Simulated Mechanical Control of Nitellopsis obtusa Under Mesocosm Conditions

Management efforts to control Nitellopsis obtusa (starry stonewort) have been limited to stressing the thalli and have not been able to directly target the reproductive bulbils. Smaller scale efforts such as the use of hand pulling can be used but hand pulling is not realistic for larger infestations. This research was conducted to test the effects of clipping stress on N. obtusa in order to give a baseline on the effect of stress on the production of bulbils and the regrowth of thalli. Mesocosms were set up under greenhouse conditions to test the effects of simulated mechanical harvesting once, twice, and four times per growing season on N. obtusa. Different seasonal timing and frequency of clipping treatments will remove different amounts of thalli biomass. The four-clipping treatment always reduced thalli biomass in this study at both 16 and 52 WAT compared to the nontreated reference, but the difference among clipping treatments was never different 52 WAT. At 16 WAT one clipping reduced bulbil density by 44% (trial 1) to 50% (trial two), two clippings reduced bulbil density by 28% (trial 2) to 52% (trial 1), and four clippings reduced bulbil density by 22% (trial 2) to 88% (trial one). At 52 WAT bulbil densities were 69% and 93% lower than that of the nontreated reference trials 2 and 1 respectively. Results from this study indicate that clipping may be effective on N. obtusa and could impact bulbil production.