The US Federal Noxious Weeds list: Species included, the listing process, and outcomes for declared noxious species

Background/Question/Methods

Invasive plants and plant pests pose large threats to agriculture, ecosystems, and commerce. To address these risks, the Noxious Weeds Act of 1974 was passed by the US Congress to prohibit the movement of declared noxious weeds into and within the United States. Under this Act, weeds can be declared noxious by the Secretary of Agriculture. This requires public proposal, followed by a public comment period, and then the final listing.  In 2000 the Noxious Weeds Act was superseded by, and incorporated into, the Plant Protection Act (PPA). The process for listing new species remains essentially unchanged. The overall goal of the noxious weeds list is to identify species that are or may become pests in the United States, and to prevent their introduction and/or spread. We have examined the process for listing species, and the number and type of species listed, to determine whether the noxious weeds list is meeting its stated goals. Specifically, we considered the time lapse between proposals for listing and official listing date, whether species listed were included proactively or retroactively, and whether species became established after listing.

Results/Conclusions

The initial group of species (n=27) was added to the Noxious Weeds List on November 12, 1976. As of April 2011, the list contained 99 species with an additional 7 proposed but not yet approved. Over the life of the list, 4 species have been removed, and a number of nomenclatural issues have been resolved. The number of proposals and listings has declined in recent decades. Prior to 1990 a total of 98 species were proposed and listed. Since 1990 there have been 18 proposals, including the seven species currently pending. Of the species currently listed, 49 are established in the United States and 50 are not. Time between species proposal and listing has ranged from 107 days to 609 days, and is not significantly different for established and non-established species (p=0.35). We conclude that the intent of new listings has been roughly equally divided between the goals of preventing introduction of new species and preventing spread of those already established. The current length of the list (n=99) is much shorter than the full list of plants and plant pests that are either already established in the US and causing harm, or that pose a risk of future invasion.