The U.S. Army Engineer Research and Development Center’s (ERDC) Aquatic Plant Management Team in the Environmental Laboratory is working alongside the U.S. Army Corps of Engineers (USACE) New England District to research and develop effective methods in managing the aquatic invasive plant species hydrilla (Hydrilla verticillata) in the Connecticut River.
Hydrilla was first detected in the Connecticut River in 2016, when the state of Connecticut discovered an unknown aquatic invasive plant species while performing aquatic plant surveys. Testing later confirmed the presence of hydrilla. At this time, other hydrilla populations existed in the United States but the physical appearance and genetics of the Connecticut River population didn’t quite match the other known populations. This particular plant population was considered “genetically distinct” and therefore, limited information was available to assist in the development of management techniques.
Over the past several years, hydrilla has aggressively spread throughout the Connecticut River system and into other lakes in the region, consuming lower tributaries, coves, and marinas. It causes significant ecological and economic harm by displacing native plants, altering critical fish and wildlife habitat, threatening endangered species, altering water quality, and impeding access and navigation.
Dr. Benjamin Sperry, lead principal investigator with ERDC’s Aquatic Plant Management Team, stated, “Hydrilla is a completely submersed aquatic plant that is very fast-growing. Since this is a new problem to Connecticut, the state had minimal hydrilla management experience, so we are here to not only conduct research on a novel invasive plant problem, but to also provide our expertise in providing guidance to our district, state, and local partners on operational aquatic plant management.”
In 2022, the Aquatic Plant Control Research Program initiated a research and demonstration project specifically on the Connecticut River hydrilla. ERDC’s Aquatic Plant Management Team proposed to simultaneously conduct small-scale background research on the biology of the plant while performing field work and developing control methods.
Sperry and his team are currently leading phenology studies to determine the lifecycle of the plant. “In order to better understand when we should implement management methods to get ahead of the population expanding, we have to understand how it grows,” Sperry said.
In addition, the team of experts is also administering dye studies using an inert fluorescent tracer dye to identify the most effective herbicide option for each infested site. After the dye is administered, it initially appears red in color, but later becomes invisible in the water. The dye allows the specialists to understand the retention time of an herbicide in an infested area, because it moves in water the same way an herbicide does.
“We use it as a surrogate to understand how the herbicide is going to move in the water. The dye is applied and then measured for a couple of weeks,” Sperry said.
Different herbicides have different exposure time requirements. The Connecticut River also presents unique herbicide use challenges because it is tidally influenced. Through the dye study, the team will match up the dye retention time to the aquatic herbicide concentration and exposure time requirements derived from the small-scale mesocosm research. They will then verify their findings next year in small plot field treatments. The goal is to figure out how long an herbicide must be in contact with the hydrilla plant to be effective, while concurrently being selective toward adjacent non-target native plants.
The entire project should require approximately five years, pending funding availability, as certain areas can only be tested during specific periods of the year based on the hydrilla’s growth cycle. Next year, the team plans to conduct herbicide treatments in the field that will be monitored for herbicide retention, hydrilla control, and native plant response.
The ultimate goal is to develop and provide verified management techniques to guide both hydrilla containment and control operations in the Connecticut River.
“We are determining which commercially available and federally registered management tools are optimal for mitigating a new invasive species problem in a dynamic system that has critical aquatic habitats and a high user base,” said Sperry.