Like any environmental issue, society must decide how much resources it will allocate to control invasive species. Because invasive species control efforts involve financial costs, and may also require changes to human behavior and trade, it is important that the projected benefits exceed the costs. Most U.S. states expend large amounts of resources to reduce the impacts of aquatic plant invasions, but these programs are rarely based on explicit cost-benefit analyses. Thus, the appropriate amount of financial investment in control activities is rarely calculated. The costs of aquatic invasive plant control are relatively simple to determine, and include the costs of surveying lakes and rivers, purchasing herbicides and equipment, and labor. In contrast, determining the benefits of controlling invasive species is difficult and rarely done. We have collected data from across the United States to determine the cost of aquatic invasive plant control in different regions of the country, the number and size of lakes that are invaded or that may become so, and the estimated benefits from controlling aquatic invasive plants.

Results/Conclusions

In southern states with long growing seasons, invaded lakes are treated on average once per year, with many of the most valuable recreation, navigation or irrigation lakes treated more often. In contrast, control efforts in lakes in temperate states that experience macrophyte die-offs are generally performed every 2+ years. The costs of aquatic invasive plant control also vary by state, with two northern states, Indiana and New Hampshire, spending $643.30±64.06(s.e.)/acre (n=58) and $625.21±100.77/acre (n=15) respectively. Florida ($315.13±10.64/acre; n=938) and South Carolina ($274.10±42.26/acre; n=42) have significantly lower costs per unit area treated, but higher overall costs per lake because the frequency of control is greater. We have used the known distribution of three invasive aquatic plant species (Myriophyllum spicatum, Hydrilla verticillata and Eichornia crassipes) to project cost of control in all currently invaded waterbodies of the U.S. We compare this to the value of those waterbodies for recreation, using surveys of lake-user expenditure, to determine whether extensive control activities are justified by public financial demand for uninvaded waterbodies. Our results show that, for the majority of states, it would be reasonable to actively control all lakes invaded by each of these species.