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THESIS

III/IllllllIll/II/l/IllllllllllII/ii/iiilfllfliiii/Yii

This is to certify that the

dissertation entitled

Pinto Bean Tolerance to
and Weed Control with Postemergence
Imazethapyr and Bentazon

presented by
Troy Allen Bauer

has been accepted towards fulfillment
of the requirements for

PhD Agriculture

 

 

degree in

X/x 0 Lida-Mu

Major professhr

Date March 25, 1993

 

MSUis an Affirmative Action/Equal Opportunity Institution 0-12771

 

LIBRARY
MIchlgan State
Unlverslty

 

 

 

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

cwmmm3¢v I

 

 

PINTO BEAN TOLERANCE TO
AND WEED CONTROL WITH POSTEMERGENCE
IMAZETHAPYR AND BENTAZON
By

Troy Allen Bauer

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

DOCTOR OF PHILOSOPHY

Department Of CrOp & Soil Sciences

1993

 

ABSTRACT
PINTO BEAN TOLERANCE TO
AND WEED CONTROL WITH POSTEMERGENCE
IMAZETHAPYR AND BENTAZON
By

Troy Allen Bauer

Dry bean producers have limited postemergence broadleaf weed control options.
Research determined (1) if bentazon improved dry edible bean tolerance to
postemergence imazethapyr, (2) if weed control was antagonized when imazethapyr
and bentazon were tank-mixed, and (3) the basis and inheritance of varietal pinto bean
tolerance to postemergence imazethapyr. Imazethapyr and bentazon were applied
with various adjuvants to ’Olathe’ pinto bean. Imazethapyr visually injured pinto
beans 7 DAT in both field and greenhouse research. When 840 g ha'1 of bentazon
was tank-mixed with 53 g ha'1 of imazethapyr, visual injury decreased as compared
to imazethapyr alone in both studies. Fifty three g ha“ of imazethapyr delayed
physiological maturity by 8 and 15 days compared to the untreated control in 1991
and 1992, respectively. Pinto bean seed yields, however were not reduced compared
to the untreated control. When 840 g ha’1 of bentazon was tankmixed with 53 g ha‘1
of imazethapyr, maturity was not delayed. l4C-Imazethapyr absorption decreased by
more than 40% and translocation from the treated pinto bean leaflet by more than

50% when tank—mixed with bentazon compared to 1“C-irnazethapyr alone. The

addition of 20 mM N a-acetate inhibited absorption of l4C-imazethapyr similar to tank-
mixing with bentazon, but did not inhibit translocation.

Imazethapyr and bentazon were applied with POA in a factorial arrangement to
weed species. Tank-mixing 840 g ha" of bentazon with 13 or 27 g ha'1 of
imazethapyr increased redroot pigweed and eastern black nightshade dry weight as
compared to Colby’s expected values in the greenhouse. However, weed control was
not antagonized in field studies. Subsequent greenhouse studies indicated that soil
interception of imazethapyr increased redroot pigweed control. Bentazon decreased
redroot pigweed leaf absorption of ”C—imazethapyr by 15% and translocation from
the treated leaf by greater than 50% as compared to 1“C-imazethapyr alone.

All rates of postemergence imazethapyr injured Olathe, Sierra, UIll4, P89405,
Aztec, and P90570 pinto bean varieties 7 DAT in 1991 and 1992 except 53 g ha‘1 of
imazethapyr applied to Sierra pinto bean in 1991. Olathe was injured more than other
varieties in 1991, and physiological maturity was delayed more than the maturity of
Sierra in both years. However, seed yields of any variety were not reduced in 1991,
and only P90570 had reduced seed yields from 53 g ha‘I Of imazethapyr in 1992.
Olathe pinto bean absorbed and translocated more than 1.4 and 1.3 times,

respectively, l“C-imazethapyr as Sierra pinto bean 24 h after application.

iii

 

ACKNOWLEDGEMENTS

I would like to extend my deepest appreciation to Dr. Karen Renner for her
guidance, support, and friendship in completing this dissertation and other aspects
of my graduate program. Gratefulness is also extended to Doc Penner for all his
help and guidance throughout my graduate program and job seeking. A special
thanks to Dr. James Kelly and Dr. Matthew Zabik for their guidance and support
throughout my graduate program also. Appreciation is extended to Dr. Jim Kells,
who did not serve on my graduate committee, but was very instrumental in my
graduate program and job seeking. I would like to acknowledge Dr. ’GQ’ Powell
for his field expertise and his technical assistance. The author will miss Dr.
Powell’s gift for keeping summer work lively. Patrick Svec deserves many thanks
for assisting in all aspects of my research and the many long hours spent
oxidizing. I would also like to thank Scott DeVuyst, Eric McPherson, and Sharon
Grant for assisting with my research. A special thanks to my friends and fellow
graduate students Aaron ’Von’ Hager, Jason ’Little Guy’ Woods, Karen ’Crunch
Berry’ Novosel, Boyd ’the Lure’ Carey, Rick Schmenk, Joe ’go Joe’ Bruce, and
Steve ’the Flame’ Hart. Thanks also to Andy Chomas for keeping life interesting
in the office.

I would like to sincerely thank my dear wife Kay for supporting my graduate
’career’ and for the time devoted so I could obtain this degree, and for her love

and understanding. Your support has been greatly appreciated.

 

TABLE OF CONTENTS

Chapter 1. Review of Literature.

Introduction ................................
Imazethapyr ................................

Bentazon ..................................
Interactions ................................
Literature Cited .............................

.1
.4

.7
.8

12

 

Chapter 2. ’Olathe’ Pinto Bean Response to Postemergence Imazethapyr and
Bentazon.

Abstract .................................. 23

Introduction ................................ 26

Materials and Methods ......................... 28
Greenhouse study .......................... 28
Field study .............................. 30
Adjuvant study ........................... 32
l“'C—Imazethapyr absorption and translocation studies . . 33
Effect of Na-acetate and UAN on l4C-imazethapyr
absorption and translocation ................... 35

Results and Discussion ......................... 36
Greenhouse study .......................... 36
Field study .............................. 38
Adjuvant study ........................... 4O
l4C-Imazethapyr absorption and translocation studies 40
Effect of Na-acetate and UAN on 14C-imazethapyr
absorption and translocation ................... 42
Literature Cited ........................... 44

Chapter 3. Selected Weed Response to Postemergence Imazethapyr and

Bentazon.
Abstract .................................. 56
Introduction ................................ 58
Materials and Methods ......................... 60
Greenhouse studies ......................... 60
Field studies ............................. 62
Herbicide soil activity study ................... 63
l“C-Imazethapyr absorption and translocation studies . . . . 64
Results and Discussion ......................... 66
Greenhouse studies ......................... 66
Field studies ............................. 68
Herbicide soil activity study ................... 70
l“C-Imazethapyr absorption and translocation studies . . . . 71
Literature Cited ............................. 73

Chapter 4. Varietal Pinto Bean Tolerance to Postemergence Imazethapyr.

Abstract .................................. 84
Introduction ................................ 86
Materials and Methods ......................... 88
Field research ............................ 88
ALS enzyme assay ......................... 90
1“C-Imazethapyr absorption, translocation,
and metabolism ........................... 92
Inheritance of imazethapyr tolerance
in pinto bean ............................. 96
Results and Discussion ......................... 98
Field research ............................ 98
ALS enzyme assay ......................... 99
l“C—Imazethapyr absorption, translocation,
and metabolism .......................... 100
Inheritance of imazethapyr tolerance
in pinto bean ............................ 102
Literature Cited ............................ 105

vi

 

Chapter 2. ’Olathe’ Pinto Bean Response to Postemergence Imazethapyr and

LIST OF TABLES

Bentazon.

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Chapter 3. Selected Weed Response to Postemergence Imazethapyr and

Soil characteristics of field studies conducted

in 1991 and 1992 ..................... 46
Olathe pinto bean response to bentazon and

imazethapyr applied alone and in combination

in the greenhouse ..................... 47
Response of Olathe pinto bean to bentazon

and imazethapyr applied alone and in combination

in 1991 in the field .................... 48
Response of Olathe pinto bean to bentazon

and imazethapyr applied alone and in combination

in 1992 in the field .................... 49
Response of Olathe pinto bean to bentazon

and imazethapyr applied alone and in combination

in the field as influenced by various adjuvants . . . . 50
The effect of Na-acetate and UAN on MC-imazethapyr
absorption and translocation 24 h after treatment

when applied alone and tank-mixed with bentazon. . 51

Bentazon.
Table 1. Soil characteristics of field studies in 1991
and 1992 ........................... 75
Table 2. Weed dry weight 14 DAT from bentazon and
imazethapyr applied alone and in
combination in the greenhouse ............. 76
Table 3. Response of redroot pigweed, velvetleaf,

and common lambsquarters to bentazon and
imazethapyr applied alone and in combination
in 1991 in the field .................... 77

vii

Table 4. Field response of redroot pigweed, velvetleaf,
and common lambsquarters to bentazon and
imazethapyr applied alone and in combination
in 1992 in the field .................... 78

Table 5. Redroot pigweed dry weight 21 DAT as
influenced by imazethapyr and bentazon with
and without soil interception of the
spray solution ........................ 79

Chapter 4. Varietal Pinto Bean Tolerance to Postemergence Imazethapyr.

Table 1. Soil characteristics of field studies

conducted in 1991 and 1992 .............. 108
Table 2. Pinto bean varietal tolerance differences

to postemergence imazethapyr applications

in 1991 ........................... 109
Table 3. Pinto bean varietal tolerance differences

to postemergence imazethapyr applications

in 1992 ........................... 110
Table 4. Partitioning of 1“C applied as l“C-imazethapyr

in Olathe and Sierra pinto bean ............ 111
Table 5. Metabolism of l“C-imazethapyr in Olathe

and Sierra pinto bean .................. 112

Table 6. The injury, sample size, and variance of
parent, F,, and F2 populations. ............ 113

viii

 

LIST OF FIGURES

Chapter 1. Review of Literature.

Figure 1.

Figure 2.

Schematic diagram of initial imazethapyr

metabolism in corn, soybean, and dry bean. ..... 19
Schematic diagram of bentazon metabolism in
tolerant higher plants ................... 21

Chapter 2. ’Olathe’ Pinto Bean Response to Postemergence Imazethapyr and
Bentazon.

Figure 1.

Figure 2.

l“C-Imazethapyr absorption when applied

alone and tank-mixed with bentazon in

Olathe pinto bean ..................... 52
1“C-Imazethapyr translocation from the

treated leaf when applied alone and tank-

mixed with bentazon in Olathe pinto bean ...... 54

Chapter 3. Selected Weed Response to Postemergence Imazethapyr and
Bentazon.

Figure 1.

Figure 2.

l“C—Imazethapyr absorption when applied alone

and tank-mixed with bentazon in redroot pigweed . 80
l“C-lmazethapyr translocation from the

treated leaf when applied alone and tank-

mixed with bentazon in redroot pigweed ....... 82

 

Chapter 4. Varietal Pinto Bean Tolerance to Postemergence Imazethapyr.

Figure 1. Olathe and Sierra pinto bean ALS enzyme

activity in the presence of imazethapyr ....... 114
Figure 2. l“C-Imazethapyr absorption in Olathe and
Sierra pinto bean varieties ............... 116

Figure 3. l“C-Imazethapyr translocation from the
treated leaflet in Olathe and Sierra
pinto bean varieties ................... 118

 

 

, :3, 7-5;8 ‘

CHAPTER 1

Introduction

Dry edible beans (Phaseolus vulgaris L.) are a major specialty crop in the state
of Michigan with 350,000 acres of production in 1990. Michigan dry bean
producers led the nation in total acreage and ranked 12'h in the production of pinto
beans (33). With the loss Of chloramben1 (3-amino-2,5—dichlorobenzoic acid) and
dinoseb (2-1(l-methylpropyI)-4,6-dinitrophenol), Michigan dry bean producers
have been searching for broadleaf weed control options. Standard weed control
programs have included metolachlor (2-chloro-N—(2-ethyl~6-methylphenyl)-N-(2-
methoxy-1-methylethyl)acetamide) plus chloramben or dinoseb applied
preemergence or trifluralin (2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)
benzenamine) plus EPTC (S-ethyl dipropylcarbamothioate) preplant incorporated
followed by chloramben preemergence (usually banded). The loss of chloramben
severely reduced broadleaf weed control options.

Bentazon [3-(1-methylethyl)-(1H)—2, l ,3-benzothiadiazin-(4(3H)-one 2 ,2
dioxide] is the only postemergence broadleaf herbicide available and dry beans are
very tolerant of bentazon (28, 72). Bentazon controls common cocklebur
(Xanthium strumarium L.), jirnsonweed (Datum strumarium L.), velvetleaf

(Abutilon theophrasti Medicus), wild mustard (Brassica kaber (DC.)

