This time of year Elodea is the most prominent species of weed in Devils Lake. Elodea is a particularly injurious aquatic perennial. In North America, it has compromised water quality, and in some waterways has grown so abundantly that boat traffic is hindered, dissolved oxygen is reduced, and native fisheries are severely impacted. Elodea is also insidious, in that only a plant fragment is needed to infest a water body because it reproduces asexually. So, what can you do to help solve this problem and how do you make sure your efforts do not make the problem worse?
DLWID Lake Treatments
The Devils Lake Water Improvement District (DLWID) began last season to actively attack the problem by treating areas of the shoreline where Parrot Feather, an extremely invasive plant, was growing. Their efforts had significantly reduced the spread of the plant. This year the District will attempt to tackle some of the plants that grow in the water column such as Vallisneria (Tape Grass) and Elodea (American Water Weed).
From currently available options, DLWID has determined that a systemic approach to herbicide application is the preferred method to prevent further spread of Elodea and Vallisneria in Devils Lake. Contact herbicides do not kill the root system of these perennial plants. Neither the District’s permit nor its budget will support lake wide herbicide application so for the time being these efforts should help curb growth but likely will not eradicate these weeds. Application areas this year will be focused where weeds grow in navigable parts of the lake and will not include areas around private docks.
Homeowners can take matters into their own hands and try to discourage weed growth in limited areas around their shoreline such as around boat moorings, and swim areas. Unfortunately, physical or mechanical control methods are ineffective for eradicating Elodea as this plant reproduces readily from small fragments. Any physical disturbance of the plant easily breaks the stems into pieces that are capable of reproducing in new locations. Any attempt at mechanical harvesting of Elodea should include a method of capturing the debris, such as nets, or floating vegetation control booms to prevent any fragments from escaping the work area. One simple approach is to attempt harvesting only when prevailing winds will carry clippings to your direct shoreline. All clippings should be removed from the lake and left on shore for a period of time to de-water. Only after the weeds have substantially dried, should the NLSS yard debris bin be used to dispose of the unwanted material.
Despite its limitations, mechanical harvesting, cutting and dredging have become widespread techniques to control outbreaks of Elodea. The most widely used instruments for mechanical aquatic weed management are weed-cutting boats, weed rakes usable from shore, or bucket-like shallow dredges. There are many aquatic rakes that might work for your situation such as the OWS Lake Rake, Jenlis Razer Rake and the Muck Razer Roller.
Unfortunately, Elodea appears to be quite resistant to cutting and plant survival is usually not impaired in the long term. On the contrary, cutting produces and spreads plant fragments with a high potential for regeneration and the residual plant tends to form more lateral branches in response to cutting. Furthermore, light availability increases in cut regions, which promotes faster re-growth. Biomass production can, however, be significantly reduced when harvests are performed at the time of the beginning of regeneration of Elodea plants after winter and can be further reduced to almost zero by a second harvest before the beginning of the fragmentation of Elodea plants in spring. Alternatively, the use of biodegradable jute matting or benthic barriers for covering Elodea has been investigated, but up to now only with effects on growth for one vegetation period; after this, the mattings are often damaged and ineffective.
There are new tools for managing submerged plants which use the very water that they grow in. This method can uproot submerged vegetation from soft sediments by using a powerful artificial water stream. Products in this category include the Aqua-Sweep, and the Aqua Thruster.
Mechanical harvesting is labor-intensive and involves problems such as uncontrolled dispersal of the harvested plant by the re-settling of ruptured plant fragments in other areas. It often represents the only applicable weed control method where other methods, such as the introduction of herbivorous fish (grass carp) and the use of herbicides, are forbidden.
The do-nothing option
It has often been observed that massive populations of invasive aquatic macrophytes have collapsed rapidly without any recognizable reason. There are numerous examples for the almost complete disappearance of Elodea from freshwater habitats. Sometimes Elodea is replaced by other aquatic macrophytes, sometimes it comes back some years later. The peculiarity of these population crashes is that they cannot be predicted. This unpredictability, however, demonstrates that the mechanisms underlying aquatic plant dynamics in freshwater ecosystems are not yet sufficiently understood. Whether and in which cases it is an option to do nothing and wait until a massive Elodea population disappears by itself depends on your specific situation.