Invasive plant species, Eno River, to be treated this summer

Hydrilla threatens watershed, management task force continues to combat problem using herbicide

You’ve probably seen this plant before, and maybe you also realized it causes a headache for boaters, lake visitors, swimmers, and of course, native species.

Hydrilla, an invasive plant species, affects a large amount of water systems in North Carolina and the Eno River Watershed is no exception.

Hydrilla crowds out native vegetation, reduces water flow, restricts recreational activities such as fishing, swimming and boating, can harbor a toxic bacteria that kills waterfowl, bald eagles and other birds of prey, and it has a dense biomass, acting as a sort of barrier between the species above and below the hydrilla, therefore affecting the entire ecosystem.

On Wednesday, March 1, over 35 community members, NC State researchers, Eno River State Park employees, and more plant and aquatic life scholars joined together at the Cedar Grove Community Center to learn and inform people about the harms that hydrilla poses, the ongoing management process, and the steps being taken this summer to fight it off. 

The plant grows surprisingly quick – a scholarly article published about hydrilla, titled, “Does Hydrilla Grow An Inch Per Day?,” was referenced during a presentation by NC State Crop and Soil Sciences Research Specialist Steve Hoyle. The answer was simple, Hoyle said: “yes, yes it does.”

Hoyle spoke about the treatment options that have been weighed and the 2-year pilot-treatment study, concluding that after multiple treatment options were considered, herbicide was the only viable option.

Herbicide treatment will begin in May and end in September to coincide with the growing season, with routine monitoring of hydrilla as well as non-target species to help determine the optimal timing of the treatment.

The targeted area will begin upstream near Lawrence Road and drift downstream for 22 miles, and by the time it would reach US-501, it will have mostly disappeared.

Hydrilla origins, past management

Hydrilla is native to Asia and was brought to the United States for the aquarium trade, showing up in North Carolina waterways, specifically Wake County in the 1980s. 

This herbicide that will be used to manage the plant has been used previously to treat hydrilla in North Carolina in Lake Gaston, Waccamaw, Tillery, and more.

There is a large history of using this herbicide without negative effects, Hoyle said, and community members can be comforted by that.

The task force has been meeting officially since 2007, as hydrilla was first discovered in this area in 2005. 

A 2-year pilot study was conducted successfully, as hydrilla coverage in the treated area decreased significantly and there was no measurable direct impact to non-target species.

Given the success of the pilot study, the Eno River Hydrilla Management Task Force decided to extend the treatment upstream roughly 6 miles to just below Lake Ben Johnson this coming summer.

But, as Rome was not built in a day, that is the unfortunate reality of treating and managing hydrilla in the Eno: it is too late for prevention, there is only one solution to control and stop the spread, and it will take a significant amount of time for this process to show significant results.

Problem details, treatment options

The Eno River is unique, as it is a flowing water system.

This designation is positive on one hand, as the Eno houses a diverse ecosystem, but in terms of controlling and removing hydrilla, the moving water presents a unique challenge. 

Over seven types of treatment have been used to control and eradicate hydrilla in other water systems – including hand weeding, benthic barriers, suction dredge, grass carp, mechanical harvesting, host specific biocontrol, and drawdown – but herbicides appear to be the only option to control hydrilla in the Eno River watershed. 

Hydrilla grows back at practically the same rate as it is removed, pointing at why hand removal or slow spot treatment with herbicide, the two methods already attempted, failed. 

Many of these options, like mechanical harvesting and drawdowns, are destructive to the landscape and river bed, not sustainable long-term, and simply not an option for the climate, or the flowing water system of the Eno.

Especially the option for a benthic barrier, also known as a lake bottom blanket, would flow downstream and harm more than help, and another option, the host specific biocontrol, could not be considered as the specific species cannot flourish in the area’s climate, with North Carolina’s short summers. 

The task force, after many attempted methodologies and a lot of research, generally keeping herbicides as the last option, came to the conclusion that herbicides are the least destructive and the only option available. 

The herbicide is EPA and NCDA approved, water-soluble, and does not bioaccumulate, which is when the substance becomes concentrated inside the bodies of living things.

Addressing concerns

The main concern voiced at the meeting was regarding potential hazards the herbicide could cause.

But one can rest assured: herbicides do not affect water consumption.

It is still safe for adults, children, and pets to swim in the river during the treatment, since the herbicide is EPA-approved and does not bioaccumulate.

Treated water should not be used for irrigation because there is a potential to injure plants, as certain houseplants, vegetables, and crops are sensitive.

As the herbicide and the concentration targeted is well within the limits approved by the EPA, this concentration will be non-toxic to fish and wildlife.