At the hearing there must be competent proof that all parties interested in the premises or property have been duly served with said notice, and that the procedure prescribed in RCW 15.08.050, 15.08.060, 15.08.070, 15.08.080, 15.08.090, and 15.08.180 has been duly followed. The report of the inspection board shall be prima facie evidence that the premises are infested and constitute a nuisance. If there is no showing that said board acted in a capricious, arbitrary or unfair manner, the court shall accept the recommendation of said board and forthwith decree the plants, produce or property on the premises to constitute a nuisance and order the inspector-at-large of the district and the county commissioners to destroy the same, or abate the nuisance in such other manner as the court may direct.

The costs of destruction or abatement, and of the proceedings shall be taxed against the defendants therein.