Balancing Fisheries Management and Water Uses for Impounded River Systems

The Use of Herbicides for Managing Aquatic Vegetation in Southern Reservoirs

Michael D. Netherland

doi: https://doi.org/10.47886/9781934874066.ch32

Abstract.—Herbicide use to control aquatic vegetation in southern reservoirs can elicit a wide range of responses and concerns from the fishing community, lake property owners, and the general public. Debates regarding the need to control aquatic plants, how much vegetation to control and where, and the herbicides chosen can be divisive. This paper will focus on the use patterns and technical features of aquatic herbicides and factors that should be considered when implementing a herbicide program for aquatic plant management in reservoirs. Both the angling community and general public often have misconceptions regarding herbicide use patterns, plant selectivity and nontarget impacts, and management objectives. There are currently 10 herbicide active ingredients registered for aquatic use. Glyphosate and imazapyr are used strictly for emergent aquatic plant control while copper, endothall, and fluridone are used almost exclusively for submersed plant control. The herbicides diquat, carfentrazone, penoxsulam, triclopyr, and 2,4-D are used for both emergent and submersed plant control. Many of the registered herbicides have been used since the 1950s and 1960s for aquatic plant management. Each compound has unique properties that impact the recommended use rates and use patterns, label restrictions, and plant selectivity. There are also several new herbicides that are currently being evaluated for aquatic plants. While herbicides are used in a wide variety of aquatic systems, reservoirs often present unique challenges due to high-flow events and vegetation growing in narrow strips along the shoreline or in open flats. Rapid dilution or dispersion of the herbicide from the target area remains a significant technical challenge in reservoirs. The introduction of invasive plants such as hydrilla Hydrilla verticillata and Eurasian watermilfoil Myriophyllum spicatum has increased the complexity of management decisions. These fast-growing submersed species can be viewed as both beneficial and detrimental to various reservoir systems. While some see these plants as invasive species that require management, others see them as providing valuable habitat in systems with limited native vegetation. Despite both social and environmental challenges, aquatic herbicides continue to provide reliable, relatively rapid results and site-specific aquatic plant management at a wide variety of scales.