Sugar beets (Beta vulgaris) are a major crop in the Red River Valley of the North. Why do you think the beets have to be harvested and stockpiled in September?

Sugar beet harvest

Explanation:

Sugar beets have to be harvested and stockpiled in September because  they have to get the root out of the ground before the ground freezes

Sugar beets are harvested with two primary pieces of equipmentThe defoliator removes the green leaves and slices a slab from the top of the sugar beet rootThis removed slab is the growing point of the sugar beet and contains high levels of impurities, which impede the factories ability to extract the sugar from the remainder of the harvested rootThe sugar beet root is then harvested with a pinch wheel harvester, which pinches the root and lifts from the soilThe sugar beet harvester also separates some soil and conveys the sugar beet into a truck to be transported to a receiving station

Distillation.  distillation is the correct answer.