During the course of an eight year monitoring effort, the
Wisconsin Department of Natural Resources documented a
significant decline in milfoil biomass and distribution in Fish
Lake, Wisconsin. Average milfoil biomass declined by 40-
50% from 374-524 g dw m
-2
during 1991-93 to 265 g dw m
-2
during both 1994 and 1995. Milfoil recovered fully in 1996-
98 to 446- 564 g dw m
-2
. The size of the milfoil bed, as discerned
from aerial photographs, shrank from a maximum
coverage of 40 ha in 1991 to less than 20 ha during 1995.
During the “crash” of 1994-95, milfoil plants exhibited typical
signs of weevil-induced damage, including darkened, brittle,
hollowed-out growing tips, and the arching and collapse
of stems associated with loss of buoyancy. Monitoring of weevils
and stem damage during 1995-98 showed highest densities
and heaviest damage occurred near shore and subsequently
fanned out into deeper water from core infestation
sites each spring. The extent of milfoil stem damage was positively
correlated with weevil densities (monthly sampling).
However, weevil densities and stem damage were lower during
1995 (when milfoil biomass was in decline) than during
1996-98 (when milfoil biomass was fully recovered)