Research has shown that aquatic weeds, particularly hydrilla

(

Hydrilla verticillata

, (L.F.) Royle), can be controlled with

exposure of 8 to 12 weeks with concentrations of 10 to 15

ppb of fluridone (1-methyl-3-phenyl-5-[3-trifluoromethyl)

phenyl]-4(1

H

)- pyridinone) (Haller et al. 1990 and Fox et

al. 1994).  Fluridone label recommendations restrict the use

of the treated waters for irrigation of turf or newly seeded

crops and seed beds for 30 days following the last application

of the herbicide.  The objective of this

research was to determine the effects of 10 weeks of irrigation

with fluridone containing water on a common Florida

residential turfgrass

Andrew, W.

Haller, W. T.

Shilling, David G.

English

Aquatic Commons

 J. Aquat. Plant Manage.
 
 41: 2003. 61
 
J. Aquat. Plant Manage.
 
 41: 61-63
NOTES
Response of St. Augustinegrass
to Fluridone in Irrigation Water
 
1
 
W. ANDREW, W. T. HALLER, AND D. G. SHILLLING
 
2
 
INTRODUCTION
 
Research has shown that aquatic weeds, particularly hyd-
rilla (
 
Hydrilla verticillata
 
, (L.F.) Royle), can be controlled with
exposure of 8 to 12 weeks with concentrations of 10 to 15
ppb of fluridone (1-methyl-3-phenyl-5-[3-trifluorometh-
yl)phenyl]-4(1
 
H
 
)- pyridinone) (Haller et al. 1990 and Fox et
al. 1994). Fluridone label recommendations restrict the use
of the treated waters for irrigation of turf or newly seeded
crops and seed beds for 30 days following the last application
of the herbicide. The time of application plus the 30 day rec-
ommended use restriction can total 75 to 100 days of recom-
mended water use restrictions if split applications are
applied. The recommended use restrictions of fluridone
were developed in the mid-1980’s and were based on the
maximum fluridone application rates of 2 to 4 kg ai/ha (ca
125 to 175 ppb) depending upon water depths (Sonar A.S.
label dated 11/87).
More recent fluridone labels (Sonar A.S. label dated 1994
and AVAST label dated 2000) recommend lower application
rates of fluridone and are based upon the concentration of
the active ingredient in water. Concentrations of 60 to 90
ppb in ponds and use of 10 to 20 ppb for whole lake treat-
ments are currently recommended. Despite these reduced
application rates, the labels continue to suggest water use re-
strictions for irrigation for up to 30 days following fluridone
applications.
Fluridone activity in soils is affected by soil organic matter
and clay content. Loh et al. (1979) reported the K
 
a
 
 (absorp-
tion coefficient) of fluridone by 14 soil types was significantly
correlated to the soil organic matter content and inversely
related to the rates of fluridone necessary to reduce growth
of 
 
Sorghum vulgare
 
 L. Weber et al. (1986) reported that fluri-
done adsorption was highly correlated (r = 0.92) with mont-
morillonite clay content in addition to the organic matter
content of 18 soil types. They also reported that fluridone ad-
sorption increased as soil pH decreased from 6.4 to 3.5. Flu-
ridone was not readily desorbed by water at the lower pH
which suggests that the weakly basic herbicide was protonat-
ed and bound by cation exchange forces. Much of peninsu-
lar Florida is characterized by sandy top soils containing little
clay or organic matter. Consequently, fluridone in treated
water applied to Florida lawns would be readily available to
actively growing turf. Homeowners typically irrigate their
lawns most often in the dry season of March to June, prior to
the beginning of summer convectional rains, the same time
period when hydrilla is beginning active growth and manage-
ment programs are begun. Therefore, the objective of this
research was to determine the effects of 10 weeks of irriga-
tion with fluridone containing water on a common Florida
residential turfgrass.
 
METHODS AND MATERIALS
 
Sod Culture
 
. St. Augustinegrass (
 
Stenotaphrum secundatum
 
(Walt.) Kuntze) variety “Floratam” sod grown on organic soil
was purchased from a local vendor in Gainesville, FL and 15
cm circles were carefully cut from the sod and planted in
commercially available nursery pots 15 cm in diameter by 13
cm deep filled to a 10 cm depth of an arredondo fine sand.
The pots were placed in a greenhouse maintained at 22 ± 2 C
with supplemental lighting providing long day conditions
(16 hr light: 8 hr dark). After fertilization with 50 ml of 10
 
