Title: Final report to the Florida department of natural resources on the project: growth retardents for aquatic weed control
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Title: Final report to the Florida department of natural resources on the project: growth retardents for aquatic weed control
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Creator: Sutton, David L.
Publisher: Agricultural Research Center, IFAS, University of Florida
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I

?'6-


Fort Lauderdale ARC Research Report FL75-1


Final Report to the Florida Department of Natural Resources

on the Project: Growth'Retardants for Aquatic Weed Control


Cooperator:


University of Florida, Agricultural Research Center

at Fort Lauderdale'a-/


Report Prepared by: f

David L. Sutton
University of Florida/
Agricultural Research Center
3205 S. W. 70th Avenub
Fort Lauderdale, Florida ,33314
"*, "'0


Copy Number


Ia In cooperation with the Agricultural Research Service, Southern

Region, Florida Area, U. S. Department of Agriculture; U. S. Army

Corps of Engineers; and the Central and Southern Florida Flood

Control District.

J/ No.portion of this report is to be reproduced in any manner

without the written consent of the University of Florida.












Table of Contents
Page No.

I. Introduction . . . . . . 1


II. Methods and Materials . . .... . 1

A. Screening program . ........ ... 1

B. Effect of Velpar on growth of hydrilla tubers . 3

C. Effect of glucose on growth of hydrilla . . 3

D. Effect of Maintain CF-125 and Velpar on lateral shoot
initiation and chlorophyll content of hydrilla stems 4

E. Evaluation of spikerush media for growth retarding
properties on hydrilla. ... . .. . 4

F. Germination of waterhyacinth seeds . . . 5


III. Results and Discussion . . ... . . 5

A. Screening program . . . .... ... 5

B. Effect of Velpar on growth of hydrilla tubers . 6

C. Effect of glucose on growth of hydrilla . . 6

D. Effect of Maintain CF-125 and Velpar on lateral shoot
initiation and chlorophyll content of hydrilla stems 7

E. Evaluation of spikerush media for growth retarding
properties on hydrilla . . . . 8

F. Germination of waterhyacinth seeds . . .... .8


IV. Summary and Conclusions ... .. . . 8


V. Distribution List . . .. . . 10


VI. Appendix . . . . ... . . 12

A. Tables . .... . ....... 12

B. Figures . . . . . .. .21











I. Introduction

This report covers the third and final year of a 3-year study designed

to investigate the potential of growth retardants as a means for aquatic

vegetation control. The primary purpose of this study was to screen and

develop herbicides which would retard the growth of aquatic vegetation,

primarily hydrilla (llydrilla verticillata Royle). In many situations the

complete removal of vegetation is not desirable, since once one plant is

eliminated another will take its place, or the plant itself will quickly

become re-established. In the overall management of a body of water, the

retardation of plant growth may offer a means to reduce the rapid growth

rate of some aquatic plants and allow other more desirable plants to become

more competitive.

II. Methods and Materials

A. Screening Program

Several well-known compounds which exhibit growth retarding effects

on terrestrial plants and a few coded compounds were screened under controlled

conditions on hydrilla. In brief, cuttings (approximately 7 to 10 cm in

length) of apical sections of hydrilla were collected from nearby canals and

rinsed to remove algae and other debris from the surface of the leaves. Then,

three cuttings were planted in a small 5.1-cm2 pot containing 100 g of a 50%

mixture of sand and muck soil. The pots, two each, were placed in a 3.7-

liter glass jar filled with pond water. Hoagland's nutrient solution was

added at a rate to result in a 0.1-strength nutrient solution in the pond

water with a chelated iron supply at 5.0 ppm Fe. Sodium bicarbonate was

added to the jar at a rate which resulted in 50 ppm of bicarbonate ion in

solution. The top of the jar was then covered with a sheet of transparent

plastic film to retard evaporation. The plants were placed in a growth room




2 .



which maintained 150 ft-c of light for 14 hr at a temperature of 22 C.

The plants were allowed to grow for 1 wk after which the chemicals were

introduced into the jars.
For this study, a single replicate consisted of one glass jar contain-

ing six cuttings. Each chemical concentration was replicated at least

four times; in some cases an entire experiment was repeated. The primary

growth response was a measurement for dry weight. In some cases a visual
evaluation of chemical damage was also conducted. After exposure of the

plants for 4 wk to the chemical, the plants were removed from the jars,

rinsed briefly in tap water, and then dried at 60 C for 7 days. Dry weights

were then taken for the combined weight of the six plants in a single

replicate. Duncan's Multiple Range Test was used to separate means for

treatment concentrations when a significant F value was obtained for a

particular experiment.

