Hydrilla (Hydrilla verticillata) is one of the worst aquatic weeds in the world and continues to spread in the United States. Tuber surveys were conducted on three North Carolina lakes and one Indiana lake in 2007 to determine the effects of specific management techniques on monoecious hydrilla tuber numbers. Sampled lakes in North Carolina included Lake Gaston, Lake Tillery, and the Tar River Reservoir, while Lake Manitou, IN, was also surveyed. Tuber counts were conducted in spring and late fall using a four-inch core sampler. Sample points were selected based upon the presence of an established tuber population. GPS coordinates of sample points were marked to ensure that repeated sampling would occur within a limited area. Management practices applied during the summer months included endothall treatment on Lake Tillery, fluridone treatment on Lake Manitou, fluridone treatment or no management on Lake Gaston, and a combination of fluridone application and drought-induced summer drawdown on the Tar River Reservoir.

On Lake Gaston, nine different sites were monitored. Three sites are control with no scheduled public treatment (Cotton, Hamlin, and Lakeview), three were treated with fluridone in 2007 and will not be treated in 2008 (Cold Springs, Hawtree, and Poe), and three were treated in 2007 and are scheduled for treatment in 2008 (Hubquarter, Lyons, and Smith). Tuber samples were collected in May and November at 6 to 12 points within each site with 10 core samples collected per point. At year end, control sites ranged from a 30% decrease in tuber numbers to a 76% increase in tuber numbers. All sites treated in 2007 had a decrease in tuber numbers at least 55% and ranged as high as 90%.

On the Tar River Reservoir, tuber sampling was conducted four times in 2007. Tuber numbers were reduced by 66% during 2007 from a combination fluridone treatment and drought-induced drawdown. When this number is extrapolated over time, a 99.5% reduction in tubers will occur in year 5.