The objective of the study described here was to determine

the effect on variable-leaf watermilfoil of various combinations

of triclopyr concentrations and exposure times

using dosage rates that controlled Eurasian watermilfoil under

laboratory and field conditions (Netherland and

Getsinger 1992, Getsinger et al. 1997, Petty et al. 1998)

Getsinger, Kurt D.

Smagula, Amy

Sprecher, Susan L.

English

Aquatic Commons

 124
 
J. Aquat. Plant Manage.
 
 41: 2003.
 
J. Aquat. Plant Manage.
 
 41: 124-126
 
NOTES
Effects of Triclopyr on Variable-Leaf Watermilfoil
 
KURT D. GETSINGER
 
1
 
, SUSAN L. SPRECHER
 
2
 
, AND AMY P. SMAGULA
 
3
 
INTRODUCTION
 
In North America, the watermilfoil genus 
 
Myriophyllum
 
contains a number of native and exotic species able to pro-
duce dense monotypic stands with the potential to out-com-
pete and displace other submersed plants, degrade water
quality, and hinder recreational use of water bodies (New-
roth 1985; Nichols and Shaw 1986). One such species, the
perennial variable-leaf or two-leaf watermilfoil (
 
Myriophyllum
heterophyllum
 
 Michx.), is native from Canada west to South
Dakota and south to Florida (Godfrey and Wooten 1981).
However, it is not native in New England where it has be-
come locally abundant and has produced dense populations
that hinder boating, fishing, and swimming (Crow and
Hellquist 1983). In New Hampshire the species produces
vegetation management problems similar to those caused
elsewhere by the exotic weed Eurasian watermilfoil (
 
Myrio-
phyllum spicatum
 
 L.). Eurasian watermilfoil occurs in more al-
kaline waters of higher conductivity (Nichols and Buchan
1997) and is present in New Hampshire at a limited number
of sites. Since its initial discovery in New Hampshire in the
1960s, variable-leaf watermilfoil has spread to 38 bodies of
water. It adapts well to the relatively acid, low alkalinity and
conductivity, and nutrient-poor conditions in these lakes
(Kimball and Baker 1983, Hoyer et al. 1996).
Variable-leaf milfoil spreads primarily via clonal reproduc-
tion, seldom forming emergent heterophyllous flower-bearing
stems, and does not generate a significant seedbank (McFar-
land et al. 2003). Thus, in New Hampshire, variable-leaf water-
milfoil acts as a softwater analog to Eurasian watermilfoil, that
is, as an aggressive non-native species. While Eurasian water-
milfoil is effectively controlled by all the aquatic herbicides
registered for submersed species control, there is relatively lit-
tle information on effective rates of these compounds on oth-
er 
 
Myriophyllum
 
 species, such as variable-leaf watermilfoil.
The triethylamine salt of triclopyr (3,5,6-trichloro-2-pyridi-
nyloxyacetic acid), which was recently granted a Section 3 la-
bel by the U.S. Environmental Protection Agency for use in
aquatic (Renovate®
 
4
 
, SePRO Corporation, Carmel, IN) and
wetland sites (Garlon® 3A, Dow AgroSciences, Indianapolis,
IN), may be an option for control of variable-leaf watermil-
foil. The mode of action of this systemic herbicide, which is
absorbed by leaves and roots and then translocated through-
out the plant, is similar to auxin-like herbicides. It targets di-
cots and seldom affects monocots. Exposure to water
concentrations of 1.5 to 2.0 mg ae triclopyr L
 
-1
 
 are reported
to control the semi-emergent parrotfeather (
 
Myriophyllum
aquaticum
 
 (Vell.) Verdc.) (Anderson 1991, Anderson and La-
nini 1993a, Anderson and Lanini 1993b). While the use of
low concentrations with adequate exposure times on Eur-
asian watermilfoil has been shown to maintain certain native
dicots and allow their release from competition (Getsinger et
al. 1997). This selective activity has potential to be of value in
New Hampshire where native submersed monocots such as
pondweeds (
 
Potamogeton
 
 spp.) and horned pondweed (
 
Zan-
nichellia palustris
 
 L.)
 
 
 
need to be maintained, and where sensi-
tive native dicots, including alternate-flowered watermilfoil
(
 
Myriophyllum alterniflorum
 
 DC.) and Farwell’s watermilfoil
(
 
Myriophyllum farwellii
 
 Morong), may require protection
from competition via invasive species (New Hampshire Natu-
ral Heritage Inventory 1998).
The objective of the study described here was to deter-
mine the effect on variable-leaf watermilfoil of various com-
binations of triclopyr concentrations and exposure times
using dosage rates that controlled Eurasian watermilfoil un-
der laboratory and field conditions (Netherland and
Getsinger 1992, Getsinger et al. 1997, Petty et al. 1998).
 
