Results of recent field trials using the chelated copper formulation

Clearigate®

4

showed that applying a 20% solution

by volume was effective for controlling populations of giant

salvinia in irrigation canals.

5

Lower rates may be efficacious,

thereby reducing chemical use and cost; however, little is

known about the dose-response effects of Clearigate®

against giant salvinia. The objective of this study was to determine

the effective rate range of chelated copper applied as

Clearigate® for control of giant salvinia

Glomski, Lee Ann M.

Nelson, L. S.

Skogerboe, J. G.

English

Aquatic Commons

 J. Aquat. Plant Manage.
 
 41: 2003. 127
 
J. Aquat. Plant Manage.
 
 41: 127-129
Clearigate
 
®
 
 Treatments
for Control of Giant Salvinia
 
LEE ANN M. GLOMSKI
 
1
 
, L. S. NELSON
 
2
 
 AND J. G. SKOGERBOE
 
3
 
INTRODUCTION
 
Giant salvinia (
 
Salvinia molesta
 
 D.S. Mitchell) is an invasive
aquatic fern native to Brazil (Thomas and Room 1986). It
was first discovered in the U.S. in 1995 (Johnson 1995), and
was most likely introduced through the aquarium and water
garden industry. Giant salvinia has been described as having
an “explosive” growth rate and can form dense mats up to
1 m thick across the water surface (Holm et al. 1977, Oliver
1993). Dense mats of giant salvinia can severely reduce the
oxygen supply to the water column by limiting gas exchange
between the atmosphere and the water. Dissolved oxygen
production from photosynthesis is also limited due to mini-
mal light penetration to phytoplankton and submersed
aquatic plants. Decreased oxygen levels can be stressful and
even detrimental to fish and other aquatic organisms (Holm
et al. 1977, Oliver 1993). In addition, the density and diversi-
ty of native submersed plants can be reduced as a result of
shading by giant salvinia mats (Oliver 1993).
Not only can giant salvinia negatively affect aquatic organ-
isms, it can also severely impact human use of waterways. Gi-
ant salvinia hinders transportation and recreation by
clogging waterways, and interferes with irrigation by slowing
the water current and increasing sedimentation in irrigation
canals (Sculthorpe 1967, Thomas and Room 1986). Giant
salvinia provides habitat for mosquitoes, which are vectors
for diseases such as dengue fever, elephantiasis, encephalitis
and malaria (Oliver 1993). With recent concerns in the U.S.
about West Nile virus (Campbell et al. 2002), researchers
speculate that giant salvinia may also harbor the mosquitoes
that spread this disease. Due to the detrimental effects giant
salvinia can have on humans and the aquatic environment, it
is important to prevent and control the spread of this plant.
An effective way to control giant salvinia is through the use of
herbicides. Small-scale outdoor studies have shown that her-
bicides such as diquat (6,7-dihydrodipyrido (1,2-a:2’,1’-c)
pyrazinediium dibromide), glyphosate (N-(phosphonometh-
yl) glycine), and copper (copper chelate) are effective
against this plant (Nelson et al. 2001, Fairchild et al. 2002).
Results of recent field trials using the chelated copper for-
mulation Clearigate®
 
4
 
 showed that applying a 20% solution
by volume was effective for controlling populations of giant
salvinia in irrigation canals.
 
5
 
 Lower rates may be efficacious,
thereby reducing chemical use and cost; however, little is
known about the dose-response effects of Clearigate®
against giant salvinia. The objective of this study was to deter-
mine the effective rate range of chelated copper applied as
Clearigate® for control of giant salvinia.
 
MATERIALS AND METHODS
 
Giant salvinia was collected from established populations
at a local field site and cultured in large outdoor tanks at the
Lewisville Aquatic Ecosystem Research Facility (LAERF), lo-
cated in Lewisville, TX (33°N latitude, 97°W longitude).
Plants were cultured in water amended with Miracle-Gro®
lawn fertilizer (36% N; 6% P; 6% K; 0.325% Fe) (Scotts,
Marysville, OH) at a rate that provided 10 mg N L
 
-1
 
 in the wa-
ter column.
One week prior to herbicide treatment, an equal amount
of fresh plant material (enough to cover 75% of the water
surface) was transferred to 76-L (20-gal) plastic containers
(approximately 50 cm diameter by 58 cm height) filled with
nutrient-amended water and place outdoors in direct sun-
light. The same nutrient additions used in the culture tanks
were utilized here. In addition to nutrients, the inert dye,
Aquashade® (Applied Biochemists, Milwaukee, WI) was add-
ed to the culture media at a rate of 1 mg L
 
-1
 
 to prevent algal
growth. Controlling algae was necessary to prevent potential
nutrient depletion and/or variation in nutrient concentra-
tion among experimental tanks. A 1-week pretreatment
growth period was needed for giant salvinia to acclimate fol-
lowing the transfer from culture tanks to experimental tanks,
and for plants to vegetatively expand and produce a single
thick layer that covered 100% of the water surface of each ex-
perimental tank.
Clearigate® was applied on August 11, 2000 as a foliar
spray at the following treatment rates: 0, 0.5, 1, 2, 5, 10, 15,
and 20% solution by volume. Treatments were applied using
a CO
 
2
 
-pressurized sprayer (R&D Sprayers, Opelousas, LA)
equipped with a hand-held, single-nozzle (TeeJet® solid
cone spray tip) spray header calibrated to deliver a spray vol-
 
1
 
Purdue University, Department of Botany and Plant Pathology, 915 W.
State St., West Lafayette, IN 47907-2054.
 
