No state agency, department or institution shall purchase any plant listed as invasive or potentially invasive pursuant to § 22a-381b, provided nothing in this section shall be construed to prohibit such purchase if such purchase is necessary to honor a state contract in effect as of the date any such plant is listed as invasive or potentially invasive pursuant to § 22a-381b. Nothing in this section shall be construed to prohibit any state agency, department or institution, or the agents of such agency, department or institution, from transporting any invasive or potentially invasive plant for educational, research or eradication purposes.