A tiny infestation of an introduced plant (Spartina patens) has resisted extermination for 16 years in Washington State. Mature plants occupied about 654 m2 of ground when control work began in 1991; at present they occupy less than one square meter. The history of the control effort, described here, shows that field workers succeeded at discovering about half of the plants actually present during most years and suggests that a new detection technique—searches by trained dogs—may greatly improve this discovery rate. Spartina patens was probably introduced to Washington during the 1920s. The numbers of plants peaked in 1995, then declined and recovered twice before they began a steep decline after 2005. Ground cover by mature S. patens was drastically reduced by the initial control work, and then expanded twice after 1995 due to growth of undiscovered and neglected patches. The control effort was rendered less effective by two tacit assumptions: (1) the whole extent of the small infestation was known, and (2) the treatments were successfully eliminating the plants. The campaign benefited from the cooperative support of private landowners, the existence of a state Spartina Coordinator's office (focused on other invasive Spartina species as well as S. patens), the persistence and dedication of control workers, the continued attention of this researcher, and recent intensified vigilance prompted by evidence of the plant's resistance to eradication. Indications are that S. patens is now succumbing to this intensified attention.

Environmental Practice 9:251–265 (2007)