The growth retardants used in this study were 1,2-dihydro-3,6-pyridazi=

nedione (MH-30); 2-chloroethylphosphonic acid (ethrel); and methyl 2-chloro-

9-hydroxyfluorene-9-carboxylate (Maintain CF 125). The coded compounds

were BAS-3512-H, TD 1123, TD 15707, TD 1796, and TD 15713. Another compound,

previously coded compound number DPX 3674, 3-cyclohexyl-6-(dimethylamino)-l-

methyl-s-triazine-2,4(II,3H)-dione (Velpar) was also screened for its

growth retarding properties on hydrilla. The structural formula of Velpar

is as follows:

0

C
-N N

I II

O N NCH









In brief, Velpar is a non-selective herbicide which can be applied to both

the foliage and leaves of a plant. This chemical is 'effective on a number

of broadleaf and grass species. Velpar has an oral LD50 of 1690 mn/kg on

male rats and 860 mg/kg for male guinea pigs.

B. Effect of Velpar on growth of hydrilla tubers

Hydrilla tubers were collected from pools at the Research Center which

had been planted with hydrilla for a year or more. The pools were drained,

and after the hydrosoil had partly dried, tubers were collected and washed.

These tubers were then planted three each in 100 g of a mixture of muck

soil and sand in the small 5.1-cm2 plastic pots. Two pots were placed in

the 3.7-liter glass cont-ainers filled with pond water. Nutrients were

added 1 wk later as previously described for the hydrilla cuttings.

Velpar was added to one set of jars to make concentrations of 0.01, 0.05,

0.10, and 0.20 ppm immediately after the tubers were placed in the glass

containers. Another set of containers were treated with the same concentra-

tions of Velpar after 1 wk. The tubers were allowed to grow for 7 wk after,

which the plants were removed, washed, and dried. Visual evaluations for

plant damage were made 1, 2, 4, 6, and 7 wk after the application of Velpar

to the second set of containers. The experiment was then repeated to give

eight replications (eight containers for each concentration). The number

of tubers which germinated were recorded for the second part of this study.


C. Effect of glucose on growth of hydrilla

This part of the study was an attempt to establish a growth medium

which would permit hydrilla cuttings to remain alive, but would not grow

large in size. Hydrilla cuttings were collected from canals in the Fort

Lauderdale and 5-cm sections of the tips and stems excised from uniformly

selected plants. The excised sections were then placed four each in 200 ml.









of 10-3, 10-2, 10-1, or 1 M solutions of glucose mixed with distilled water

in transparent plastic containers. The containers were placed under 500 ft-c

of light in a growth room maintained at 22 C. One section was removed

after 1, 2, 3, and 4 wk and analyzed for chlorophyll content. The sections

were also measured for length and the number of lateral shoots noted. Each

concentration was duplicated.

Another group of stem sections were placed in 200 ml of solution of

10-3 or 10-4 M glucose in distilled 120, 10-3 or 10-4 M glucose in tris-buffer

plus nutrients, or distilled water. Each solution was replicated 10 times.

The stems were observed during a 4-wk growth period for lateral shoot

initiation.

D. Effect of Maintain CF-125 and Velpar on lateral shoot initiation and
chlorophyll content of hydrilla stems.

Excised hydrilla sections 5 cm in length were placed in 200 ml 10-3

M glucose solutions containing 0.001, 0.01, 0.1 ppm of Velpar, and 0.005,

0.05, 0.5, and 5.0 ppm of Maintain. Four stem sections were used for

each concentration, and each concentration was repeated eight or more times.

Environmental conditions were the same as those described in the previous

section. Lateral shoot initiation was noted during a 4-wk period. Chloro-

phyll content was determined as the end of the growth period.

E. Evaluation of spikerush media for growth retarding properties on hydrilla

A freeze-dried concentrate of media in which a spikerush (Eleocharis

sp.) had been growing for approximately 6 wk was evaluated for possible

growth retarding properties on hydrilla. In some areas of the country this

spikerush is able to out-compete other aquatic plants. One possible explana-

tion is that the spikerush produces a chemical which inhibits growth of

other plants. The spikerush media used in this study was supplied by
Dr. Dick Schumacher of the USDA aquatic laboratory in Denver, Colorado.




5.




