congruence across US states. Likewise, agronomic dissimilarities, represented by the share of
irrigated land and field crops in a state’s arable land, bring about regulatory differences across
states. Together, ecological and agronomic characteristics account for two-thirds of the
explained variation in the size and composition of NXWS and NXW lists of US states.
Stakeholders’ interest in noxious weed regulations is modeled using their political
contributions. Consumers’ lobby impact on regulations reveals their interest in ecosystem
protection over the market-price effects embodied in such regulations. However, commodity
producers’ lobby impacts show a preference for the agronomic protection provided by these
regulations over market-price impacts. Our results identify an upward-sloping relationship
between regulatory congruence and seed producers’ lobby. That is, a stronger seed lobby leads
to greater regulatory congruence. This result can arise if seed producers’ perceive noxious weed
regulations as export barriers. Evidence of such perception can be found in the activities of the
Association of American Seed Control Officials, American Nursery and Landscape Association
and others, who recommend conformity of weed laws across states.
Nevertheless, the limited weed regulatory congruence across states should be a concern
to policymakers working toward a more integrated seed and horticultural product markets among
US states. Lobbies of states with significant seed production or national seed organizations
appear to support such integration, while some interest groups within the state (e.g., commodity
producers) are likely concerned about agronomic consequences. The challenge is to work
toward a more uniform definition of noxious weed regulations and greater overlap across states
without compromising concerns of commodity producers. The next question to address is
whether or not the limited regulatory overlap affects interstate trade flows in plant and plant
products.
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