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This is to certify that the

dissertation entitled

The Controlled Release of
Water Soluble Herbicides

presented by

Bruce D. Riggle

has been accepted towards fulfillment
of the requirements for

Ph.D. degreein Crop & Soil Sciences

 

Major professor

Donald Penner

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CONTROLLED RELEASE OF WATER
SOLUBLE HERBICIDES

BY
Bruce Dale Riggle

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Crop and Soil Sciences

1985

©1985

BRUCE DALE RI GGLE

All Rights Reserved

ABSTRACT

THE CONTROLLED RELEASE OF WATER

SOLUBLE HERBICIDES

BY
Bruce Dale Riggle

Pine kraft lignin was used to control the release
of metribuzin (4-amino-6-Eggg-butyl-3-(methythiol-gg-triazin-
5(4H)-one) and alachlor (2-chloro-2',6'-diethyl-N-methoxy-
methyl acetanalide). Soil thin layer chromatography (TLC)

l4C-alachlor demonstrated

analysis using l4C-metribuzin and
that NB-5203-S8 series and PC940 series kraft lignins could
retard the mobility of both herbicides after multiple soil
TLC plate developments with water. Soil column chromato-
graphy analysis demonstrated that PC94OC could retard the
mobility of both herbicides after soil column water leaching
by positioning the herbicides in the top portion of the soil
column where the PC940C-herbicide mixture had been applied.
There was a concentration effect where, as more PC940C was

used, more l4C-labelled herbicide was retained in the top

portion of the soil columns. Soil column chromatography and

3a-PC94oc was

soil TLC plate analysis demonstrated that
immobile. Finally, PC94OC significantly reduced metribuzin
related phytotoxicity to field and greenhouse grown soybeans
(Glycine mag (L.) Merr.) which had been treated with PC94OC
rates of 0.77 and 1.15 L/ha and metribuzin rates of 0.42 and

14C-metribuzin and 14C-alachlor

0.84 kg/ha. The results for
as well as the reduction in metribuzin related phytotoxicity
to soybeans suggests that PC94OC can effectively control the

release of metribuzin and alachlor.

ACKNOWLEDGMENT

The author wishes to express his sincere appreciation
to his major professor, Dr. Donald Penner, for his guidance
throughout this study and his friendship. The experience
received through involvement in the controlled release
project was very rewarding and appreciated. The assistance
of Dr. A.R. Putnam, Dr. G.L. Hosfield, and Dr. M.E. Zabik as
Guidance Committee members is gratefully acknowledged. A
special thanks to Mr. Frank Roggenbuck for his technical

assistance in the laboratory and greenhouse.

ii

TABLE OF CONTENTS

PAGE
LIST OF TABLES O O O O O O O I O O O O O O O O O O O O 0 v
LIST OF FIGURES O O O O O O O O O O O O O O O O O O O 0 vii

INTRODUCTION 0 O O O O O O C O O O O O O O O O O O O O O 1

CHAPTER 1. LITERATURE REVIEW . . . . . . . . . . . . . 3
LITERATURE C ITED O O O O O O C O O C O O O O O O O O 1 7
CHAPTER 2. CONTROLLED RELEASE OF METRIBUZIN AND
ALACHLOR BY KRAFT LIGNINS AS MEASURED
BY SOIL THIN LAYER CHROMATOGRAPHY . . . . . 24
ABSTRACT I O O O O O O O O O O O O O O O O O O O O O 2 4
INTRODUCTION 0 O C O O O C O O O O O O O I C O C O C 2 6
MATERIALS AND METHODS . . . . . . . . . . . . . . . . 28
RESULTS AND DISCUSSION . . . . . . . . . . . . . . . 33
LITERATURE C ITED O O C C O O O O O O O O O O O C O O 4 3
CHAPTER 3. CONTROLLED RELEASE OF METRIBUZIN AND
ALACHLOR BY PC94OC AS MEASURED BY SOIL
COLUMN CHROMATOGRAPHY . . . . . . . . . . . 46

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . 46

INTRODUCTION . . . . . . . . . . . . . . . . . . . . 48
MATERIALS AND METHODS . . . . . . . . . . . . . . . . 50
RESULTS AND DISCUSSION . . . . . . . . . . . . . . . 55
LITERATURE CITED . . . . . . . . . . . . . . . . . . 66

iii

PAGE

CHAPTER 4. PC940C PROTECTION OF FIELD AND
GREENHOUSE GROWN SOYBEANS FROM
METRIBUZIN INJURY . . . . . . . . . . . . . 69
ABSTRACT O O O O O O O O O O O O O O O O O O O O O O 6 9
INTRODUCTIObI O O O O O O O O O O 0 O O O C O O O O O 7 0
MATERIALS AND METHODS O O I O O O O I O O O O O O O O 7 2
RESULTS AND DISCUSSION . . . . . . . . . . . . . . . 76

LITERATURE CITED . . . . . . . . . . . . . . . . . . 87

iv

LIST OF TABLES

we
CHAPTER 2

1. Effect of lignins on the percentage of
14C-metribuzin retained at the point of
origin on soil TLC plates after three
developments . . . . . . . . . . . . . . . . . . . 34

2. Effect of NB-5203-58B on the percentage
of l4C-metribuzin retained at the point
of origin on soil TLC plates after three
developments . . . . . . . . . . . . . . . . . . . 3S

3. Effect of lignins on the percentage of
4C-metribuzin retained at the point of
origin on soil TLC plates after three
developments . . . . . . . . . . . . . . . . . . . 37

4. Effect of formulated and nonformulated
PC940C on the percentage of 14C-metribuzin
retained at the point of origin on soil TLC
plates after two developments . . . . . . . . . . 39

5. Effect of lignins on the percentage of
4C-alachlor retained at the point of
origin on soil TLC plates after three
developments . . . . . . . . . . . . . . . . . . . 41

CHAPTER 3

1. The effect of PC940C on 14C-metribuzin

distribution in a Wando sandy loam soil

column following one or two leaching

periods with 2.54 cm of water . . . . . . . . . . 56
2. The effect of PC940C on 14C-alachlor

distribution in a Wando sandy loam soil

column following one or two leaching

periods with 2.54 cm of water . . . . . . . . . . S7

PAGE

3. Percentage of 14C-metribuzin in various
depth sections of a Wando sandy loam soil
column following application of a metribuzin-
alachlor mixture leached with 2.54 cm water
over a 2 h time period . . . . . . . . . . . . . . 58

4. Percentage of 14C-alachlor in various depth
sections of a Wando sandy loam soil column
following application of a metribuzin-
alachlor mixture leached with 2.54 cm water
over a 2 h time period . . . . . . . . . . . . . . 60

5. The influence of PC940C on the recovery of
4C-metribuzin from Wando sandy loam soil
columns following the two leaching and drying
treatments . . . . . . . . . . . . . . . . . . . . 61

6. Percentage of 3H-PC940C in various depth
sections of a Wando sandy loam soil column
following leaching with 2.5 cm of water . . . . . 64

CHAPTER 4

l. Rainfall and irrigation data for 1984 at
East Lansing, Michigan after 22 June . . . . . . . 74

2. Soybean injury ratings as affected by
metribuzin and PC940C at 32 D.A.E. . . . . . . . . 77

3. Soybean injury ratings as affected by
metribuzin and PC94OC at 46 D.A.E. . . . . . . . . 78

4. Soybean injury ratings as affected by
metribuzin and PC94OC for greenhouse
grown plants at the third trifoliar
stage . . . . . . . . . . . . . . . . . . . . . . 84

5. Effect of PC940C on metribuzin injury to

soybeans grown in greenhouse as measured
in dry weight of third trifoliar plants . . . . . 86

vi

LIST OF FIGURES

PAGE

CHAPTER 4

1. Soybeans treated with 0.42 kg/ha
metribuzin and O L/ha PC94OC and
rated at 32 DOAOE. I 0 O O O O O O O O O O O O O O 80

2. Soybeans treated with 0.42 kg/ha

metribuzin and 0.77 L/ha PC94OC
and rated at 32 D.A.E. . . . . . . . . . . . . . . 82

Vii

INTRODUCTION

A basic problem with the use of several water soluble
preemergence herbicides is their rapid dissipation and
subsequent dilution as water is added to the soil. Excessive
water can result in reduced weed control and in the herbi-
cide being positioned in the root zone of the crop species
and/or movement to the ground water. These disadvantages
are associated with metribuzin (4-amino-6-tggt-butyl-3-
(methythio)-g§-triazin-5(4H)-one) and alachlor (2-chloro-
2',6'-diethyl-N-methoxymethyl acetanilide). Metribuzin is
mobile in neutral and alkaline pH soils and can cause injury
to soybeans (Glycine max (L.) Merr.). Alachlor, while not

phytotoxic to corn (Zea mays L.) or soybeans, could, over

 

time, be more effective if leaching was reduced.

Controlled release agents used in combination with
herbicides such as metribuzin and alachlor could potentially
increase herbicide efficacy. This could be achieved by
reducing herbicide dissipation and dilution in the soil zone
containing weed seeds. The result would be an increase or
extension of weed control, a reduction in crop plant
phytotoxicity, and a reduction in ground water contamina-

tion.

b.)

The objectives of this study were: (1) to test pine
kraft lignins for controlled release of metribuzin and
alachlor by soil thin layer chromatography, (2) to test the
most promising lignin for controlled release of metribuzin
and alachlor by soil column chromatography, and (3) to test
the most promising lignin for controlled release of

metribuzin using greenhouse and field grown soybeans.

CHAPTER ONE

LITERATURE REVIEW

A basic problem with the use of several water soluble
preemergence herbicides is their rapid dissipation and
subsequent dilution as water is added to the soil. Even
though water is essential to mobilize these surface-applied
herbicides and move them into the soil to control
germinating weed species, the addition of water over time
can establish a diffusion gradient. This can result in the
removal of a majority of the herbicide from the top portion
of the soil and consequently reduce weed control. Herbicide
activity may be further reduced by soil microorganism
metabolism of the herbicide and the adsorption of the
herbicide on soil clay and organic matter colloids.
Excessive water leaching can also result in the herbicide
being positioned in the root zone of the crop species and/or
movement to the ground water. This may further result in
phytotoxicity to non target plants and pollution of ground
water.

A possible modification to the conventional approach of
water-soluble preemergence herbicide application is the use

of controlled release agents to control or delay the

movement of herbicide from the soil surface. This approach
could reduce herbicide dissipation and dilution into the
soil zone containing weed seeds and consequently increase or
extend weed control, reduce crap plant phytotoxicity, and
reduce ground water contamination.

Other goals of a controlled release strategy include
increased herbicide efficacy throughout the growing season
as well as the possible expansion of the weed control
spectrum. Because the efficacy is usually dependent upon a
dose response, a reduction in the dose or amount of
herbicide present in the soil will reduce the potential weed
control. The amount that will microbially or chemically
degrade is generally dependent upon the first order rate law
(9) and thus the persistence of herbicide activity may be
increased by a reduction of the first order rate constant
(9). This could be achieved by reducing the amount of free
herbicide in the soil as compared to the amount of herbicide
that would be currently adsorbed to the controlled release
agent. The rate of herbicide release from the controlled
release agent would also have a first order rate constant
(26) which would determine, depending upon the magnitude,
how’ quickly or slowly the herbicide would be released.
Ideally for herbicides with short half-lives, a large rate
constant for release is desirable. This approach might

require more herbicide than the conventional approach (8),

however, this cost would be offset by the potential to
increase the herbicide efficacy.

