There's one difference...right now I'm flying a turbine Dromader, not an air tractor.
When coming across the gate, you're physically removing the low pitch stops. At low power settings, the prop is windmilling, and has experienced an airflow change on the propeller disc. In the helicopter world it's called an airflow reversal, where airflow is striking the blade back rather than the face, and the slipstream is imparting more energy to the propeller than the engine.
In such a case, especially at higher airspeeds, you may experience a prop overspeed. Someone had mentioned using beta or reverse during a descent. I can't imagine why someone would do that in an ag airplane (how far have you got to descend), but I do a lot of fire work where we do have extended descents, and steep ones. I have known people in single engine airplanes to apply reverse on the descents, or attempt to use BETA, and not only is it pointless, but dangerous and represents a lack of understanding of how the system works.
Outside the normal governing range for the propeller, such as beta and reverse, governing takes place by fuel topping using an air bleed orfice in the propeller governor. This airbleed orfice reduces control bleed air to the fuel controller, or allows it to increase by restricting the orfice.
When your engine is trimmed for reverse capability on the ground, it doesn't take into account airflow through the propeller, driving the propeller. The fuel limiting function of the governor slows the propeller by slowing engine speed, and assumes that you're traveling at landing speed or less, decelerating.
If you're flying through the air, you can experience a propeller runaway. If your prop speed runs away while out of the governing range, your governor is trying to take fuel away, but it's not fuel driving the prop, it's airflow, and the only thing protecting it has been removed; the low pitch stops (when you came over the gate into ground range).
Yes, your drag can increase exponentially and yes, it can form an effective "airbrake" (because it's absorbing so much energy from the airflow that's driving it)...but folks have found out the hard way that it may not come back out, and the aircraft may be less controllable (--or uncontrollable) as the overspeed worsens.
As the overspeed worsens, it also affects airflow over the tail, which includes both the vertical and horizontal stabilizers. This means less rudder authority, but it also means less elevator and horizontal stab download authority. As most conventionally loaded aircraft, ag or not, utililize a download on the horizontal stab for stability, this download is interrupted, and the result can be a loss of pitch control. As the downloading effect is interrupted by the lack of airflow, the nose can pitch down, and there may very well be insufficient time to recover.
That's not conjecture, it's happened.
What does your engine manufacturer, airframe manufacturer, and propeller manufacturer say about using reverse and ground range in flight? Ever wonder why?
As for needing to go around in ground idle vs. flight idle...planning ahead for that event and keeping the engine partially spooled up to begin with is proper technique in any turbine powered airplane. It responds better when slightly spooled. If you're at idle and having to bring in power quickly to go around, count on a lag regardless of weather you are flying in ground idle or flight idle.
Someone else asked me if the owner of this aircraft (which isn't me) knows I fly the engine the way I do. Yes, he does, and he flies it the same way. So does his father, who has flown more ag than I probably ever will, and who like us, is also a mechanic.
Use it where you need it, but even in daily operations in extreme mountainous terrain, I haven't found a need to come out of ground idle yet.