The pilot planned an aerial application flight and filled the airplane with fuel and grass seed. He reported that as he started a crosswind takeoff, he applied full rudder and aileron. As the airplane gained speed, it encountered turbulence from nearby buildings, and veered left. The pilot was unable to straighten the turn before the airplane exited the runway surface. Prior to coming to a stop, the airplane collided with a runway approach light and the left wing impacted the ground. An examination of the airplane revealed substantial damage to the left wing’s spar.