MATERIALS AND METHODS
 
Variable-leaf watermilfoil plants were cultured and treated
in a controlled-environment growth chamber at the Army En-
gineer Research and Development Station (ERDC), Vicks-
burg, MS. Apical shoot segments of variable-leaf watermilfoil
were harvested from a shallow pond with low pH and alkalini-
ty in New Hampshire, and planted in the growth chamber the
next day. Plants were clean, robust, and in excellent condition
at time of planting. Four 20- to 30-cm apical segments were
planted into 300-mL glass beakers that contained a moistened
3:1 (v/v) mixture of sphagnum peat (SunGro Horticulture,
Canada, Ltd.) and potting soil (Hyponex® All-Purpose, The
Scotts Company, Columbus, OH) and a 1-g dose of 18-6-12
slow-release fertilizer (Osmocote®, The Scotts Company, Co-
lumbus, OH). Ten beakers, holding a total of 40 shoots, were
placed in each of 51 vertical aquaria (26 by 26 by 77 cm). Each
aquarium was filled to a height of 68 cm with deionized water
to give a volume of 46 L. Water chemistry measurements were
 
1
 
U.S. Army Engineer Research and Development Center, Environmental
Laboratory, 3909 Halls Ferry Road, Vicksburg, MS 39180; e-mail:
Kurt.D.Getsinger@erdc.usace.army.mil.
 
2
 
18391 Westover Drive, South Bend, IN 46637.
 
3
 
Water Division, New Hampshire Department of Environmental Services,
P.O. Box 95, 6 Hazen Drive, Concord, NH 03302. Received for publication
September 16, 2002 and in revised form April 17, 2003.
 
4
 
Citation of trade names does not constitute an endorsement or approval
of the use of such commercial products.
 J. Aquat. Plant Manage.
 
 41: 2003. 125
pH 5.51, 1.75 mg L
 
-1
 
 as CaCO
 
3
 
 alkalinity, and 4.1 µS cm
 
-1
 
 at 25
C conductivity. The aquaria were maintained at 22 ± 2 C 14
hours of light provided daily by a photosynthetic photon flux
density of 378 ± 14.0 µE m
 
-2
 
 sec
 
-1
 
 at the water surface. The cul-
ture solution was constantly aerated, and half of the water vol-
ume of each aquarium was exchanged every 2 to 3 days via a
flow-through system. In order to mimic growth conditions in
water bodies where the plant occurs at weedy levels in New
Hampshire, CO
 
2
 
 was bubbled through the aquaria media via
the aeration mechanism from a gas cylinder for a 1.0-minute
interval twice a week for 18 days.
Twenty-seven days after planting and a day before triclo-
pyr treatment, the aquatic medium was changed from deion-
ized water to a standard aquatic plant culture solution
described by Smart and Barko (1984). The solution pH was
7.9 with alkalinity at 60 mg L
 
-1
 
 as CaCO
 
3
 
 and conductivity of
280 µS cm
 
-1
 
 at 25 C. At this time, an estimate of dry weight
(DW) of plant biomass present in each aquarium at time of
treatment was determined by removing one randomly select-
ed beaker of plants from each unit and by harvesting shoot
tissue. Harvested shoots were dried at 70 C to a constant
weight before determining mass. The average DW value ob-
tained per beaker was 7.6 
 
±
 
 3.2 g. This value was multiplied
by the nine remaining beakers of each aquarium to estimate
amount of biomass at the time of application of herbicide.
Triclopyr treatments were applied 28 days after planting.
Sixteen treatment combinations of five herbicide concentra-
tions of 0.5, 1.0, 1.5, 2.0 and 2.5 mg ae triclopyr L
 
-1
 
 and six ex-
posure times of 12, 24, 36, 48, 60 and 72 hours (Table 1)
were applied to three replicate aquaria in a randomized
block design. Treatments were blocked on the basis of varia-
tion in plant growth as a result of light conditions in the
growth chamber and response to CO
 
2
 
. Three aquaria re-
mained untreated as a reference. Herbicide was applied to
the 48 treated aquaria based on a 46-L treatment volume, us-
ing a 5-mg ae triclopyr mL
 