For the control release agent or polymer to
successfully extend the half-life of a herbicide, it would
have to serve as a barrier to microbial or chemical
degradation. This degradation or dissipation of herbicide
could be due to conversion to a nonphytotoxic substance by
either some form of partial metabolism or by a conjugation
process. There may also be nonbiological processes involved
such as an interaction with clay surfaces resulting in
conversion of the herbicide to a nonphytotoxic material.

The theoretical amount of herbicide that would be
needed in conjunction with a controlled release agent would
not be less than the conventional amount necessary to
achieve the desired weed control (8). Furthermore, the
amount needed could be more than that used for multiple
applications but less than that needed for a single
application (8). The predicted savings would be the
possible elimination of multiple or split applications of
herbicide.

Various approaches have been tried to find effective
controlled release polymers for water-soluble herbicides.
Combinations of cross-linked starch and 2,4-D (2,4-dichloro-
phenoxy acetic acid) which form 2,4-D esters of high acyl
content have resulted in the controlled release of varying

amounts of 2,4-D and water-soluble 2,4-D esters (28).

Amylase-metribuzin (4-amino-6-Eggt-butyl-3-(methylthio)-a§-
triazin-5(4H)-one) polymers have been demonstrated to
release metribuzin in a zero order manner as measured by
HPLC analysis (26). However, amylose-metribuzin polymers
have not. been tested. with soil and plants in field. or
greenhouse environments. Starch xanthide combinations with
chloramben (3-amino-2,S-dichlorobenzoic acid) methyl ester
salts have been tested and did not differ in weed control
from chloramben ester formulations (33). Plaster of Paris
tablet encapsulated alachlor (2-chloro-2',6'-diethy1-N-
methoxymethyl acetanalide) has been shown to successfully
control weeds and protect ornamental flowering plants from
alachlor injury (39). Linear and cross-linked copolymers of
polyvinyl alcohols were substituted with pendent metribuzin
which resulted in varying release rates of metribuzin
(17,25). Pine kraft lignin combined with 2,4-D esters has
successfully controlled the release of 2,4-D at a zero order
rate for use as a plant growth regulator (11). Multiple
pesticide-lignin polymer combinations have been attempted,
such as combining 2,4-D and 3,4,5,6-tetrachloropthalic
anhydride with kraft lignin polymers by the use of triazine
functional groups which were covalently linked to the lignin
polymer (2).

Problems can arise from using most of these controlled
release polymers and combinations. Polysaccharides such as

starch and amylose are readily available carbon sources for

soil microorganisms and thus would not be a good barrier to
protect herbicides from microbial decomposition. In
addition, the presence of polysaccharides in holding tanks
or spray tanks would risk fermentation with resulting
by-products which could result in clogged lines and nozzles.
Polyvinyl polymers of pendent substituted herbicides is a
very expensive technique and has not yet been successfully
tested in greenhouse or field situations for weed control or
crop plant protection from metribuzin phytotoxic effects.
Furthermore, these pendent formulations would require
enormous sums of money to test the toxicological effects of
the chemically altered herbicide as well as the
effectiveness of the new compounds as herbicides. Plaster
of Paris tablet encapsulated herbicide would not be a
practical formulation for field grown crops but. may' be
suitable for ornamentals and perennial horticultural crops.

One of the most promising controlled release polymers
is kraft lignin. The material is relatively cheap compared
to polyvinyl polymers and not rapidly degraded as
polysaccharides. Because of the multifunctionality (l4) and
adsorptive capacity of kraft lignin (12), it should. be
capable of readily adsorbing compounds such as metribuzin
and alachlor.

Lignin has been referred to as the most abundant
aromatic source in nature (11) and is produced in the cell

walls of higher plants via the shikimic acid pathway (36).

Lignin's function appears to be to provide both structural
and turgor-stress counteracting strength as well as serving
as an anti-microbial agent (42). The anti-microbial
properties are thought to be due to the multi-hydroxyl
functional groups that are abundant in lignin (42). The
natural structure has been defined by milling woody tissue
(27). In addition there are differences in lignin structure
that vary according to the location in the cell wall and
middle lamella (27). How lignin is associated with
cellulose and hemicellulose is not clear although some
research has described this association as 'snake cages' in
which polymers of lignin are wrapped around the cellulose
and hemicellulose fibers which in turn imparts strength to
the cell wall (14).

Lignin is persistent and remains in the soil for long
periods of time because of the presence of multifunctional
groups (36). It is slowly degraded by white rot fungi,
Basidiomycetes sp., (36) and is believed to be the source of
aromatic groups used in the formation of soil organic matter
components such as humic and fulvic acid (40).

Lignin is very similar in structure to humic acid and
both have been found to have a high adsorptive capacity
for atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-§-
triazine) (12). Atrazine adsorption to humic acid has been
found to be mainly due to hydrogen bonding with carboxylic

and hydroxyl groups of the humic acids to amine groups of

the triazine as measured by infrared spectrometry (41).
Because of the similarity in structure between lignin and
humic acid, the findings suggest that lignin would adsorb
triazine herbicides in a similar manner.

The concept of using natural unaltered lignin for a
lignin herbicide complex or as a controlled release mixture
is impractical since unaltered lignin can only be obtained
under laboratory conditions and only in small amounts. A
more plentiful and realistic source is industrial grade
lignin which is a by-product of the paper pulping industry.

The two major types of industrial lignin are sulfite
and alkaline kraft lignin. The source of these lignins is
typically from conifer trees and the differences between the
two lignins depend upon differences in the chemical pulping
processes. Sulfite pulping includes sulfonation, hydrolyses,
and condensation which in turn produces highly water-soluble
lignin, sulfate and sulfite salts, alcohols, aldehydes, and
carbohydrates (13). Sulfite lignin is not suitable as a
controlled release agent for water soluble herbicides due to
the water solubility factor and the accompanying impurities.
Alkaline pulping is a more complex method which utilizes
sodium sulfite and sodium hydroxide to solubilize and strip
lignin away from wood chips. The lignin is then precipitated
out of the pulping liquors by acidification. The most
popular form of alkaline pulping is the kraft process which

uses sodium polysulfide, sodium thiosulfate, and sodium

10

carbonate, in addition to sodium sulfide and sodium
hydroxide (27). The result is a relatively pure
methoxylated water-insoluble lignin which contains
approximately 1.5% sulfur (27).

The exact physical nature of kraft lignin is not fully
known because of the distribution of functional groups and
the cross linkage of the basic carbon six to carbon three
(CG-C3) lignin units. The major C6-C3 units in pine lignin
is sinapyl alcohol (31). Methoxyl groups make up
approximately 14% of pine kraft lignin and for every 100
C6-C3 units there are approximately 120 on groups and 16
COOH groups. The average pine kraft lignin is thought to
have 20 or more C6-C3 units for an average molecular weight
of 1800. Some researchers have found molecular weights as
high as 50,000 or more. These large molecular weight
fractions consist of smaller units held together by
secondary linkages to form larger units (11). Viscosity
analysis suggests spherical shapes but other research
suggests small plate-like structures (11). There are free
unattached low molecular weight catachol derivatives such as
vanillin and protocatechuic acid in the lignin and these are
produced by the time-controlled precipitation in the kraft
process; the exact percentage composition of these water
soluble compounds is not known but estimates are about as

much as 1% of the total weight (27).

11

The following laboratory techniques can be employed to
test the potential of kraft lignin as a controlled release
agent for water-soluble herbicides such as metribuzin and
alachlor in soil systems. Two standard methods that can be
used to measure the movement of radio-labelled compounds are
soil thin-layer chromatography (TLC) and soil column
chromatography.

Soil thin-layer chromatography has been extensively

14C-labelled pesticides

used to study the mobility of
(15,18,19,22,35,37,48). A change in the soil pH can effect
the mobility of herbicides such as metribuzin which can be
easily detected using the soil TLC plate method (22).
Differences in herbicide mobility can also be observed by
altering the organic matter or clay content percentages of
the tested soil (35,37). Neither the soil layer thickness,
nor the removal of coarse sand, nor the amount of
radiolabelled material used affect the Rf or mobility of the
tested pesticides (15).

The mobility of a compound can be easily tested by
developing soil TLC plates with water and measuring
radio-labelled herbicide movement by autoradiography,
radiochromatogram scanning, and zonal extraction of
radio-label (15). The resulting Rf values from soil TLC
plates corresponds very closely to those of inverted soil
columns (16,35). Unfortunately, an important factor missing

in soil TLC plate analysis is the gravitational effect on

12

the movement of herbicides in soil systems. The only force
measured in soil TLC plate systems is diffusion or capillary
movement.

Soil column chromatography has been used to study the
movement of radio-labelled pesticides (46). This method
includes both the gravitational effect and diffusion. The
initial moisture status of the soil column can have a
pronounced effect on the mobility of the tested herbicide.
Saturated flow conditions, prior to herbicide addition to
the column, can sometimes lead to a greater displacement of
the herbicide in the column (1,10). With unsaturated flow,
such as intermittent watering, there is both a downward and
upward movement of the herbicide in the column due to the
soil drying effect (46). This last approach appears to be
the most realistic of the two since saturated flow is rarely
encountered in agricultural conditions.

Two herbicides which could potentially benefit from the
use of a controlled release agent such as kraft lignin are
metribuzin and alachlor. The former is typically used in
soybean (Glycine ma_x_ (L.) Merr.) production and may injure
soybeans due to downward mobility in soil (23). The latter
is also mobile in the soil. By controlled release it may be
possible to position both compounds in the upper zone of the
soil for longer periods of time.

Metribuzin has a molecular weight of 214.3, a water

solubility of approximately 1200 ppm at 20 C, and relative

13

stability when exposed to ultraviolet radiation (47).
Alachlor has a molecular weight of 269.8 and a water
solubility of 242 ppm at 25 C (47).

Both compounds are typically tank-mixed for preemer-
gence application for soybean production while alachlor is
also used in corn (Egg mgyg L.) production. Metribuzin is
used for the control of many annual dicotyledonous weed
species and alachlor is used for the control of many of the
annual monocotyledonous weed species.

Both herbicides are absorbed by germinating weed
seedlings. Alachlor is believed to prevent protein
synthesis by interference with transfer RNA (21). Alachlor
is also believed to inhibit growth of epicotyl segments by
controlling the function of GA3 at the molecular level (29).
A consequence of alachlor exposure is a reduction in cell
division in the developing root system. Metribuzin inhibits
plant growth by blocking electron transport in photosystem
II at the B protein complex (3,32). This can result in the
formation of free radicals ‘which in turn can cause the
disruption of the chloroplasts membrane and necrosis of the
surrounding cell.