Apical sections of hydrilla were placed in 200 ml of 0.1-strength

Hoaglands nutrient solution or in 10-3 M of glucose with and without the

spikerush media. A pondweed (Potamogeton sp.) was also used in this experi-

ment. Effect of the spikerush media was evaluated by measuring the growth

in length of the plants for a 2-wk period. The experiment was repeated.

F.. Germination of watcrhyacinth seeds

An additional objective of this study was to evaluate waterhyacinth

(Eichhornia crassipes Mart.) Solms) seed germination from seeds collected

in the greenhouse. Seeds were collected during January and February 1973

from plants growing in the greenhouse by placing a container of water

under a flower after it had flowered, and the stalk produced a curvature

which results in the flower extending under the water. The seeds were

allowed to fall to the bottom of the container. They were not allowed to

become dry prior to the germination tests. After sufficient seeds had

been collected, they were placed 10 each on absorbent paper in small plastic.

containers on 28 February 1974. Distilled water (150 ml) was added to

three containers and 150 ml of pond water was added to three other containers.

The water level was maintained by addition of either distilled or pond.water.

Sand or a muck soil was added to other containers, and distilled water was

added in sufficient quantities to just cover the surface. The-waterhyacinth

seeds were placed on top of the sand or soil. Only six seeds were used for

each of the three containers with sand.

III. Results and Discussion

A. Screening program

The terrestrial growth retardants rH11-30 and Ethrel did not affect

growth of hydrilla (Table 1). Maintain CF-125 did not affect growth of

hydrilla at low concentrations (Table 2), but 5.0 ppm of this chemical









resulted in a 48% decrease in plant dry weight after 4 wk (Table 3). The

coded compound BAS-3512--II alone or in combination with copper sulfate did

not affect growth of hydrilla (Table 4). The other coded compounds TD 1123,

Td 15707, TD 1796, and TD 15713 were also not effective in retarding the

growth of hydrilla (Table 5).

Velpar exhibited both herbicidal and growth retarding properties

(Figure 1). Concentrations of 0.2 ppm or higher were toxic to hydrilla,

while concentrations of 0.05 to 0.1 ppm reduced the growth of hydrilla.

The 0.05 ppm concentration resulted in a 50% decrease in dry weight of

hydrilla.

B. Effect of Velpar on growth of hydrilla tubers

Growth of hydrilla tubers was reduced by concentrations of 0.01 ppm

or higher of Velpar (Figure 2). Velpar exhibited some residual properties

since the dry weight of the plants was essentially the same whether the

chemical was applied immediately after planting or whether it was applied

after the tubers had germinated. Velpar did not affect the sprouting of

the hydrilla tubers (Table 6). .Appearance of the plants was essentially

the same whether Velpar was added after the tubers were plants or after

the tubers had germinated.

C. Effect of glucose on growth of hydrilla

Hydrilla tips in the 10-3 M glucose solution averaged 7.4 cm by the

end of the 4-wk growth period, but no lateral shoots were formed. On the

other hand, the hydrilla stems had formed an average of 1.5 lateral shoots

per stem by the end of the growth period in the 10-3 M glucose solution.

The initial Chl content for a and Total was slightly higher in the

apical sections of hydrilla than in the stem portions of the plant (Figures

3 to 8). In general the Chl content of the excised tissue decreased'during









the 1st wk followed by a gradual increase for the remaining 3 wk. The stem

sections did not recover as well as the apical portions of the plant. The

1.0, 10-1, and 10-2 l solutions of glucose resulted in death and decay of

the hydrilla sections. Also these sections were covered with algal

growth which appeared to contribute to the demise of these sections.

Lateral stem initiation was lower in Hoagland's nutrient solution with

tris-buffer than in glucose (Table 7). Growth of algae in the nutrient

solution appeared to be one of the major factors responsible for inhibition-

of lateral shoot initiation

D. Effect of Maintain CF-125 and Velpar on lateral shoot initiation and

chlorophyll content of hydrilla stems

The control stems produced an average of 7.0 lateral shoots per four-

stem sections by the end of the 4-wk growth period. Stems in the 0.5 and

5.0 ppmw of Maintain CF-125 produced an average of 13.8 and 12.1 lateral

shoots per four stem sections which was significantly higher than the

control (Figure 9). The 0.005 and 0.05 ppmw concentrations of Maintain

CF-125 did not affect lateral shoot production. A decrease in lateral

shoot initiation occurred for the stem sections exposed to the 0.1 ppmw

concentration (Figure 10). Velpar at concentrations of 0.001 and 0.01 ppmw

did not affect lateral shoot production.