-1
 
 stock solution made from the
Garlon® 3A formulation. After stipulated exposure periods,
during which aeration was applied continuously, herbicide
was removed from aquaria by draining and refilling two-
thirds of each unit’s volume three times.
Water samples of 1-L volume were collected from each
aquarium 15 min after treatment and following the final
draining. Samples were frozen before being analyzed for tri-
clopyr residues at the water chemistry laboratory at the ERDC
Lewisville Aquatic Ecosystem Research Facility, Lewisville,
TX, using high performance liquid chromatography (HPLC)
methods developed by Dow AgroSciences as described in
Getsinger et al. (2000). The untreated reference aquaria
were subjected to the same draining and re-filling procedure.
Treated plants were maintained in the standard culture so-
lution with flow-through water exchange carried out as be-
fore and were monitored visually until 31 days after treatment
(DAT). Each aquarium was visually assessed for plant re-
growth as shown by the presence (+) or absence (-) of newly
emerging apical or axillary shoots (Table 1). Viable shoot tis-
sue in the nine beakers remaining in each experimental unit
was then harvested, pooled, and weighed after drying at 70 C.
Post-treatment biomass was determined by averaging shoot
tissue DW from the three replicate aquaria from each treat-
ment. Analyses of variance were used to examine differences
among treatments (SigmaStat 2.0, Jandel 1995). Biomass data
were distributed non-normally due to numerous zero quanti-
ties among replicates within treatments.
 
RESULTS AND DISCUSSION
 
At the time of treatment, DW biomass in the 676 cm
 
2
 
 sur-
face area of each aquarium comprised 124.7 g m
 
-2
 
. This may
be compared to field biomass in Eurasian watermilfoil of 185
g DW m
 
-2
 
 determined by Grace and Wetzel (1978) in sites in
the Southeast US.
Triclopyr residue analyses of water immediately after treat-
ment showed that applications were close to the nominal rates
selected. Treatment concentrations in water samples were 2.5
 
±
 
 0.6; 2.2 
 
±
 
 0.2; 1.6 
 
±
 
 0.3; 1.1 
 
±
 
 0.3; and 0.8 
 
±
 
 0.2 mg L
 
-1
 
 for the
applied rates of 2.5, 2.0, 1.5, 1.0, and 0.5 mg L
 
-1
 
, respectively.
 
T
 
ABLE
 
 1. M
 
EAN
 
 (±SD) 
 
BIOMASS
 
 (
 
G
 
 DW) 
 
OF
 
 
 
VARIABLE
 
-
 
LEAF
 
 
 
WATERMILFOIL
 
 
 
IN
 
 
 
EXPERIMENTAL
 
 
 
UNITS
 
 
 
AT
 
 31 
 
DAYS
 
 
 
AFTER
 
 
 
TREATMENT
 
 
 
WITH
 
 
 
TRICLOPYR
 
A
 
. N
 
EGATIVE
SIGN
 
 (-) 
 
INDICATES
 
 
 
NO
 
 
 
NEW
 
 
 
GROWTH
 
 
 
OF
 
 
 
APICAL
 
 
 
MERISTEMS
 
 
 
OR
 
 
 
AXILLARY
 
 
 
BUDS
 
 
 
IN
 
 
 
AN
 
 
 
INDIVIDUAL
 
 
 
REPLICATE
 
; 
 
POSITIVE
 
 
 
SIGN
 
 (+) 
 
INDICATES
 
 
 
NEW
 
 
 
GROWTH
 
 
 
ON
 
 
 
ONE
 
 
 
OR
MORE
 
 
 
PLANTS
 
.
Triclopyr
(mg ae L
 
-1
 
)
Exposure time (hours)
0 12 24 36 48 60 72
2.5 0.09 ± 0.13
(- - +)
0.01 ± 0.01
(- - +)
0.01 ± 0.01
(- - -)
0.0 ± 0.0
(- - -)
2.0 0.03 ± 0.30
(- - +)
0.0 ± 0.0
(- - -)
0.0 ± 0.0
(- - -)
1.5 0.0 ± 0.0
(- - -)
0.86 ± 1.25
(+ + +)
0.02 ± 0.04
(- - +)
0.0 ± 0.0
(- - -)
1.0 0.08 ± 0.07
(- + +)
0.19 ± 0.32
(- - +)
0.07 ± 0.12
(- - +)
0.5 0.35 ± 0.44
(- + +)
0.02 ± 0.02
(- + +)
0 5.3 ± 2.2
(+ + +)
 
a
 
Biomass was significantly different among the untreated reference and all of the triclopyr-treated units (p = <0.001, Tukey’s multiple comparison). There
were no significant differences among the herbicide treatments (p = 0.289, ANOVA on raw data; p = 0.136, Kruskal-Wallis ANOVA on ranks).
 126
 
