Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

156
TEN YEARS OF VARIABLE WATER MILFOIL CONTROL IN BASHAN LAKE. WHAT
HAVE WE LEARNED. G. Bugbee, Connecticut Agricultural Exp. Station, New Haven.
ABSTRACT
Variable water milfoil is an invasive aquatic plant that can restrict the recreational
use of lakes and eliminate desirable native aquatic plants. It is found in all northeastern
states except Vermont. Since 1994, the CT Agricultural Experiment Station (CAES) has
been monitoring the milfoil problem in Bashan Lake, East Haddam, CT, and testing
management options. The goal is to rid the lake of variable milfoil and allow native
plants to repopulate. The Connecticut Department of Environmental Protection
(CTDEP), the U.S. Department of Agriculture, the town of East Haddam and the Bashan
Lake Association have supplied CAES with grants to study the use of the herbicide 2,4-
D. This herbicide has the advantage of being a granular product suitable for spot
treating milfoil while not harming many native plants. In 2000, CAES procured a USEPA
experimental use permit (EUP) to test the use of the ester formulation of 2,4-D in
Bashan Lake. The EUP required notification of those irrigating with lake water to not use
the water until tests showed 2,4-D levels were below 100 ppb. The success of this
protocol contributed to the permanent change in the labeling for product containing 2,4-
D ester (Navigate and AquaKleen). From 2000-05 areas of Bashan Lake were treated
with 2,4-D (2,4-D ester). Late summer application of 2,4-D are likely as effective as the
traditional spring treatments and rates can be reduced to 75 – 100 lbs/A. Most treated
areas stay nearly milfoil free for at least 2 yr. Certain shallow areas with mucky bottoms
can show regrowth within 1 yr. Because these areas are often in coves that collect
floating plant fragments from untreated portions of the lake, more permanent control will
require eliminating all remaining milfoil. Regrowth is also possible from uncontrolled
roots or seeds. New GIS linked underwater video equipment is allowing more accurate
assessments of milfoil. In 2004, large areas not known to contain milfoil were
discovered with the video equipment in water 3 – 6 meters deep. This milfoil could be
the source of plant fragments. In Sept 2004 2,4-D was applied to a large deep-water
area of milfoil in the eastern portion of the lake and little regrowth was apparent the
following year. In Sept 2005, a similar treatment was performed in the northern portion.
Lake water has been tested for 2,4-D following treatments. Typically highest 2,4-D
concentrations occur near the bottom in the treatment areas and levels are above the
irrigation limit of 100 ppb for less than 3 wk. Yearly tests on nearby groundwater wells
have not detected 2,4-D.
------------
Greg Bugbee has been employed since 1979 in the Dept. of Soil and Water at the
CAES in New Haven. Currently an assistant scientist researching techniques for
managing nuisance aquatic vegetation with emphasis on targeted herbicides
applications. Research includes successful control of variable water milfoil with 2,4-D
and procurement of EUP to allow 2,4-D use in lakes when irrigation is restricted. PI in
CAES Invasive Aquatic Plant Program that is currently surveying aquatic vegetation in
CT lakes and ponds, correlating with water quality and making information available to
the public via web page (www.caes.state.ct.us/AquaticPlants).
138