a stall turn as a funny thing
)