J. Aquat. Plant Manage.
 
 41: 2003.
Aqueous triclopyr levels after aquaria were drained were all
below detection, indicating that the procedure was successful
in removing herbicide residues following treatment.
Plants treated at all herbicide concentrations and expo-
sure times had typical auxin-like epinastic symptoms of twist-
ing and bending in leaves, stems and apical meristems 4 days
after application of triclopyr. By this time plants in some of
the replicate units treated at 1.5 mg L
 
-1
 
 for 36, 48 and 60 hr
and at 2.5 mg L
 
-1
 
 for 24 hr had sunk half-way down the water
column due to partial loss of buoyancy. At 7 DAT, most treat-
ments remained symptomatic, and plants treated with 1.0 mg
L
 
-1
 
 for 36 hr, 2.0 mg L
 
-1
 
 for 24 hr, and 2.5 mg L
 
-1
 
 for 36 hr, had
also lost buoyancy and had settled low in the water column.
However, newly emerging apical growth in plants treated at
0.5 mg L
 
-1
 
 for 72 hr lacked epinasty and looked normal. Un-
treated reference plants remained upright with normal leaf
and stem morphology.
At 17 DAT, plants treated at 1.0 mg L
 
-1
 
 for 48 hr had sunk
below the surface, and those that had previously dropped
out of the water column had not regained buoyancy. Older
leaf tissue in treated units was decomposing and colonized
by algae, but continued stem viability was indicated where
plants had newly emerging axillary shoots or regrowth of api-
cal meristems. Some algal infestation was also present in two
reference units. Auto-fragmentation of viable apical shoots
was not observed during the post-treatment period.
At the time of post-treatment harvest at 31 DAT, 10 of the
16 treatments had produced some new growth although DW
data showed that no treatment had recovered to more than
10% of pretreatment biomass levels (Table 1). Untreated
plants had decreased 30% in biomass from time of treatment
(i.e., 7.6 g to 5.3 g), due to decline in older shoot tissue dur-
ing the course of the study. However, at the conclusion of the
study all of the untreated plants exhibited healthy, actively
growing shoots, and the differences in biomass between un-
treated and all treated units were highly significant.
Analysis of variance on post-treatment DW biomass showed
no block effect on treatment results (p = 0.42), and further
analysis was based on one-way ANOVA of a completely ran-
domized design. While all treated material was significantly
lower than untreated reference plants (p = < 0.001, Tukey’s
multiple comparison versus control), there were no statistical
differences in biomass among treatments (p = 0.289, ANOVA
on raw data; p = 0.136, Kruskal-Wallis ANOVA on ranks). Re-
sults from this study suggest that triclopyr may be efficacious
against variable-leaf watermilfoil in the field over a wide range
of concentrations and exposure times. These data indicate a
broad dose/response range that could allow for maximum
flexibility in controlling 
 
M. heterophyllum 
 
with triclopyr under
field situations where water exchange characteristics and size
of plant infestations dictate application strategies.
 
ACKNOWLEGMENTS
 
This research was conducted under the U.S. Army Corps
of Engineers Aquatic Plant Control Research Program, U.S.
Army Engineer Research and Development Center. Permis-
sion to publish this information was granted by the Chief of
Engineers. Financial support was also provided by the New
Hampshire Department of Environmental Sciences. Product
used in this study was supplied by Dow AgroSciences. The au-
thors thank D. Honnell for analytical support, and A. Poovey
and L. Nelson for earlier reviews of the manuscript.
 
LITERATURE CITED
 
Anderson, L. 1991. Control of parrotfeather with Garlon 3a: Foliar and in-
water application. USDA-ARS Ann. Rep. Aquat. Weed Contr. Investiga-
tions 1993. p. 21-23.
Anderson, L. and T. Lanini. 1993a. Foliar application of Garlon 3a for con-
trol of parrotfeather (
 
Myriophyllum aquaticum
 
). USDA-ARS Ann. Rep.
Aquat. Weed Contr. Investigations 1993. p. 11-12.
Anderson, L. and T. Lanini. 1993b. Effect of in-water application of Garlon
3a on parrotfeather (
 
