Mo. Rev. Stat. § 226.585
The state transportation department may cut and trim any vegetation on the highway right-of-way which interferes with the effectiveness of or obscures a lawfully erected billboard, or the highways and transportation commission shall promulgate reasonable rules and regulations to permit the cutting and trimming of such vegetation on the highway or right-of-way by the owner of such billboard. The right to a vegetation permit by an outdoor advertising permit holder shall be issued in accordance with the current rules and regulations promulgated by the highways and transportation commission and shall not be denied without good cause. Such rules and regulations shall be promulgated within twelve months after August 28, 1992, or the commission shall suspend the collection of the biennial inspection fees prescribed by section 226.550 until such rules are promulgated, and such rules may include authority to charge a reasonable fee for such permit. This section shall not apply if its implementation would have the effect of making Missouri be in noncompliance with requirements of Title 23, United States Code, Section 131.
§ 226.585, RSMo