Many crOp species are able to detoxify these two
compounds. Corn and soybean are able to conjugate alachlor
with glutathione and thiol containing compounds (24). Many
soybean varieties are able to metabolize metribuzin to a

nonphytotoxic compound called deaminated diketo metribuzin

l4

(DADK) (38) and. then conjugate the DADR: with. glycosides
(38).

Alachlor and metribuzin have some similarities as well
as differences in their behavior in soils. Both compounds
are adsorbed and desorbed from soil clay and organic
fractions.

Alachlor has a greater affinity for organic matter than
for clay (45). The adsorption of alachlor to calcium-
saturated organic matter has been reported to be 3 um
alachlor/g of organic matter at a alachlor mole equivalent
of 3 X 10-5. The adsorption of alachlor to calcium
saturated montmorillonite clay has been reported to be 3 um
alachlor/g of montmorillonite at a alachlor mole equivalent

5 (45). Results from acetanilide

concentration of l X 10-
adsorption studies suggest strong hydrogen bonding between
the imino hydrogen of the adsorbate and the carbonyl oxygen
or alternate site of the adsorbent (43). However, the level
of organic matter in the soil does not appear to affect weed
control with alachlor (30).

The half-life for alachlor has been found to vary from

9 days in a clay loam to 11 days in a sandy loam as measured

by a sorghum bioassay (Sorghum bicolor (L.) Moench) (49).

 

Other research has found the half-life to vary from 2 to 14
days with the majority of the dissipation due to microbial
activity (5). A half-life of 2 to 14 may not provide long

term weed control. An additional problem in the field is

15

the loss of alachlor due to leaching and this problem could
be exacerbated in soils with low organic matter and clay
content.

Metribuzin is predominately adsorbed by organic matter
rather than by clay (34) with a reduction in herbicide
mobility (37). Maximum adsorption of triazines usually
occurs in soils with low pH levels (22,44). It has been
suggested that the protonation of the amine group of the
compound at the lower pH values gives the compound a
positive charge which is then attracted to the negatively
charged organic matter clay colloids (22,41). As the pH of
the soil is increased, the metribuzin becomes more mobile
(22) and. in the case of soybean production, this could
result in an increase in phytotoxicity to soybean (23).
Additions of organic matter with a low pH to greenhouse
grown potted soybeans resulted in a reduction in
phytotoxicity to the soybeans as well as a reduction in

giant foxtail (Setaria faberi Herrm.) control (7). These

 

results demonstrate that metribuzin is very mobile in
neutral and alkaline soils, especially those 'with sandy
textures and low organic matter content.

The half-life of metribuzin has been reported to be
from 5 to 20 days (4,6,20,34). Lower half-life values were
obtained when the soil was warmed from 20 C to 35 C

indicating the importance of microbial activity (20,34).

16

Controlled release of both metribuzin and alachlor
could benefit users by keeping more of each compound in the
upper 'weed seed zone' portion of the soil for an extended
period of time. Also, less of each herbicide would migrate
into the lower horizons of the soil profile where it could
be absorbed by non target crop species or enter the ground

water supply.

LITERATURE CITED

Abernathy, J.R. and J.M. Davidson. 1971. Effect of
calcium chloride on prometryne and fluometuron
adsorption in soil. Weed Sci. 19:517-521.

Allan, G.G., J.W. Beer, M.J. Cousin, and R.A. Mikels.

1980. The ‘biodegradative controlled release of
pesticides. Pages 7-20 i3 Controlled Release

Technologies: Methods, Theory, and Applications. Vol.
II. ed. A.F. Kydonieus. CRC Press. Boca Raton,
Florida.

Ashton, F.M. and A.S. Crafts. 1981. Mode of action of
herbicides. Wiley-Interscience, New York.

Banks, P.A. and E.L. Robinson. 1982. The influence of
straw mulch on the soil reception and persistence of
metribuzin. Weed Sci. 30:164-165.

Beestman, G.B. and J.M. Deming. 1974. Dissipation of
acetanilide herbicides in soils. Aqro. J. 66:308-311.
Bouchard, D.C., T.L. Levy, and D.B. Marx. 1982. Fate
of metribuzin, metolachlor, and fluometuron in soil.
Weed Sci. 30:629-632.

Coble, H.D. and J.W. Schrader. 1973. Soybean

tolerance to metribuzin. Weed Sci. 21:308-309.

17

10.

11.

12.

13.

14.

18

Collins, R.L., S. Doglia, R.A. Mazak, and E.T.
Samulski. 1973. Controlled release of herbicides -
theory. Weed Sci. 21:1-5.

Collins, R.L. and S. Doglia. 1973. Concentration of
pesticides slowly released by diffusion. Weed Sci.
21:343-349.

Davidson, J.M. and J.R. McDougal. 1973. Experimental
and predicted movement of three herbicides in a
water-saturated soil. J. Environ. Qual. 2:428-433.
DelliColli, H.T. 1980. Pine kraft lignin as a
possible delivery system. Pages 225-234 ig Controlled
Release Technologies: Methods, Theory, and Applica-
tion. Vol. II. ed. A.F. Kydonieus. CRC Press, Boca
Raton, Florida.

Dunigan, E.P. and T. MacIntosh. 1971. Atrazine soil
organic matter interaction. Weed Sci. 19:279-282.
Glennie, D.W. 1971. Reactions in sulfite pulping.
Pages 597-631 ‘ig Lignin Occurrence, Formation,
Structure, and Reactions. ed. K.U. Sarkanen and C.H.
Ludwig. Wiley Interscience, New York.

Goring, D.A.I. 1971. Polymer properties of lignin and
lignin derivates. Pages 697-761 ig Lignin Occurrence,
Formation, Structure, and Reactions. ed. K.U. Sarkanen

and C.H. Ludwig. Wiley Interscience, New York.

15.

16.

17.

18.

19.

20.

21.

22.

19

Green, R.E. and J.C. Corey. 1971. Pesticide adsorption
measurement by flow’ equilibrium and subsequent
displacement. Soil Sci. Soc. Am. Proc. 35:561-565.
Harris, C.I. 1967. Movement of herbicides in soil.
Weeds 15:214-216.

Harris, F.W. 1980. Polymers containing pendent
pesticide substituents. Pages 63-82 i3 Controlled
Release Technologies: Method, Theory, and Applications.
Vol. II. CRC Press, Boca Raton, Florida.

Belling, C.S. and B.C. Turner. 1968. Pesticide
mobility: Determination by soil thin-layer chromato-
graphy. Science 162:562-563.

Helling, C.S. 1971. Pesticide mobility in soils. I.
Parameters of thin-layer chromatography. Soil Sci.
Soc. Amer. Proc. 35:731-737.

Hyzak, D.L. and R.L. Zimdahl. 1974. Rate of
degradation of' metribuzin and two analogs in soil.
Weed Sci. 22:75-79.

Jaworski, E.G. 1969. Analysis of the mode of action
of herbicidal a-chloroacetamides. J. Agri. and Food
Chem. 17:165-170.

Ladlie, J.S., W.F. Meggitt, and D. Penner. 1976.
Effect of soil pH on microbial degradation, adsorption,

and mobility of metribuzin. Weed Sci. 24:477-481.

23.

24.

25.

26.

27.

28.

20

Ladlie, J.S., W.F. Meggitt, and D. Penner. 1976.
Effect of pH on metribuzin activity in the soil. Weed
Sci. 505-507.

Leavitt, J.R.C. and D. Penner. 1978. $2 yiggg
conjugation of glutathione and other thiols with
acetanilide herbicides and EPTC sulfoxide and the
action of the herbicide antidote R-25788. J. Agri.
Food Chem. 27:533-536.

McCormick, C.L. and M.M. Fooladi. 1980. Controlled
activity polymers with labile bonds to pendent
metribuzin. Pages 317-330 _i_r_1_ Controlled Release of
Bioactive Materials. ed. R. Baker. Academic Press,
New York.

McCormick, C.L., K.W. Anderson, J.A. Pelezo, and D.K.
Lichatowich. 1981. Controlled release of metribuzin,
2,4-D, and model aromatic amines from polysaccharides
and poly (vinyl alcohol). Pages 147-158 ig Controlled
Release of Pesticides and Pharmaceuticals. ed. D.B.
Lewis. Plenum Press, New York.

Marton, J. 1971. Reactions in alkaline pulping.
Pages 639-689 ig_ Lignins Occurrence, Formation,
Structure, and Reactions. ed. K.U. Sarkanen and C.R.
Ludwig. Wiley-Interscience, New York.

Mehltretter, C.L., W.B. Roth, F.B. Weakley, T.A.

McGuire, and C.R. Russell. 1974. Potential controlled-

29.

30.

31.

32.

33.

34.

35.

36.

21

release herbicides from 2,4-D esters of starch. Weed
Sci. 22:415-418.

Narsai‘ah, D.B. and R.G. Harvey. 1977. Alachlor and
gibberellic acid interaction on corn tissues. Weed
Sci. 25:197-199.

Parochetti, J.U. 1973. Soil organic matter effect on
activity' of acetanilides, CDAA, and atrazine. Weed
Sci. 21:157-160.

Pearl, LA. 1964. Lignin chemistry. Chemistry and
Engineering News. July 6 issue :81-92.

Pfister, K. and C.J. Arntzen. 1979. The mode of
action of photosystem II. Specific inhibitors in
herbicides-resistant weed biotypes. z. Naturforsh
34C:966-1009.

Raboy, U. and H.J Hopen. 1982. Effectiveness of
starch xanthide formulations of chloramben for weed
control in pumpkin (Cucurbita. moschata). Weed Sci.
30:169-174.

Savage, R.E. 1976. Adsorption and mobility of
metribuzin in soil. Weed Sci. 24:525-528.

Savage, R.E. 1977. Metribuzin persistence in soil.
Weed Sci. 25:55-59.

Schubert, W.J. 1965. Lignin Biochemistry. Academic

' Press, New York.

37.

38.

39.

40.

41.

42.

43.

44.

22

Sharom, M.S. and C.R. Stephenson. 1976. Behavior and
fate of metribuzin in eight Ontario soils. Weed Sci.
24:153-160.

Smith, A.E. and R.E. Wilkinson. 1974. Differential
absorption, translocation, and metabolism of metribuzin
4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-
one by soybean cultivars. Plant Physiol. 32:253-257.
Smith, A.E. and B.P. Verma. 1977. Weed control in
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Stevenson, F.J. 1982. Humus Chemistry Genesis,
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study of the interaction of s-triazine herbicides with
humic acids from three different soils. Soil Sci.
106:42-52.

Swain, T. 1979. Tannins and lignins. Pages 674-681
it; Herbivores Their Interaction with Secondary Plant
Metabolites. ed. G.A. Rosenthal and D.B. Jansen.
Academic Press, New York.

Ward, T.M. and R.P. Upchurch. 1965. Role of the amido
group in adsorption mechanisms. J. Agr. Food Chem.
13:334-340.

Weber, J.B., S.B. Weed, and T.M. Ward. 1969.
Adsorption of s-triazines by soil organic matter. Weed

Sci. 17:417-421.

45.

46.

47.

48.

49.

