LIMNOLOGY 623
infauna, and non-target plants may also be inadvertently
removed during this process.
A new mechanical method of controlling aquatic plant
growth is weed rolling. The method uses a commercially
available, low-voltage power unit that drives an up-to-25-foot
long roller set on the lake bottom through an adjustable arc of
up-to 270. A vertical drive head mounts to a dock. A reversing
action built into the drive automatically brings the roller back
to complete the cycle. The 25 feet of roller includes flexi-
ble couplers to follow the contour of the lake bottom. The
device operates on the principle of the “well-worn path.”
Whole plants or plant stems and leaves can be removed.
Fins on the rollers detach some plants from the soil, while
the rollers force other plants flat, gradually inhibiting growth.
Detached plants and plant fragments need to be removed from
the water with a rake or net.
Once plants are cleared from the area, the weed rolling
device can be used weekly or less often to prevent regrowth.
The device requires little maintenance, lasts for at least five
years, and can be moved from dock to dock which allows
sharing by a lake association.
A weed rolling device was tested on three lakes in King
County, Washington, during the summer of 1995 and was
found to be easy to operate and effective in reducing the den-
sity of both milfoil and water lilies. Weed rolling has also
been effective in removing unwanted aquatic plants from
many Midwestern lakes.
Advantages of weed rolling are that it creates and main-
tains areas of open water adjacent to docks, installation is
simple, operating costs are low (similar to the costs of using
a 75 watt lightbulb), and the treatment area can be modi-
fied by varying the number of roller tube sections used and
adjusting the roller tube travel arc.
There are several disadvantages. Although it is easy to
operate a weed rolling device, collection of the resulting
plant fragments is labor-intensive. If the plant fragments are
not collected, invasive plants may be spread from one area of
the lake to the other. Weed rolling may disturb some bottom-
dwelling animals and may interfere with fish spawning.
There are also some safety considerations. People cannot
be allowed in the water near where the weed rolling device
is operating. After each use, the rollers must be unplugged
from the power source, moved, and stored under or along-
side a dock.Chemical Methods Chemical control of aquatic plants
in lakes is accomplished through the use of aquatic herbi-
cides. Systemic herbicides are absorbed by and translocated
throughout the entire plant, and kill the entire plant. Contact
herbicides kill the parts of the plant with which they come in
contact, leaving roots alive and capable of regrowth. To be
most effective, herbicides must be applied to plants during
the period when they are growing most rapidly. Because of
environmental risks from improper application, aquatic her-
bicide use is regulated. Some expertise in using herbicides
is necessary in order to be successful and avoid unwanted
impacts. Generally, applicators must be licensed by and
obtain permits from a local, state or federal agency. A certainpercentage of all aquatic plants in each lake must usually
remain untreated in order to provide food and habitat for fish
and wildlife.
Some aquatic herbicides that are registered with the U.S.
Environmental Protection Agency include glyphosate, fluri-
done, endothall, and copper compounds. Glyphosate (com-
mercial name Rodeo) is a non-selective, broad-spectrum
herbicide used to control floating-leafed plants like water
lilies and emergent plants like purple loosestrife and cat-
tails. It is generally sprayed or painted in liquid form on plant
leaves. Symptoms of herbicidal activity are apparent after
seven days and include wilting and yellowing of plants, fol-
lowed by complete browning and death. Since glyphosate is
a systemic herbicide, it is effective in long-term plant control.
It dissipates quickly from natural waters, is low in toxicity to
benthic infauna, fish, birds, and mammals, and does not
prohibit use of a lake for swimming, fishing, and irrigation
while treatment of plants is underway. The major draw-
back of glyphosate is that it can affect non-target plant
species. Careful application to prevent drift will minimize
this possibility.
Fluridone (commercial name Sonar) is a slow-acting
systemic herbicide used to control Eurasian watermilfoil and
other submersed plants. Applied to the lake water as either
a liquid or pellet, this chemical begins to show effects 7–10
days after application, with full control of target plants often
requiring 6–12 weeks. Fluridone acts by damaging plant
chlorophyll and preventing photo-synthesis; hence dying
plants exhibit retarded growth and bleached out leaves before
falling to the lake sediments and decomposing. The best time
for fluridone application is early in the growing season for
the target plant, usually spring or early summer, because of
the amount of time required for full plant control.
As is the case with glyphosate, long-term plant control
can be achieved with the use of fluridone. Fluridone has a
very low order of toxicity of aquatic animals and humans.
Disadvantages of its use are that it is very slow-acting and
therefore not effective in flowing water. Fluridone can drift
out of the treatment zone, thereby affecting non-target plants.
Consequently, it is most suitable for whole-lake treatments,
not for treating a defined area within a large, open lake. As the
affected plants decay, they may consume dissolved oxygen
from and release nutrients to the water column. Furthermore,
fluridone-treated water may result in injury to irrigated veg-
etation. Therefore, use of lake water for irrigation is delayed
following treatment. To protect drinking water sources, flu-
ridone should not be applied within 1/4 mile of a lake water
intake.
Endothall (commercial name Aquathol) is a fast-acting
contact herbicide which is applied in either a granular or
liquid form and destroys the plant stems and leaves but does
not kill the roots. It is used for short-term control of aquatic
plants, i.e., a few weeks to a few months, with no carryover
to the next growth season. Advantages of endothall are that
plant death occurs in one to two weeks and there is little or
no drift impact from proper application of this chemical. On
the other hand, non-target plant impacts are possible because
many aquatic plants are susceptible to endothall. FollowingC012_002_r03.indd 623C012_002_r03.indd 623 11/18/2005 10:36:48 AM11/18/2005 10:36:48 AM