Maintenance control as a framework for integrated pest management in natural systems: a case study with giant salvinia

Maintenance control is a strategy in aquatic plant management where invasive populations are maintained at low densities through frequent monitoring and targeted intervention. This is a promising solution for giant salvinia ( Salvinia molesta D.S. Mitchell) management in the southeastern United States, where single management tools are not effective. It also has potential to serve as a framework for integrated pest management approaches, which have been historically difficult to evaluate in natural systems. Field experiments were conducted at three sites in the southern United States using a factorial design that combined herbicide treatment thresholds (5%, 25%, 50%, 100% cover) and introduction of the biological control agent Cyrtobagous salviniae Calder & Sands. Plots were monitored monthly for 6 months over two growing seasons. Lower thresholds maintained lower seasonal mean cover (14.6 ± 3.7% and 13.7 ± 3.7% at 5% and 25% thresholds, compared to 27.6 ± 3.7% and 32.8 ± 3.7% at 50% and 100% thresholds). The lowest threshold required more frequent applications but did not increase cumulative herbicide volume. Addition of the weevil biocontrol agent reduced cover by 7% and decreased herbicide use by 37%, demonstrating that maintenance control can quantify biocontrol efficacy even when control is incomplete. With maintenance control, lower intervention thresholds maintained giant salvinia cover below roughly 15% without increasing herbicide inputs. These results not only support implementation of maintenance control for giant salvinia, but more broadly demonstrate how maintenance control provides a tractable framework for evaluating integrated strategies in systems where traditional thresholds are difficult to define.