23

Weber, J.B. and C.J. Peter. 1982. Adsorption,
bioactivity, and evaluation of soil tests for alachlor,
acetochlor, and metolachlor. Weed Sci. 30:14-20.
Weber, J.B. and D.M. Whitacre. 1982. Mobility of
herbicides in soil columns under saturated and
unsaturated conditions. Weed Sci. 30:579-584.

Weed Science Society of America. 1983. Herbicide
Handbook, 5th Ed. WSSA, Champaign, IL 131-318 pp.

Wu, C.H. and P.W. Santelmann. 1975. Comparison of
different soil leaching techniques with four
herbicides. Weed Sci. 23:508-511.

Zimdahl, R.L. and S.K. Clark. 1982. Degradation of
three acetanalide herbicides in soil. Weed Sci.

30:545-548.

CHAPTER TWO

CONTROLLED RELEASE OF METRIBUZIN AND ALACHLOR BY KRAFT
LIGNINS AS MEASURED BY SOIL THIN LAYER CHROMATOGRAPHY

ABSTRACT

The controlled release of metribuzin (4-amino-6-tert-
butyl-3-(methythio)-g_§-triazin-5(4H)-one) and alachlor (2-
chloro-Z',6'-diethyl-N-methoxymethyl acetanilide) from pine

14C-labelled herbicides and

kraft lignin was studied using
3H-labelled lignin on soil thin layer chromatography.
NB-5203-58 series and PC940 series kraft lignins adsorbed
and desorbed metribuzin as soil plates were developed with
water. PC671, a former‘ kraft lignin commercial control
release product, did not show control release properties
with metribuzin. NB-5203-58B and PC940C were the most
promising of their respective series of kraft lignins.
PC940C appeared to be the most suitable of the two since
NB-5203-58B was obtained by a complicated and costly method
of ultrafiltration. PC940C, when formulated with surfactant

agents, was less active as a controlled release agent for

metribuzin than nonformulated PC940C. PC940C was also found

24

25

to be an excellent controlled release agent for alachlor.
The mechanism of adsorption possibly involved hydrogen

bonding.

INTRODUCTION

The advantage of a controlled release agent for readily
degradable water-soluble herbicides would be to increase the
period of activity of the compound (2). Furthermore, if the
bound herbicide is slowly released with the addition of
water, potentially less herbicide would be leached through
the soil. The possible savings would be in a reduction or
elimination of multiple applications of the same or other
herbicides (1).

The controlled release of water-soluble herbicides has
been extensively studied. Polysaccharides have been tested
as control release agents with metribuzin (11), chloramben
(3-amino-2,S-dichlorobenzoic acid) (13), and 2,4-D (2,4-
dichlorophenoxy acetic acid) (12). Unfortunately, polysac-
charides can also serve as a readily available carbon source
for microorganisms, and, consequently, the controlled
release agent will have a short half-life. Alachlor has
been encapsulated in plaster of Paris for effective weed
control in perennial ornamentals (13), however, this concept
would not be suitable for agronomic purposes. The mobility
of metribuzin has been successfully reduced when formulated

in polymers of polyvinyl alcohols (5,10). Because there are

26

27

covalent linkages formed between metribuzin and the
controlled release polymer, the product is a series of
compounds similar in structure to metribuzin. Kraft lignins
have successfully controlled the release of 2,4-D (3). Pine
kraft lignin has been shown to bind atrazine (2-chloro-
4-(ethylamino)-6-(isopropylamino)-§-triazine) (4). Although
little is known about the physical properties of kraft
lignin, they have a large number of hydroxyl, carboxylic,
and carbonyl keto groups (3), which may participate in
hydrogen bonding herbicides.

The purpose of this research was to evaluate various
commercial and experimental kraft lignins in both formulated
and nonformulated forms for controlled release properties
with metribuzin and alachlor as measured by soil thin layer

14

chromatography techniques (6,7,8) using C-labelled

herbicides and 3H-labelled kraft lignin.

MATERIALS AND METHODS

Materials Used. Thin layer soil plate analysis was done in
the following fashion. Glass plates with dimensions of 20
by 20 cm and 0.4 cm thick were cleaned with soap and water,
dried, and then coated with a slurry of 106 mm sieved soil
using a Desage Heidelgerg plate spreader. The soil type
used was a Spinks sandy loam with an organic matter content
of 0.8% and a pH of 6.5.

Materials tested as possible controlled release agents
were the following pine kraft lignins: NB-5203-58A,
NB-5203-58B, NB-5203-58C, INDULIN AG, PC940A, PC9408, and
PC940C1. The NB-5203-58 series was prepared by ultra-
filtration of INDULIN AG to three molecular size classes
which were less than 10,000, 10,000-100,000, and greater
than 100,000. The corresponding codes for the NB-5203-58
series were A, B, and C. INDULIN AG was a commercial kraft
lignin. PC940A was a high surface kraft lignin which was
prepared by chemical alterations and PC9408 and PC940C were

prepared from caustic solutions.

1Obtained from Westvaco Corp.

28

29

PC671, which is a combination of INDULIN AG and
surfactants, was also tested. Two different mixtures of
surfactants, designated as WP8 and WPlO, were also used to
formulate PC940C.

14

Radio-labelled materials used were: C-metribuzin

14C-alachlor with a

with a specific activity of 21.9 mCi/mM,
Specific activity of 1.76 mCi/mM, and 3H-PC940C with an
activity of 0.73 mCi/mg.

Stock solutions of metribuzin and alachlor were made
using 90% pure technical grade metribuzin and 958 pure
technical grade alachlor. The metribuzin stock was 1800 ppm
and the two stocks of alachlor were 200 ppm and 2400 ppm.

All stocks were made in distilled water and refrigerated.

NB-5203-581 PC671, INDULIN AG, and surfactants with
14C-metribuzin. The first study was designed to determine
the controlled release effect of’ the ‘NB-5203-58 series,
PC671, INDULIN AG, and the surfactant mix of PC671 on
metribuzin. Five m1 of metribuzin stock solution was added
to 25 mg of solid lignin, or in the case of PC671 or the
surfactant. mix, 78 mg of liquid. These materials were
placed in a 10 ml test tube and the tube was shaken using a
table top mixer for approximately 15 sec; 250 111 of this
mixture was transferred to a vial containing 5 ul of
14

C-metribuzin. This vial was then shaken for 1 hr and then

stored for 24 h prior to application. After 24 h, the vial

30

was again shaken and 10 pl subsamples were withdrawn and
spotted on the soil plates. The brown colored lignin was
easily detected on the soil plates. Subsamples were also
radioassayed via liquid scintillation spectrometry' which
showed that a 10 (41 sample contained approximately 90,000
disintegrations per ndnute (DPM). Soil plates were
developed in holding tanks with distilled water to an
approximate height of 12.5 cm and then dried. Soil plates
were then scanned. using' a iBerthold 2D-TLC-Scanner' L8276
using' methane as the carrier gas. Disintegrations were

14C remained at the

integrated to determine how much of the
point of application and how much had migrated with the
water. The following studies also used the same procedures
as described above and all studies had two replications and
were repeated.

NB-5203-588 with 14

C-metribuzin. This study used only
NB-5203-58B and the surfactants found in PC671. Rates of
NB-5203-588 to metribuzin stock were 5 mg/ml (IX) and 12.5
mg/ml (2.5x). The rate of surfactant was 15.6 mg/ml of
liquid and this contained approximately 460 ug/ml of solid
material. The purpose of this study was to determine how

NB-5203-58B's potential as a controlled release agent would

be effected by the addition of surfactants.

31

14C-metribuzin. The PC940 series was used with

PC940 with
metribuzin at a ratio of 10 mg/ml. An exception to the
first study was a storage period of only 1 h prior to
application. The rest of this study was identical to the
first. The purpose was to test the controlled release
properties of the PC940 series and identify the most
suitable for the controlled release of metribuzin.

PC940 with surfactants and 14

C-metribuzin. A study was
designed to test the effect of formulation on the controlled
release potential of the most effective lignin in the PC940
series. The lignin was mixed with the surfactants used to
make the commercial formulations WP8 and WP102. The
materials were mixed as dry powders which were 93.7% lignin.
The rates of nonformulated and formulated lignin used were
9.59 mg/ml and 19.17 mg/ml to the metribuzin stock. The
remainder of this study was identical to the first study.

pc94o with 1‘

C-alachlor. A study was also done to test the
potential of the PC940 series for the controlled release of
alachlor. Five m1 of 200 and 2400 ppm alachlor stock
solution were added to 25 mg of PC940 lignin. After a 15
sec mixing period as described above, 100 pl was transferred

14

to a vial with 10 ul of C-alachlor. This vial was shaken

and stored for l h and then 10 ul subsamples were spotted on

2Products of the Westvaco Corp.

32

the soil plates. Subsamples were radio-assayed by liquid
scintillation spectrometry, which showed that a 10 ul sample
had approximately 17,000 DPM. The rest of the procedures
used were identical to those of the first study.

3H-PC940C. The last study was done to examine the mobility

 

of PC940C when analyzed separately. PC940C was tritiated by
New England Nuclear using a straight tritium gas exchange
method. Two m1 of distilled water plus 19.2 mg of PC940C
were mixed together and shaken for 15 sec and 100 ul of this
was transferred to a vial containing 0.3 mg of 3H-PC940C.
The vial was shaken for l h and 1 ul subsamples were spotted
on soil thin layer plates. Each 1 ul sampled contained
approximately 4.8 x 106 DPM as determined by liquid scintil-
lation radioassay. The remaining procedures were identical

1

to those used with 4C-labelled materials.

RESULTS AND DISCUSSIONS

PC671, the PC671 surfactants, and INDULIN AG did not
retard the movement of metribuzin from the point of origin
(Table 1).

However, the NB-5203-58 series significantly retarded
the movement of metribuzin. NB-5203-58C was the most
effective in retarding the movement of metribuzin for all
three developments than NB-5203-58A and NB-5203-58B.
However, NB-5203-58C did not release metribuzin after
subsequent developments. There was approximately a 50%
decrease in the percentages retained for NB-5203-58A and
NB-5203-SBB after the third development. There was a direct
relationship between the amount of metribuzin immobilized
and the molecular size of the three NB-5203-58 lignins with
the largest size, greater than 100,000 molecular size,
having the highest percentage retained and the smallest
size, less than 10,000 molecular size, having the lowest
percentage retained.

Since the NB-5203-58 series was derived from
ultrafiltration of INDULIN AG, this may have exposed active
sites for the adsorptive process.

As the concentration of NB-5203-58B increased (Table

2), the amount of metribuzin immobilized at the point of

33

Table 1. Effect of lignins on the percentage of

14

TLC plates after three developments.

34

C-metribuzin retained at the point of origin on soil

 

 

 

Developmentsa

Treatments 1 2 3

----------- (% of Total)b-----------
NB-5203-58A 10.9 bc 4.2 c 3.8 c
NB-5203-588 17.6 b 8.7 bc 8.6 bc
NB-5203-58C 36.3 a 33.5 a 33.9 a
PC-67l 0 d 0 d 0 d
INDULIN AG 0 d 0 d 0 d
PC671 Surfactants 0 d 0 d 0 d
Metribuzin Control 0 d 0 d 0 d

 

aDevelopments are multiples of approximately 12.5 cm.

b

Numbers followed by the same letter are not significantly

different according to Duncan's multiple range test at the

0.05 level.

