Ind. Code § 15-16-6-15

Sec. 15. To raise money necessary to meet the expenses of horticultural and quarantine associations, the board of directors shall assess the individual members of the association in proportion to the service derived, procured, or obtained by the members from the association. The assessment must be based on the acreage or number of trees, plants, vines, or other herbaceous plants in equitable proportion as the directors consider just.