All assessments shall be paid to the commission by the handler first handling avocados who shall be primarily and personally liable for the payment of the assessment. Failure of the handler to collect the assessment from any producer shall not exempt the handler from that primary liability. Any producer or handler subject to this section who fails to file a return or pay any assessment within the time required shall pay to the commission a penalty of 10 percent of the amount of the assessment determined to be due, and, in addition, 112-percent interest per month on the unpaid balance.