 

lPrairie Farmer. 1990. Amiben’s loss limits dry bean herbicide options. Jan.
2’ pp 8'9.

 

2

L.C.Wheeler), and common ragweed (Ambrosia anemisiifolia L.). However,
bentazon does not control redroot pigweed (Amaranthus retroflexus L.) or eastern
black nightshade (Solanum ptycanthum Dun.) (72), two problem weeds in dry
edible beans.

Imazethapyr (2—[4,5-dihydrO-4-methyl-4-methyl-4-(1-methylethyl)-5-oxo—1H—
imidazol-2-yl]-5-ethy1-3-pyridinecarboxylic acid) effectively controls redroot
pigweed, eastern black nightshade, wild mustard, and common cocklebur. The
activity on redroot pigweed and eastern black nightshade would complement
bentazon’s weed spectrum. Soybeans (Glycine max L.) and other legumes are
tolerant of postemergence imazethapyr (13, 65, 71). However, dry edible beans
have shown susceptibility to imazethapyr applications (16, 70), and the pinto bean
class of dry beans appears to be particularly sensitive to postemergence
imazethapyr (18). Early season injury symptoms include stunting, leaf crinkling,
and interveinal chlorosis, while late season injury is characterized by reduced plant
height and delayed maturity. Wilson and Miller (70) Observed seed yield
reductions one year following the application of 100 g ha" (a 2X standard
application) of imazethapyr.

While screening for postemergence herbicide programs for dry bean
producers, researchers (48) noted that bentazon safened dry edible bean response
to imazethapyr. However, reductions in weed control have been reported (11)

when bentazon is tank-mixed with imazethapyr.

 

3

Two or more herbicides are tank-mixed to increase the weed control spectrum
over that achieved from either herbicide applied alone. When herbicides applied
in a tank-mix act independently and the weeds controlled predicted by the
performance of each herbicide applied alone, the effect is considered additive (21).
However, the weed control spectrum may not follow the predicted performance.
Hatzios and Penner (1985) described an interaction as antagonistic when biological
activity decreased compared to that of each herbicide applied alone. Conversely,
an interaction that resulted in enhanced of biological activity was termed
synergistic.

Numerous studies have determined herbicide interactions on various species.
Many have reported antagonized grass control when bentazon was tank-mixed with
sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)pr0pyl]-3-hydroxy-2-
cyclohexen-l-one) (9, 20, 51). Wanamarta and Penner (1989) concluded that
reduced quackgrass (Elytrigia repens (L.) Nevski) control was due to inhibited
absorption of 14C-sethoxydim in the presence Of the sodium salt of bentazon.
Conversely, pitted momingglory (Ipomoea lacunosa L.) control synergistically
increased from combinations of imazaquin (2-[4,5-dihydrO-4-methyl-4-(1-
methylethyl)-5-oxo-lH-imidazol-Z-yl]-3-quinolincarboxylic acid) and imazethapyr
(54). An increase in morningglory control was also observed when imazapyr
(( i)-2-[4,5-dihydrO-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-

pyridinecarboxylic acid) was combined With either imazaquin or imazethapyr (53,

 

 

69).

Formulated bentazon has been implicated as an antagonist when tank-mixed
with a number of other herbicides (9, 16, 20, 23, 51, 58). Bentazon is formulated
as a sodium salt (Na+) (72). Sodium ions in the bentazon formulation appear
responsible for many instances of antagonism by contributing alkaline cations that
can form salts of acidic herbicides such as imazethapyr and sethoxydim which are
not readily absorbed by plants (66). The Na+ ion added as Na-acetate has been
shown to inhibit uptake of sethoxydim and imazethapyr on quackgrass and pinto
bean, respectively (5, 66). However, in both cases and others the absorption can
be restored to levels previously observed by adding NH4 in the form of either
UAN or (NH,,)2SO4 (16, 23). This addition of an organic acid to the spray
solution can overcome the antagonism by preventing the formation of the sodium
salt. Adding abundant ammonium may also prevent or overcome this antagonism

(44)-

Imazethapyr. Imazethapyr is a member of the imidazolinone herbicide family of
whichimazapyr, imazamethabenz (( i )-2-[4, 5-dihydro-4-methyl-4-( 1 -methylethy1)-
5—oxo-1H—imidazol-2-yl]—4(and 5)-methylbenzoic acid (3:2)), and imazaquin also
belong. Imazethapyr can be applied pre—plant incorporated, preemergence, or
postemergence for selective control of various weed species in soybeans and other

legumes. Imazethapyr is absorbed by both roots and shoots, and is translocated

-‘?5—‘A—-7

5

to the meristematic tissues, characteristic of a phloem mobile herbicide (13, 56).
The primary site of imazethapyr and other imidazolinone herbicide action has been
reported to be the inhibition of the acetolactate synthase (ALS, also called
acetohydroxyacid synthase) (2, 38). ALS is the first common enzyme in the
synthesis of the branched chain amino acids valine, leucine, and isoleucine. The
ALS enzyme is believed to reside in the plastids of plant cells (35). The plant
genes coding for ALS have been isolated and characterized (31). The regulation
of ALS is believed to be feedback inhibition by its products (32, 34). Both valine
and leucine are inhibited by their own synthesis but are more inhibitive when
supplied together (36). The sulfonylurea and the triazolopyrimidine sulfonanilide
herbicides have also been reported as potent inhibitors of ALS (24, 47, 62)

It has been proposed that plants treated with the imidazolinone herbicides are
slowly starved of valine, leucine, and isoleucine (57). However, subsequent
research has been proposed suggesting that the death of the plant may be due to
the toxic buildup of intermediates. The buildup of a-ketobutyrate has been
triggered in plants treated with chlorosulfuron and sulfometuron methyl (50).
Subsequent research has shown that a-ketobutyrate accumulation can be toxic (25).

Selectivity of imazethapyr is based primarily on metabolism (13). The half-life

of imazethapyr in soybeans, a tolerant species, is 1.6 days while in redroot

6
pigweed, a susceptible species, it is 32.1 daysz. Wilcut et a1. (1988) determined

the half-life of imazaquin, another imidazolinone, in tolerant soybean, to be 4.4
days while in susceptible cocklebur the half life was 39.8 days (67). Selectivity
of the sulfonylurea herbicides has also been shown to be primarily based on
metabolism (68).

Soybean, corn (Zea mays L.), and dry edible bean convert imazethapyr to 5-
hydroxyethyl-imazethapyr followed by glucose conjugation (Figure 1). The rate
of conversion to the glucose conjugate follows the order soybean > dry edible
bean > corn, which results in reduced dry bean and corn tolerance2'3(6). Five-
hydroxyethyl-imazethapyr is herbicidally active, but five times less active than
imazethapyr?

Some plants possess ALS isozymes that are less sensitive to imidazolinone and
sulfonylurea inhibition, thereby increasing their tolerance (3, 19). Genetic studies
of sulfonylurea resistance in soybean (55), Lactuca spp. (41), and imidazolinone
resistant com (30) has indicated that the resistance trait is inherited as a single

nuclear gene in a semidominant fashion.

 

2AC-263-499 Technical Information Report. 1985. American Cyanamid CO.,
Princeton, NJ 08540.

3Personal communication. Dale Shaner, American Cyanamid CO., Princeton,
NJ 08540.

 

 

7

Bentazon. Bentazon is a selective postemergence herbicide commonly used in
soybean, dry bean, and corn for control Of several weed species (28, 72). The
primary site of bentazon action is the inhibition of non-cyclic electron transport
while photosystem I is unaffected (7). Bentazon was also shown to inhibit the Hill
reaction activity of isolated chloroplast from both hot pepper (Capsicum chinense
L.) and sweet pepper (Capsicum annuum L.) (4). More specifically, the site of
bentazon inhibition of the photosynthetic electron transport is at the reducing side
Of photosystem H, between the primary electron acceptor Q and plastoquinone
(63). Others (46) have shown that light was required for necrosis to develop in
bentazon treated leaves.

The mechanism of bentazon selectivity is based primarily on metabolism (37).
Large amounts of metabolites were detected in bentazon tolerant plants, but only
small amounts were present in plants susceptible to bentazon (37). Differences in
spray retention and the rate of bentazon metabolism contributed to the selective of
bentazon between soybean and Canada thistle (Cirsium arvense (L.) Scop.) (43).
The rapid metabolism of bentazon in navy bean accounted for its tolerance as
compared to more sensitive cocklebur and black nightshade (29). The unifoliate
navy bean leaf metabolized bentazon more slowly than the trifoliolate leaf (28).

Differential susceptibility between corn inbreds and soybean genotypes is the
result of differential metabolism (8, 10). At 72 h after treatment, 63% Of the

absorbed l“C-bentazon remained as parent in the susceptible corn inbred as

 

 

8

compared to 25% in the tolerant (8). Neither absorption nor translocation could
account for tolerance differences between soybean genotypes. However, tolerant
genotypes metabolized 80 to 90% of the absorbed bentazon within 24 h as
compared to only 10 to 15% metabolism in susceptible genotypes (10). Analysis
of bentazon sensitivity among various corn inbreds and single crosses suggested
this trait is recessive and controlled by a single gene designated ben (15).
Bentazon tolerant crops first hydroxylate and then conjugate bentazon to
glucose (Figure 2). In bentazon tolerant crops such as rice (Oryza sativa L.), rye
(Hordeum vulgare L.), barley (Secale cereale L.), corn, wheat (Triticum aestivum
L.), and peas (Pisum sativa L.), the glucose conjugate is formed primarily from
6-hydroxy-bentazon (37, 42, 49). Small amounts of 8-hydroxy-bentazon are also
formed but in much smaller concentrations. Soybean is unique because it forms

both glucose conjugates in a 1:1 ratio (42).

Interactions. In recent years, crop producers often combine two or more
herbicides in the same spray tank to reduce the number of ’passes’ across the field
and to increase the number of weed species controlled. Reducing the number of
passes reduces application costs and soil compaction. However, in some instances,
a herbicide may control a weed when applied alone, but not when tank-mixed with
a second herbicide. In a different scenario, two herbicides could be tank-mixed,

and control a weed better than when either herbicide is applied alone. These

9

phenomena are referred to as interactions. Hatzios and Penner (1985) described
an interaction as antagonistic when biological activity decreased compared to the
performance of each herbicide alone. Conversely, an interaction that enhanced
biological activity was synergistic.

An interaction has been defined and redefined for several different research
areas. The strict statistical definition is when the effect of a factor deviates more
than can be attributed to chance, then the differential response is called the
interaction of two factors (59). Drury (14) stated that an interaction was a calculus
phenomena and the statistical concept of an interaction was over-simplistic.
Drury’s calculus method for the study of an interaction was based on the use of
a multiple regression polynomial model for fitting data and determining the partial
derivative of each equation with respect to each factor and the second partial
derivative with respect to both factors (as their interaction). The numerical factors
were then calculated and plotted and finally comparisons of the sign of the
interaction used to determine the synergism or antagonism of each factor at a
specific point. To analyze an interaction by this method, one must construct an
isobole. A range of data from around each herbicide’s I50 value must be collected
and graphed, and the 150 value interpolated.

Several Others (1, 64) have also proposed the use of isoboles to present
interaction data. Others (26, 39, 40) have utilized regression estimate analysis to

evaluate interaction studies. Clearly, most of these methods for the presentation

10

of interaction data require computer analysis, since the calculations and plotting
are very complex. These methods have failed to gain widespread acceptance
because of the mathematical intricacies involved. Another reason these methods
have not gained widespread acceptance is that many studies are conducted with
herbicide rates approximating field rates, which generally exceed greater than 50%
control.

Most methods of describing and quantifying interactions have failed because
of their complexities. However, Colby (1967) proposed a formula used frequently
by weed scientists in describing the effect of a herbicide mixture on plants. The

formula is:

XtY
100

 

where E, X, and Y are the expected growth as a percent of control with
herbicides, growth as a percent of control with herbicide A at p lb A", and growth
as a percent of control with herbicide B at q 1b A", respectively. When the
observed response is greater than expected, the combination is synergistic and
when less than expected, it is antagonistic. If the observed responses are equal,
the combination is additive. Statistical significance between the actual value and
the expected value can be determined by using the modified Least Significance

Difference equation developed by Hamill and Penner (17). However, when values

 

11

approach extremes (either 0 or 100 %), this method is too discretionary (personal
observation). More recently, significance has been determined by using Fisher’s
protected LSD to compare Colby’s expected with the observed (53, 54, 69). This
method appears to provide the optimum amount of discretion and separation.
Analyzing and quantifying herbicide interactions remains a confusing and
complex research. More statistical research is needed to help identify methods to
analyze herbicide interactions. With increased use of postemergence herbicides
for broad spectrum weed control, there will continue to be a need to understand

herbicide interactions both statistically and biologically.