×
 
Hoaglands solution, the newly planted grass was allowed to
grow for approximately 10 days at which time the sod was
clipped and grown for approximately 10 more days, clipped
and culled for uniformity.
The pots (five replicates) were irrigated on Tuesday and
Thursdays with 0.8 cm of water containing 0, 2.5, 5, 10, 15,
30, 60, 120, and 240 ppb fluridone. In order to maintain an
adequate water supply to the plants and attempt to simulate
natural events, 2.5 cm of water containing no fluridone was
added to the pots on each Sunday. Irrigation water was ap-
plied by slowly pouring the water from beakers over the pots,
wetting the foliage, and taking care not to allow any overflow
or runoff from the surface of the pots.
Stock solutions of technical grade fluridone (10 ppm)
were made up with de- ionized water in clean, methanol
rinsed glassware and stored in opaque poly bottles in a refrig-
erator. Appropriate amounts of stock solution were added to
de-ionized water to be applied to each pot. Glassware was
washed after each treatment in water and methanol to pre-
vent contamination.
 
1
 
Published as Journal Series Number R-08897 of the Florida Agriculture
Experiment Station. Received for Publication June 8, 2002 and in final form
November 18, 2002.
 
2
 
Graduate Research Assistant, currently Horticulturist, Walt Disney-
World, Lake Buena Vista, Florida; Professor, UF/IFAS Center for Aquatic
and Invasive Plants, 7922 NW 71
 
st
 
 Street, Gainesville, FL 32653 (correspond-
ing author) and Professor and Center Director, Mid-Florida Research and
Education Center, Apopka, FL 32703
 62
 
J. Aquat. Plant Manage.
 
 41: 2003.
The irrigation schedule described above was carried out
for 10 weeks, and shoots were harvested at approximately
weeks 4, 7, and 10 by clipping the pots to a height of 1.0 cm.
The plant clippings were dried and weighed and the pots
were fertilized with 50 ml of 10
 
×
 
 Hoaglands nutrient solution
at the time of each harvest.
 
Sand Culture
 
. The sand culture study was conducted in ex-
actly the same manner as described for the sod experiments
except for initial establishment of the plants. Vegetative
sprigs of St. Augustinegrass were obtained by thoroughly
washing the organic soil from sod and planting sprigs into 15
cm diameter nursery pots similar to those used in the sod
culture study. The nursery pots were filled with washed build-
ers sand.
After sprigging the grass into the sand, the plants were fer-
tilized as before and the grass was permitted to establish for 4
weeks before selecting for uniformity and assigning the treat-
ments. Due to the low water holding capacity of the sand,
dishes were placed under the pots to maintain soil moisture
during establishment. These dishes were kept under the pots
for the first 3 weeks of the treatment period at which time
root growth in the pots increased the water holding capacity
of the pots to the point where irrigation water was retained
by the pots. Due to the low fertility of this soil, fertilizer(10
 
×
 
Hoaglands) was applied five times during the course of the
sand culture study.
Following the 10 week greenhouse irrigation schedule
with fluridone treated water, the plants were placed on a ta-
ble outdoors, exposed to full sunlight and ambient condi-
tions and watered (no fluridone) as needed to supplement
rainfall. After several weeks of outdoor growth, the plants
were evaluated to determine recovery from the previous flu-
ridone irrigation phase.
The organic matter content of the potting media of both
studies was determined by collecting samples from three rep-
licate containers selected randomly from each study. Soil
samples were collected from the surface, center and bottom
2.5 cm layers. The samples were dried at 80 C and sieved
through a 20-mesh screen to separate roots from soil.
Weighed soil samples were ashed at 550 C in a muffle fur-
nace and reweighed to determine organic matter content of
the soils.
Statistical analysis of the data was conducted by analysis of
variance and treatment means were separated by Duncan’s
Multiple Range Test at the 5% confidence level.
 
