Crop dusting is covered by
https://www.gpo.gov/fdsys/pkg/CFR-2...FR-2011-title14-vol3-part137.xml#seqnum137.51 FAA 137.51. The actual flight plans are "Canned" i.e. you write them once for a parcel of land and then just keep resubmitting it every time you fly that parcel also most application services have a "company flight manual" which covers all the procedures such as emergency landings, wire clearance etc etc.
Since most farms are covered by class G airspace the communication and control is pretty non-existent
Here are the class g rules
Class G airspace includes all airspace below FL600, not otherwise classified as controlled. There are no entry or clearance requirements for class G airspace, even for IFR operations. Class G airspace is typically the airspace very near the ground (1,200 feet or less), beneath class E airspace and between class B-D cylinders around towered airstrips.
Radio communication is not required in class G airspace, even for IFR operations. Class G is completely uncontrolled.
VFR visibility requirements in class G airspace are 1 mile (1.6 km) by day, and 3 miles (5 km) by night, for altitudes below 10,000 feet (3,050 m) MSL but above 1,200 ft AGL. Beginning at 10,000 feet MSL, 5 miles (8 km) of visibility are required, day and night. Cloud clearance requirements are to maintain an altitude that is 500 ft below, 1,000 ft above, 2,000 ft horizontal; at or above 10,000 ft MSL, they are 1,000 ft below, 1,000 ft above, and 1 mile laterally. By day at 1,200 feet (370 m) AGL and below, aircraft must remain clear of clouds, and there is no minimum lateral distance.
It should be noted that there are certain exceptions where class G extends above 1,200 feet AGL. This is usually either over mountainous terrain (e.g., some areas in the
Rockies), or over very sparsely populated areas (e.g., some parts of Montana and Alska).