12

LITERATURE CITED

Akobundu, I. O., R. D. Sweet, and W. B. Duke. 1975. A method of
evaluating herbicide combinations and determining herbicide synergism.
Weed Sci. 23:20-25.

Anderson, P. C. and K. A. Hibberd. 1985. Evidence for the interaction of
an imidazolinone herbicide with leucine, valine, and isoleucine
metabolism. Weed Sci. 33:479-483.

Anderson, P. C. and M. Georgson. 1986. Selection of an imidazolinone
tolerant mutant corn. Page 437 in D. A. Somers, B. G. Gengenback, D.
D. Biesboer, W. P. Hackett, and C. E. Green, eds. VI International
Congress of Plant Tissue and Cell Culture Abstracts, Univ. Minnesota,
Minneapolis.

Baltazar, A. M., T. J. Monaco, and D. M. Peele. 1984. Bentazon
selectivity in hot pepper (Capisicum chinense) and sweet pepper
(Capsicum annuum). Weed Sci. 32:243-246.

Bauer, T. A., K. A. Renner, and D. Penner. 1993. ’Olathe’ pinto bean
(Phaseolus vulgaris) response to postemergence imazethapyr and bentazon.
Weed Sci. (Submitted).

Bauer, T. A., K. A. Renner, D. Penner, and J. D. Kelly. 1993. Pinto bean
(Phaseolus vulgaris) tolerance to postemergence imazethapyr. Weed Sci.
(Submitted).

BOger, P., B. Beese, and R. Miller. 1977. Long-term effects of herbicides
on the photosynthetic apparatus H. Investigations on bentazone inhibition.
Weed Res. 17:61-67.

Bradshaw, L. D., M. Barrett, and C. G. Poneleit. 1992. Physiological
basis for differential bentazon susceptibility among corn (Zea mays)
inbreds. Weed Sci. 40:522-527.

Cambell, J. R. and D. Penner. 1982. Compatibility of diclofop and BAS
9052 with bentazon. Weed Sci. 30:458-462.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

 

.I‘l. «7 .1 ‘h

13

Connolly, J. A., M. D. Johnson, J. W. Gronwald, and D. W. Wyse. 1988.
Bentazon metabolism in tolerant and susceptible soybean (Glycine max)
genotypes. Weed Sci. 36:417-423.

Cantvvell, J. R., R. A. Liebl, and F. W. Slife. 1989. Imazethapyr for weed
control in soybean (Glycine max). Weed Technol. 3:596-601.

Colby, S. R. 1967. Calculating synergistic and antagonistic responses of
herbicide combinations. Weeds 15 :20-22.

Cole, T. A., G. R. Wehtje, J. W. Wilcut, and T. V. Hicks. 1989.
Behavior of imazethapyr in soybeans (Glycine max), peanuts (Arachis
hypogaea), and selected weeds. Weed Sci. 37:639-644.

Drury, R. B. 1980. Physiological interaction, its mathematical expression.
Weed Sci. 28:573-579.

Fleming, A. A., P. A. Banks, and J. G. Legg. 1988. Differential response
of maize inbreds to bentazon and other herbicides. Can. J. Plant Sci.

68:501-507.

Gerwick, G. C., L. D. Tanguay, and F. G. Burroughs. 1990. Differential
effects of UAN on antagonism with bentazon. Weed Technol. 4:620-624.

Hamill, A. S. and D. Penner. 1973. Interaction of alachlor and carbofuran.
Weed Sci. 21:330-335.

Hart, R., E. Lignowski, and F. Taylor. 1991. Imazethapyr herbicide. pp
247-259. in D. L. Shaner and S. L. Conner, ed. The Imidazolinone
Herbicides. CRC Press, Inc. Boca Raton, Florida.

Hart, S. E., J. W. Saunders, and D. Penner. 1993. Semi-dominant nature
of monogenic sulfonylurea herbicide resistance in sugarbeet (Beta
vulgaris). Weed Sci. (in press)

Hartzler, K. K. and C. L. Foy. 1983. Compatibility of BAS 9052 OH with
acifluorfen and bentazon. Weed Sci. 31:597-599.

Hatzios, K. K. and D. Penner. 1985. Interactions of herbicides with other
agrochemicals in higher plants. Rev. Weed Sci. 1:1-73.

 

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

14

Inskeep, W. P. and P. R. Bloom 1985. Extinction coefficients of
chlorophyll a and b in N,N-dimethylformamide and 80% acetone. Plant
Physiol. 77:483-485.

Jordan, D. L., A. C. York, F. T. Corbin. 1989. Effect of ammonium
sulfate and bentazon on sethoxydim absorption. Weed Technol. 3:674-
677.

LaRossa, R. A. and J. V. Schloss. 1984. The sulfonylurea herbicide
sulfometuron methyl is an extremely potent and selective inhibitor of
acetolactate synthase in Salmonella typhimuriom. J. Biol. Chem.
259:8753-8757.

LaRossa, R. A., T. K. Van Dyk, and D. R. Smulski. 1987. Toxic
accumulation of a—ketobutyrate caused by inhibition of the branched-chain
amino acid biosynthesis enzyme acetolactate synthase in Salmonella
typhimurium. J. Bacteriol. 169:1372-1378.

Lin, C. C. and T. W. Waldrop. 1978. Linear, non-linear, and linear
plateau models used in herbicide experiments. 18:211.

Lowry, O. H., N. S. Rosebrough, A. L. Farr, and R. S. Randall. 1951.
Protein measurement with the folin phenol reagent. J. Biol. Chem.
193:265-275.

Mahoney, M. D. and D. Penner. 1975. Bentazon translocation and
metabolism in soybean and navy bean. Weed Sci. 23:265—270.

Mahoney, M. D. and D. Penner. 1975. The basis for bentazon selectivity
in navy bean, cocklebur, and black nightshade. Weed Sci. 23:272-276.

Mallory-Smith, C. A., D. C. Thill, M. J. Dial, and R. S. Zemetra. 1990.
Inheritance of sulfonylurea herbicide resistance in Lactuca spp. Weed
Technol. 42787-790.

Mazur, B. J., C. F. Chui, and J. K. Smith. 1987. Isolation and
characterization of plant genes coding for acetolactate synthase, the target
enzyme of two classes of herbicides. Plant Physiol. 85:1110-1117.

32.

33.

34.

35.

36.

37.

38.

39.

40.

41.

42.

43.

15

McDonald, R. A., T. Satyanarayana, and J. G. Kaplan. 1973. Biosynthesis
of branched-chain amino acids in Schizosaccharomyces pombe: properties
of acetohydroxy acid synthase. J. Bacteriol. 114:332-340.

Michigan Agricultural Statistics. 1991. Michigan Department of
Agriculture. Lansing, MI.

Miflin, B. J. 1971. Cooperative feedback control of barley acetohydroxyacid
synthetase by leucine, isoleucine, and valine. Biochem. Biophys.
146:542-550.

Miflin, B. J. 1975. The location of nitrate reductase and other enzymes
related to amino acid biosynthesis in the plastids of root and leaves. Plant

Physiol. 54:550-555.

Miflin, B. J. and P. R. Cave. 1972. The control Of leucine, isoleucine, and
valine biosynthesis in a range of higher plants. J. Exp. Bot. 23:511-516.

Mine, A., M. Miyakado, and S. Matsunaka. 1975. The mechanism of
bentazon selectivity. Pest. Biochem. Phys. 52566-574.

Muhitch, M. J ., D. L. Shaner, and M. A. Stidham. 1987. Imidazolinones
and acetohydroxyacid synthase from higher plants. Plant Physiol. 83 :45 1-
456.

Nash, R. G. 1980. Comparison of several methods for evaluating pesticide
interactions. 34:58-68.

Nash, R. G. 1981. Phytotoxic interaction studies - techniques for evaluation
and presentation of results. Weed Sci. 29:147-155.

Newhouse, K. E., T. Wang, and P. C. Anderson. 1991. Imidazolinone
resistant crops. pp 139-150. in D. L. Shaner and S. L. Conner, ed. The
Imidazolinone Herbicides. CRC Press, Inc. Boca Raton, Florida.

Otto, S., P. Beutel, N. Decker, and R. Huber. 1978. Investigations into the
degradation of bentazon in plant and soil. Adv. Pestic. Sci. 3:551-556.

Penner, D. 1975. Bentazone selectivity between soybean and Canada
thistle. Weed Res. 15:259-262.

 

 

45.

46.

47.

48.

49.

50.

51.

52.

53.

16

Penner, D. 1989. The impact of adjuvants on herbicide antagonism. Weed
Technol. 3:227-231.

Poehlman, J. M. 1987. Quantitative inheritance in plant breeding. pp. 70-
81 in Breeding Field Crops. 3rd ed. AVI Publishing CO. Inc., Westport,

Conn.

Potter, J. R. and W. P. Wergin. 1975. The role of light in bentazon
toxicity to cocklebur: physiology and ultrastructure. Pest. Biochem.
Phys. 5:458-470.

Ray, T. B. 1984. Site of action Of chlorsulfuron. Plant Physiol. 75:827-
831.

Renner, K. A. and G. E. Powell. 1988. Dry edible bean tolerance to
postemergence herbicides. N CWCC Proc. 43:36.

Retzlaff, G. and R. Hamm. 1976. The relationship between CO2
assimilation and the metabolism of bentazon in wheat plants. Weed Res.
16:263-266.

Rhodes, D., A. L. Hogan, L. Deal, G. C. Jamieson, and D. Haworth.
1987. Amino acid metabolism of Lemna minor L.. Plant Physiol.
84:775-780.

Rhodes, G. N. and H. D. Coble. 1984. Influence of application variables
on antagonism between sethoxydim and bentazon. Weed Sci. 32:436-
441.

Rhodes, D. G. and H. D. Coble. 1984. Influence of bentazon on the
absorption and translocation of sethoxydim in goosegrass (Eleusine indica
L.). Weed Sci. 32:595-597.

Riley, D. G. and D. R. Shaw. 1988. Influence of imazapyr on the control
of pitted morningglory (Ipomoea lacunosa) and johnsongrass (Sorghum
halepense) with chlorimuron, imazaquin, and imazethapyr. Weed Sci.
36:663-666.

 

 

54.

55.

56.

57.

58.

59.

60.

61.

62.

63.

17

Riley, D. G. and D. R. Shaw. 1989. Johnsongrass (Sorghum halepense)
and pitted morningglory (Ipomoea lacunosa) control with imazaquin and
imazethapyr. Weed Technol. 3:95—98.

Sebastian, S. A., G. M. Fader, J. F. Ulrich, D. R. Forney, and R. S.
Chaleff. 1989. Semidominant soybean mutation for resistance to
sulfonylurea herbicides. Crop Sci. 29: 1403-1408.

Shaner, D. L., P. C. Anderson, and M. A. Stidham. 1984. Imidazolinones
-potent inhibitors of acetohydroxyacid synthase. Plant Physiol. 76:545-
546.

Shaner, P. L. and M. L. Reider. 1986. Physiological responses of corn
(Zea mays) to AC 243,997 in combination with valine, leucine, and
isoleucine. Pest. Biochem. Phys. 25:248-257.

Sorensen, V. M., W. F. Meggitt, and D. Penner. 1987. The interaction of
acifluorfen and bentazon in herbicidal combinations. Weed Sci. 35:449-
456.

Steel, R. G. D. and J. H. Torrie. 1980. Analysis of variance III: factorial
experiments. pp. 336-376. in Principles and procedures of statistics: A
biometrical approach. 2“d ed.

Stidham, M. A. and B. K. Singh. 1991. Imidazolinone-acetohydroxyacid
synthase interactions. pp 71-90. in D. L. Shaner and S. L. Conner, ed.
The Imidazolinone Herbicides. CRC Press, Inc. Boca Raton, Florida.

Sterling, T. M. and N. E. Balke. 1988. Use of soybean (Glycine max) and
velvetleaf (Abutilon theophrastz) suspension-cultured cells to study
bentazon metabolism. Weed Sci. 36:558-565.

Subrananian, M. V., V. Loney-Gellant, J. M. Dias, and L. C. Mireles.
1991. Acetolactate synthase inhibiting herbicides bind to the regulatory
site. Plant Physiol. 96:310-313.

Suwanketnikon, R., K. K. Hatzios, and D. Penner. 1982. The site of
electron transport inhibition of bentazon (3-isopropyl-lH-2,1,3-
benzothiadiazin-(4)3H-one 2,2-dioxide) in isolated chloroplasts. Can. J.
Bot. 60:409-412.

 

 

65.

66.

67.

68.

69.

70.

71.

72.

18

Tammes, P. M. L. 1964. Isoboles, a graphic representation of synergism
in pesticides. Neth. J. Plant Pathol. 70:73-80.