RESULTS AND DISCUSSION
 
Dry weight of St. Augustinegrass grown in the greenhouse
and irrigated with water containing fluridone are shown for
in Figures 1A and 1B. The different shading on the bar
graphs indicate individual harvests and the heights of the
bars is the total or cumulative dry weight of the grass for the
three clippings. Data from the subsequent 10-week grow out
period showed that the 240 ppb (sod) survived, but the sand-
sprigged grass treated at fluridone concentrations of 30 ppb
and higher died (data not shown).
The effects of fluridone on the sod-cultured St. August-
inegrass (Figure 1A) was not evident during the first 3 to 4
weeks of the study. At the 10-week harvest, weight of grass
clippings at the 240 ppb irrigation rate was greatly reduced
compared to the other treatments, but this treatment subse-
quently recovered after irrigation with fluridone treated wa-
ter was discontinued. The organic matter content of the
organic soil grown sod was 28 ± 16% and that of the underly-
ing Arredondo fine sand was 1.5 ± 0.2%.
St. Augustinegrass grown in sand culture containing only
0.6 ± 0.3% organic matter was much more susceptible to flu-
ridone in the irrigation water (Figure 1B). Significant de-
creases in clipping weight occurred at the first harvest at 120
ppb, the second harvest at 15 ppb and at the final harvest,
reduced growth was evident at 10 ppb. No vegetation was
harvested at the final harvest at concentrations of 30 ppb or
higher, as these plants were dead and did not recover dur-
Figure 1. Interactive effects of fluridone treated irrigation water and soil
type on the growth of St. Augustinegrass. Figure 1A (top) represents shoot
biomass of grass clippings (gm dry wt/pot) harvested from sod grown St.
Augustinegrass at 4 weeks (1st harvest) = open, 7 weeks (2nd harvest) = dots
and 10 weeks (3rd harvest) = bars. The lower case letters are means compari-
sons (Duncan’s) of each harvest and can be compared horizontally. The
capital letters compare the cumulative means of the grass clippings over the
10-week herbicide treatment period. Figure 1B (bottom) same as above
except grass was sprigged and grown in sand containing minimal (<1%)
organic matter.
 J. Aquat. Plant Manage.
 
 41: 2003. 63
ing a subsequent 10-week grow out period when irrigated
with fluridone-free water. By the end of the 10-week herbi-
cide irrigation period, all sand culture plants, except control
plants, were exhibiting chlorosis and fluridone symptoms
which ultimately disappeared during the subsequent grow
out period.
Other fluridone irrigation studies have been conducted.
West and Parka (1992) irrigated 26 crops in different geo-
graphical field locations with 123 ppb fluridone. These stud-
ies were done to collect residue data in field crops and did
not evaluate any effects of fluridone on growth or produc-
tion. In contrast, Kay et al. (1994) irrigated greenhouse
grown tobacco (
 
Nicotiana tabacum
 
 L.) and vegetable crop
seedlings with several concentrations of fluridone to deter-
mine growth effects. Kay et al. noted that plants grown in
sand culture were much more susceptible to fluridone in irri-
gation water compared to those grown in an organic potting
soil (Metromix®). Two weeks following a single irrigation
with fluridone containing water, tobacco grown in sand ex-
hibited symptoms at 10 ppb compared to 100 ppb when
plants were grown in potting soil. Two weeks of irrigation
three times per week with fluridone treated water reduced
growth of three vegetable crops at concentrations of 50 to
250 ppb, evidence that species have a wide range of suscepti-
bilities to fluridone.
The presence of organic matter in the sod grown grass
provided very significant protection from fluridone in irriga-
tion water in this study. However, many Florida lawns are es-
tablished on sand containing very little organic matter and
despite lowered application rates of fluridone, these data in-
dicate caution is warranted and it appears prudent to follow
the suggested irrigation restrictions on the fluridone label.
In addition, this study showed that St. Augustinegrass will
likely recover if irrigation with fluridone treated water is
stopped when fluridone symptoms first noted occur.
 
LITERATURE CITED
 
Fox, A. M., W. T. Haller and D. G. Shilling. 1994. Use of fluridone for hyd-
rilla management in the Withlachoochee River, Florida. J. Aquat. Plant
Manage. 32:47-55.
Haller, W. T., A. M. Fox and D. G. Shilling. 1990. Hydrilla control program
on the upper St. Johns River, Florida USA. Proc. EWRS 8
 
th
 
 Symp. Aquat.
Weeds 8:111-116.
Kay, S. H., D. W. Monks, S. T. Hoyle and D. K. Robinson. 1994. Sensitivity of
tobacco (
 
Nicotiniana tabacum
 
) and vegetable crop seedlings to fluridone
in irrigation water. Weed Technology 8:250-257.
Loh, A., S. J. Parka, R. Albritton and C. C. Lin. 1979. Use of adsorption coef-
ficients and soil properties to predict fluridone herbicidal activity. Weed
Sci. 27(4):456-459.
Weber, J. B., P. J. Shea and S. B. Weed. 1986. Fluridone retention and release
in soils. Soil Sci. Soc. Am. J. 50(3):587-588.
West, S. D. and S. J. Parka. 1992. Residues in crops and soils treated water con-
taining the aquatic herbicide fluridone. J. Agric. Food Chem. 40:160-164.


Response of St. Augustinegrass

to Fluridone in Irrigation Water

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Response of St. Augustinegrass to Fluridone in Irrigation Water

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