In the state of Washington, the drive to picking fruit at night is driven by legislation, not temperature. Our migrant workforce from Mexico lives and thrives in much higher temperatures than anything we have in Eastern Washington, but our state legislature has decreed that there are special rules for picking above 89F, and thus, by the ironclad rule of unintended consequences, work stops at 89F and more harvest is now happening at night. -source is having worked in the apple industry and having many friends and relatives still in it.