The lateral shoots produced by the stems exposed to the Maintain CF-125

at the 0.5 and 5.0 ppmw were small and pale in color.. The original stem,

however, remained green and healthy-looking.

Hydrilla stems exposed to Maintain CF-125 at the 5.0 ppmw concentration

resulted in an approximate 50% reduction of chlorophyll content as compared

to the control stems (Figure 11). All three measurements for chlorophyll

content, total, chl a, and chl b were lower than the control for those stems








exposed to the Maintain CF-125. Chlorophyll content of stems exposed to

Velpar at 0.1 ppmw was only slightly lower than the control stems for the

4-wk growth period.(Figoure 12).

E.. Evaluation of spikerush media for growth retarding properties on hydrilla

The spikerush media did not reduce the growth rate of hydrilla or the

pondweed (Table 8). But rather an increase in growth was noted for the

hydrilla apical sections in glucose with the spikerush media as compared to

plants in only the glucose. Apparently the mineral nutrients which had been

concentrated when the spikerush media was freeze-dried were sufficient to

help promote growth of the hydrilla. Similar growth as the hydrilla was

noted with the pondweed propagules.

F. Germination of waterhyacinth seeds

The number.of waterhyacinth seeds which had germinated after-37 and 51

days is presented in Table 9. Seeds in the pond water and muck soil were

coated with algae soon after germination; however, these conditions apparently

did not inhibit germination of these seeds. In this test the seeds were

removed from the collection containers and immediately placed in the germina-

tion containers. This initial test indicates that waterhyacinth seeds do

not require a drying period prior to germination.

IV. Summary and Conclusions

Of the chemicals s'crecned for growth retarding effects on hydrilla,

Velpar was the most effective.. This chemical reduced dry weight as well as

lateral shoot initiation. Chlorophyll content of hydrilla was only slightly

lower than the control. Additional studies are needed to determine the

feasibility of using this chemical in an aquatic management program.

Maintain CF-125 also reduced the growth of hydrilla; however, the amount of

chemical required was considerably higher than Velpar. Also, the chlorophyll









content of the hydrilla exposed to the Maintain CF-125 was considerably

lower than the control. One of the goals of the screening program was

to find a chemical which would reduce the growth rate of hydrilla and at

the same time allow the plant to retain its color. Velpar came the

closest to meeting these requirements of all the chemicals screened.

This study indicates that is is possible to reduce the growth rate

of a noxious aquatic plant. Whether this approach to aquatic plant

management will become an effective method will require more attention.

In many cases the removal of one problem plant results in the appearance

of another or the regrowth of the original one. The desirability of

maintaining a cover of plants in a slow growing state should receive more

study. Hopefully, the results of these studies will stimulate an interest

for additional research on the feasibility of using growth retardants in

an effective aquatic management program.










V. Distribution List

Copy Number

1 Dr. Alva P. Burkhalter, Coordinator
Aquatic Plant Research and Control
Florida Department of Natural Resources
Room 595, Larson Building
Tallahassee, 1:I 32304

2 Dr. John F. Gerber, Director
Center for Environmental Programs and Natural Resources
University of Florida IFAS
2014 McCarty Hall
Gainesville, FL 32611

3 Dr. Sherlie II. West, Assistant Dean
University of Florida IFAS
1022 McCarty Hall
Gainesville, FL 32611

4 Dr. Edward 0. Gangstad, Chief
Aquatic Plant Control Planning Division
Department of the Army
Office of the Chief of Engineers
Washington, D. C. 20314

5 Mr. Zeb Grant, Director
Maintenance and Operations
Central and Southern Florida Flood Control District
P. 0. Box 1671
West Palm Beach, FL 33408

6 Dr. Kerry K. Steward, Acting Location Leader
USDA, ARS
3205 S. W. 70 Avenue
Fort Lauderdale, FL 33314

7 Dr. Peter A. Frank
University of California
USDA, ARS, CRD
Botany Department
Davis, CA 95616

8 Dr. Bill Haller
University of Florida IFAS
Department of Agronomy
304 Newell Hall
Gainesville, FL 32611

9 Dr. Jim Foret
University of Southwestern Louisiana
Department of Plant Industry
P. O. Box 487
Lafayette, LA










10 Dr. Dick Schumacher
USDA, ARS
Room 212, Building 56
Denver Federal Center
Denver, CO 80225

11 Mr. Bob Sutton
Biochemicals Department
E. I.'du Pont de Nemours & Co., Inc.
Box 2348, Manatee Station
Bradenton, FL 33505

12 Dr. William B. Ennis, Jr.
USDA, ARS
Room 319, North Building
National Program Staff Weeds
Plant Industry Station
Beltsville, MD 20705














Table 1. Effect of Mil-30 and Ethrel on growth of hydrilla in

3.785-liter glass containers.