Vencill, W. K., H. P. Wilson, T. E. Hines, and K. K. Hatzios. 1990.
Common lambsquarters (Chenopodium album) and rotational crop
response to imazethapyr in pea (Pisum sativum) and snap bean (Phaseolus
vulgaris). Weed Technol. 4:39-43.

Wanamarta, G., D. Penner, and J. J. Kells. 1989. The basis of bentazon
antagonism on sethoxydim absorption and activity. Weed Sci. 37:400-
404.

Wilcut, J. W., G. R. Wehtje, M. G. Patterson, and T. A. Cole. 1988.
Absorption, translocation, and metabolism of foliar-applied imazaquin in
soybeans (Glycine max), peanuts (Arachis hypogaea), and associated
weeds. Weed Sci. 36:5-8.

Wilcut, J. W., G. R. Wehtje, M. G. Patterson, T. A. Cole, and T. V.
Hicks. 1989. Absorption, translocation, and metabolism of foliar-applied
chlorimuron in soybeans (Glycine max), peanuts (Arachis hypogaea), and
selected weeds. Weed Sci. 37:175-180.

Wills, G. D. and C. G. M‘Whorter. 1987. Influence of inorganic salts and
imazapyr on control of pitted morningglory (Ipomoea lacunosa) with
imazaquin and imazethapyr. Weed Technol. 1:328—331.

Wilson, R. G. and S. D. Miller. 1991. Dry edible bean (Phaseolus
vulgaris) response to imazethapyr. Weed Technol. 5:22-26.

Wilson, R. G. 1989. New herbicides for weed control in established alfalfa
(Medicago sativa). Weed Technol 3:523-526.

WSSA Herbicide Handbook Committee. 1989. Herbicide Handbook. 6'h
ed. Champaign, IL.

 

 

19

Figure 1. Schematic diagram of initial imazethapyr metabolism in corn, soybean,
and dry bean. IM represents the imidazolinone chemical structure.

20

 

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21

Figure 2. Schematic diagram of bentazon metabolism in tolerant higher plants.
Structures of bentazon and its metabolites are (top) bentazon, (upper left) 6-OH-
bentazon, (lower left) 6-O-B-glucose-bentazon, (upper right) 8-OH-bentazon, and
(lower right) 8-O-B-glucose-bentazon (Modified from Sterling and Balke (61)).

22

 

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23

’Olathe’ Pinto Bean (Phaseolus vulgaris) Response to Postemergence

Imazethapyr and Bentazonl

T. A. BAUER, K. A. RENNER, and D. PENNER2

Abstract. Dry bean producers have limited postemergence broadleaf weed control
options. Research determined whether bentazon increased dry edible bean
tolerance to postemergence imazethapyr applications. Imazethapyr and bentazon
were applied with POA in a factorial arrangement to ’Olathe’ pinto bean in field
and greenhouse research. In a separate study, imazethapyr with various adjuvants
was applied alone and in combination with bentazon and pinto bean response
Observed. Imazethapyr visually injured pinto bean 7 DAT in both field and
greenhouse research. Chlorophyll a content, a quantitative measure Of bean
chlorosis, decreased compared to the untreated control following imazethapyr
application. Chlorophyll a content decreased with imazethapyr plus POA or Dash,

but not when imazethapyr was applied with Sunit H or Sylgard 309. When 840

 

1Received for publication and in revised form

 

 

2Res. Asst, Assoc. Prof, and Prof, Mich. State Univ., East Lansing, MI
48824-1325, respectively.

 

 

g ha‘1 of bentazon was tank-mixed with 53 g ha'1 of imazethapyr, visual bean
injury decreased and chlorophyll a increased as compared to imazethapyr alone in
both studies. Fifty three g ha'1 of imazethapyr delayed physiological maturity by
8 and 15 days compared to the untreated control in 1991 and 1992, respectively.
Pinto bean seed yields, however were not reduced compared to the untreated
control. When 840 g ha‘1 of bentazon was tankmixed with 53 g ha‘1 of
imazethapyr, maturity was not delayed. l“C-Imazethapyr absorption decreased by
more than 40% and translocation from the treated leaf by more than 50 % when
tank-mixed with bentazon compared to l“C-imazethapyr alone. The addition of 20
mM Na-acetate inhibited absorption of l“C-irnazethapyr, but did not inhibit
translocation. The decreased absorption and translocation of imazethapyr when
tank-mixed with bentazon likely accounts for the safening effect Observed in

greenhouse and field studies.

Nomenclature: Dry bean (Phaseolus vulgaris L.) #9 PHAVU; bentazon, [3—( 1-
methylethyl)-(1H)-2,1,3-benzothiadiazin-(4(3H)-one 2,2 dioxide]; imazethapyr, 2-
[4,5-dihydro-4-methyl-4-methyl—4-(1-methylethyl)-5—oxo—1H-imidazol-2-yl]-5-ethyl-

3-pyridinecarboxylic acid.

 

3Letters following this symbol are a WSSA-approved computer code from
Composite List of Weeds, Weed Sci. 32, Suppl. 2. Available from WSSA, 309
West Clark Street, Champaign, IL 61820.

 

 

25
Additional index words. Interaction, antagonism, PHAVU, AMARE, ABUTH.

 

26

Introduction

With the recent loss of chloramben (3-amino-2,5-dichlorobenzoic acid), dry
edible bean producers lack herbicide options for broadleaf weed control‘.
Bentazon is the only postemergence broadleaf weed control option available. Dry
edible beans are tolerant of bentazon (11, 22), which controls cocklebur (Xanthium
strumarium L.), jimsonweed (Datura strumarium L.), velvetleaf (Abutilon
theophrasti Medicus) , and common ragweed (Ambrosia artemisiifolia L.).
However, bentazon does not control redroot pigweed (Amaranthus retroflexus L.)
or eastern black nightshade (Solanum ptycanthum Dun.) (22), two common weed
species in dry edible beans.

Imazethapyr effectively controls redroot pigweed, eastern black nightshade,
and common cocklebur. The activity on these weed species could complement
bentazon’s spectrum of control when tank-mixed. Soybeans and other legumes are
tolerant of postemergence applications of imazethapyr (5, 18, 21). However, dry
edible beans have shown susceptibility (20). Early season injury symptoms include
stunting, leaf crinkling, and interveinal chlorosis. Soybeans and dry beans first

convert imazethapyr to 5-hydroxyethyl-imazethapyr and then to the glucose

 

‘Amiben’s loss limits dry bean herbicide options. Prairie Farmer. Jan. 2,
1990. pp 8-9.

 

 

27

conjugate (1). The conversion to the glucose conjugate is faster in soybean than
in dry bean, which may result in the lower dry bean tolerance observed since 5—
hydroxyethyl-imazethapyr is herbicidally active5. However, 5-hydroxyethyl-
imazethapyr is five times less herbicidally active than imazethapyr".

Reductions in weed control from the addition of bentazon to imazethapyr
applications have been reported (3). Numerous papers have been published on the
antagonized grass control resulting when bentazon is applied jointly with
sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-
cyclohexen-l-one) (2, 8, l4). Wanamarta and Penner (1989) concluded that
reduced quackgrass control was due to inhibited absorption of l“C-sethoxydim in
the presence of the sodium salt of bentazon. The absorption reduction caused by
Na-bentazon was mimicked by mixing Na—acetate with l4C-sethoxydim.
Conversely, UAN increased absorption of l4C-sethoxydim in the presence of both
the sodium salt of bentazon and Na-acetate (12, 19).

In preliminary research (13), bentazon reduced injury to dry edible beans when
tank-mixed with imazethapyr compared to imazethapyr alone. Twenty eight
percent UAN increased dry bean response from 12 to 24% as compared to POA

(13). The objectives of this research were to (1) determine if bentazon improved

 

5Personal communication. Dale Shaner, American Cyanamid Co. , Princeton,
NJ 08540.

6AC-263-499 Technical Information Report. 1985. American Cyanamid CO.,
Princeton, NJ 08540.

 

28

dry edible bean tolerance to imazethapyr in greenhouse and field studies, (2)
determine if adjuvant selection influenced dry edible bean response, (3) determine
if bentazon decreased absorption and/or translocation of 1“C-imazethapyr when the
two herbicides were tank-mixed, and (4) assess if N a-acetate influenced the
absorption and/or translocation of 14C-imazethapyr similar to bentazon, since it is
postulated than the N a-ion in the bentazon formulation inhibits absorption of some

herbicides (14, 19).

Materials & Methods

Greenhouse Study. Olathe pinto bean seed were planted in BACCTO7
greenhouse potting soil in 946 ml plastic pots. Environmental conditions were
maintained at 25 C j; 4 C, and plants were grown in a 16 h photoperiod of natural
and supplemental metal halide lighting with a midday photosynthetic photon flux
density of 1000 #13 m‘2 5“. After emergence, plants were thinned to one per pot.
Plants were surface watered as needed and fertilized weekly with 0.1 g of water
soluble fertilizer solution (20% N, 20% P205, 20% K20). All herbicide treatments

were applied postemergence with a continuous belt-link sprayer equipped with a

 

7Baccto is a product of Michigan Peat Co. Houston, TX 77098.

 

29

single 8001 even flat fan nozzle8 calibrated to deliver 205 L ha'l at a spray
pressure of 210 kPa. Belt speed was set at 1.5 km h". Olathe pinto bean was
treated at the ISI trifoliolate leaf stage (9 cm).

Imazethapyr at 0, 53, 106, and 212 g ha“, bentazon at 0, 420, 840, and 1680
g ha", and their combinations were applied to Olathe pinto bean to observe
sensitivity. Treatments were applied in a factorial arrangement with 1.2 L ha‘l
POA9. Olathe was selected as the dry bean variety since preliminary studies (data
not reported) demonstrated that this variety was particularly sensitive to
imazethapyr. All pots were arranged in a completely randomized design and the
experiments were repeated twice in time with four replications. Data were
subjected to ANOVA. Interactions were not present between experiments and
treatments, and therefore data were combined over time. For the herbicide
combinations, the expected herbicide injury value was calculated following Colby’s
method (4). This calculation was determined for greenhouse data only since the
expected value is most useful when approximating the IG50 value (4). Mean
comparisons were made using Fisher’s Protected LSDa=0_05.

Injury to Olathe pinto bean was visually evaluated 7 DAT on a scale ranging

from 0 (no visible injury) to 10 (total plant necrosis). To quantitatively measure

 

8Teejet flat fan tips. Spraying Systems CO., North Ave. and Schmale Road,
Wheaton, IL 60188.

9Herbimax, 83% petroleum oil, 17% adjuvant, Loveland Industries, Inc.
Greeley, CO 80632.

30

pinto bean chlorosis, three leaf discs, 6.5 mm in diameter, were harvested from
the middle leaflet of the third trifoliolate from each bean plant. Chlorophyll was
extracted with 3 ml of N,N-dimethylformamide (10). Total chlorophyll,
chlorophyll a, and chlorophyll b levels were determined using UV-VIS
spectrophotometry as described by Inskeep and Bloom (1985). Through statistical
analysis, chlorophyll a levels were determined to be the most sensitive indicator
of herbicide injury, and only chlorophyll a levels will be reported. Trifoliolate dry
weights were measured as an additional indication of herbicide injury. The
trifoliolates were cut next to the stem and dried. The first trifoliolate was not
included.

Field Study. Field experiments were conducted in 1991 and 1992. Plots were
maintained weed—free the entire season to eliminate the confounding factor of weed
interference on pinto bean maturity and yield. Soil characteristics and locations
for each experiment are summarized in Table 1.

Seedbed preparation consisted of fall moldboard plowing followed by two
passes with a Danish S-tine field cultivator10 in the spring, the second pass
perpendicular to the first pass in both years. Pinto beans were planted June 13,
1991 and June 9, 1992 in plots 2.8 m by 6.1 m with crop row spacings of 71 cm

at a seeding rate of 172,000 seeds ha". Herbicide treatments were applied on July

 

loKongskilde. Kongskilde Corp. Bowling Green, OH 43402.

31

3, 1991 and July 6, 1992 when beans were at the second trifoliolate growth stage.

Pinto bean injury was measured 7 and 14 DAT on a scale ranging from 0 (no
visible injury) to 100 (total plant necrosis). To quantitatively measure pinto bean
chlorosis 7 DAT, a single leaf disc 6.5 mm in diameter was harvested from the
middle leaflet of the third trifoliolate from three randomly selected bean plants in
the middle two rows of each plot. Chlorophyll was extracted as previously
described for the greenhouse studies. The number of growing days required to
reach physiological maturity was recorded. Plots were considered physiologically
mature when 90% of the pods had turned from green to a golden-bronze color.
Yields were measured by hand harvesting two, 4.6 m lengths from the middle two
rows of each plot. Yields were adjusted to 18% moisture.