2
 
U.S. Army Engineer Research and Development Center, Waterways
Experiment Station, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199; e-
mail: nelsonl@wes.army.mil.
 
3
 
U.S. Army Engineer Lewisville Aquatic Ecosystem Research Facility, 201
E. Jones St., Lewisville, TX 75057. Received for publication February 7, 2003
and in revised form June 27, 2003.
 
4
 
Clearigate® is a registered trademark of Applied Biochemists, Milwau-
kee, WI.
 
5
 
Wescott, P. Aquatic vegetation control in irrigation conveyance systems
and treatment results on 
 
Salvinia 
 
molesta with Clearigate aquatic herbicide.
Aquatic Plant Management Society 40
 
th
 
 Annual Meeting. July 16-20, 2000,
San Diego, CA. p. 21.
 128
 
J. Aquat. Plant Manage.
 
 41: 2003.
ume of 1,870 L ha
 
-1
 
 (200 gal A
 
-1
 
). Each tank was shielded dur-
ing the application of herbicide to prevent cross
contamination of spray material between treatments.
Visual ratings of percent giant salvinia control were re-
corded 1, 3, 7, 14, 21, 28, and 42 days after treatment (DAT).
Giant salvinia control was assessed on a scale of 0 to 100
where 0 = no control; and 100 = complete plant mortality.
Observations of plant stunting, discoloration, wilting, plant
deformity, and re-growth were also noted at each evaluation
period. These observations were not assigned numerical rat-
ings or statistically analyzed however, they were used to de-
scribe overall treatment performance. All living plant
material of giant salvinia was harvested at the conclusion of
the study (42 DAT) and dried at 70 C to a constant weight.
Treatments were randomly assigned and replicated three
times. Visual ratings of percent control were analyzed using
the Waller-Duncan 
 
k
 
-ratio 
 
t
 
 test at the 0.05 level of significance.
Final plant biomass data were subjected to regression analysis.
 
RESULTS AND DISCUSSION
 
Visual ratings of percent control showed that low rates of
Clearigate® at 0.5, 1, and 2% were not effective against giant
salvinia (Table 1). Compared to untreated plants, Clearigate®
at 5 and 10% provided significant plant control throughout
the study, however percent control readings decreased over
time. A similar trend was seen with Clearigate® treatments of
15 and 20%, where initial control was 85% and 92%, respec-
tively, then gradually decreased to 73% by the end of the study
period. This decrease in percent control was due to re-growth
of plant tissues not initially killed, and is a common response
following treatment with contact herbicides, which have limit-
ed translocation throughout plant tissues (Lembi and Ross
1985). Re-growth of giant salvinia was also reported by Nelson
et al. (2001) when plants were treated with the copper formu-
lation Komeen®
 
6
 
 (derived from copper-ethylenediamine
complex and copper sulfate pentahydrate).
Visual observations of the plants showed that symptoms
were present 1 DAT for all Clearigate® treatments and persist-
ed throughout the study. Symptoms ranged from slight brown-
ing and yellowing at low rates of 0.5 and 1%, to severe necrosis
and sinking of plant tissue at rates of 5 to 20%. Chlorotic new
growth was observed 3 DAT for the 1 and 2% treatments, 7
DAT for the 5% treatment, and 14 DAT for the 10, 15, and
20% treatments. Enough new growth occurred at 0.5% that
biomass was similar to untreated controls by 42 DAT.
The effect of Clearigate® on giant salvinia biomass 42
DAT is shown in Figure 1 and can be described as an expo-
nential curve. Biomass was reduced by 10 to 88% for the 0.5
to 20% treatments. In many of the treatments, there was
enough living biomass remaining to re-infest a treated area.
Although the objective of the study was to determine if low
rates of Clearigate® were efficacious, it is clear from the data
that higher rates of 15 and 20% were the most effective at con-
trolling giant salvinia, reducing biomass by 84 and 88% respec-
tively. Nelson et al. (2001) however, reported that a low rate of
2.5% Komeen® reduced biomass by 92%. Differences in activ-
ity between the copper products may be attributed to differ-
ences in formulation; Komeen® contains 8% active ingredient
whereas Clearigate® contains only 3.8%. The gradual de-
crease in percent control readings over time in the present
 
T
 
ABLE
 
 1. P
 
ERCENT
 
 
 