Chemical Concentration Visual evaluation Plant dry,/
(ppmw) 2 wk 4 wk we eight mg-


Mil-30 0.5 0 0 431 a

Mil-30 1.0 0 0 354 a

M?-30 10.0 0 0 362 a

Ethrel 0.5 0 0 332 a

Ethrel 1.0 0 0 355 a

Ethrel 10.0 0 0 416 a

Control 0 0 388 a

a/
- 0 = No effect; 100 = complete kill.

/ Values followed by the same letter are not significantly different

at the 5% level as determined by Duncan's Multiple Range Test.

Each value is the mean of four replications.










S














Table 2. Effect of Maintain CF-125 on hydrilla grown in 3.7-liter glass

containers under controlled conditions during a 4-wk period.


Concentration
(ppmw)


a/
Dry weighta
mg


Visual evaluation -K


0 342 0

0.25 356 0

0.50 367 0

1.0 280 0


a/ Values followed by the same letter are not significantly different

at the 5% level as determined by Duncan's Multiple Range Test. Each

value is the mean of eight replications.

-- 0 = No effect; 100 = plants killed.




14


Table 3. Effect of Maintain CF-125 on hydrilla grown in 3.7-liter

glass containers under controlled conditions during a 4-wh

period.


Concentration Dry weight/ Visual evaluation/
(ppmw) mg


0 771 b 0

0.5 717 b 0

1.0 806 b 5

5.0 405 a 20


a/ Values followed by the same letter are not significantly different

at the 5% level as determined by Duncan's Multiple Range Test.

Each value is the mean of eight replications.

b/ 0 = No effect; 100 = plants killed.













Figure 4.


Effect of BAS-3512-H and copper sulfate on growth of

hvdrilla in 3.7-liter glass containers during a 4-wk

period under controlled conditions.


Herbicide' Concentration Plant dry ,
weight mg--


Control 0 381 a

BAS-3512-H 0.1 366 a

CuSO4 0.1 291 a

BAS-3512-II plus CuSO4 0.1 plus 0.1 297 a

BAS-3512-11 0.5 345 a

CuSO4 0.5 327 a

BAS-3512-HI plus CuSO4 0.5 plus 0.5 303 a

a/
/ Values followed by the same letter are not significantly

different at the 5% level as determined by Duncan's Multiple

Range Test. Each value is the mean of four replications.















Table 5. Effect of various coded compounds on hydrilla grown in 3.7-

liter glass containers under controlled conditions during

a 4-wk period.


Compound Concentration Visual phytotoxicity Dry weight
(ppm) after-4 weeks a/ after 4 weeks
(mg) _/


Control 0 437 a

TD 1123 1.0 2 437 a

TD 15707 1.0 4 476 a

TD 1796 1.0 2 407 a

TD 15713 1.0 5 363 a

TD 1123 0.1 0 384 a

TD 15707 0.1 0 386 a

TD 1796 0.1 0 468 a

TD 15713 0.1 0 413 a


a 0
a 0 = No effect; 100 = plants killed.

b/ Values followed by the same letter are not significantly different

at the 5% level as determined by Duncan's Multiple Range Test.

Each value is the mean of four replications.




















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Table 7. Lateral shoot initiation from hydrilla stems in various media.


a/
No. of lateral shoots jer four stem sectons--

Weeks of observation


Distilled water

10-3 M Glucose in distilled water

10-4 M Glucose in distilled water

10-3 M Glucose in tris-buffer
plus 0.1-strength Hoagland's

10-4 M Glucose in tris-buffer

plus 0.1-strength lHoagland's

Tris-buffer plus 0.1-strength
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a/ Values followed by the same letter are not significantly different at the 5%

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i


Media


___


--
--













Table 8. Evaluation of spikerush media for growth retarding properties

on hydrilla and pondwced.