35

Table 2. Effect of NB-5203-58B on the percentage of

14C-metribuzin retained at the point of origin on soil

TLC plates after three developments.

 

 

 

Developmentsa
Treatments 1 2 3
b
----------- (% of Total) -----------
NB-5203-588 (1X) 17.6 bc 8.7 de 8.6 de
NB-5203-58B (2.5X) 33.3 a 19.2 be 13.7 cd

NB-5203-58B (2.5K)
+ 21.5 b 11.1 de 7.2 e

PC671 Surfactants (lX)

 

aDevelopments are multiples of approximately 12.5 cm.
bNumbers followed by the same letter are not significantly
different according to Duncan's multiple range test at the
0.05 level.

36

origin also increased after the first two developments.
With the addition of the surfactants found in PC671, there
was a significant reduction in the percentage of metribuzin
retained at the point of origin for the 2.5x rate. This
would suggest that there was a competitive effect between
the surfactant mixture and metribuzin for the adsorptive
sites of NB-5203-588.

INDULIN AG, did not desorb metribuzin but could be
altered via ultrafiltration to produce new materials which
could desorb metribuzin, this would suggest that INDULIN AG
had been chemically or physically altered during
manufacture.

To test whether or not INDULIN AG had been altered,
three other kraft lignins were tested which had been
produced from the INDULIN AG precursor. PC940A was a
chemically altered high surface area kraft lignin and PC9408
and PC940C were made from INDULIN AG subjected to caustic
treatment.

All lignins of the PC940 series were able to desorb
metribuzin from. the point. of' origin on the soil plates
(Table 3). PC940C was the superior of three tested in terms
of the greatest amount of metribuzin retained at the origin
after each of the three developments. PC9408 had similar
but significantly lower percentages for metribuzin retained
at the point of origin than did PC940C. The differences

between PC9408 and PC940C may be due to PC940C being treated

37

Table 3. Effect of lignins on the percentage of

l4C-metribuzin retained at the point of origin on soil

TLC plates after three developments.

 

 

 

Developmentsa
Treatments 1 2 3
------- -------(% of Total)b---------------
PC940A 17.1 d 8.5 fg 5.3 g
PC9408 41.6 b 21.6 d 11.4 ef-
PC940C 47.4 a 29.2 c 16.2 de

 

aDevelopment are multiples of approximately 12.5 cm.
bNumbers followed by the same letter are not significantly
different according to Duncan's multiple range test at the
0.05 level.

38

under caustic conditions for a longer period of time than
PC9408. The lowest percentages for each development were
those of PC940A. This may suggest that an increase in
surface area may not have been the best way to restore the
potential of INDULIN AG to desorb metribuzin.

Whereas both PC9408 and PC940C similarly retained
metribuzin at the point of origin after a single development
as NB-5203-588, NB-5203-58C did not desorb additional
metribuzin with the second and third. developments.
NB-5203-588 desorbed similar amounts of metribuzin with
subsequent developments as PC9408 and PC940C.

The adjuvants of WP8 and WP10 decreased the performance
of PC940C by interfering with desorption of metribuzin
(Table 4). The nonformulated PC940C had significantly
higher percentages of metribuzin retained at the point of
origin after the first two developments than PC940C with the
WP8 and WP10 surfactants; only half as much PC940C was used
with the nonformulated treatment as compared to the two
adjuvant treatments. This reduction in the performance of
PC940C was very similar to the reduction in the performance
of N8-5203-58B when it was mixed with the adjuvants found in
PC671 (Table 2). The WP8 and WP10 surfactants were dry
materials, whereas PC671 was in a liquid state. Since the
only major difference between the two WP formulations and
PC671 was water, it may be assumed that the negative

responses of PC940C and NB-5203-58B to the surfactants was

39

Table 4. Effect of formulated and nonformulated PC940C on

14

the percentage of C-metribuzin retained at the point of

origin on soil TLC plates after two developments.

 

 

 

Developmentsa
Treatments 1 2
----(% of Total)b -----
WP8 Surfactant Formulation 24.0 be 6.9 d
WP10 Surfactant Formulation 17.3 c 3.6 d

Nonformulated 47.4 a 29.2 b

 

aDevelopments are multiples of approximately 12.5 cm.
bNumbers followed by the same letter are not significantly
different according to Duncan's multiple range test at the
0.05 level.

40

due to a similar type of competitive interaction between a
component in the surfactant mixture for the adsorptive sites
of the two lignins.

The PC940 series desorbed alachlor from the point of
origin (Table 5). As was the case with metribuzin, PC940C
was superior to PC9408 with significantly higher percentages
of alachlor with the first two developments. PC940A had
percentages that were not significantly different from
PC9408, but the PC940A treatment had twice as much lignin
material used than either the PC9408 or the PC940C
treatment.

Comparisons of the PC940 series for desorption of
metribuzin and alachlor (Tables 3 and 5) were very similar.
PC940A was used at identical rates for both metribuzin and
alachlor and the percentages for each were very similar.
Twice the amount of PC9408 and PC940C were used for the
metribuzin analysis (Table 3) as compared to the alachlor
analysis (Table 5). Consequently, if the amount of lignin
is taken into consideration, the response of these two
lignins was almost identical with each herbicide.

Although there is little resemblance between the
chemical structures of nwmribuzin and alachlor, desorption
percentages of each compound were almost identical for the
PC940 series. This is probably due to an abundance of
hydrogen bonding possibilities that exist between the

lignins and the herbicides. These possibilities are the

41

Table 5. Effect of lignins on the percentage of

14C-alachlor retained at the point of origin on soil

TLC plates after three developments.

 

 

 

Developmentsa
Treatments 1 2 3
--------------- (% of Total)b---------------
PC940A 19.4 b 6.7 de 2.1 e
PC9408 15.1 be 10.7 cd 6.4 de
PC940C 29.1 a 21.0 b 10.1 cd

 

aDevelopments are multiples of approximately 12.5 cm.
bNumbers followed by the same letter are not significantly
different according to Duncan's multiple range test at the
0.05 level.

42

keto and primary amine group of metribuzin and the keto and
tertiary amine group of alachlor being hydrogen bonded to
the hydroxyl, carboxylic, and carbonyl groups of the tested
kraft lignins. Similar observations have been reported with
different materials such as humic acids (15,16).

Tritiated PC940C ‘was not. mobile since most of the
radiolabel was detected at the point of origin. After two

38 had moved from the

developments, only from 3 to 5% of the
origin and the majority of this was at the water solvent
front on the soil TLC plates. This small percentage is
similar to that calculated to be the amount of water-soluble
small molecular weight materials found in kraft lignin (9).
However, there is also the possibility that there was some
38 exchange that took place between the lignin and the water
or water-soluble materials in the soil. If there was 3H
exchange taking place, this would mean that the percentages
of 3H-PC940C measured at the point of origin were under-
estimated.

In summary, PC940C appeared to be the most suitable
pine kraft lignin of the lignins tested to be used as a
controlled release agent for metribuzin and alachlor. It
had the highest retention percentages of the PC940 series.
It appeared to be equal to the performance of NB-5203-588
but NB-5203-588 required a costly and time consuming
filtration process while PC940C only required. a caustic

treatment .

LITERATURE CITED

Colins, R.L., S. Doglia, R.A. Mazak, and E.T. Samulski.
1973. Controlled release of herbicides-theory. Weed
Sci. 21:1-5.

Collins, R.L. and S. Doglia. 1973. Concentration of
pesticides slowly released. by' diffusion. Weed Sci.
21:343-349.

DelliColli, E.T. 1980. Pine kraft lignin as a
pesticide delivery system. Pages 225-234 12 Controlled
Release Technologies: Methods, Theory, and Application.
Vol. II. ed. A.F. Kydonieus. CRC Press. Boca Raton,
Florida.

Dunigan, B.P. and T. MacIntosh. 1971. Atrazine-soil
organic matter interaction. Weed Sci. 19:279-282.
Harris, F.W. 1980. Polymers containing pendent
pesticide substituents. Pages 63-82 £2 Controlled
Release Technologies: Methods, Theory, and Application.
Vol II. ed. A.F. Kydonieus. CRC Press. Boca Raton,
Florida.

Helling, C.S. and B.C. Turner. 1968. Pesticide
mobility: determination knr soil thin-layer chromato-

graphy. Science 162:562-563.

43

10.

11.

12.

44

Helling, C.S. 1971. Pesticide mobility in soils. I.
Parameters of thin-layer chromatography. Soil Sci.
Soc. Amer. Proc. 35:731-737.

Ladlie, J.S., W.F. Meggitt, and D. Penner. 1976.
Effect of soil pH on microbial degradation, adsorption,
and mobility of metribuzin. Weed Sci. 24:477-481.
Marton, J. 1971. Reactions in alkaline pulping.
Pages 639-689 in Lignins Occurrence, Formation,
Structure, and Reactions. ed. K.U. Sarkanen and C.R.
Ludwig. Wiley-Interscience. New York.

McCormick, C.L. and M.M. Fooladi. 1980. Controlled
activity polymers with labile bonds to pendent
metribuzin. Pages 317-330 3.3 Controlled Release of
Bioactive Materials. ed. R. Baker. Academic Press,
New York.

McCormick, C.L., K.W. Anderson, J.A. Pelezo, and D.K.
Lichatowich. 1981. Controlled release of metribuzin,
2,4-D, and model aromatic amines from polysaccharides
and polyvinyl alcohol. Pages 147-158 3:11 Controlled
Release of Pesticides and Pharmaceuticals. ed. D.B.
Lewis. Plenum Press, New York.

Mehltretter, C.L., W.B. Roth, F.B. Weakley, T.A.
McGuire, and C.R. Russell. 1974. Potential controlled-
release herbicides from 2,4-D esters of starches. Weed

Sci. 22:415-418.

13.

14.

15.

16.

45

Raboy, V. and H.J. Hopen. 1982. Effectiveness of
starch xanthide formulations of chloramben for weed
control in pumpkin (Cucurbita moschata). Weed Sci.
30:169-174.

Smith, A.E. and B.P. Verma. 1977. Weed control in
nursery stock by controlled release of alachlor. Weed
Sci. 25:175-178.

Sullivan, J.D., Jr. and G.T. Felbeck, Jr. 1968. A
study of the interaction of s-triazine herbicides with
humic acids from three different soils. Soil Sci.
106:42-52.

Ward, T.M. and R.P. Upchurch. 1965. Role of the amido
group in adsorption mechanisms. J. Agr. Food Chem.

13:334-340.

