Control of Aquatic Weeds by Chronic Intoxication

19 Control of Aquatic Weeds by Chronic Intoxication GEORGE E. JANES

Downloaded by TUFTS UNIV on June 3, 2018 | https://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0033.ch019

Creative Biology Laboratory, Inc., 3070 Cleveland-Massillon Road, Barberton, Ohio 44203

Laboratory studies by the Creative Biology Laboratory and others have shown that biologically active chemicals can be released from specially compounded elastomers at relatively constant rates over long periods of time. The chemicals or "pesticides" thus released demonstrate the same biological activity as if they were conventionally applied. The controlled release system, however, offers advantages or variations in approach that are not possible or at best are impractical with conventional application. Chronic intoxication of pest aquatic weeds with a constant low level herbicide dosage is one example. Obviously the high cost of conventional spreading or spraying herbicides precludes daily applications of ultra low concentrations and dictates that a single acute dose be applied. Chronic intoxication of aquatic weeds by i t s e l f , is not an advantage in favor of controlled release. Ultimately there must be an economic or environmental advantage. Thus it is not sufficient to simply extend the toxicant disbursal time. There must be an accompanying enhancement of efficacy, an extention of the time between applications, a reduction in toxicant usage, or some other factor altered that can be converted into a dollar savings or environmental benefit. With this in mind, we were quick to note during the course of this effort that the mortality curve, in many instances, was not proportional to the dosages used, i.e. i f 0.1 ppm/day dose killed in one week and the concentration/time (Ct) equation were accurate, then a 0.01 ppm/day dose should give the same results in 10 weeks. Both in laboratory and pond tests, this was not so. The time factor was about 1.7 and not 10. Thus, i t was hypothesized that whereas a Ct relationship probably held for acute terminal dosages where the time period was confined to several days, i.e. conventional treatment; the ultralow agent concentrations experienced with slow release methodology leads to a terminal chronic intoxication whose mechanism of action is different. It is also suspected that the slow release mechanism results 231 Paul and Harris; Controlled Release Polymeric Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1976.


232

CONTROLLED RELEASE POLYMERIC FORMULATIONS

in a truly molecular concentration in the water envelope, whereas conventional use of granules, emulsions, etc. lead to molecular aggregrates. The s t a t i s t i c s of contact as well as the absorbtivity of the agent by the plant may be significantly different. This "chronicity" phenomenon was investigated in a study involving two basic experiments. In one the herbicide was added daily and the toxicant was allowed to accumulate. In the other case the herbicide was also added daily, but the test water was changed so that the agent concentration was held f a i r l y constant. Watermilfoil, Elodea, Cabomba, Vallisneria and Southern naiad were evaluated i n one gallon jars, each with 3 l i t e r s of water. Plants were potted, three to the jar, in 200 ml. cups. Gro-lux lighting was used in indoor tests with intensity adjusted for optimum growth. Other plants were tested in 5 gallon plastic lined containers. Plants were conditioned for 4 to 8 weeks prior to instituting a poisoning regime. Test containers were observed daily and plant mortality subjectively rated on a 100 (healthy) to 0 (mortality) scale with the degree of thinning and browning serving as the rating c r i t e r i a . Evaluations performed during the course of this effort tend to confirm the hypothesis that the Ct relationship does not hold when ultralow herbicide concentrations are maintained for extended periods of time. This is shown in the following data. TABLE 1 EFFECTS OF FIVE TOXICANTS ON WATERMILFOIL:

DOSE ACCUMULATIVE

Toxicant

Dose (ppmw)

Days to Given % Mortality 100% 90% 50%

Diquat tt it tt

1.0 0.1 0.01 0.001

9 9 10 18

13 12 16 24

14 13 19 38

Fenac

1.0 0.1 0.01 0.001

14 24 never

19 42 43 never

21 43 48 never

1.0 0.1 0.01 0.001

8 18 18 never

13 23 20 never

18 27 21 plants recovered

1.0 0.1 0.01 0.001

8 8 13 21

12 14 20 never

14 18 24 recovery

tt II tl

Silvex it 11 II

2,4-D It II II

acid

22

Paul and Harris; Controlled Release Polymeric Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1976.

19.