Plant length (cm)/

Plant condition Weeks

0 1 2


A. Hydrilla plus Hoagland's

With spikerush media 5 a 11.2 b 15.1 c

Without spikerush media 5 a 11.5 b 15.9 c


B. Hydrilla plus Glucose (10-3 M)

With spikerush media 5 a 7.3 c 8.1 d

Without spikerush media 5 a 6.6 b 7.4 c


C. Pondweed plus Hoagland's

With spikerush media 6.5 a 15.3 b 19.7 c

Without spikerush media 5.9 a 15.1 b 20.8 c
........................................................................

D. Pondweed plus Glucose (10-3 M)

With spikerush media 6.3 a 12.5 c 13.4 c

Without spikerush media 5.6 a 9.8 b 10.1 b


a/ Values within each plant condition followed by the same letter are

not significantly different at the 5% level as determined by Duncan's

Multiple Range Test. Each value is the mean of 12 plants.














Talle 9. Germination of waterhyacinth seeds.


Germination (%)

Germinating condition Days after planting

37 51


Pond water 40.0 73.3

Distilled water 20.0 73.3

Muck soil covered with
distilled water 0 0.3

Sand covered with
distilled water 0 50.0


SValues are the average of three containers with ten seeds each

except for the sand covered with distilled water which was

planted with six seeds.



























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Figure 9. Lateral shoot production of
hydrilla stems exposed to various
concentrations of Maintain CF-125.


MAINTAIN


CF-125


---- CONTROL
..-0. 005
.---- 0.05


-- -


/-


0.5


: J ------ --~~ ~--~ --~lar,~l.-


GROWTH


12


/
/


(PPvM/I)


~


.0
-*")*


(WK)


PERIOD










Figure 10.


Lateral shoot production of
hydrilla stems exposed to
various concentrations of Velpar.


-b ~


VELP R.- %


- ~ ~ r ~ -CC1"O


_- ---- 0.001
------ O. 01
--- -0.1


I. 2 3


PERIOD (WK)


(PPr r


GROWTH












Figure 11. Chlorophyll content of hydrilla
stem sections exposed to
Maintain CF-125 for 4 wk.


.. ~, ,,.... ;. r r r r r r ;r;r r
..;.....' .''. '.'.'' '''.. ... .'''. ;~:`.' .... '
~~ ............ .. .. .' .r .. ~ '
''' : '.' '.' '''
~~ ~~ ~~ ~~ ~~ ~~ ~~ :~ ...... . :... ..''::~ '...:-'. ''''~''
.'... ............. .'
~~~ ~~~~~~ ~~ ~.~ ~.~~~.~ ~~~.~ .~...~ .....~... .... ~ '..` .''.''' '
'''
.._. .::~ .. '. " .......'.' '~ '~ "


J|TOTAL
-t -- *^ ,,*::.'-~l A A!i -&A BU A i~ i AJA j Ji^r..............-^i W i^ii t*^.AI


(CrHLOrOCPHYLL


* 4,4 *.4 4'4 4 .. 44 .~':.. ... ..
.~..,.444.44,.4.4.. 4 4 4
444 *~ *~ *4 444 *' 44
4 4 4.' 4 4. 44 444 4 4 4 44 44 4 4 44 *


. . ..3~


CHLOROP; -iYLL


44 44444 444 4 ~.4. 4
4 4 4 4444444 *4 *444
44444 .44 4 4 4 4444 44


CHLOROPHYLL B


E CcZM:rol

h r, AC-A ira


5.0 PPtMi


I I


0.6

FRESH


1.2


0.9

WEIGHT


0.3

* MG/G


--


--


A


.........
..........~--
............-
...............--
--
.........-
1:II'I1rI1::::::::::::::::::5:::::::::::
--.--~1llIIlll:::
-1
-'
.











Figure 12. Chlorophyll content of hydrilla
stem sections exposed to
Velpar for 4 wk.


. ,-..-.........---..................-.....--.-..i.i.i. .ii iii-i ii iiiii. :::: : .....i.....i.--.. .


TOTAL CL L. '.- HYLL-


........... *. *. .*

.... ... ... .... ... ... ......
-.........--....- ....
... .. .. .. .. ..


CH LOC ( YLL


4. 4. 4. .. 4. 4. 4. 4. 4....
~~'.4 4...44.,,....... *4
44~ *,444 4.~ 4~4~~4. 4*~~


CHLORF~Yr't LL


... J l...i i. -. .. ii... .i.. ......i.... ........




Vcfpcr


0.1 PPMrv


0.3
MG/G


0.6


0.9


FRESH WEIGHT


0.0


1.2


~ --




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