Imazethapyr was applied at 0, 53, 106, and 212 g ha", while bentazon was
applied at 0, 420, 840, and 1680 g ha". All postemergence herbicides were
applied with a tractor-mounted compressed air sprayer in a total volume of 205 L
ha'1 at a spray pressure of 210 kPa. The boom was adjusted to 61 cm above the
soil surface and equipped with 8002 flat fan nozzles spaced 51 cm apart.
Herbicide treatments were applied in a factorial arrangement with 1.2 L ha'l POA.
Treatments were arranged in a randomized complete block design with four
replications. All data were subjected to AN OVA. Year by treatment interactions
were present so 1991 and 1992 data are presented separately. Means comparisons

were made by Fisher’s Protected LSDa=0.05.

32
Adjuvant study. Soil characteristics for 1991 and 1992 field experiments are

summarized in Table 1. Prior to planting, the soil was moldboard plowed in the
spring followed by a single pass with a Danish S-tine field cultivator. Olathe pinto
beans were planted on June 4, 1991 and June 12, 1992 in 3 m by 7.6 m plots with
crop row spacings of 76 cm at a seeding rate of 203,000 seeds ha"1 and 172,000
seeds ha‘1 in 1991 and 1992, respectively. Herbicide treatments were applied on
June 24, 1991 and July 6, 1992 when beans were at the second trifoliolate growth
stage.

Visual injury to Olathe pinto bean was measured 7 DAT on a scale ranging
from 0 (no visible injury) to 100 (total plant necrosis). To quantitatively measure
pinto bean chlorosis 7 DAT, a single leaf disc 6.5 mm in diameter was harvested
from the middle leaflet of the third trifoliolate from three randomly selected bean
plants in the middle two rows of each plot. Chlorophyll was extracted as
previously described.

Imazethapyr at 0 and 53 g ha'1 and bentazon at O and 840 g ha", and various

combinations thereof, were applied with POA, NIS“, DASH”, M80”, and

 

“X-77 Non-Ionic Surfactant. A mixture of alkylarylpolyoxyethleneglycols, free
fatty acids and isopropanol. Valent U.S.A. Corp., Walnut Creek, CA 94956.

12Dash is a commercial adjuvant product marketed by BASF, 100 Cherry Hill
Rd., Parsippany, NJ 07054.

l3Sunit H methylated seed Oil marketed by American Cyanamid CO., Princeton,
NJ 08540.

33

Sylgard 309”. All postemergence herbicides were applied with a tractor-
mounted compressed air sprayer in a total volume of 205 L ha“l at a spray pressure
of 210 kPa. The boom was adjusted to 61 cm above the soil surface and equipped
with 8002 flat fan nozzles spaced 51 cm apart. Herbicide treatments were applied
in a factorial arrangement with the various adjuvants. Treatments were arranged
in a randomized complete block design with four replications. All data were
subjected to ANOVA. Year by treatment interactions were present so 1991 and
1992 data are presented separately. Mean comparisons were made by Fisher’s

Protected LSDFMS.

l‘C-Imazethapyr absorption and translocation studies. l“C-Irnazethapyr
(pyridine ring labelled, 6'h position with specific activity = 784.4 MBq/g)

absorption alone and tank-mixed with bentazon was evaluated. Olathe pinto bean
was planted in BACCTO greenhouse soil in 946 ml plastic pots. All experiments
were conducted in growth chambers with day/night temperatures of 26/22 C.
Chambers were maintained at 68% relative humidity with a 16 h photoperiod from
fluorescent and incandescent lighting with a photosynthetic photon flux density of

750 uE m'2 8". Plants were top-watered as needed. A 2 aL drop containing 370

 

l“Sylgard 309 is a silicon adjuvant mixture of 2-(3-hydroxypropyl)-
heptamethyltrisiloxane, ethyloxylated, acetate EO glycol, -allyl, -acetate marketed
by Dow Corning Corp., Midland, MI 48686.

 

 

34

Bq of l4C—imazethapyr was applied with a micro-syringe” between the leaflet
mid-vein and the edge of the leaflet approximately Va of the distance from the
leaflet tip to the base of the leaflet. Special care was taken to not place the spot
on a leaf vein. The spotting solution contained l“C-imazethapyr with the
appropriate amounts of formulation blank, unlabelled commercial imazethapyr“,
commercial bentazonl7 (when appropriate) POA, and water to simulate a spray
solution containing imazethapyr at 53 g ha", bentazon at 840 g ha", and POA at
1.2 L ha’1 in a total volume of 205 L ha".

The treated leaflet for Olathe pinto bean was the middle leaflet of the first
trifoliolate. At 0, 1, 2, 4, 8, 24, and 48 h after treatment (spotting), the leaflet
was excised and rinsed in a 20 ml glass scintillation vial containing 3 ml of
methanol : H20 (2:1 v/v), and gently swirled for 30 s. The leaflet was then
washed with a minimal amount of rinsing solution and then 15 ml of scintillator”
was added. The unabsorbed l“C-imazethapyr was quantified by liquid scintillation

spectroscopy (LSS)19 and absorption determined by subtracting the amount of 1“C-

 

‘sHamilton microsyringe. Hamilton Co. Reno, NV 89520-0012.
l“"Pursuit 2A8 herbicide. American Cyanamid Co. Princeton, NJ 08540.
”Basagran 4L, BASF Corp. Parsippany, NJ 07054.

18Safety-Solve. Research Products International Corp. Mount Prospect, H.
60056.

19Model 1500. Packard Instrument Corp. Downers Grove, H. 60515.

 

 

35

imazethapyr recovered in the washoff solution from the amount of 1“C-imazethapyr

applied.

The treated leaflet was saved and combusted in a biological oxidizer“). The
CO2 was trapped in a solution of scintillator : CO2 absorber21 (2:1 v/v). Total
radioactivity in the sample was then determined by LSS. The amount of I“C-
imazethapyr in the treated leaflet was calculated by subtracting the amount of 1“C
recovered in the treated leaf from what was absorbed. This amount was then
subtracted from 100% to calculate 1"C-imazethapyr translocated from the treated
leaflet.

Effect of Na-acetate and UAN on l‘C-imazethapyr absorption and
translocation. 14C-Imazethapyr was applied alone and with various combinations
of commercial formulated bentazon, 20 mM Na-acetate, and 4% (v/v) UAN. All
treatments were applied with the appropriate amount of formulation blank,
unlabelled commercial imazethapyr, commercial bentazon, POA, and water to
simulate a spray solution containing imazethapyr at 53 g ha", bentazon at 840 g
ha", and POA at 1.2 L ha"1 in a total volume of 205 L ha". All absorption and

translocation measurements were carried out as outlined above except only 24 h

measurements were recorded.

 

20OX-300. R. J. Harvey Instrument Corp. Patterson, NJ 07642.
21Carbo-Sorb H. Packard Instrument Co. Meriden, CT 06450.

 

36

All pots for the absorption and translocation studies were arranged in a
completely randomized design with five replications. Absorption and translocation
experiments were conducted at least twice. All data were subjected to AN OVA
and data were combined over time. Mean comparisons were made by Fisher’s
Protected LSDFMS.

l“C-Imazethapyr absorption and translocation from the treated leaf studies were
subjected to curvilinear regression analysis and coefficient values determined (15).
The absorption and translocation data were fit to the curvilinear equation Y =
(I*X)/(1+(I/A)*X), where Y and X are the Y - axis and X - axis coordinates, I
is the percentage absorption as time approaches 0, and A is the percentage
absorption as time approaches infinity. This type of regression equation is useful

to explain absorption trends.

Results and Discussion

Greenhouse studies. Bentazon did not cause any visual injury to pinto bean 7
DAT (Table 2). When imazethapyr was applied at 53 g ha“, injury increased to
2 (scale of 0 to 10). When bentazon was tank-mixed with 53 g ha"1 of imazethapyr
(1X application rate), injury was not greater than that of the untreated control.

Injury from imazethapyr at 106 and 212 g ha‘l (2X and 4X application rates)

 

37

increased to 2.5 and 4.5, respectively. Again, pinto bean injury decreased when
bentazon was tank-mixed as compared to each respective rate of imazethapyr alone
(Table 2). Colby’s expected values indicated strong antagonism (safening) with
all tank-mixes.

Trifoliolate dry weights followed the same pattern. Bentazon did not decrease
dry trifoliolate weight, while imazethapyr at 1X, 2X, and 4X application rates
decreased trifoliolate dry weights to 27, 45, and 45 %, respectively, compared to
the untreated control. Trifoliolate dry weights were greater than Colby’s expected
values with each tank-mix combination, demonstrating the safening effect of
bentazon when applied with imazethapyr on pinto bean.

Chlorophyll a measurements quantitatively determined pinto bean chlorosis.
Chlorophyll a was reduced from bentazon alone at 840 and 1680 g ha“ and all
imazethapyr applications. The observed chlorophyll a levels were greater than
Colby’s expected values except when 420 g ha‘1 of bentazon was tank-mixed with
either 53 or 212 g ha'1 imazethapyr, which demonstrated less pinto bean injury
when bentazon was tank-mixed.

Imazethapyr caused significant visual injury, trifoliolate dry weight reduction,
and loss of chlorophyll a compared to the untreated control or bentazon. When
bentazon was tank-mixed with imazethapyr, visual injury decreased, trifoliolate
weight increased, and chlorophyll a levels increased over the expected values

compared to the untreated control or bentazon alone, demonstrating that bentazon

 

38

safened pinto bean response to imazethapyr.

W. In 1991, postemergence bentazon did not visually injure Olathe
pinto bean 7 DAT, decrease chlorophyll a levels, delay maturity, or influence seed
yields (Table 3). Imazethapyr at 53 g ha"l (1X use rate) caused 8% injury 7 DAT.
These injury symptoms included leaf chlorosis, plant stunting, and proliferation of
secondary shoots from plant nodes. The 7 DAT injury for the tank-mix
application of imazethapyr at the 1X rate plus bentazon at the 1X rate was not
different than that of the untreated control. Chlorophyll a levels decreased from
53 g ha'1 of imazethapyr compared to the untreated control. However, when 840
g ha‘1 of bentazon was tank-mixed with 53 g ha" of imazethapyr, chlorophyll a
levels did not differ significantly from the untreated control. Olathe pinto bean
required 78 days to reach physiological maturity, and 86 days following the 1X
rate of imazethapyr. Bentazon tank-mixed with imazethapyr decreased the days
to maturity to that of the untreated control. No herbicide combination decreased
dry bean seed yields in 1991.

In 1992, bentazon did not cause significant dry bean injury, decrease
chlorophyll a levels, delay maturity, or reduce seed yield, indicating Olathe pinto
bean tolerance to bentazon. At 7 DAT, 53 g ha‘1 imazethapyr caused 13% visual
injury (Table 4). When any rate of bentazon was tank-mixed with 53 g ha‘1 of

imazethapyr, pinto bean injury decreased to that of the untreated control. By 14

39

DAT, pinto bean response to the 1X rate of imazethapyr was not evident.
However, injury at the 2X and 4X rates remained at 15 and 33%, respectively.
Tank-mixing any rate of bentazon with either the 2X or 4X rate of imazethapyr
decreased pinto bean injury.

Imazethapyr at all rates decreased chlorophyll a levels compared to the
untreated control. Olathe pinto bean required 86 days to reach physiological
maturity in 1992, 8 days longer than the previous year. This was primarily due
to the less favorable growing season (cooler temperatures) in 1992. Imazethapyr
applied at the 1X rate increased the days to reach physiological maturity to 101
days. When any rate of bentazon was tank-mixed with the 1X rate of imazethapyr
the days required to reach physiological maturity decreased to that of the untreated
control. Imazethapyr alone at 106 and 212 g ha'l decreased seed yields as
compared to the untreated control. When bentazon at 840 or 1680 g ha'l was tank-
mixed with 106 g ha“ of imazethapyr, seed yields were not reduced.

In both growing seasons, imazethapyr caused significant early season injury
and delayed maturity of pinto beans. The observed injury was more prominent in
1992 than 1991. Only in 1992 were the dry bean seed yields reduced from 106
or 212 g ha" of imazethapyr compared to the untreated control. However, in both
years when 840 g ha'1 of bentazon was tank-mixed with 53 g ha" of imazethapyr,
early season injury was reduced and late season injury (maturity delay and reduced

seed yields) was not observed.

