(a) All assessments imposed under § 51.305(a) shall be paid in installments at the times fixed by the board.
(b) If a crop for which water was furnished by the district is harvested before the due date of any installment payment, the entire unpaid assessment becomes due at once and shall be paid within 10 days after the crop is harvested and before the crop is removed from the county or counties in which it was grown.