within 0.5 mile (0.8 km) of potable water intakes.
There is no waiting period
for water use after application.
Table 18 summarizes the effectiveness of commonly used herbicides
Westerdahl and Getsinger (1988) have developed
against some aquatic plants.
thorough guide to the types of aquatic plants that may appear in reservoirs
and have listed the herbicides that are effective against them.
Readers con-
templating a herbicide application should examine this report.
of herbicide treatments range widely.
Plant density, area to be
treated, types of plants, and other factors will influence cost greatly.
Table 12 (Part X) is a comparison of cost ranges for harvesting and
In the Midwest, cost ranges are clearly comparable (about
0 ha-l) for these two techniques and will be affected by some of the local
factors listed above.
In Florida (and other areas with dense, rapidly growing
populations of exotic plants such as waterhyacinth), herbicide treatments are
In some southern waters, harvesting
usually less costly than harvesting.
not keep up with plant growth and becomes a continuous operation, whereas
herbicide applications may be sufficient to manage the problem in one or a few
applications.
Limitations and Concerns
Brooker and Edwards (1985) point out that most discussions of the nega-
tive effects of algicides and herbicides deal only with direct toxic effects
to selected species.
Some of these effects have been briefly outlined in a
previous section.
While these reports provide some useful information, they
are not very informative about the effects of the addition of toxic materials
to reservoirs.
Reservoirs are complex units of interacting biological, chemi-
cal, and physical components called ecosystems.
The ecosystem is the actual
level of biological organization to which herbicides and algicides are
applied, not the species level.
There are very few studies about the effects
of thes e chemicals on reservoir or lake ecosystems.
Some of these studies are
briefly outlined here, based upon the list of concerns in Conyers and Cooke
(1982, 1983) and Cooke (1983).
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