Eurasian milfoil predominantly spreads through stem fragmentation. That is, if one plant gets cut into 10 pieces, those fragments will eventually grow 10 more plants. Spreading by germination is considered a minor concern. Milfoil can exist on a lake for 1 or 2 decades without becoming a major issue.
However, once milfoil spreads into high boat traffic areas it can spread extremely quickly. For example, a small powered boat travelling through an infestation can chop up the milfoil resulting in thousands of fragments leading to as many new plants. In one case, a milfoil infestation on a specific lake tripled in size and less than 3 years.
Milfoil grows down to about 25 feet deep (8 m), but is most dense down to about 12 feet (4m) deep. This is the littoral area of a lake where most of the vegetation grows and where many fish spawn. Milfoil can significantly dominate those areas creating dense mats of vegetation with up to 250 plants per yd2 (300/m2). It is common for it to cover 30% to 50% of that area and has covered over 80% of that area in some cases.
Treatment is only done down to only 8 to 12 feet deep. Any milfoil in deeper areas usually does not grow close to the surface and is therefore not at risk for creating fragmentation from boat traffic. Therefore, deeper depths do not require treatment.
It is typically cost prohibitive to eradicate milfoil from a given lake. However, it can be managed so that it remains a minor issue. The goal is to treat a lake from a holistic perspective and not just discrete infestations to eliminate the primary sources of fragmentation. The need is to remove the milfoil from all high traffic areas! This includes high traffic public areas like common passage ways and boat launches, as well as private dock and swimming areas.
The large public areas would be treated with the “LakeSaver”; an industrial barge system that will provide a large-scale cost-effective, environmentally safe solution. The private dock and swimming areas would be treated by owners with do-it-yourself (DIY) dock kits to suit their specific needs. Dock kits can also be used to create a path from a dock to the open un-infested waterway.
Figure 1 shows a typical lake with milfoil shown as the green shaded areas. Private docks are shown as small black rectangles. The approach to treat a lake like this would include the following (shown in brown in Figure 2).
On a regular basis a lake can be checked for those fragments floating in the lake. If all the high traffic areas have been properly treated the fragmentation in the lake should be minimal. However, if fragmentation persists, then the high traffic areas have not been effectively treated.
Some areas may only require the installation of marker buoys and good communication. The most cost-effective solution is marking off an infestation to keep boat traffic out of the area.
Figure-1: A typical lake with milfoil shown in green shading and cottage docks as black rectangles
Figure-2: A lake treated with burlap (in brown) to remove milfoil in high traffic areas