per square meter lifted less than 20 cm.
After 35 days, plant decomposition
beneath the panels
complete. Perkins concluded that Dartek was
effective."
and Trvelson (1984) report that Dartek, on the
average, was effective for 2 years.
Polypropylene
Polypropylene is a spun-bonded, woven, semipermeable sheeting with
itive buoyancy.
It is sold under various trade names, such as Typar (DuPont)
and Terratrack (Terratrack Ltd.,
Ontario).
(1982) reports that
-1
Typar (1984 price) costs about ,000 ha
plus installation. Terratrack
-1
(Lewis, Wile, and Painter 1983) costs about ,254 ha
Cooke and Gorman (1980) found
Typar, anchored with cement blocks,
was completely effective in eliminating rooted plant biomass in the treatment
area for one season.
No evaluation in subsequent seasons was made.
algae grew profusely on the surface of the Typar in shallow water.
(1984) also found that Typar completely controlled vegetation during the first
Removal and repositioning were difficult, and plants regrew on Typar
year.
after sediments accumulated on the panels.
contrast, Terratrack, anchored
with concrete blocks, did not allow Eurasian watermilfoil to reroot on it over
summers, even though fragments were found (Lewis, Boston, and Curren
1983).
and Trvelson (1984) report that the use of sand to anchor
Typar provided a substrate for rerooting of plants.
Other materials
The experiences with polyethylene sheeting have not been satisfactory,
largely because polyethylene is impermeable and buoyant (Armour, Brown, and
1979; Nichols 1974; Petersen, Born, and Dunst 1974;
1982;
and Nichols 1984).
Since polyethylene floats, it is very difficult to apply,
and the anchoring must: be very secure
that the sheets do not move under the
SO
influence of waves.
Sand has been used as an anchor, but plants grow on it.
Also, large slits must be cut to allow the escape of gases, the material
deteriorates in sunlight, and it will slip down steep inclines (Armour, Brown,
and
1979).
not very expensive, however.
Armour, Brown, and
-1
report a price of about ,600 ha
prices), plus
installation.
a synthetic rubber,
effective due to its strength and weight
It is also very costly.
but is impermeable.
In 1984, the inflation-corrected
(Armour, Brown, and
ice was ,270 ha
1979).
was also
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