401 Webbs Mills Road, Raymond, Maine 04071 - Tel: 207-655-4742 Fax: 207-655-3024

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How Can Milfoil Be Controlled?
 

There are several methods of controlling milfoil, but they all have drawbacks. (When speaking of milfoil, we prefer to use the word "control" rather than "eradicate." If a new infestation is caught early enough, it may actually be possible to eliminate it quickly by pulling or killing the plants and checking the area every year for regrowth. But once a colony is firmly established, it is only possible to control with persistent removal, consistent surveying and re-growth harvesting.)

 

Please note: removal of milfoil requires a permit from the Maine DEP, and if you don't know the correct technique, you can make the infestation worse. Individuals should not attempt to remove milfoil on their own. See "what can I do" in the milfoil section.

 

Benthic Barriers ("tarping")

 

In shallow areas where nothing else is growing except milfoil, it is sometimes possible to put "tarps," or weighted sheets of opaque material, on the bottom to block the sunlight from reaching the plants. These sheets are left in place for 30 - 60 days, killing the plants underneath. While this method works, it's only practical in shallow water that is not going to be disturbed by boat traffic; it requires trained divers to place and remove the tarps; and it can't be used in areas where there are native waterplants, because the tarps kill everything indiscriminately. RWPA has used tarps successfully in the upper Jordan River.

 

Hand Pulling

 

In very shallow water (less than 3' deep) it is sometimes possible to pull up the individual milfoil plants. We have also used this method in the upper Jordan River. No one should attempt to pull milfoil unless they have had the proper training, because careless pulling can actually help the plants to spread. Since most of the milfoil in our area is in waters more than 3' deep, this method has limited use. In deeper water, divers can pull plants, bag them, and hand the bags to tenders in small boats; but this approach is very slow and tiring, so it's used only in very limited circumstances.

 

DASH Boat

 

DASH stands for Diver Assisted Suction Harvesting, but it would more properly be called "Suction Assisted Diver Harvesting." With this approach, divers pull the plants by hand, but instead of carrying each plant to the surface, one by one, they feed the plants into a suction hose, which takes the plants to a boat where they are filtered out and stored in bags or baskets for later disposal. This is currently the most popular and successful approach to milfoil removal, but it's labor-intensive and expensive to hire trained divers and operate the DASH boat. RWPA has one DASH boat, and hopes to outfit a second boat, if we can raise the necessary funds.

 

Chemical Treatment

 

The State of Maine has used it twice, and only in places where a dense stand of invasive plants can be isolated from the rest of the water body, and where the chemicals will have minimal impact on the environment. It would certainly not be appropriate for use in Sebago, which provides drinking water for 15% of Maine's population.

 

Dredging

 

Dredging of infested areas has been tried, but it is enormously disruptive of the lakebed environment and removes native and invasive plants indiscriminately; and some instances suggest that, rather than eliminating the milfoil, it actually promotes new growth. It disturbs layers of sediment which may contain chemicals inimical to lake health.

 

Biocontrols

There has reportedly been some success in developing an insect that kills the milfoil without damaging native plants. Unfortunately, this does not currently work with the species of milfoil that we have in Sebago Lake and surrounding lakes. It will require a great deal of effort, time, and caution; the history of introducing new species to control other species is fraught with examples of unintended disasters. But someday, many years from now - fingers crossed - this may be the best answer to the milfoil problem. (The following link has to be considered advertising, and we don't mean to imply any support for the company or the product in question; but the video may still be of interest for those concerned wtih milfoil control: http://friendsofdcl.org/2011/02/eurasian-watermilfoil-controls/ )

 

Mowing

 

In some states, where they've given up all hope of eradicating the milfoil, people have turned to mowing, which uses a mechanical harvester to cut the milfoil off several feet below the surface of the water. This can provide a path for boats to travel through the infested areas, but it creates fragments which ultimately spread the infestation farther.  The harvesting machines are very expensive - much more expensive than DASH boats. This approach is only suitable for areas that have thrown up their hands in despair of ever controlling the weed.

 


What is milfoil?

But we've had it forever?

How did it get here?

So, what's the problem?

Where is milfoil now?

How do we fix it?

What can I do?

Is milfoil the only problem?

What does the future hold?

 

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