Weeding through the water

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Contractors who specialize in aquatic weed control will be in demand for the foreseeable future due to the unrelenting march of invasive species in lakes, ponds and other bodies of water. Treating these requires a good deal of knowledge of aquatic systems ecology, the plants that inhabit them and the treatment options available.

“The problem is huge,” says Jason Broekstra, vice president of Great Lakes Operations for PLM Lake & Management Corp. “People really don’t understand that if management of invasive species did not take place in our lakes, we wouldn’t have lakes. We’d have swamps; we’d have property values that would be worth nothing.”

Broekstra says his organization takes pains to educate people on aquatic weed control so they will understand why treatment of water bodies is often necessary.

“One of the misconceptions is that people think by using herbicides to manage nuisance species in lakes, everything is going to die,” he says. “Therefore, you’re going to throw off the balance in the ecosystem by taking oxygen production out of the lake and have fish kills. And basically, that’s not true.

A boat anchored in the center of a treatment zone allows workers from PLM Lake & Management Corp., to move the injection line throughout the treatment zone.

“If you manage the invasive species selectively, you can promote native plant diversity, get it more to its natural state. We’re trying to find the sustainability within that ecosystem. By controlling invasive species, you’re actually promoting native plants.”

Understanding aquatic weed management

Aquatic weed management is a specialized area requiring a thorough knowledge of aquatic ecosystems, plant biology, plant life cycles and control methods. Aquatic weed control contractors like PLM Lake & Management Corp. employ biologists, environmental scientists and other professionals to treat specific invasive and nuisance weeds and algae.

“Management can be a lot of different things depending on the type of pond and what it is being used for,” says Rob Richardson, associate professor and Extension specialist at North Carolina State University and president of the Aquatic Plant Management Society.

Water weeds

Common aquatic invasive plants, according to the U.S. Dept. of Agriculture, National Invasive Species Information Center.

  • Alligatorweed
  • Caulerpa, Mediterranean clone
  • Common reed
  • Curly pondweed
  • Didymo
  • Eurasian watermilfoil
  • Giant reed
  • Giant salvinia
  • Melaleuca
  • Purple loosestrife
  • Water chestnut
  • Water hyacinth
  • Water lettuce
  • Water spinach

“The site may also dictate whether specific plants should be controlled or not,” he says. “Irrigation ponds generally need to be weed-free. In contrast, vegetation is desirable in water bodies managed for waterfowl. High-risk plants like state and federal noxious weeds should be controlled. Native, non-aggressive plants may not need to be controlled depending on the setting.”

There is a lot of information out there, such as that offered by the Aquatic Plant Management Society, for the contractor who wants to offer these services. It’s imperative, though, that they contact state and local environmental and licensing agencies to see what the protocol is for applying chemicals to a water body in a specific locale.

Survey the water body

The first task of an aquatic weed contractor is to survey the body of water that is to be treated. Broekstra says that every lake is different in terms of depth, concentration, flow and hydraulic retention time (the average length of time water remains in a storage unit, such as a lake or pond.)

“The first thing is to conduct a full survey of the lake and document the density of invasive species throughout, get an idea of how many acres of invasive plants you have,” Broekstra says. “Is it widespread or just pockets? We’ll determine what the client’s interest and financial abilities are, then we’ll look at a variety of herbicide options from auxin-based to 2-4D or contact ones.”

Identify the plant

Any plant regulated as a noxious weed that interferes with the form and function of the body of water should generally be controlled, Richardson says.

There are many avenues for identifying the species of plants that need to be controlled or eradicated. Contractors can talk to local and regional university extension agents, search the internet or identify it using the NCSU Aquatic Plants App. From there, they can choose which products to use.

“We work with vendors and they come up with a prescription for us based on environmental factors and the state we’re working in,” says Greg Blackham, aquatic specialist with SOLitude Lake Management, a company that services the mid-Atlantic states.

There are dozens of invasive species that keep people up at night. Some of the more common ones are Eurasian water milfoil, phragmites (mostly a shoreline species of common reed) and different species of hydrilla, which Blackham says is marching into the more northern states.

Apply herbicides

Aquatic control companies attack invasive species by land, sea and air. In most situations they can go out in a boat with a sprayer or boom and deploy the chemicals needed to control species. In other situations, like managing huge swaths of phragmites, companies deploy vehicles with tracks and may even attack it from the air.

“We had an ATV go airborne trying to get through phragmites,” Broekstra says. He says they resorted to using a land rover type of vehicle with tracks to get through it. He added that they have also sprayed from an airplane. In dense wetland areas, airboats are deployed by companies like SOLitude who work in these environments.

The company owns the airboats, which can cost between $10,000 and $20,000.

Richardson says there are about 14 herbicides registered with the EPA for aquatic application. Some companies are also using mechanical and biological control measures.

Mechanical control is removing the plant, root and all. An example of biological control is using beetles to control purple loosestrife and bacterial-based applications.

Herbicides can be applied in granular form and be distributed over an infested area like you might spread a product on a lawn. Companies can also insert a hose beneath the water and release the herbicide. Contact applications with sprayers is also used for many different species.

“Emergent plants are typically treated with foliar spray of liquid products,” says Mike Mumper, technical specialist for SePRO, a plant protection and management products developer.

Aquatic weed control can be performed using boats with a sprayer or a boom, or by vehicle or airplane.
“Submersed and floating plants can be treated with liquid and pellet or granular products.”

He says aquatic weed technicians use sprayers with mix tanks for liquids, backpack blowers for small granular treatments and boat-mounted spreaders or other equipment to disperse granules for larger treatments.

Aquatic specialists agree that the earlier the troublesome species comes to light and is treated, the better it is in terms of getting it under control with the least expense to the property owner.

“It is much easier to reduce or eliminate an early infestation,” Mumper says.

“Heavy infestations can produce copious amounts of propagules (in sediments), outcompete beneficial native species and spread to other waterbodies.”

He says mature plants are more difficult to control with herbicides, require more of them and can produce large amounts of decaying biomass that can deplete oxygen in the water, potentially putting fish in distress.

“In small ponds, most plants can be brought under control or possibly eradicated,” Richardson says. “It is more difficult to eradicate plants from large water bodies and on a regional basis.

Well-established weeds like Eurasian watermilfoil, hydrilla, water hyacinth, etc., are far past the point of regional, or greater, level of eradication.”

Managing invasive species isn’t a one-shot deal. Depending on the water body and level of infestation, aquatic weed control companies will monitor a pond or lake on a monthly basis, or at least two or three times a year.

“We’re making a lot of headway,” Broekstra says.

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