CHAPTER THREE

CONTROLLED RELEASE OF METRIBUZIN AND ALACHLOR BY
PC940C AS MEASURED BY SOIL COLUMN CHROMATOGRAPHY

ABSTRACT

PC940C, a pine kraft lignin, controlled the release

14

of C-metribuz in (4-amino-6-tert-butyl-3- (methythio) -as-

l4C-alachlor (2-chloro-2',6'-diethy1-

triazin-5(4H)-one) and
N-methoxymethyl acetanilide) as measured by leaching soil
columns with water. As more PC940C was used, a
concentration effect was found with more of the two
herbicides being retained in the top portions of the soil
columns. Combinations of alachlor and metribuzin applied
with PC940C did not alter the retention of either l4C-
metribuzin or 14C-alachlor as compared to each herbicide
applied with PC940C alone. This would suggest that, at the
rate of PC940C used, there was no competition between either
herbicide for the controlled release sites on PC940C. The

14 14C-alachlor retained by

percentage of C-metribuzin and
PC94OC in the top portion of the columns was very similar.

Since the compounds are not similar in structure, this would

46

47

suggest that the mechanism involved in controlled release is

hydrogen bonding. Combinations of umtribuzin and alachlor

14

without PC940C retarded the mobility of both C-metribuzin

14

and C-alachlor. This would suggest that hydrogen bonding

also occurred between metribuzin and alachlor which resulted

3u-pc94oc

in a larger, less water-mobile molecule. Finally,
was found to be very immobile in soil columns leached with
water. There was a beneficial effect of combining PC940C
with either metribuzin or alachlor: however, a three way

combination of PC940C, metribuzin, and alachlor resulted in

the lowest amount of 3H-PC940C remaining in the top portion

of the soil columns.

 

INTRODUCTION

A controlled release agent applied with triazine and
acetanalide herbicides could increase weed control as more
herbicide would remain in the top portion of the soil. It
would also extend the activity of the herbicide (l). The
advantages of a controlled release mechanism would be the
reduction in herbicide injury to deeper rooted crop species
as well as the possibility of increasing the weed control
spectrum of the herbicide over time. The potential would be
to reduce or even eliminate multiple applications of the
same or other expensive herbicides (2). In addition, a
controlled release strategy would have the potential
environmental benefit of having less herbicide leached
through the soil and into the ground water.

These advantages would appear to be applicable to
metribuzin and alachlor. Metribuzin is mobile in neutral
and alkaline pH soils (7) and can cause injury to soybean
(Glycine may (L.) Merr.) (8). Alachlor, while not phyto-
toxic to corn (£23 mayg L.) or soybean, could over time be
more effective if leaching was reduced.

Several controlled release :methods have been tested

with metribuzin and alachlor. Pendent metribuzin attached

48

49

to polyvinyl alcohol polymers have resulted in a reduction
in metribuzin mobility (6,9). However, this approach
necessitates covalent bonding of metribuzin to the polymers
and results in a series of compounds which incorporate a
portion of the metribuzin molecule and have questionable
herbicidal value. Metribuzin has also been tested. with
polysaccharides (10), but unfortunately polysaccharides are
short termed readily available carbon sources for soil
microorganisms. Alachlor has been successfully tested in
encapsulated forms with plaster of Paris for weed control in
azalea (Rhododendrum sp.) planting (13). However, this
technique would not be a practical one to use with current
agronomic practices.

A material that would have the potential to control the
release of both metribuzin and alachlor is pine kraft
lignin. Lignin has already been successfully used as a
controlled release agent for 2,4-D (2,4-dichlorophenoxy
acetic acid) (3) and has been shown to have a high
adsorptive capacity for atrazine (2-chloro-4-(ethylamino)-6-
(isopropylamino)-§-triazine) (4), possibly via hydrogen
bonding (5).

The purpose of this study was to determine the
controlled release properties of the pine kraft lignin

PC940C with metribuzin and alachlor.

MATERIALS AND METHODS

Soil columns 'were ‘prepared. using' polyvinyl chloride
tubing with dimensions of 4.6 cm diameter and 36 cm length.
The columns were packed uniformly with air dried 2 mm mesh
sieved soil. Tubes were split lengthwise and taped back
together and the bottom end of the columns were covered with
cheese cloth to keep the soil in the columns. Soil used was
a Wando sandy loam with 1.7% organic matter, 79.6% sand,
7.2% silt, 13.2% clay, 7.1 pH, and a low 4.2 m.e.q./100 g of
soil cation exchange capacity.

The controlled release agent was PC940C1. This is a
dry pine kraft lignin prepared from caustic treated INDULIN
A62.

Stock solutions of metribuzin (1800 ppm) and alachlor
(9600 ppm) were made using 90% technical grade metribuzin

@3

and 15% granular LASSO form of alachlor.

1Provided by the Westvaco Corp.
2Product of the Westvaco Corp.

3Product of the Monsanto Corp.

50

51

Labelled materials used were the following: 14C-

14

metribuzin (specific activity of 21.9 mCi/mM), C-alachlor

(specific activity of 1.76 mCi/mM), and 3

H-PC940C (specific
activity of 0.73 mCi/mg).

Two leaching treatments were used. The first, a single
leaching of 51 ml (equivalent of 2.54 cm) of distilled
water, was uniformly applied to the soil surface over a 2 h
time period. The second was identical to the first but with
a 6 day drying period followed by an additional 51 m1 of
water which was also uniformly applied to the soil surface
over a 2 h time period: for the drying period, the leached
columns were placed under sodium halide lamps located in the
greenhouse. The height of the lamps was approximately 30 cm
above the soil surface and the illumination was approxi-

mately 1000 11E.m-2-s-l

with the lamps set for a 15 h
illumination period.

Radio-labelled material distribution in the soil
columns was determined by the following. The columns were
split open and the moist soil removed at 2.54 cm increments
with the first increment split in 1.27 cm portions. The
water front was typically 15 cm from the soil surface. The
entire segments of collected soil were transferred to long
necked 250-ml Erlenmeyer ground glass flasks. Fifty ml of
extraction solvent was added and the flasks were shaken for

2 h using a table top wrist action shaker at 200 reciproca-

tions/min. Samples from. each flask: were transferred to

52

50-m1 glass centrifuge tubes and centrifuged at 1000 rpm for
10 min. Between 1 to 5 m1 of collected supernatant was
removed by using a 5-ml disposable glass pipette and added
to a .20-ml glass vial. which contained. 10 ml of liquid
scintillation radioassay fluid. Samples were radioassayed
with a liquid scintillation spectrometer.

14

The extraction solvent used for C-alachlor and

l4C-metribuzin was acetone and methanol was used for

3H-PC940C. The extraction efficiency was over 90% for all

three radio-labelled materials.

Controlled Release of Metribuzin by PC940C. A study was
done to evaluate the potential of PC940C to control the
release of metribuzin in soil columns. PC940C was used at
0, 2x, 4x, and 16x levels and these were multiples of 2.6 mg
PC940Cfiml of metribuzin stock solution. These rates
simulated the concentration equivalents of 0, 2.24, 4.48,
and 17.92 kg/ha of PC940C in 94.6 L of water with 0.42 kg/ha
of metribuzin.

The corresponding amount of PC940C, depending upon the
rate tested, was weighed out and mixed with 1 m1 of
metribuzin stock solution in a lO-ml glass test tube. This
was shaken for 15 sec using a table top shaker and 200 ul
transferred to a vial which contained 5 pl of 14C-

metribuzin. The vial was shaken for l h using the same

53

shaker and then the entire contents of the vial was
transferred to the soil surface of the column.
Both leaching treatments we re used in this study and

14C-label

following treatment, the columns were sampled for
distribution patterns. The study had two replications and

was repeated two times.

Controlled Release of Alachlor by PC940C. A study ‘was
designed to measure the potential of PC940C to control the
release of alachlor in soil columns. The same four levels
of PC940C were used as in the metribuzin study and identical

procedures employed.

Possible Competitive Effect Between Alachlor and Metribuzin.
A study was designed to test the possible competitive effect
between metribuzin and alachlor for the controlled release
potential of PC940C. PC940C was used at rates of 0, 2X, and
4X with multiples of 5.2 mg PC940C added to 1 m1 of
metribuzin stock solution plus 1 m1 of alachlor stock
solution. Mixtures were shaken for 15 sec using a table top
shaker and 200 ml samples were transferred to a vial
containing 5 ul of l4C-metribuzin or l4C-alachlor. Only the
single leaching treatment was used. Extraction procedures
and method of analysis were identical to those already
described. This study also had two replications and was

repeated two times.

54

Mobility of PC940C. The last study was designed to test the

311-909404

mobility of after a single leaching and if this
mobility or lack of mobility was affected by the addition of
one or both of the tested herbicides. Consequently the
following four treatments were used: PC940C, PC940C +
metribuzin, PC940C + alachlor, and PC940C + metribuzin +
alachlor. A 2X rate of nonlabelled PC940C was used which
corresponded to 2.6 mg PC940C/2 ml of herbicide stock
solution. For the PC940C treatment, 2 m1 of distilled water
was added, while, with the PC940C + metribuzin + alachlor
treatment, 1 ml of each herbicide stock solution was used.
For the PC940C treatments with each individual herbicide, 2
ml of metribuzin or alachlor stock solution was used. These
mixtures were shaken for 15 sec as previously described and
100 pl samples were transferred to vials which contained 0.1
mg 3H-PC940C. Vials were shaken for l h and a 10 ul sample
was transferred from the vial to the soil surface.

Extraction and analysis were identical to other studies.

This study had two replications and was repeated two times.

4Tritiated by New England Nuclear using a straight tritium

gas exchange method.

RESULTS AND DISCUSSION

PC940C controlled the release of :metribuzin in the

Wando sandy loam soil columns and kept more of the

14C-metribuzin in the top portion of the columns (Table l)

with less moving to the lower portion of the column. The
effect occurred in both single and double leaching
treatments and was linear as the concentration of PC940C

increased. Although there was a significant decrease in the

14 14

percentages of C-label from C-metribuzin that remained

in the top 1.27 cm of soil at the 2X and 4x rate of PC940C

with the double leaching, the double leaching did not

14C-label with the 16X rate of

increase the movement of
PC940C.
The effect of PC940C on the controlled release and

mobility of 1"

C-alachlor was similar to that observed with
metribuzin (Table 2). However, 14C-metribuzin was more
mobile in the columns than was l4C-alachlor, possibly
because metribuzin is almost five times more water soluble
than alachlor (l4).

Combination of alachlor with metribuzin did not

14

interfere ‘with C-metribuzin retention and release from

PC940C at the 2X and 4X rates of PC940C (Table 3). This

55

56

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57

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A

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+ seaseeNc + ueNseeN< + eeHeeeNc
bmeusoauooua

 

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«a

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.N oHAmh

58

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«A

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.m «Name

59

would suggest that alachlor did not compete with
14C-labelled and non-labelled metribuzin for the active
binding sites on PC940C, or if it did, the PC940C binding
sites were not over-saturated at the 2X rate. Since a rate

14C-metribuzin retention between

response was observed fer
the 2x and 4x PC940C rates, the latter is not probable.
Combination of metribuzin with alachlor also did not

14C-alachlor retention and release’ from

interfere with
PC940C at the 2X and 4x rates (Table 4). This would suggest
that metribuzin did not interfere with 14C-alachlor for the
active sites on PC940C.

