2008 Statewide Strategic Plan for Eurasian Watermilfoil in Idaho

Diver dredging can be highly effective under
appropriate conditions. Removal efficiency
depends on sediment condition, density of
aquatic plants, and underwater visibility. This
technique works well to control early, low-level
infestations of Eurasian watermilfoil. It can also
be used as a maintenance tool following
herbicide treatments.
This control method is site and speciesspecific.
Plant parts are collected for later
Figure 15. Diver dredging
disposal, minimizing the spread of fragments, which is important in the control of
Eurasian watermilfoil. Diver dredging can cover a much larger area than is
practical for hand-pulling and it can be effective in soft sediments. It can also be
easily operated around obstacles.
Diver dredging is labor intensive and very costly. Turbidity caused by the machine
can create poor visibility, slowing the process. Some sediment and nontarget
vegetation may inadvertently be removed during the process. Some fragments
may be expected if dredged slurry is directly returned to the lake.
Sites suitable for diver dredging include water bodies lightly to moderately infested
with Eurasian watermilfoil and for follow-up Eurasian watermilfoil removal after a
herbicide treatment. Diver hand-pulling is more effective in lightly scattered
patches of Eurasian watermilfoil, whereas diver dredging may be more
appropriate in denser milfoil beds. Diver dredging may also be applicable in water
bodies where herbicide use may not be appropriate. Theoretically diver dredging
could be used in any water body to eradicate Eurasian watermilfoil; however the
costs for large scale projects would be astronomical.
3. Hand-cutting
This is also a manual method but does not involve hand-pulling the roots. The
plants are cut or torn using tools that can be pulled through the weed beds
manually or by boat. This work can be done using hand held cutting tools, some of
which may be powered. Items such as rakes, chains, logs, railroad ties are
dragged across the bottom to collect plants. Collected plants are disposed of on
shore. Because roots are not removed, this is a less intensive removal technique.
Mechanized weed cutters are also available that can be operated from the surface
for small-scale control (similar to an underwater lawnmower). Mechanized weed
rollers, which flatten and wear down weeds by frequent agitation, are also
available for consideration.
Root systems and lower stems are left intact with the hand-cutting technique. As a
result, effectiveness is usually short-term as rapid regrowth is possible from the
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