Myriophyllum aquaticum
 
). USDA-ARS Ann. Rep.
Aquat. Weed Contr. Investigations. p. 13-14.
Crow, G. E. and C. B. Hellquist. 1983. Aquatic Vascular Plants of New
England: Part 6. Trapaceae, Haloragaceae, Hippuridaceae. New Hamp-
shire Ag. Exp. Sta., Univ. New Hampshire, Durham, NH.
Getsinger, K. D., E. G. Turner, J. D. Madsen and M. D. Netherland. 1997.
Restoring native vegetation in a Eurasian water milfoil-dominated plant
community using the herbicide triclopyr. Reg. Rivers: Res. Manage.
13:357-375.
Getsinger, K. D., D. G. Petty, J. D. Madsen, J. G. Skogerboe, B. A. Houtman,
W. T. Haller and A. M. Fox. 2000. Aquatic dissipation of the herbicide tri-
clopyr in Lake Minnetonka, Minnesota. Pest Manage. Sci. 56:388-400.
Godfrey, R. K. and J. W. Wooten. 1981. Aquatic and Wetland Plants of Southeast-
ern United States: Dicotyledons. Univ. Georgia Press, Athens, GA. 933 pp.
Grace, J. B. and Wetzel, R. G. 1978. The production biology of Eurasian
watermilfoil (
 
Myriophyllum spicatum
 
 L.): A review. J. Aquat. Plant Manage.
16:1-11.
Hoyer, M. V., D. E. Canfield, Jr., C. A. Horsburgh and K. Brown. 1996. Flor-
ida Freshwater Plants: A Handbook of Common Aquatic Plants in Flor-
ida Lakes. Univ. Florida, Inst. Food Ag. Sci., Gainesville, FL. 264 pp.
Jandel Corporation. 1995. SigmaStat 2.0 for Windows. Version 2.0. Jandel
Corporation, San Rafael, CA. 800 pp.
Kimball, K. D. and A. L. Baker. 1983. Temporal and morphological factors
related to mineral composition in 
 
Myriophyllum heterophyllum
 
 Michx.
Aquat. Bot. 16:189-205.
McFarland, D. G., A. G. Poovey and J. D. Madsen. 2003. Evaluation of the
potential of selected nonindigenous aquatic plant species to colonize
Minnesota water resources. Tech. Rep. ERDC/EL-03-, U.S. Army Eng.
Res. Develop. Center, Vicksburg, MS. 100 pp. (in press).
Netherland, M. D. and K. D. Getsinger.1992. Efficacy of triclopyr on Eur-
asian watermilfoil: Concentration and exposure time effects. J. Aquat.
Plant Manage. 30:1-5.
New Hampshire Natural Heritage Inventory 1998. http://web-
ster.state.nh.us/nhinfo/plant_1.html. Rare Plant Species in New Hamp-
shire. Accessed: January 1, 1998.
Newroth, P. R. 1985. A review of Eurasian watermilfoil impacts and manage-
ment in British Columbia. Proc. 1
 
st
 
 Int. Symp. Watermilfoil (
 
Myriophyllum
spicatum
 
) and related Haloragaceae Species, Vancouver, British Columbia,
July 23-24, 1985, Aquat. Plant Manage. Soc., Clermont, FL. p. 139-153.
Nichols, S. A. and L. A. J. Buchan. 1997. Use of native macrophytes as indica-
tors of suitable Eurasian watermilfoil habitat in Wisconsin lakes. J. Aquat.
Plant Manage. 35:21-24.
Nichols, S. A. and B. H. Shaw. 1986. Ecological life histories of three aquatic
nuisance plants, 
 
Myriophyllum spicatum
 
, 
 
Potamogeton crispus
 
, and 
 
Elodea
canadensis
 
. Hydrobiol. 131:3-21.
Petty, D. G., K. D. Getsinger, J. D. Madsen, J. G. Skogerboe, W. T. Haller,
A. M. Fox and B. A. Houtman. 1998. Aquatic dissipation of the herbicide
triclopyr in Lake Minnetonka, Minnesota. Tech. Rep. A-98-01, U.S. Army
Eng. Waterways Exp. Sta., Vicksburg, MS. 96 pp.
Smart, R. M. and J. W. Barko. 1984. Culture Methodology for Experimental
Investigations Involving Rooted Submersed Aquatic Plants. Misc. Paper
A-84-6, U.S. Army Eng. Waterways Exp. Sta., Vicksburg, MS. 20 pp.


Effects of Triclopyr on Variable-Leaf Watermilfoil

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Effects of Triclopyr on Variable-Leaf Watermilfoil

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