The following article was written for the spring issue of the DES publication The Sampler by DES limnologists Scott Ashley, Jody Connor and Amy Smagula. The Sampler and related publications are available online from the DES website, www.des.nh.gov.

Concord — May 5, 2009 — For the past two years, limnologists with the DES Biology Section, in cooperation with several individuals including divers and fabrication specialists, have developed a diver-assisted suction harvester device (milfoil machine or DAMM) to assist with managing exotic aquatic plant growth in New Hampshire’s waterbodies.

Exotic aquatic plant managers understand the importance of the integrated approach to provide long-term and more effective control of exotic plant infestations. A combination of scaled approaches is the proven method to manage exotic plants. The DAMM unit is one more tool available for the control of exotic plants in New Hampshire.

What It Is
The DAMM is essentially an aquatic vacuum cleaner used by divers to remove hand- pulled exotic plants and their roots from bottom sediments. This device is operated by specially licensed divers who hold Weed Control Diver certification through the Professional Association of Dive Instructors.

The suction harvester is best suited to physically manage small to moderately sized infestations. However, a suction harvester has been working in large infested areas of Smith Cove, Lake Winnipesaukee, for the past two summers and is making excellent progress at controlling the variable milfoil growth in the cove.

The unit is constructed on a floating platform, such as a pontoon boat, barge, or even a swim platform mounted on pontoons. The deck of the platform is modified by cutting a 2′ x 3′ rectangle in the floor. The floor hole is lined with a plant collection net that retains any plants and roots that are suctioned from the bottom sediments.

Mounted on the deck is a vortex pump to draw plants pulled by the diver. A special low-density, large-diameter hose connected to the pump extends into the water from the vessel is used by the divers to suction the bottom plants.

A certified diver works to systematically hand-remove the exotic plant by the roots and then feeds the plant and the roots up the hose. The plants, water and a small amount of sediment are discharged into the net-lined cut-out in the platform. The water filters through the net fabric while the plants remain in the net.

The deckhand sorts through the net contents to remove and set free any mussels or other aquatic life, then scoops the plants into a 20 gallon bucket or container to measure actual exotic plants and root volumes removed from the system. The material is then bagged for disposal in a landfill or compost site that is located a distance from a surface waterbody. During the summer of 2008, the DES-operated harvester pulled over 3,000 gallons of milfoil.

For maximum cost effectiveness, the DAMM is best used for small to moderately sized infestations. It is not a technique that can be cost effective when used in large areas of exotic aquatic plant infestation. The most cost effective method for large area infestations is the use of permitted herbicides by licensed applicators. Also, DAMM is not intended for use in controlling native aquatic plants.

How Many Units Are There?
DES currently has one serviceable unit and available parts to construct one other unit. Our limited staff time only allows the unit to be effectively used one to two days per week from June to October. DES is working with the Milfoil Legislative Working Committee to increase program funds to hire seasonal divers to work full-time operating the DES unit and to expand our suction harvester fleet.

There are also three or more privately owned units throughout New Hampshire and neighboring Maine. Each of the operators of these devices is certified through the New Hampshire Weed Control Diver program so that their techniques have been validated and approved by DES biologists.

These private contractors notify DES if they have been solicited to perform exotic plant control activities in New Hampshire waterbodies. They are required under their certification to provide a pre- and post-dive summary of their work so that DES can keep track of progress made in managing exotic aquatic plants throughout the state. The three companies are: Divemaster Service in Gilford; New England Environmental Diving in Plymouth; and New England Milfoil in Brownfield, Maine.

[Editor’s note: New England Milfoil, owned by Cliff Cabral, has used suction-harvesting for the past two seasons as part of the Danforth Pond milfoil control program.]

We plan to continue to modify and expand this program each year so that it becomes a standard component within our multi-tiered approach at controlling exotic aquatic plants. If you have questions regarding the DAMM or suction harvest removal of invasive aquatic plants please contact Amy Smagula at Amy.Smagula@des.nh.gov; Jody Connor at Jody.Connor@des.nh.gov; or Scott Ashley at Scott.Ashley@ des.nh.gov; or by phone at (603) 271-3503.