Lake Tillery Hydrilla Management Project

Introduction

Lake Tillery is a part of the Yadkin-Peedee River basin in North Carolina and flows between Montgomery and Stanly Counties. Lake Tillery has long since been a popular location for recreational activities such as fishing, swimming and boating. In 2006, the first reported sighting of hydrilla in Lake Tillery was documented near the Swift Island boat ramp. Shortly after the first sighting of hydrilla, herbicide treatments began. Since treatment began, there have been collaborations with the Aquatic Weed Control Program (AWCP), North Carolina Wildlife Resource Commission (WRC) and Duke Energy to combat the spread of Hydrilla.

Treatment Activities

Managing hydrilla can prove to be a difficult task as it is hearty and easily survives cold temperatures and drought. Hydrilla also reproduces quickly and easily through fragmentation. With these facts in mind, the approaches take to managing the hydrilla infestation at Lake Tillery included both herbicide applications and biocontrol via grass carp.

Herbicide applications come in two primary forms: quick and slow-release. Quick release herbicides typically come in liquid form and are then diluted and sprayed directly onto the target plant, and take effect within a few days to weeks. Slow-release herbicides typically come in pellet form, and are scooped into the water across the general location that hydrilla has been detected in. The slow-release herbicides continue to have an effect on the hydrilla for weeks to months by slowly dissolving in the water.

In larger lakes such as Lake Tillery, the Aquatic Weed Control Program will sometimes implement the use of grass carp as a long-term and more natural form of managing the infestation of hydrilla. These Grass Carp are bred specifically to be sterile triploid carp that are then delivered to the lake as juveniles in the Spring. Over the course of five to seven years, the carp will eat hydrilla and other vegetation which will lead the plant to be unable to reproduce or survive. After about five to seven years, these carp will die out leaving the other native fishes to resume their roles in the ecosystem because the Grass Carp are unable to reproduce.

Every season, to measure the efficacy of our treatment applications, submersed aquatic vegetation (SAV) surveys are conducted. The surveys collect data using sonar that detects the presence of SAV, and SAV sampling by raking the bottom of the lake at randomly selected predetermined locations to determine the species and density of SAV. The data collected is then converted into survey maps to visualize the severity of Hydrilla infestation. This data is used the following year to determine if any adjustments need to be made to the treatment activities.