An interaction between alachlor and metribuzin retarded

14 14C-alachlor at all

the mobility of both C-metribuzin and
levels of PC940C. This suggests that there was an
interaction taking place between the two compounds which
would result in both becoming less mobile in the soil
columns. Hydrogen bonding may have occurred between the two
compounds, possibly between the primary amine group of
metribuzin and the carbonyl group of alachlor. This would
result in a larger and probably less mobile molecule.

With the double leaching treatment for the 14C-
metribuzin treatment, there were significantly larger

14C-label extracted from. the 16x rate of

percentages of
PC940C than from the other three levels of PC940C (Table 5).
The amount extracted was almost twice as much as compared to

PC940C rates of 0, 2X, and 4X. Since metribuzin is very

60

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«u:«fiud«ua

 

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61

Table 5. The influence of PC940C on the recovery of

14C-metribuzin from Wando sandy loam soil columns following

the two leaching and drying treatmentsa.

 

 

 

Treatments
b Metribuzin+ Metribuzin+ Metribuzin+
Metribuzin PC940C (2X) PC940C (4X) PC940C (16X)
---------------------- (DPM Recovered)-----------------------
263,130 C 255,002 C 250,715 C 557,569 A

 

aNote that each treatment received approximately 576,000 DPM
of C metribuzin.

bNumbers followed by the same letter are not significantly
different according to Duncan's multiple range test at the
0.05 level.

62

soluble in acetone, the lower values would suggest that

14

there was metabolism of the C-metribuzin during the 6-day

drying period prior to the last leaching. Since the amount

of 14

C-label extracted was higher at the 16x rate, there was
little or no metabolism of metribuzin with this treatment.
This type of analysis does not rule out the possibility that
a non-phytotoxic metabolite of metribuzin was extracted by
the acetone. However, the data suggests that PC940C at the
high rate was able to increase the activity period of
metribuzin. Because lignin has been found to be relatively
impervious to microbial decomposition in a short period of
time (12), PC940C may have served as a barrier between
metribuzin and soil microorganisms.

There were no significant differences in the amount of

l4C-label recovered for the single leaching treatment of

14 14

C-metribuzin and. of C-alachlor’ between the rates of
PC940C used. Because the single leaching treatment was done
in such a short period of time, there was probably not
enough time for any appreciable microbial decomposition of
either herbicide.

There was also no significant difference in the amount

14

of C-label recovered after the double leaching treatment

l4C-alachlor between the rates of PC940C used. This

of
would suggest that alachlor was more persistent in the Wando

sandy loam soil columns than metribuzin.

63

PC940C was not mobile in the soil columns as determined
by the 3H-labelled experiments (Table 6). The greatest

3H-PC940C remained in the top 1.27 cm

portion of the applied
of the soil. This was also supported by visual observation
since the material tended to remain on the soil surface
after repeated leachings.

A combination of metribuzin and alachlor retained less

3H-PC940C at the soil surface than did the treatments of

3H-PC940C plus alachlor and 3H-PC940C plus metribuzin. The
treatment of 3H-PC940C with no alachlor or metribuzin had a
smaller percentage of 3H-label remaining in the top 1.27 cm
of the soil than did the treatments with alachlor or with
metribuzin. However, the treatment with no alachlor or
metribuzin had more retained in the top 1.27 cm of the soil
than did the treatment with both metribuzin and alachlor.

The retention of more 3

H-label in the top 1.27 cm of
the soil columns when PC940C was mixed with metribuzin or
with alachlor may have been due to hydrogen bonding between
the more mobile fractions of PC940C and either herbicide.
This may have reduced the mobility of highly water-soluble

3H-labelled fractions. However, an explanation for' what

3H-PC940C,

happened with the three way interaction of
alachlor, and metribuzin is more difficult. It was found
that metribuzin and alachlor interacted with one another

(Tables 3 and 4) and this interaction may be partially

64

3H PC940C in various depth sections

Table 6. Percentage of
of a Wando sandy loam soil columns following leaching with

2.5 cm of water.

 

 

 

Treatments
PC940C
PC940C PC940C (2X)+
Sample PC940C (2X)+ (2x)+ Metribuzin+
Depth ( 23061b Metribuz in Alachlor Alachlor
(cm) ----------------- (% of Total) -----------------
0-l.27 86.7 B a 91.2 A a 89.0 AB a 80.0 C a
1.27-2.54 2.3 B bcd 1.9 B be 2.3 8 be 3.5 A bc
2.54-5.08 2.0 8 cd 1.1 C c 1.7 BC c 2.7 A c
5.08-7.62 1.7 B d 0.9 D c 1.2 C c 3.1 A be
7.62-10.16 3.5 B be 2.1 B be 2.0 B be 5.5 A b
10.16-12.70 3.8 A b 2.8 A b 3.8 A b 5.3 A b

 

aNumbers followed by the same capital letter in the same row
are not significantly different according to Duncan's
multiple range test at the 0.05 level.

bNumbers followed by the same lower case letter in the same

column are not significantly different according to

Duncan's multiple range test at the 0.05 level.

65

responsible for less 3H-label being retained in the top 1.27
cm of the soil columns.

The water solubility of 3H-PC940C can be estimated.
Previous soil plate analysis of 3I-I-PC940C after multiple

3H-label

developments, showed that only 3 to 5% of the
migrated with the water solvent front (11). If a value of
approximately 4% is assigned for the water-soluble fraction
of 3H-PC940C, than the amount of 3H-PC940C which perculated
into the soil column ranged from 5 to 16%.

To summarize, PC940C effectively controlled the release
of metribuzin and alachlor in soil columns with two leaching
treatments. PC940C, at the 16x rate, appeared to inhibit
the decomposition of metribuzin. PC940C was also found to
be mostly non-mobile in the soil columns when leached with
water. Water insolubility of PC940C is a prerequisite for a

successful controlled release agent. of *water-soluble

herbicides.

LITERATURE CITED

Collins, R.L., S. Doglia, R.A. Mazak, and E.T.
Samulski. 1973. Controlled release of herbicides
theory. Weed Sci. 21:1-5.

Collins, R.L. and S. Doglia. 1973. Concentration of
pesticides slowly released. by’ diffusion. Weed Sci.
21:343-349.

DelliColli, H.T. 1980. Pine kraft lignin as a
pesticide delivery system. Pages 225-234 i3 Controlled
Release Technologies: Methods, Theory, and Application.
ed. A.F. Kydonieus. Vol. II. CRC Press. Boca Raton,
Florida.

Dunigan, B.P. and T. MacIntosh. 1971. Atrazine-soil
organic matter interaction. Weed Sci. 19:279-282.
Goring, D.A.I. 1971. Polymer properties of lignin and
lignin derivatives. lg Lignins Occurrence, Formation,
Structure, and Reactions. ed. K.U. Sarkanen and C.H.
Ludwig. Wiley Interscience, New York.

Harris, F.W. 1980. Polymers containing pendent
pesticide substituents. Pages 63-82 ig Controlled

Release Technologies: Methods, Theory, and Application.

66

10.

11.

12.

67

ed. A.F. Kydonieus. Vol. II. CRC Press. Boca Raton,
Florida.

Ladlie, J.S., W.F. Meggitt, and D. Penner. 1976.
Effect of soil pH on microbial degradation, adsorption,
and mobility of metribuzin. Weed Sci. 24:477-481.
Ladlie, J.S., W.F. Meggitt, and D. Penner. 1976.
Effect of pH on metribuzin activity in the soil. Weed
Sci. 24:505-507.

McCormick, C.L. and M.M. Fooladi. 1980. Controlled
activity polymers with labile bonds to pendent
metribuzin. Pages 317-330 in; Controlled Release of
Bioactive Materials. ed. R. Baker. Academic Press,
New York.

McCormick, C.L., K.W. Anderson, J.A. Pelezo, and D.K.
Lichatowich. 1981. Controlled release of metribuzin,
2,4-D, and model aromatic amines from polysaccharides
and poly (vinyl alcohol). (Pages 147-158 £2 Controlled
Release of Pesticides and Pharmaceuticals. ed. D.H.
Lewis. Plenum Press, New York.

Riggle, 8.0. and D. Penner. Controlled release of
metribuzin and alachlor by pine kraft lignins as
measured by soil thin layer chromatography. (in
preparation)

Schubert, W.J. 1965. Lignin Biochemistry. Academic

Press, New York.

13.

14.

68

Smith, A.E. and B.P. Verma. 1977. Weed control in
nursery stock by controlled release of alachlor. Weed
Sci. 25:175-178.

Weed Science Society of America. 1983. Herbicide

Handbook, 5th Ed. WSSA, Champaign, IL. 13 and 318 pp.

CHAPTER FOUR

PC940C PROTECTION OF FIELD AND GREENHOUSE
GROWN SOYBEANS FROM METRIBUZIN INJURY

ABSTRACT

PC940C, a pine kraft lignin, combined with metribuzin
(4-amino-6-Eggg-butyl-3-(methylthio)-gg-triazin-5(4H)-one),
significantly reduced metribuzin related phytotoxicity to
field and greenhouse grown soybeans (Glycine 22$ (L.)
Merr.). PC940C rates of 0.77 and 1.15 L/ha protected field
grown soybeans treated with metribuzin rates of 0.42 and
0.84 kg/ha. PC940C rates of 1.15 and 2.30 L/ha also
protected greenhouse grown soybeans treated with metribuzin
of 0.64 kg/ha. PC940C did not interfere with the effective
weed control of redroot pigweed (Amaranthus retroflexus L.)

and common lambsquarters (Chenopodium album L.). PC940C

 

did not appear to have any herbicidal activity and did not
appear to injure soybeans. These results suggest that
PC940C effectively controlled the release of metribuzin in

field and greenhouse soil.

69

INTRODUCTION

A controlled release agent used with metribuzin could
be most beneficial for use in soybean production. The net
result would be a reduction in mobility of this highly
water-soluble herbicide (11) in neutral and alkaline pH
soils (4), and, consequently, a reduction in metribuzin
related. phytotoxicity' of soybeans, since less herbicide
would migrate into the soybean root zone.

Different controlled release materials have been
tested with metribuzin. Pendent metribuzin, which was
attached to polyvinyl alcohol polymers, resulted in a
reduction of metribuzin mobility (3,6); however, this
approach necessitates covalent bonding of metribuzin with
the polymers and results in a series of compounds which
incorporate a portion of the metribuzin molecule and have
questionable herbicidal value. Metribuzin has also been
tested with polysaccharides (7), but unfortunately
polysaccharides are short term readily available carbon
sources for soil microorganisms.

A material that would have the potential as a
controlled release agent for metribuzin is pine kraft

lignin. Pine kraft lignin has already been successfully

70

71

used with 2,4-D (2,4-dichlorophenoxy acetic acid) (1) and
has been demonstrated to have high. adsorptive capacity
for atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-g-
triazine) (2). In addition, pine kraft lignin has been
shown to control the release of metribuzin and alachlor
(2-chloro-2',6'-diethyl-N-methoxymethyl acetanilide) as
demonstrated by soil thin layer chromatography (8) and soil
column chromatography (9).

