Title: Efficacy of benthic barriers as a control measure for Eurasian watermilfoil
Abstract: The utilization of benthic barriers alone or in combination with other control methods could initiate the eradication of pioneer populations of Eurasian watermilfoil (Myriophyllum spicatum L.) and facilitate maintenance of acceptable population levels in waterbodies where the weed is widely established. We evaluated the effects of duration of geotextile fabric panel placement on small Eurasian watermilfoil population control and non-target plant abundance. In 2006 benthic barriers were placed over Eurasian watermilfoil infestations and removed at intervals of 4, 8, 10 and 12 weeks. The four week duration reduced Eurasian watermilfoil biomass 75%, and all other duration treatments reduced Eurasian watermilfoil biomass 100%. The 4 week treatment had no effect on native plant biomass while other treatments reduced native plant biomass by 79 to 93%. At the conclusion of the 12 week study, Eurasian watermilfoil biomass had increased in the 4 week treatment, but did not reestablish within treatment plots of longer duration. Native plant biomass had increased to 21% of the untreated control in the 8 week barrier treatment. Results suggest the eight week duration is sufficient for removal of Eurasian watermilfoil while allowing regrowth of native aquatic plants. A walk-in growth chamber experiment was established to evaluate the effect of sediment accumulation on benthic barrier. Eurasian watermilfoil fragments grown on sediment depths of 0 cm to3 cm did not differ for shoot or root biomass. At sediment depths of 4 and 5 cm, Eurasian watermilfoil root and shoot biomass increased when compared to the control suggesting benthic barrier maintenance should include sediment removal when sediment reaches a depth of 4 cm.