THE PLT STATED THAT THE FLT DEPARTED WITH ABOUT 7 GALS OF FUEL. AFTER COMPLETING THREE SPRAY PASSES AND WHILE PULLING UP TO RETURN TO LAND, THE ENG LOST POWER AT ABOUT 150 FT AGL. DURING THE FORCED LANDING IN THE FIELD, THE WINGS & LANDING GEAR WERE DAMAGED. AN EXAM OF THE AIRPLANE REVEALED THAT THE ENG HAD LOST POWER DUE TO FUEL EXHAUSTION.