The purpose of this study was to evaluate PC940C as a
controlled release agent for preemergence applied
metribuzin as measured by the reduction of metribuzin
related phytotoxicity to field and greenhouse grown

soybeans.

MATERIALS AND METHODS

Material Studied. PC940C is a pine kraft lignin made from
caustic treated INDULIN AGl. PC940C was used in a 15%
solid water slurry fornl which kept the water-insoluble

lignin in a suspension.

Field Study. A field experiment was conducted in 1984 at

 

East Lansing, Michigan. The soil was a Capac fine loam
(fine loamy, mixed mesic Aeric Ochraqualfs) with 2.6%
organic matter and pH of 7.8. The experiment was designed
as a completely randomized block two factor factorial with
four levels of metribuzin and four levels of PC940C for a
total of sixteen treatments with four replications. The
metribuzin rates were 0, 0.42, 0.64, and 0.84 kg/ha: PC940C
rates were 0, 0.38, 0.77, and 1.15 L/ha. Four hours prior
to application, metribuzin, and PC940C were mixed together
in l-L plastic bottles and allowed to stand. Treatments of
metribuzin and PC940C ‘were applied preemergence 'with. a

tractor-mounted sprayer that delivered 215 L/ha at 207 kPa

1Product of Westvaco Corp.

72

73

pressure. Four rows of soybeans, Corsoy 79, were planted
in each plot. Plot size was 9.1 m by 3 m with 0.76 row
width spacing. Planting date was June 22, 1984. Rainfall
(Table 1) was sparse for that year and so plots were
periodically irrigated (Table 1). All plots ‘were hand
weeded as needed early in the growing season. Soybean
injury ratings (0 = no injury; 100 I complete kill) was
measured 32 and 46 days after emergence (D.A.E.). Weed
control ratings were recorded (0 a no control: 100 I
complete control) for redroot pigweed and common
lambsquarters at 32 and 46 D.A.E. Due to technical
difficulties, the 0.64 kg/ha metribuzin treatment was

discarded.

Greenhouse Study. Greenhouse experiments were conducted in
1984 and 1985 at East Lansing, Michigan. Soil type used to
pot plants was a Spinks sandy loam (sandy, mixed mesic
Psammentic Hapludalfs) with 0.8% organic matter and pH of
6.5. Three soybean seeds (Corsoy 79) were planted in l-L
plastic pots with drainage holes. Pots were placed in
250-ml aluminum pans to allow for daily subirrigation with
water. A combination of PC940C and metribuzin was applied
preemergence and the experimental design was a two factor
factorial with metribuzin applied at two rates and PC940C
applied at three rates. The rates for metribuzin were 0

and 0.64 kg/ha; the rates for PC940C were 0, 1.15, and 2.30

74

Table l. Rainfall and irrigation data for 1984 at East

Lansing, Michigan after 22 June.

 

 

Month Rainfall Irrigation
(cm) (cm)

June 0 2.54

July 3.18 6.35

August 8.13 0

 

75

L/ha. Materials were mixed together in plastic 1-L
bottles, shaken, and allowed to stand for 1 h prior to
application. Materials were applied with a belt sprayer
with a pressure of 104 kPa and a spray volume of 234 L/ha.
All treatments were arranged in the greenhouse in a
completely randomized design and six replications were
used. Container-grown plants were kept in greenhouse at 20
to 30 C with natural illumination and sodium halide
supplemental lighting at 500 uE-m-z-s-1. When plants were
in the third trifoliar growth stage (approximately 35
D.A.E.), they were rated for injury (0 I no injury, 100
complete kill) and the dry weights measured. Data for dry

weights is expressed as percentage of control.

RESULTS AND DISCUSSION

Irrigation was essential for the field experiment
since enough water had to be present to insure that the
metribuzin would be mobilized into the soil profile.
Research has shown that the movement of water-soluble
herbicides into the soil is necessary and is enhanced under
high moisture conditions (10).

PC940C successfully reduced metribuzin related phyto-
toxicity to the soybeans in the field at 32 and 46 D.A.E.
(Tables 2 and 3). There was a significant reduction in
phytotoxicity at 32 D.A.E. when 0.77 and 1.15 L/ha rates of
PC940C were used with a 0.42 kg/ha rate of metribuzin.
However, only a 0.77 L/ha rate of PC940C significantly
reduced phytotoxicity when a 0.84 kg/ha rate of metribuzin
was used. There was also a significant reduction in
phytotoxicity at 46 D.A.E. when PC940C was used with the
two rates of metribuzin.

There was no apparent injury to the plants which had
been treated with just PC940C. This would suggest that
PC940C did not have any herbicidal activity.

The two week interval between the two injury rating

dates was apparently enough time for the PC940C plus

76

77

Table 2. Soybean injury ratings as affected by metribuzin

and PC940C at 32 D.A.E.a.

 

 

 

Metribuzinb
(kg/ha)
PC940C 0 0.42 0.84
(L/ha) ------------------ (a) -------------------
0 0 d 48 ab 66 a
0.38 0 d 32 bc 52 ab
0.77 0 d 20 cd 38 be
1.15 0 d 22 cd 43 abc

 

aInjury index rating is based on the following: 0 I no
injury, 100 8 total kill.

bNumbers followed by the same letter are not significantly

different according to Duncan's multiple range test at the
0.05 level.

78

Table 3. Soybean injury ratings as affected by metribuzin

and PC940C at 46 D.A.E.a.

 

 

 

Metribuzinb
(kg/ha)
PC940C 0 0.42 0.84
(L/ha) ------------------ (g) ------------------
0 0 d 45 a 43 a
0.38 0 d 26 bc 28 b
0.77 0 d 12 cd 20 bc
1.15 0 d 16 bc l7 bc

 

aInjury index rating is based on the following: 0 a no
phytotoxicity, 100 = total kill.

bNumbers followed by the same letter are not significantly
different according the Duncan's multiple range test at
the 0.05 level.

79

metribuzin treated plants to out-grow their metribuzin
induced injury as compared to the non-PC940C metribuzin
treated plants.

The protective effects of PC940C are readily apparent
from photographs taken at 32 D.A.E. (Figures 1 and 2).
There was an improvement in both height and vigor of the
plants.

PC940C did not interfere with metribuzin related weed
control at the two testing dates for both redroot pigweed
and common lambsquarters which were the predominate
broadleaf weed types present in the study. There was also
no observed PC940C effect for either weed type.

The similarity in the degree of phytotoxicity for both
the 0.42 and 0.84 kg/ha rate of metribuzin may have been
due to the high pH of the soil which was 7.7. Research has
shown that, as the soil pH increases, the degree of
metribuzin related injury to soybeans also increases (5).

The results obtained in the greenhouse were very
similar to those of the field study. There was a
significant reduction in metribuzin related phytotoxicity
with plants treated with PC940C; 0.64 kg/ha rate of
metribuzin treated soybeans had a 50% reduction in injury
when treated with PC940C at rates of both 1.15 and 2.30
L/ha (Table 4). Since there appeared to be no
concentration effect of PC940C in terms of injury

reduction, it can be assumed that some saturation point had

80

Figure l. Soybeans treated with 0.42 kg/ha metribuzin and 0

L/ha PC940C and rated at 32 D.A.E.

81

 

82

Figure 2. Soybeans treated with 0.42 kg/ha metribuzin and

0.77 L/ha PC940C and rated at 32 D.A.E.

83

 

84

Table 4. Soybean injury ratings as affected by metribuzin
and PC940C for greenhouse grown plants at the third

trifoliar stagea.

 

 

 

Metribuzinb
(kg/ha)
PC940C 0 0.64
(Ia/ha) ------------- (a) ............. -
0 0 c 22 a
1.15 0 c 10 b
2.30 0 c 11 b

 

aInjury index rating is based on the following: 0 a no
injury, 100 a total kill.

bNumbers followed by the same letter are not significantly

different according to Duncan's multiple range test at the
0.05 level.

85

been reached at the 1.15 L/ha rate. PC940C did not appear
to injury or alter the percentage dry weight of the
container grown plants (Table 5).

In conclusion, PC940C successfully reduced metribuzin
related phytotoxicity to both field and greenhouse grown
soybeans and did not interfere with metribuzin related weed
control as measured in the field. These results suggest
that PC940C controlled the release of metribuzin both in

the field and greenhouse.

86

Table 5. Effect of PC940C on metribuzin injury to soybeans
grown in greenhouse as measured in dry weight of third

trifoliar plantsa.

 

% Dry Weight

 

Metribuzin PC940C ' of Controlb
(kg/ha) (L/ha) (3)
0 1.15 95.6 a
2.3 91.7 ab
0.64 0 73.0 c
1.15 77.8 C
2.3 81.4 bc

 

aEffects on dry weights are as percentages of the untreated
control.

bMeans with common letters are not significantly different
according to Duncan's multiple range test at the 0.05

level.

LITERATURE CITED

DelliColli, H.T. 1980. Pine kraft lignin as a
pesticide delivery system. Pages 225-234 i2
Controlled Release Technologies: Methods, Theory, and
Application. Vol. II. ed. A.F. Kydonieus. CRC
Press, Boca Ration, Florida.

Dunigan, E.P. and T. MacIntosh. 1971. Atrazine soil
organic matter interaction. Weed Sci. 19:279-282.
Harris, F.W. 1980. Polymers containing pendent
pesticide substituents. Pages 63-82 i§_ Controlled
Release Technologies: Methods, Theory, and Applica-
tion. Vol. II. ed. A.F. Kydonieus. CRC Press, Boca
Raton, Florida.

Ladlie, J.S., W.F. Meggitt, and. D. Penner. 1976.
Effect of soil pH on microbial degradation,
adsorption, and mobility of metribuzin. Weed Sci.
24:477-481.

Ladlie, J.S., W.F. Meggitt, and D. Penner. 1976.
Effect of pH on metribuzin activity in the soil. Weed
Sci. 24:505-507.

McCormick, C.L. and M.M. Fooladi. 1980. Controlled

activity polymers with labile bonds to pendent

87

10.

11.

88

metribuzin. Pages 317-330 i_p_ Controlled Release of
Bioactive Materials. ed. R. Baker. Academic Press,
New York.

McCormick, C.L., K.W. Anderson, J.A. Pelezo, and D.K.
Lichatowich. 1981. Controlled release of metribuzin,
2,4-D, and model aromatic amines form polysaccharides
and poly (vinyl alcohol). Pages 147-158 ig Controlled
Release of Pesticides and Pharmaceuticals. ed. D.H.
Lewis. Plenum Press, New York.

Riggle, B.D. and D. Penner. Controlled release of
metribuzin and alachlor by kraft lignins as measured
by soil thin layer chromatography. (in preparation)
Riggle, B.D. and D. Penner. Controlled release of
metribuzin and alachlor by PC940C as measured by soil
column chromatography. (in preparation)

Ritter, W.F., H.P. Johnson, and W.G. Lovely. 1973.
Diffusion of atrazine, propachlor, and diazon. Weed
Sci. 21:381-384.

Weed Science Society' of .America. 1983. Herbicide

Handbook, 5th Ed. WSSA, Champaign, IL. 318 pp.

RIES

"‘iliil‘yyylllllllllll

31