American pondweed (

Potamogeton nodosus

Poir.) is commonly

found in northern California irrigation canals. The

purpose of this study was to test the hypothesis that exposure

of American pondweed winter buds to dilute acetic acid under

field conditions would result in reduced subsequent biomass

Elmore, C. L.

Ksander, G. G.

Roncoroni, J. A.

Spencer, D. F.

English

Aquatic Commons

 J. Aquat. Plant Manage.
 
 41: 2003. 65
 
J. Aquat. Plant Manage.
 
 41: 65-68
Influence of Dilute Acetic Acid Treatments
on American Pondweed Winter Buds in
the Nevada Irrigation District, California
 
D. F. SPENCER
 
1
 
, C. L. ELMORE
 
2
 
, G. G. KSANDER
 
1
 
, AND J. A. RONCORONI
 
2
 
ABSTRACT
 
American pondweed (
 
Potamogeton nodosus 
 
Poir.) is com-
monly found in northern California irrigation canals. The
purpose of this study was to test the hypothesis that exposure
of American pondweed winter buds to dilute acetic acid un-
der field conditions would result in reduced subsequent bio-
mass. The treatment consisted of adding either 1703 or 3406
L of 2.3% acetic acid per 83-m
 
2
 
 plot. Acetic acid was applied
using either drip tape or soaker hoses. We collected nine
samples 6 weeks after treatment from each plot for biomass
determination. American pondweed biomass was reduced by
the acetic acid application. The reduction was observed for
samples collected from the sides as well as the canal bottom
when 3406 L per plot were applied. At the lower rate, there
was slightly more biomass on the sides of the canal. These re-
sults confirm findings from earlier laboratory/greenhouse
experiments, and suggest that application of a 2.3% acetic
acid solution by drip irrigation tape may be useful in the
management of American pondweed in systems that can
have the water removed temporarily.
 
Key words:
 
 aquatic weeds, irrigation canal, drip tape, sedi-
ment treatments
 
, Potamogeton nodosus.
 
INTRODUCTION
 
American pondweed is a common weed in northern Cali-
fornia irrigation systems. It reproduces by fragmentation, sto-
lons, subterranean winter buds, and seeds. Like many other
weedy aquatic species (van Vierssen 1993), the underground
vegetative propagules are particularly important to American
pondweed’s long-term survival in a particular habitat. To
date there have been few attempts to manage this important
life cycle stage. Some have suggested that it may be possible
to disrupt propagule formation or dormancy (Ogg et al.
1969, Spencer and Ksander 1992, MacDonald et al. 1993, van
Vierssen 1993) but, there have been few attempts to manipu-
late their survival in the sediment (Ogg et al. 1969, Haller et
al. 1976, Godfrey and Anderson 1994, Godfrey et al. 1994).
Previous work (Spencer and Ksander 1995, 1997) indicat-
ed that 0.1 to 5% solutions of the natural sediment compo-
nent, acetic acid, (Ponnamperuma 1972, Miller et al. 1979,
King and Klug 1982, Sansone and Martens 1982) greatly re-
duced survival and sprouting of vegetative propagules of
pondweeds (
 
Potamogeton
 
 spp.) and hydrilla (
 
Hydrilla verticilla-
ta
 
 (L.f.) Royle) in laboratory and greenhouse trials. Spencer
and Ksander (1999) demonstrated reduced survival of mo-
noecious hydrilla tubers in the Oregon House Canal follow-
ing treatment of either 2.5% or 5% acetic acid to plants in
plots with dimension of 1 by 1 m. Recently, Tenuta et al.
(2002) demonstrated that dilute solutions of acetic acid
present in liquid swine manure killed microsclerotia of the
wilt fungus, 
 
Verticillium dahliae 
 
Kleb., when applied to soils.
The purpose of this study was to evaluate the efficacy of
2.3% acetic acid at reducing American pondweed winter bud
survival and subsequent growth when applied at two rates
1703 or 3406 L per 83-m
 
2
 
 plot using drip tape or soaker hoses
under field conditions.
 
MATERIALS AND METHODS
 
Part of this research was conducted in the Nevada Irriga-
tion District’s Wolf Hannaman Canal located in Nevada
County, California, about 100 km northeast of Sacramento.
The approximate location is 39°02’ 43.18928” N, 121°12’
31.41053” W and the altitude is approximately 270 m. This is
a shallow canal with a mean water depth 1 m which typically
conveys water between April 15 and October 15. American
pondweed is the dominant plant growing in the canal al-
though elodea (
 
Elodea canadensis
 
 Michx.) plants occur occa-
sionally during the period when flowing water is present.
Elodea plants are apparently from fragments that enter the
canal when water is introduced in the spring.
On April 11 and 12, 2002 we applied dilute acetic acid of
2.3% to nine plots measuring 16.6 by 5 m. Three plots each
received one of the following treatments: 1703 L of solution
applied using drip tape; 3406 L of solution applied using
drip tape; or 1703 L of solution applied using soaker hoses,
or untreated. The acetic acid solution was prepared by add-
ing 197 L of 80% acetic acid to 6624 L of water in water tank-
er truck. Mixing occurred as the truck was driven to a site
adjacent to the canal. Approximately 946 L of the solution
were transferred to 1230 L polyethylene tanks mounted in
the bed of pickup trucks. Using pumps that maintained 68 to
83 kPa, the acetic acid solution was pumped from these tanks
into tubing connected to either drip tape or soaker hoses
placed in the canal. An in-line flow meter recorded the vol-
ume of material applied to each plot (1703 L required about
 
1
 
USDA-ARS Exotic & Invasive Weeds Research Unit, Robbins Hall, 1
Shields Avenue, Davis, CA 95616.
 
