Beginning on the 22nd day after the date of delivery, the merchant, unless otherwise agreed to in writing by the parties involved, shall be liable to the grower for interest on the unpaid balance of sums due. Unless otherwise agreed to by the parties involved, the interest is to be simple interest at the rate published by the Secretary of Revenue pursuant to section 806 of the act of April 9, 1929 (P.L. 343, No. 176), known as The Fiscal Code.
3 P.S. § 1404