   

40
Adjuvant study. In 1991, POA, Dash, and Sunit H applied with imazethapyr

caused more pinto bean injury 7 DAT than N IS (Table 5). All adjuvants applied
with imazethapyr in 1992 caused similar injury. Less pinto bean injury was
observed 7 DAT in both years when bentazon was tank-mixed with imazethapyr.
In 1991, chlorophyll a levels were reduced by imazethapyr plus POA, Dash, or
NIS. In 1992, chlorophyll a levels were reduced by imazethapyr plus Dash or
NIS. Regardless of adjuvant, bentazon safened pinto bean to imazethapyr

applications .

l"C-Imazetha abso tion and translocation in Olathe into bean. At 1, 2,

4, 8, and 24 h after treatment, the presence of bentazon in the spray solution
decreased absorption of l“C-imazethapyr in dry edible bean as compared to 1“‘C-
imazethapyr alone (Figure 1). By 8 h after treatment, l“C-imazethapyr absorption
when applied alone was greater than 75 % of applied. The asymptotic value for
l“C-imazethapyr absorption was 82% of applied. By contrast, when l4C-
imazethapyr was tank-mixed with bentazon, absorption at 8 h after treatment was
less than 45% of applied and the asymptotic value was 48%. At 8 h or greater,
“C-imazethapyr absorption decreased by z 40% when tank-mixed with bentazon
compared to l“C-imazethapyr applied alone.

More l“C-imazethapyr was translocated from the treated leaf at 4, 8, 24, and

48 h after treatment when applied alone versus tank-mixed with bentazon (Figure

 

41
2). At 24 and 48 h after treatment, 28% and 38% of absorbed l“C-imazethapyr,

respectively, translocated from the treated leaf. Translocation from the treated leaf
decreased to 12% and 17% of absorbed at 24 and 48 h after treatment,
respectively, when bentazon was tank-mixed with l“C-imazethapyr. This is greater
than a 50% reduction in 14C translocation from the treated leaf compared to that
of l“C-imazethapyr applied alone.

The reduction in translocation of l“C-imazethapyr from the treated leaf by
tank-mixing with bentazon may also contribute to the safening in Olathe pinto
bean. The translocation of a phloem mobile herbicide, such as imazethapyr, may
be inhibited when the production and translocation of photoassimilate is also
inhibited (6). Bentazon is known to reduce photoassimilate production and
translocation by inhibition of electron transport in photosystem H (7, 17). It is
therefore reasonable to assume that bentazon will reduce the phloem transport of
imazethapyr.

Bentazon decreased both absorption and translocation of imazethapyr in Olathe
pinto bean. Bentazon has been noted to decrease absorption of both sethoxydim
and acifluorfen (5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid) ( 14,
16, 19). The decrease in absorption and translocation of imazethapyr apparently
accounts for the safening effect that bentazon exerts on imazethapyr when applied

postemergence to Olathe pinto bean in greenhouse and field studies.

 

42
Effect of Na-acetate and UAN on l‘C-imazethapy; absorption and

translocation. When l4C-irnazethapyr was applied alone, 82% of the herbicide
was absorbed by 24 h (Table 6). When bentazon or Na-acetate was tank-mixed
with l“C-imazethapyr, absorption decreased to 61% and 58%, respectively. UAN
did not increase absorption over that of l“C-irnazethapyr applied alone, but
overcame the decreased l4C-irnazethapyr absorption when bentazon or Na-acetate
were in the solution.

When l“C-irnazethapyr was applied alone, 29% of the absorbed herbicide was
translocated from the treated leaf. Bentazon tank-mixed with l“C-imazethapyr
decreased translocation to 18%. Neither UAN or Na-acetate altered translocation
when applied with bentazon and l“C—irnazethapyr or with MC—imazethapyr alone.

Previous research (19) has shown that Na-acetate can inhibit the absorption of
sethoxydim similar to the inhibited absorption caused by bentazon. Similarly, l“C-
irnazethapyr absorption decreased with the addition of 20 mM Na-acetate similar
to the addition of bentazon. The addition of UAN to each tank-mix previously
mentioned reversed the decreased absorption observed (19).

lrnazethapyr can cause early season visual injury as well as delay maturity of
Olathe pinto beans. However, when bentazon is tank-mixed with imazethapyr,
early and late season injury (maturity delay and decreased seed yields) was not
observed. Studies utilizing l“C-imazethapyr indicate that formulated bentazon

decreases both absorption and translocation of imazethapyr, resulting in increased

 

43

tolerance of Olathe pinto bean to imazethapyr. However, Na-acetate did not alter
translocation as did bentazon. We concur with Wanamarta and Penner who
hypothesized that the Na-ion, with which bentazon is formulated, disassociates
from bentazon and associates with imazethapyr, altering the polarity of this
molecule and decreasing its absorption (12, 19). This decreased absorption can

be overcome by the use of UAN which supports this hypothesis.

 

11.

12.

44
LITERATURE CITED

Bauer, T. A., K. A. Renner, D. Penner, and J. K. Kelly. 1993. Pinto bean
(Phaseolus vulgaris) varietal tolerance to postemergence imazethapyr. Weed
Sci. (Submitted).

Cambell, J. R. and D. Penner. 1982. Compatibility of diclofop and BAS
9052 with bentazon. Weed Sci. 30:458-462.

Cantwell, J. R., R. A. Liebl, and F. W. Slife. 1989. Imazethapyr for weed
control in soybean (Glycine max). Weed Technol. 32596-601.

Colby, S. R. 1967. Calculating synergistic and antagonistic responses of
herbicide combinations. Weeds 15:20-22.

Cole, T. A., G. R. Wehtje, J. W. Wilcut, and T. V. Hicks. 1989. Behavior
of imazethapyr in soybeans (Glycine max), peanuts (Arachis hypogaea), and
selected weeds. Weed Sci. 37:639-644.

Devine, M. D., H. D. Bestman, and W. H. Vanden Born. 1990.
Physiological basis for different phloem mobilities of chlorsulfuron and
chlopyralid. Weed Sci. 3821—9.

Fuerst, E. P. and M. A. Norman. 1991. Interactions of herbicides with
photosynthetic electron transport. Weed Sci. 39:458-464.

Hartzler, K. K. and C. L. Foy. 1983. Compatibility of BAS 9052 OH with
acifluorfen and bentazon. Weed Sci. 31:597-599.

Hatzios, K. K. and D. Penner. 1985. Interactions of herbicides with other
agrochemicals in higher plants. Rev. Weed Sci. 1:1—73.

. Inskeep, W. P. and P. R. Bloom. 1985. Extinction coefficients of

chlorophyll a and b in N,N-dimethylformamide and 80% acetone. Plant
Physiol. 77:483-485.

Mahoney, M. D. and D. Penner. 1975. Bentazon translocation and
metabolism in soybean and navy bean. Weed Sci. 23:265-270.

Penner, D. 1989. The impact of adjuvants on herbicide antagonism. Weed
Technol. 32227-231.

18.

20.

21.

22.

45

. Renner, K. A. and G. E. Powell. 1988. Dry edible bean tolerance to

postemergence herbicides. Proc. North Cent. Weed Cont. Conf. 43:36.

. Rhodes, G. N. and H. D. Coble. 1984. Influence of bentazon on absorption

and translocation of sethoxydim in goosegrass (Eleusine indica L.). Weed
Sci. 32:595-597.

. Steel, R. G. D. and J. H. Torrie. 1980. Principles and procedures of

statistics: A biometrical approach. 2"d ed. p. 341.

. Sorensen, V. M., W. F. Meggitt, and D. Penner. 1987. The interaction of

acifluorfen and bentazon in herbicidal combinations. Weed Sci. 35:449-
456.

. Suwanketnikon, R., K. K. Hatzios, and D. Penner. 1982. The site of

electron transport inhibition of bentazon (3-isopropyl-1H—2,l,3-
benzothiadiazin-(4)3H—one 2,2—dioxide) in isolated chloroplasts. Can. J.
Bot. 60:409-412.

Vencill, W. K., H. P. Wilson, T. E. Hines, and K. K. Hatzios. 1990.
Common lambsquarters (Chenopodium album) and rotational crop response
to imazethapyr in pea (Pisum sativum) and snap bean (Phaseolus vulgaris).
Weed Technol. 4:39-43.

. Wanamarta, G., D. Penner, and J. J. Kells. 1989. The basis of bentazon

antagonism on sethoxydim absorption and activity. Weed Sci. 37:400—404.

Wilson, R. G. and S. D. Miller. 1991. Dry Edible bean (Phaseolus
vulgaris) response to imazethapyr. Weed Technol. 5:22-26.

Wilson, R. G. 1989. New herbicides for weed control in established alfalfa
(Medicago sativa). Weed Technol. 3:523—526.

WSSA Herbicide Handbook Committee. 1989. Herbicide Handbook. 6‘h ed.
Champaign, IL.

 

46

 

Table 1. Soil characteristics of field studies conducted in 1991 and 1992.

 

 

 

 

Year
Study 1991 1992
Pinto Bean sandy clay loam clay
Herbicide Tolerance 2.9% OM pH 7.1 2.4% OM pH 6.5
51% sand 19% silt 30% clay 23% sand 16% silt 61% clay

Parkhill sandy clay loam
(Mollic Haplaquept, fine-
loarny, mixed, mesic)

Misteguay clay (Aeric
Haplequept, fine-loamy, mixed,
mesic)

 

 

Adjuvant Study

 

loamy sand
1.7% OM pH 5.5
82% sand 10% silt 7% clay

Capac loamy sand (Aeric
Ochraqualfs, fine-loamy,
mixed, mesic)

 

sandy clay loam

3.4% OM pH 7.0

55% sand 24% silt 21% clay
Capac sandy clay loam (Aeric
Ochraqualfs, fine-loamy, mixed,
mesic)

 

 

47

Table 2. Olathe pinto bean response to bentazon and imazethapyr applied alone and in
combination in the greenhouse. A ' indicates significant antagonism when comparing the
observed data to the predicted value‘.

 

 

Visual Dry
Rate injury trifoliolate Chlorophyll
Treatment 7 DATb wt a
-g ha“-— -—g-— ——mg L"----
Untreated - - O l .1 11.4
Bentazon 420 0 1 .0 10.9
Bentazon 840 O 1 . 1 9.6
Bentazon 1680 0 1 . l 8.6
Imazethapyr 5 3 2 0.8 8. 1
Imep+bentc 420 0 (2)' 0.9 (0.7)' 8.3 (7.2)
Imep+bent 53+840 0 (2)' 1.0 (0.8)" 7.9 (6.1)'
Imep+bent 53 +1680 0 (2)' 1.0 (0.8)' 8.3 (5.3)'
Imazethapyr 106 2.5 0.6 6.3
Imep+bent 106 +420 1 (2.5)' 0.9 (0.6)' 7.6 (5.9)'
Imep+bent 106+840 l (2.5)' 0.9 (0.6)' 8.0 (5.2)"
Imep+bent 106+ 1680 0 (2.5)' 1.0 (0.7)' 8.0 (4.6)'
Imazethapyr 212 4.5 0.6 5.8
Imep+bent 212+420 3 (4.5)' 0.7 (0.5)' 6.4 (5.5)
Imep+bent 212+840 2 (4.5)' 0.8 (0.6)' 6.9 (4.8)'
Imep+bent 212+ 1680 1.5 (4.5)' 0.7 (0.6)' 8.7 (4.3)'
LSDa-m 0.5 0.1 1.7

 

 

3The predicted values, enclosed in parenthesis, are calculated using Colby’s
method.

bVisual injury was rated on a scale of 0 (no visible injury) to 10 (total plant
necrosis).

cImep and bent are the approved codes for imazethapyr and bentazon,
respectively. 1991. NCWSS Proc. 46:164.

48

Table 3. Response of Olathe pinto bean to bentazon and imazethapyr applied alone and in
combination in 1991 in the field.

 

 

Chlorophyll Physiological Seed

Treatment Rate 7 DAT 14 DAT a maturity yields

—g ha"—- -- % visual injury— mg L" days kg ha"
Untreated - - 0 O 5.1 78 2690
Bentazon 420 0 0 5 79 2810
Bentazon 840 0 0 4.9 79 2190
Bentazon 1680 3 3 5 .4 79 2440
Imazethapyr 53 8 5 4.3 86 2270
Imep+bent 53 +420 3 3 4.7 78 1990
Imep+bent 53 +840 0 O 4.7 81 2620
Imep+bent 53 +1680 5 3 4.8 81 2340
Imazethapyr 106 8 5 3.5 90 2190
Imep+bent 106+420 3 3 4.2 82 2310
Imep+bent 106+ 840 5 3 4.2 80 1984
Imep+bent 106+1680 5 3 4.1 80 2174
Imazethapyr 212 15 13 3.4 91 1900
Imep+bent 212+420 10 5 3.6 87 1990
Imep+bent 212+840 5 5 4.1 86 2210
Imep+bent 212+1680 5 3 4.1 85 2020
LSDPMS 3 3 0.9 4 NS

 

49

Table 4. Response of Olathe pinto bean to bentazon and imazethapyr applied alone and in
combination in 1992 in the field.

