If from a check of the petition together with the facts and evidence which are adduced at the hearing, it is established that the petition to terminate is signed by the required 40 percent of the producers of the commodity in the zone that produced at least 40 percent of the proration commodity affected which was produced within the zone during the last preceding season, the director shall terminate the marketing program. Any marketing program on a seasonal commodity shall not, however, be terminated except at the end of its marketing season.