2
 
Weed Science Program, Department of Vegetable Crops, University of
California, Davis, 1 Shields Avenue, Davis, CA 95616. Received for publica-
tion January 9, 2003 and in revised form May 7, 2003.
 66
 
J. Aquat. Plant Manage.
 
 41: 2003.
90 minutes to apply; 3406 L required about 3 hr to apply).
Ten 16.6 m sections of drip tape (TSX5XX-08-670, T-Tape
North America) were arranged in the canal bottom so that
the entire bottom from the water-line (i.e., indicated by the
presence of terrestrial plants on the side of the canal) on
each side was treated (Figure 1).
To verify that the acetic acid solution actually soaked into
the ground, we measured soil moisture content with a Hy-
drosense Moisture Meter with 12 cm long probes (Campbell
Scientific Inc., Logan, UT) prior to and shortly after the ace-
tic acid solution was applied. We collected data from the cen-
ter and from each side of the canal as shown in Figure 2.
At the time the treatments were applied terrestrial forms
of American pondweed were present in the canal (Spencer
and Ksander 1992). Prior to application, we estimated their
abundance by counting the number present in 60 randomly
deployed square quadrats (25 cm by 25 cm). One week after
this treatment nine sediment samples were collected from
each plot. Samples were collected from each side of the ca-
nal and in the middle. The sediment samples were returned
to the laboratory facility, placed in plastic containers with di-
mensions of 25 cm in length by 18 cm in width by 12 cm in
depth, and placed in a large outdoor container filled with
water to a depth of 65 cm. These samples were exposed to
ambient conditions for 11 weeks. Samples were harvested,
washed over 2-mm mesh metal screens to separate plant ma-
terial from the soil. Plant material was separated by species
and dried at 80 C for 48 hr and weighed.
Six weeks following the treatments we collected nine 15-
cm diameter cores from each plot and from adjacent non-
treated canal sections which served as controls. Within each
plot three cores were collected from the center and either
side of the canal. The cores were transported to the laborato-
ry facility in Davis, California and washed over 2-mm mesh
metal screens to separate plant material from the soil. Plant
material was dried at 80 C for 48 hr and weighed. Dry weight
per sample was subjected to analysis of variance with treat-
ment method (i.e., drip tape and volume) and location as
the treatment factors.
 
RESULTS AND DISCUSSION
 
At the time these treatments were made there were 486 ±
120 plants m
 
-2
 
 (N = 60). Based on previous reports for a close-
ly related species this represents from 34 to 96% of the total
number of winter buds present (Spencer and Ksander 1992).
The moisture content of treated sediments increased to lev-
els characteristic of saturated soils indicating the acetic acid
solution was penetrating the soil to at least 12 cm deep (Fig-
ure 2). Pondweed winter buds and tubers have been reported
to occur at greater sediment depths (Spencer and Ksander
1990, Spencer 1987) but these were for samples collected
from the canal bottom and not on the sides of the canal.
American pondweed biomass 6 weeks after treatment
(Figure 3) was significantly reduced by the 2.3% acetic acid
applications (ANOVA, P < 0.001). The greatest reduction was
for plots that received 3406 L applied with drip tape. For this
treatment biomass was greatly reduced on the canal sides as
well as on the bottom. Plots which received 1703 L whether
by drip tape or soaker hoses had somewhat greater biomass,
especially on the canal sides, indicated by the significant ef-
fect of location (ANOVA, P = 0.03). The acetic acid by loca-
tion interaction was not significant (P = 0.14).
Results from samples placed in outdoor tanks and allowed
to grow for 11-week period are shown in Figures 4 and 5.
Figure 1. Diagram of drip tape arrangement for applying acetic acid solu-
tion. The drip tape sections (A) were 0.3 m apart. The flexible tape could be
adjusted to fit the canal width by overlapping the two sections of drip tape.
Drip tape was connected by carrier tubes (B) to the polyethylene tank (C),
the pump (D), and the in-line flow meter (E).
Figure 2. Soil Moisture (%) to 12 cm deep before and after acetic acid solu-
tions were applied. Locations correspond to those illustrated in the canal
cross section diagram.
 J. Aquat. Plant Manage.
 
 41: 2003. 67
American pondweed biomass was significantly reduced by
the dilute acetic acid treatments. The effect of location was
not significant in this case (P = 0.99) perhaps due to the
longer growing period compared to the samples collected
from the canal. Likewise, the acetic acid by location interac-
tion was not significant (P = 0.19). Interestingly, growth of
another aquatic plant, spikerush (
 
Eleocharis sp.
 