Chlorophyll Physiological Seed

 

Treatment Rate 7 DAT l4 DAT a maturity yield
--g ha"-- -— % visual injury- mg L" days kg ha"
Untreated - — 0 0 3 .9 86 2520
Bentazon 420 0 0 4.3 86 2180
Bentazon 840 0 0 3 .9 87 2190
Bentazon 1680 0 0 4.3 88 2120
Imazethapyr 53 13 5 3 .3 101 2280
Imep + bent 53 +420 3 3 3.8 87 1750
Irnep + bent 53 + 840 3 0 4.2 87 2190
lmep +bent 53 +1680 0 0 4.2 87 1940
Imazethapyr 106 18 15 2.8 103 1880
Imep + bent 106 +420 10 5 3 .3 93 1900
Imep+bent 106+ 840 10 5 3.3 91 2060
Imep+bent 106+1680 10 5 3.3 88 2060
Imazethapyr 212 28 33 2.5 l 10 1380
Imep+bent 212+420 20 18 2.4 103 1400
Imep+bent 212+840 18 18 2.8 103 1610
Imep+bent 212+1680 18 13 2.7 98 1550

LSDa-0_05 3 3 0.6 3 660

 

 

 

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51

Table 6. The effect of Na—acetate and UAN on l4C-irnazethapyr absorption
and translocation 24 h after treatment when applied alone and tank-mixed
with bentazon. All treatments were applied with the equivalent of 1.2 L

 

 

ha'1 POA.
Treatment Absorption Translocation
--% of applied-- --% of absorbed--

”C-imazethapyr 82 29
l“C-imazethapyr + bentazon 61 18
l4C-irnazethapyr + Na—acetate 58 26
l4C-imazethapyr + UAN 92 24
l4C-imep + bentazon + UAN 86 19
1“C—imep + Na-acetate + UAN 92 22
LSD,=0,,, 11 5

 

52

Figure 1. MC-Irnazethapyr absorption when applied alone and tank-mixed with
bentazon in Olathe pinto bean. Regression equation for l4C—imazethapyr when
applied alone is Y = (113*X)/(1+(113/82)*X) (R2=0.7l) and when tank-mixed
with bentazon is Y = (73*X)/(1+(73/48)*X) (R2=0.84). LSDa=005 bars are
centered over data points.

 

53

mm mm VN NN

3 as?

ONmrwvaNForm w v N o

 

— — — q u — — _ — —

acmm

———l—ld-—~_——u—q‘_————__—~uu—~—-—__-__—_—-

+ QOETOEOT QoETOthr

 

 

 

00—.

(peudde IO %) uoudiosqv

54

Figure 2. 14C-Imazethapyr translocation from the treated leaf when applied alone
and tank-mixed with bentazon in Olathe pinto bean. Regression equation for 14C-
imazethapyr when applied alone is Y = (3.7*X)/(l +(3.7/45)*X) (R2=0.82) and
when tank—mixed with bentazon is Y = (2.3*X/(1 +(2.3/18)*X) (R2=0.74).
LSD,,=O_O5 bars are centered over data points.

55

 

 

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\ _
M _
\ _
\.
[gilllllllllggllllllllllll 4
O O O O O O
In 1' (‘0 N ‘-

(paqiosqe Io %) uoiieomsueij

15 2o 25 30 35 4o 45 50
Time (h)

10

Response of Selected Weed Species to Postemergence Imazethapyr and

Bentazonl

T. A. BAUER, K. A. RENNER, and D. PENNER2

Abstract. Imazethapyr and bentazon were applied with POA in a factorial
arrangement to weed species in greenhouse and field research to determine if
postemergence weed control by imazethapyr was antagonized when bentazon was
tank-mixed. Tank—mixing 840 g ha" of bentazon with 13 or 27 g ha" of
imazethapyr increased redroot pigweed and eastern black nightshade dry weight
as compared to Colby’s expected values in the greenhouse. However, weed
control was not antagonized in field studies. Subsequent greenhouse studies
indicated that soil interception and resulting root uptake of imazethapyr increased
redroot pigweed control. Bentazon decreased absorption of l“C-imazethapyr by
15% and translocation from the treated leaf by greater than 50% as compared to

I4C-irnazethapyr alone.

 

‘Received for publication and in revised form

2Res. Asst., Assoc. Prof, and Prof, Mich. State Univ, East Lansing, NH
48824—1325 , respectively.

 

 

57
Nomenclature: Bentazon, [3-( 1 -methylethyl)-( 1H)-2, l ,3-benzothiadiazin-(4(3H)-
one 2,2 dioxide]; imazethapyr, 2-[4,5-dihydro-4-methyl-4-methyl-4-(1-
methylethyl)-5-oxo-1H-imidazol-2—yl]—5-ethyl-3-pyridinecarboxylic acid; dry bean
(Phaseolus vulgaris L.) #3 PHAVU; redroot pigweed (Amaranthus retroflexus L.)
# AMARE; eastern black nightshade (Solanum ptycanthum Dun.) # SOLPT;
common ragweed (Ambrosia anemisiifolia L.) # AMBEL; common lambsquarters

(Chenopodium album L.) # CHEAL; velvetleaf (Abutilon theophrasti Medicus) #

ABUTH .

Additional index words. Interaction, antagonism, AMARE, ABUTH.

 

3Letters following this symbol are a WSSA—approved computer code from
Composite List of Weeds, Weed Sci. 32, Suppl. 2. Available from WSSA, 309
West Clark Street, Champaign, IL 61820.

58

Introduction

Two or more herbicides are often tank-mixed to increase the weed control
spectrum over that achieved when each herbicide is applied alone. When
herbicides applied in a tank-mix combination act independently and the weed
spectrum controlled can be predicted by the performance of each herbicide applied
alone, the effect is termed additive (8). However, weed control may not follow
the predicted performance. Hatzios and Penner (1985) described an interaction as
antagonistic when the observed activity of the combination decreased compared to
the performance of each herbicide applied alone. Conversely, an interaction that
enhanced biological activity was referred to as synergistic.

Numerous studies have determined herbicide interactions on various weed
species. Bentazon applied jointly with sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-
ethylthio)propy1-3-hydroxy-2-cyclohexen—1-one) resulted in antagonized grass
control (1, 7, 11). Wanamarta and Penner (1989) concluded that reduced
quackgrass (Elytrigia repens (L.) Nevski) control was due to inhibited diffusion of
l“C-sethoxydim into quackgrass in the presence of the sodium salt of bentazon.
Conversely, pitted morningglory (Ipomoea lacunosa L.) control increased
synergistically from combinations of imazaquin (2-[4,5-dihydro-4-methyl-4-(l-

methylethyl)-5-oxo-1H-imidazol-Z-yl-3-quinolincarboxylic acid) and imazethapyr

 

59

(14). An increase in morningglory control was also observed when imazapyr
(( i)-2-[4,5-dihydro-4-methyl-4-(1-methyl)-5-oxo-1H-imidazol-2-yl]—3—
pyridinecarboxylic acid) was applied in combination with either imazaquin or
imazethapyr (13, 19).

With the recent loss of chloramben (3-amino-2,5-dichlorobenzoic acid), dry
edible bean producers have limited herbicide options for broadleaf weed control“.
Bentazon is the only postemergence broadleaf weed control option, and dry edible
beans are very tolerant of bentazon (9, 22), which controls cocklebur (Xanthium
strumarium L.), jimsonweed (Datura strumarium L.), velvetleaf, and common
ragweed. However, bentazon does not control redroot pigweed or eastern black
nightshade.

Imazethapyr effectively controls redroot pigweed, eastern black nightshade,
and common cocklebur. Activity on these weed species complements the weed
control spectrum of bentazon. Soybeans (Glycine max L.) and other legumes are
tolerant of postemergence applications of imazethapyr (4, 17, 21). However, dry
edible beans have shown susceptibility to imazethapyr applications (20). Early
season injury symptoms include stunting, leaf crinkling, and interveinal chlorosis.

In earlier research (10), bentazon improved dry edible bean tolerance to

postemergence imazethapyr. However, decreased weed control from addition of

 

‘Amiben’s loss limits dry bean herbicide options. Prairie Farmer. Jan. 2.,
1990. pp 8-9.

 

‘-"""" .. .. . A . . _ m_ . .
umdm.._m_-. .__-_»¢ »-* a _.__ -I _- ~_,....-.u..._

ll

60

bentazon to imazethapyr has been reported (2). The objectives of this research
were to (I) investigate whether weed control in greenhouse studies and field
studies was enhanced or reduced when imazethapyr and bentazon were tank-mixed,
(2) assess if soil interception of imazethapyr increased redroot pigweed control,
and (3) determine if tank-mixing bentazon altered absorption and/or translocation

of 14C-irnazethapyr in redroot pigweed.

Materials and Methods

Greenhouse Studies. Locally collected seed of redroot pigweed, eastern black
nightshade, velvetleaf, and common ragweed were planted in BACCTO5
greenhouse potting soil in 946 ml plastic pots. Environmental conditions were
maintained at 25 C i 4 C, and plants were grown in a 16 h photoperiod of natural
and supplemental metal halide lighting with a midday photosynthetic photon flux
density of 1000 pE rn‘2 5". After emergence, plants were thinned to one per pot.
Plants were surface watered as needed and fertilized weekly with 0.1 g of water
soluble fertilizer solution (20% N, 20% P205, 20% K20). All herbicide treatments

were applied postemergence with a continuous belt-link sprayer equipped with a

 

5Baccto is a product of Michigan Peat Co. Houston, TX 77098.

61

single 8001 even flat fan nozzle6 calibrated to deliver 205 L ha" at a spray
pressure of 210 kPa. Belt speed was set at 1.5 km h". Redroot pigweed, eastern
black nightshade, velvetleaf, and common ragweed were treated at the fifth leaf
(6 cm), fourth to fifth leaf (2.5 to 4 cm), third to fourth leaf (6 to 7.5 cm), and
second to fourth leaf (5 cm) stage, respectively.

Imazethapyr was applied at 0, 13, 27, and 53 g ha", while bentazon was
applied at 0, 210, 420, and 840 g ha". The treatments were applied in a factorial
arrangement with 1.2 L ha" POA7. To measure weed control, the plants were
excised at the soil surface 14 DAT, dried, and weights recorded. All pots were
arranged in a completely randomized design and the experiments were repeated in
time with four replications in each experiment. All data were subjected to
ANOVA. Interactions were not present between experiments and treatments so
the experimental data were combined over time. For the herbicide combinations,
the expected weed control value was calculated following Colby’s method (3).
This calculation was carried out only on the greenhouse data since the expected
value is most useful at the GR50 values (3), which the greenhouse data approached.

Mean comparisons were made using Fisher’s Protected LSD,=0.05.

 

°Teejet flat fan tips. Spraying Systems CO., North Ave. and Schmale Road,
Wheaton, H. 60188.

7Herbimax. 83% petroleum oil, 17% adjuvant. Loveland Industries, Inc.
Greeley, CO 80632.

 

   

62

Field Studies. Field experiments were conducted in 1991 and 1992 in a
conventional row dry edible bean crop. Soil characteristics for each experiment
are summarized in Table 1. Locally collected velvetleaf and redroot pigweed
seeds were spread uniformly across the field site both years to ensure adequate
weed populations. Weed seeds were shallowly incorporated 2 to 3 cm using a
Danish S-tine field cultivator“. Immediately following weed seed incorporation,
Olathe pinto beans were planted in 3 m by 7.6 m plots with crop row spacings of
76 cm at a population of 203,000 seeds ha" and 172,000 seeds ha" in 1991 and
1992, respectively. Planting dates were June 4, 1991 and June 12, 1992.
Herbicides were applied on June 24, 1991 and July 6, 1992 when weeds were at
the desired growth state.

Imazethapyr was applied at 0, 53, and 106 g ha", while bentazon was applied
at 0, 420, and 840 g ha". In 1992, 27 g ha" of imazethapyr was also applied.
Herbicides were applied with a tractor-mounted compressed air sprayer in a total
volume of 205 L ha" at a spray pressure of 210 kPa. The boom was adjusted to
61 cm above the soil surface and equipped with 8002 flat fan nozzles spaced 51
cm apart. Treatments were applied in a factorial arrangement with 1.2 L ha"
POA. Treatments were arranged in a randomized complete block design with four

replications. All data were subjected to AN OVA. Year by treatment interactions

 

8Kongskilde. Kongskilde Corp. Bowling Green, OH 43402.

63

were present so 1991 and 1992 data are presented separately. Mean comparisons
were made by Fisher’s Protected LSDFO'OS.

Plots were visually evaluated 14 DAT to measure weed control. Control was
measured on a scale of 0 (no control) to 100 (total plant necrosis). To
quantitatively measure weed control, four uniformly sized redroot pigweed and
velvetleaf plants between the center two rows were marked using a plastic garden
stake 3 to 5 days prior to herbicide application. At 21 DAT, the plants were
harvested at ground level and the dry weight of each species was averaged for each
herbicide treatment.