JANES

Control of Aquatic

233

Weeds

TABLE I (cont.) EFFECTS OF FIVE TOXICANTS ON WATERMILFOIL:

DOSE ACCUMULATIVE

Toxicant

Dose (ppraw)


2,4-D BEE

1.0 0.1 0.01 0.001

10 10 10 10

" "

13 15 14 IS

15 17 18 22


Water Controls average 6% mortality Solvent Controls average 16% mortality TABLE II EFFECTS OF FIVE TOXICANTS ON WATERMILFOIL:

DOSE CONSTANT

Toxicant

Dose (ppmw)


Diquat

1.0 0.1 0.01 0.001

8 9 9 23

10 14 13 27

11 19 16 32

1.0 0.1 0.01 0.001

19 never 23 35

never never never never

recovery recovery recovery recovery

1.0 0.1 0.01 0.001

8 20 21 never

11 never never never


1.0 0.1 0.01 0.001

12 20 never never



1.0 0.1 0.01 0.001

7 6 13 20

10 13 22 38

13 19 24 never

It f! II

Fenac II II II

Silvex II ft tt

2,4-D acid π It It

2,4-D BEE It II 11

Water Controls 31% mortality Solvents Controls 35% mortality



234

Days:


0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Figure 1.

Diquat vs. watermilfoil: dose accumulative

Figure 2.

Diquat vs. watermilfoil: dose constant


19. JANES

of Aquatic

Weeds

235

The preceding data represents an average reading of four test aquaria, or a total of 12 plants, for each toxicant at each concentration. Control data i s an average of 12 jars or 36 plants each. The data on 2,4-D BEE and Diquat i s shown i n graph form i n Figures 1 through 4 to better illustrate the minimal time penalties incurred to achieve control at ultra-low toxicant concentrations. A controlled release formulation of copper sulfate monohydrate (JL) with a measured release rate of only a fraction of one percent of total available toxicant per day was evaluated against Vallisneria, Cabomba. duckweed, watermilfoil and algae to see i f the chronicity phenomenon" was reflected in the results. Planting, preparation and rating was the same as in the previous experiments. Toxicant pellets were added at 10 ppm, 50 ppm and 100 ppm by rubber weight with respective copper ion contents of 1.75 ppm, 8.75 ppm and 17.5 ppm. Jars were also treated with a 0.03 ppm copper ion solution to approximate the actual release from a 100 ppm pellet. Table III shows the data for the Cabomba exposure and the information i s charted in Figure 5. The "chronic ity phenomenon" i s pronounced here i n that a difference of only 5 days i s noted for a 100% k i l l between the lowest and highest rates. (2) f,


Control

M

Figure 3.

BEE vs. watermilfoil: dose accumulative


236



Figure 4. 2,4-D BEE vs. watermilfoil: dose constant

Days:

0

5

10

15 20

Figure 5.

25

30

35 40 45

50

55 60

E-51 vs. Cabomba caroliniana


19. JANES

Control

of Aquatic

237

Weeds

TABLE III E-51 vs. Cabomba carolintana Mortality at a given time (day)*


5 10 15 20 25 30 35 40 45 50 *

CirH- 0.03 ppm/dav

Control

Day

3% 10% 24 30 30 30 40 30 25 25

10% 30 35 40 45 65 65 90 100

10 ppm

50 ppm

100

23% 33 50 66 80 90 93 100

37% 60 82 85 85 92 100

26% 40 60 78 78 90 100

ι

--

—

— —

—

average of replicates

The presence or absence of the "chronicity phenomenon" as noted i n these studies to date i s summerized in Table IV.

TABLE IV Presence (+) or Absence (-) of the "Chronicity Phenomenon"

Herbicide

Vallisneria

Cabomba

Plants M i l f o i l Elodea

Southern Naiad

2,4-D BEE

+

+

+

+

UNK

Diquat

+

+

+

+

-f-

Silvex

-'r

+

+

UNK

Fenac

+

+

+

2,4-D Acid

-

+

-

Endothall

-

+

Fenuron

-

+

UNK

+

UNK

Copper

+

+

+

+

UNK

+ +

UNK +


238


Conclusions The studies indicate that chronic intoxication of aquatic plants occurs and that very low doses of herbicides w i l l destroy pest weeds given a long enough period of time. Furthermore, there i s i n many instances a beneficial chronic effect which minimizes the time penalty. This "chronicity phenomenon" indicates that control with slow release materials could significantly reduce environmental contamination as well as lowering costs and minimizing field hazards in handling toxicants.


Acknowledgements Support of research on the "Chronicity Phenomenon" and controlled release aquatic herbicides by the Army, Office of the Chief of Engineers, i s gratefully acknowledged. Literature Cited 1. Walker, K.E., Cardarelli, N.F. "Development of Slow Release Copper as a Molluscicide" INCRA Ann. Rep. Proj. 203(Jul 1, 1974). 2. Janes, G.A., B i l l e , S.M. "Chronicity Phenomenon and Controlled Release Copper", WSSA 16th Meeting (Feb. 2-5, 1976)


Control of Aquatic Weeds by Chronic Intoxication

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