Circumstances for night ag ops:
1. Grubs/bugs are more active at night
2. Less wind, evaporation, turbulence at night meaning longer chemical coverage, better deposit and less drift.
3. Steady flying conditions
4. Better engine performance in the cooler air
Statitics:
Don't know, but it would be difficult to make an accurate comparison because the more experienced pilots fly at night (general statement).
Can it be done anywhere:
No. Reasonably flat ground is best. Power lines stand out like spider webs in the light and if there's room, the pilots go under them.
Do they need to:
It wouldn't be done if there wasn't a need.