), in these
samples was unaffected by the acetic acid treatments (Figure
5). This confirms the differential susceptibility of aquatic
plants to dilute acetic acid solutions noted previously (Spen-
cer and Ksander 1995) and further suggests the possibility of
enhancing the growth of spikerush which is considered to be
a more desirable species in irrigation systems (Ashton and
Bissell 1987, Yeo and Thurston 1984).
These results suggest that using drip irrigation tape to ap-
ply dilute solutions of acetic acid in irrigation canals that
have had the water removed may be a practical method for
treating canal sides as well as the bottom. Previous work ap-
plied the material by flooding the canal. This required more
water and consequently more acetic acid. The use of drip ir-
rigation tape and perhaps soaker hoses allowed the material
to be applied at a slower rate over a longer period of time
and to saturate the soil in the treated area. This not only
killed sufficient winter buds to greatly reduce subsequent
pondweed biomass, but also reduced the amount of material
required for the treatment. The slightly higher biomass in
samples collected from the canal sides may be partly ex-
plained by the irregular topography of the canal sides in this
canal. The canal traverses an area used by cattle and as a re-
sult some of the plots had deep footprints in the sides and
bottom. We noticed that the acetic acid solution tended to
collect in these depressions and this may have prevented the
material from spreading in the sediment as it did in other
plots that did not have so many cattle footprints. In our expe-
rience, most irrigation canals are not impacted by cattle in
this way and thus greater efficacy might be expected if these
canals received similar treatments.
Underground vegetative propagules are important to the
long-term survival of some species of aquatic plants and, ap-
pear to be particularly important in the life cycles of weedy
species (van Vierssen 1993). To date, attempts to manage this
important life cycle stage have been aimed at disrupting
Figure 3. American pondweed biomass six weeks after treatment at three
locations (either side, N (near), F (far), or M (middle)) within plots that
received different acetic acid treatments (DT = drip tape, soaker = soaker
hoses, 1703 L per plot and 3406 L per plot). Plotted values are the mean
and 95% confidence intervals. Effects of the acetic acid treatment were sig-
nificant (ANOVA, P < 0.001) as were those of location (P = 0.03). The acetic
acid by location interaction was not significant (P = 0.14).
Figure 4. American pondweed biomass after 11 weeks in an outdoor tank in
Davis, California. Samples were collected from three locations (either side,
N (near), F (far), or M (middle)) within plots that received different acetic
acid treatments. Plotted values are the mean and 95% confidence intervals.
Effects of the acetic acid treatment were significant (ANOVA, P < 0.001).
The effects of location (P = 0.99) and the acetic acid by location interaction
were not significant (P = 0.19).
Figure 5. Spikerush biomass after 11 weeks in an outdoor tank in Davis, Cal-
ifornia. Samples were collected from three locations (either side, N or F, or
middle, M) within plots that received different acetic acid treatments. Plot-
ted values are the mean and 95% confidence intervals. Effects of the acetic
acid treatment were not significant (ANOVA, P = 0.72). The effects of loca-
tion (P = 0.61) and the acetic acid by location interaction were not signifi-
cant (P = 0.75).
 68
 
J. Aquat. Plant Manage.
 
 41: 2003.
their formation or dormancy (Ogg et al. 1969, Spencer and
Ksander 1992) and we know of few attempts to manipulate
tuber survival in the sediment (Haller et al. 1976, Godfrey
and Anderson 1994, Godfrey et al. 1994). Results of this
study indicate that a 2.3% solution of acetic acid, equivalent
to slightly less than one-half the strength of vinegar, was ef-
fective in reducing survival of American pondweed winter
buds under the conditions prevalent in this field test. These
results imply that it may be possible to develop a novel meth-
od for managing this important life-cycle stage by manipulat-
ing the sediment environment, as has been suggested by
Gunnison and Barko (1989) and Kremer (1993). Use of a
naturally occurring, short-lived, low molecular weight organ-
ic compound, such as acetic acid may be especially attractive
in this regard. Continued evaluation of this approach in ad-
ditional habitats with different sediment characteristics such
as clay content, organic content, porosity, and other charac-
teristics may be illuminating and are essential to understand-
ing the broader applicability of this approach.
 
ACKNOWLEDGMENTS
 
This work was supported in part by the Nevada Irrigation
District, Grass Valley, California. Mr. Bruce Early was especial-
ly helpful in the completion of this study. We appreciate the
comments of Dr. Mark Renz, Dr. John Madsen, and Dr. Tom
Lanini who read an earlier version of the manuscript. Men-
tion of trade names or commercial products in this article is
solely for the purpose of providing specific information and
does not imply recommendation or endorsement by the
U.S. Department of Agriculture.
 
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Influence of Dilute Acetic Acid Treatments

on American Pondweed Winter Buds in

the Nevada Irrigation District, California

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Influence of Dilute Acetic Acid Treatments on American Pondweed Winter Buds in the Nevada Irrigation District, California

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