2008 Statewide Strategic Plan for Eurasian Watermilfoil in Idaho

3. Fluridone
Fluridone (Trade names include: Sonar® and Avast!®) is a slow-acting systemic
herbicide used to control Eurasian watermilfoil and other submersed plants. It may
be applied as a pellet or as a liquid. Fluridone can offer excellent control of
submersed plants where there is very little water movement and an extended time
for plants to absorb the herbicide is allowed. Its use is most applicable to wholelake
or isolated bay treatments where dilution is minimized.
Since fluridone interferes with a susceptible plant’s ability to synthesize chlorophyll,
symptoms of fluridone use are whitened leaves, retarded growth, and plant
mortality. Effects of fluridone treatment are noticeable 7-10 days after application
with control of target plants often taking 60-90 days to become evident. Because of
the delayed nature of control, the herbicide is best applied during the early growth
phase of the target plant, usually spring or early summer.
Lakes and ponds suitable for whole-lake fluridone treatments are heavily infested
with Eurasian watermilfoil throughout the littoral zone. Fluridone is not suitable for
spot treatments since it is difficult to maintain enough contact time between the
plant and the herbicide to kill the weed. Fluridone is available in slow and fast
release pellet formulations to adapt treatment application strategies to water flow,
depth, and control site parameters.
Up to 100 percent of the Eurasian watermilfoil in a lake can be killed. However, in
inlets or areas where the herbicide may be diluted by flowing water, Eurasian
watermilfoil may be under-treated and must be physically removed or treated with
a contact-type herbicide for control to be successful. These areas should be
identified during plan development and additional methods should be evaluated
and/or integrated into the management strategy as warranted. For example; while
Eurasian watermilfoil is under stress from a fluridone treatment, a contact-type
herbicide like 2, 4-D or triclopyr may be applied at a lower rate than is typically
required to provide additional control over large areas.
The littoral zone of the lake should be thoroughly inspected by divers in the fall of
the treatment year and the following spring to identify any Eurasian watermilfoil
plants that may have been under-treated. Susceptible areas include lake bottoms
with springs or near inlet streams. Any remaining Eurasian watermilfoil plants
should be hand pulled or covered with bottom barriers. Inspections must continue
at least twice a year during the growing season on an ongoing basis. Survey work
should be as frequent as can be afforded, since small Eurasian watermilfoil plants
may be easily overlooked.
4. Triclopyr
Triclopyr (Trade names include Renovate and Renovate OTF). There are two
formulations of triclopyr. Triclopyr, applied as a liquid, is a relatively fast-acting,
systemic, selective herbicide used for the control of Eurasian watermilfoil and other
broad-leaved species such as purple loosestrife. Triclopyr can be effective for spot
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