CONTROL
 
 
 
OF
 
 
 
GIANT
 
 
 
SALVINIA
 
 
 
AFTER
 
 
 
TREATMENT
 
 
 
WITH
 
 C
 
LEARIGATE
 
®.
Clearigate® (%)
 
2
 
Days after treatment (percent control)
 
1
 
1 3 7 14 21 28 42
0 0 c 0 e 0 d 0 e 0 d 0 c 0 d
0.5 0 c 0 e 0 d 0 e 0 d 2 c 7 d
1 0 c 12 d 2 d 6 e 2 d 3 c 0 d
2 1 c 25 c 7 d 20 d 13 cd 10 c 15 cd
5 68 b 73 b 33 c 38 c 27 c 17 c 30 c
10 83 a 78 ab 80 b 58 b 53 b 43 b 57 b
15 85 a 87 a 83 ab 75 a 70 ab 53 ab 73 a
20 92 a 88 a 88 a 85 a 82 a 75 a 73 a
 
1
 
Percent control is a visual assessment of plant mortality and is expressed on a scale of 0 to 100% where 0% equals no control and 100% equals complete
control. Means in a column followed by the same letter do not significantly differ (
 
α
 
 = 0.05, Waller-Duncan 
 
k
 
-ratio 
 
t
 
 test).
 
2
 
Rate is based on a percent solution mixed v:v and delivered in a total spray volume of 1,870 L ha
 
-1
 
 (200 gal A
 
-1
 
).
 
6
 
Komeen® is a registered trademark of Griffin L.L.C., Valdosta, GA.
Figure 1. Dry weight biomass of giant salvinia 42 days after treatment with
Clearigate® applied as a percent solution.
 J. Aquat. Plant Manage.
 
 41: 2003. 129
study indicates that follow-up treatments may be necessary to
prevent giant salvinia from re-colonizing a treated area. Al-
though high rates of Clearigate® followed by reapplication to
control surviving plants may be discouraging, there are some
situations when using Clearigate®
 
 
 
may be advantageous. As
demonstrated by Nelson et al. (2001) and Fairchild et al.
(2002), diquat and glyphosate are very effective at controlling
giant salvinia, but both herbicides are inactivated by soil parti-
cles. In situations where the plant frond surfaces are covered
with mud deposits or are soiled from turbid waters, Cleari-
gate®, which is not inactivated by soil particles, would be a
more effective herbicide. Also, there are no water use restric-
tions when applying Clearigate® to irrigation canals and it can
be applied near potable water intakes. Although they provide
excellent control, diquat-treated water cannot be used to irri-
gate crops for 5 DAT and glyphosate cannot be applied to wa-
ter within 0.8 km (0.5 mile) of potable water intakes.
Clearigate® at rates of 15 and 20% provide natural resource
managers another option for controlling giant salvinia.
 
ACKNOWLEDGMENTS
 
The authors would like to thank the Aquatic Ecosystem
Restoration Foundation for sponsoring this project, and Ap-
plied Biochemists, Inc., for providing the herbicide prod-
ucts. Permission was granted by the Chief of Engineers to
publish on this information. Citation of trade names does
not constitute an official endorsement or approval of the use
of such commercial products.
 
LITERATURE CITED
 
Campbell, G. L., A. A. Marfin, R. S. Lanciotti and D. J. Gubler. 2002. West
Nile virus. The Lancet Infectious Diseases 2(9):519-529.
Fairchild, J. F., A. L. Allert, J. S. Riddle and D. R. Gladwin. 2002. Efficacy of
glyphosate and five surfactants for controlling giant salvinia. J. Aquat.
Plant Manage. 40:53-58.
Holm, L. G., D. L. Plucknett, J. V. Pancho and J. P. Herberger. 1977. The
World’s Worst Weeds: Distribution and Biology. The University Press of
Hawaii, Honolulu. p. 409-415.
Johnson, D. 1995. Giant salvinia found in South Carolina. Aquatics 17(4):22.
Lembi, C. A. and M. A. Ross. 1985. Applied Weed Science. Macmillan Pub-
lishing Co., New York, NY. 340 pp.
Nelson, L. S., J. G. Skogerboe and K. D. Getsinger. 2001. Herbicide evalua-
tion against giant salvinia. J. Aquat. Plant Manage. 39:48-53.
Oliver, J. D. 1993. A review of the biology of giant salvinia (
 
Salvinia molesta
 
Mitchell). J. Aquat. Plant Manage. 31:227-231.
Sculthorpe, C. D. 1967. The Biology of Aquatic Vascular Plants. Edward
Arnold Ltd., London. 610 pp.
Thomas, P. A. and P. M. Room. 1986. Taxonomy and control of 
 
Salvinia
molesta
 
. Nature 320 (17):581-584.


Clearigate

®

Treatments

for Control of Giant Salvinia

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Clearigate ® Treatments for Control of Giant Salvinia

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