Weed seedling densities in 1991 for redroot pigweed, velvetleaf, and common
lambsquarters were established at 60 to 100, 40 to 60, and 10 to 50 plants m",
respectively, and in 1992, 40 to 110, 50 to 90, and 10 to 90, respectively. The
redroot pigweed, velvetleaf, and common lambsquarters were 4 to 6 leaves (6 to

8 cm), 3 to 5 leaf (7 to 9 cm), and 4 to 6 leaf (5 to 7 cm), respectively.

Herbicide soil activig studies. Redroot pigweed seeds were planted in a Capac
loamy sand (Aeric Ochraqualfs, fine-loam, mixed, mesic) soil as previously
described in the greenhouse studies section.

Imazethapyr was applied at 0 and 53 g ha" while bentazon was applied at 0
and 840 g ha". Herbicides were applied with 1.2 L ha" POA with a continuous

belt-link sprayer equipped with an 8001 even flat fan nozzle calibrated to deliver

64
205 L ha" at 210 kPa. Belt speed was set at 1.5 km h". Treatments were applied

to redroot pigweed at the fifth leaf stage (6 cm) in greenhouse pots both with and
without 1.5 cm of vermiculite on the soil surface. By placing vermiculite on the
soil surface, soil interception of the spray solution was limited, thus restricting the
soil activity of the herbicides in the spray solution. To measure weed control, the
plants were excised at the soil surface 14 DAT, dried, and weights recorded. The
experimental design was a split-plot with the vermiculite and no vermiculite
treatments as the main plots and the herbicide treatments as the sub-plots. The
pots were completely randomized and the experiment repeated in time with four
replications each time. Interactions were not present between experiments and

treatments, and the data were combined for analysis.

l‘C-imazethapyr absorption and translocation studios Absorption of 14C-

imazethapyr (pyridine ring labelled, 6"I position with specific activity = 784.4
MBq/g) applied alone and tank-mixed with bentazon was determined. Redroot
pigweed seed were planted in BACCTO greenhouse soil in 946 ml plastic pots.
All experiments were conducted in growth chambers with day/night temperatures
of 26/22 C. Chambers were maintained at 68% relative humidity with a 16 h
photoperiod from fluorescent and incandescent lighting with a photosynthetic

photon flux density of 750 IIE m“2 3". Plants were surface-watered as needed. A

65

2 pL drop containing 370 Bq of l“C-imazethapyr was applied with a micro-
syringe9 between the fifth leaf mid-vein and the edge of the leaf approximately Vs
of the distance from the leaf tip to the base of the leaf. Special care was taken to
not place the Spot on a leaf vein. The spotting solution contained MC—imazethapyr
with the appr0priate amounts of formulation blank, unlabelled commercial
imazethapyr”, commercial bentazon“ (when appropriate), POA, and water to
simulate a spray solution containing imazethapyr at 53 g ha", bentazon at 840 g
ha", and POA at 1.2 L ha" in a total volume of 205 L ha".

At 0, 1, 2, 4, 8, 24, and 48 h after treatment (spotting), the leaf was rinsed
in a 20 ml glass scintillation vial containing 3 ml of methanol : H20 (2:1 v/v), and
gently swirled for 30 s. The leaf was then washed with a minimal amount of
rinsing solution and 15 ml of scintillatorl2 was added. The unabsorbed 1‘C-
imazethapyr was quantified by liquid scintillation spectrometry (LSS)” and
absorption calculated by subtracting the amount of l"C-imazethapyr recovered in

the washoff solution from the amount of ”C-imazethapyr applied.

 

9Hamilton microsyringe, Hamilton Co. Reno, NV 89520-0012.
10Pursuit 2AS herbicide. American Cyanamid Co. Princeton, NJ 08540.
“Basagran 4L, BASF Corp. Parsippany, NJ 07054.

12Safety-Solve. Research Products International Corp. Mount Prospect, H.
60056.

l3Model 1500. Packard Instrument Corp. Downers Grove, H. 60515.

66

The treated leaf was saved and combusted in a biological oxidizer”. The
CO2 was trapped in a solution of scintillator : CO2 absorber”. Total radioactivity
in the sample was then determined by LSS. The amount of l4C-imazethapyr in the
treated leaf was calculated by subtracting the amount of 14C recovered in the
treated leaf from what was absorbed. This amount was then subtracted from

100% to calculate l“C-imazethapyr translocated from the treated leaf.

Results and Discussion

Greenhouse studies. Imazethapyr at 13, 27, and 53 g ha" reduced dry weight of
redroot pigweed by 82, 87, and 85%, respectively, as compared to the untreated
control (Table 2). Bentazon at 210, 420, and 840 g ha" decreased redroot
pigweed dry weight by 36, 25, and 42%, respectively. When 210 or 420 g ha"
of bentazon was tank-mixed with 13 g ha" of imazethapyr or when 420 g ha" of
bentazon was tank-mixed with 27 g ha" of imazethapyr, redroot pigweed dry
weights increased as compared to each respective rate of imazethapyr. When dry

weight data were compared to Colby’s expected values, antagonized weed control

 

l4OX—300. R. J. Harvey Instrument Corp. Patterson, NJ 07642.
lSCarbo-Sorb H. Packard Instrument Co. Meriden, CT 06450.

 

67

was noted when any bentazon was tank-mixed with 13 or 27 g ha" of imazethapyr
(Table 2). When imazethapyr was applied at 53 g ha", antagonism from bentazon
was not observed.

Bentazon or imazethapyr applied alone at the highest rates decreased eastern
black nightshade dry weight by 68 and 62% , respectively (Table 2). A significant
increase in plant dry weight occurred only when 53 g ha" of imazethapyr was
tank-mixed with 210 g ha" of bentazon as compared to 53 g ha" of imazethapyr
alone. Six of the nine tank-mix combinations resulted in less plant dry weight
reduction than expected as calculated by Colby’s method. However, a loss in
eastern black nightshade control by imazethapyr when tank-mixed with bentazon
was not evident, indicating the increased sensitivity of this species to bentazon.

Similar trends were noted with common ragweed. Bentazon and imazethapyr
applied alone at the highest rates decreased dry weight by 74 and 50% ,
respectively. A loss of common ragweed control was not observed when
imazethapyr and bentazon were tank-mixed, again indicating the sensitivity of this
weed species to bentazon.

Bentazon and imazethapyr applied alone at the highest rates decreased
velvetleaf dry weight by 30 and 38%, respectively. Velvetleaf control was less
than expected in the greenhouse possibly due to vigorous growth (personal
observation) under greenhouse conditions. N 0 reduction or enhancement of weed

control occurred with any tank-mix combination.

68

Redroot pigweed and eastern black nightshade displayed antagonistic responses
as indicated by Colby’s expected values when bentazon was tank-mixed with
imazethapyr. No antagonism was observed in common ragweed control and
velvetleaf control was poor with all herbicide treatments. Redroot pigweed and
eastern black nightshade are both controlled by imazethapyr applied at field rates
but are not controlled by bentazon. Control of common ragweed and velvetleaf
is better with bentazon than with imazethapyr (2). Thus, weed control may be
antagonized when imazethapyr and bentazon are tank-mixed if the weed species

are more susceptible to imazethapyr than bentazon.

Field Studies. Redroot pigweed control in the field was not reduced either year
when bentazon was tank-mixed with imazethapyr. Imazethapyr at 53 g ha" or 106
g ha" provided 98 to 99% control of redroot pigweed 14 DAT both years (Tables
3 and 4). Tank-mixing 420 or 840 g ha" of bentazon with any rate of imazethapyr
did not reduce redroot pigweed control. Redroot pigweed dry weight responded
similarly. Imazethapyr at 53 or 106 g ha" reduced redroot pigweed dry weight 87
and 93%, respectively, in 1991 and 84 and 93%, respectively, in 1992. Tank—
mixing bentazon at 420 or 840 g ha" with either rate of imazethapyr did not effect
redroot pigweed dry weight as compared to each respective rate of imazethapyr
applied alone in 1991. However in 1992, adding 840 g ha" of bentazon improved

redroot pigweed control with each respective rate of imazethapyr, compared to

69
imazethapyr alone (Table 4).

Velvetleaf control increased both years when bentazon was tank-mixed with
imazethapyr as compared to imazethapyr or bentazon alone. Bentazon at 420 and
840 g ha" provided 18 and 78% velvetleaf control, respectively, 14 DAT in 1991
and 78 and 92% velvetleaf control, respectively, in 1992. Imazethapyr provided
75 to 80% velvetleaf control in 1991, and 60 to 68% control in 1992. Velvetleaf
control from 420 g ha" of bentazon increased when 53 or 106 g ha" of
imazethapyr was tank-mixed in 1991 and 1992.

In 1991, velvetleaf dry weight reduction was improved 60 and 51 % when 420
g ha" of bentazon was tank-mixed 53 or 106 g ha" of imazethapyr, respectively.
In 1992, bentazon at 420 and 840 g ha" decreased velvetleaf dry weight by 92 and
100%, respectively. When bentazon at 840 g ha" was tank-mixed with either rate
of imazethapyr, a reduction in plant dry weight was observed as compared to each
respective rate of imazethapyr applied alone.

Bentazon applied alone at 840 g ha" provided 90% control of common
lambsquarters in 1991 and 98% control in 1992. Imazethapyr alone gave poor
control of common lambsquarters. Adding imazethapyr to the bentazon treatment
did not improve or reduce common lambsquarters control in 1991 and 1992.

In greenhouse studies, redroot pigweed and eastern black nightshade control
was reduced when bentazon was tank-mixed with 13 or 27 g ha" of imazethapyr.

However, this antagonized redroot pigweed control was not observed in the field.

 

70

Control of weed species that are controlled by bentazon as well as by imazethapyr,
such as velvetleaf, common ragweed, and common lambsquarters, was not
antagonized in field or greenhouse studies. Further greenhouse research

determined the possible mechanism for the reduction in redroot pigweed control.

H_epb_iciie_s_oil_ac_tm'ty_stLdies_. Greenhouse studies were designed to determine
if the soil interception of the spray solution played a role in redroot pigweed
control by imazethapyr. When vermiculite was not spread on the soil surface,
bentazon at 840 g ha" reduced redroot pigweed dry weight 21 % as compared to
the untreated control (Table 5). Imazethapyr alone or tank-mixed with bentazon
reduced redroot pigweed dry weight by 86 and 79%, respectively, as compared
to the untreated control plant.

When comparing across soil treatments, dry weight of the untreated redroot
pigweed in the presence of vermiculite was lower than where vermiculite was not
placed on the soil surface (Table 5). This was unexpected but may be due to the
increased handling of the greenhouse pots with vermiculite on the soil surface and
subsequent removal of the vermiculite. When imazethapyr was applied alone or
tank-mixed with bentazon, redroot pigweed dry weight was greater when
vermiculite was placed on the soil surface, demonstrating that soil activity from

imazethapyr increased redroot pigweed control.

71
l“C-Imazethapyr absorption and translocation in redroot pigweed. At 4, 8,

and 24 h after treatment, the presence of bentazon in the spray solution decreased
absorption of l4C-imazethapyr by redroot pigweed as compared to l“C-irnazethapyr
applied alone (Figure 1). By 8 h after treatment, l“C-imazethapyr absorption when
applied alone was greater than 95 % of applied. When bentazon was applied with
l“C-imazethapyr at 8 h, absorption was s 80% of applied. Redroot pigweed are
extremely sensitive to imazethapyr. A 15% decrease in absorption may not totally
account for the reduced weed control observed in earlier greenhouse studies.

More l“C-imazethapyr was translocated from the treated leaf 24 and 48 h after
treatment when l‘lC-imazethapyr was applied alone than when bentazon was present
(Figure 2). At 24 and 48 h after treatment, 27% and 30% of absorbed 1“C was
translocated from the treated leaf. However, when bentazon was tank-mixed with
l“C-irnazethapyr, translocation was only 11% and 19% of absorbed 1“C at 24 and
48 h after treatment, respectively. This is greater than a 50% reduction in 1“C
translocated from the treated leaf compared to l“C-imazethapyr alone.

The reduction in translocation of l“C-imazethapyr from the treated leaf by
tank-mixing with bentazon may contribute to the antagonized redroot pigweed
control in initial greenhouse studies. The translocation of a phloem mobile
herbicide, such as imazethapyr, may be inhibited when the production and
translocation of photoassimilate is also inhibited (5). Bentazon is known to reduce

photoassimilate production and translocation by inhibition of electron transport in

72

photosystem H (6, 16). It is therefore reasonable to assume that bentazon will
reduce the phloem transport of imazethapyr.

Bentazon decreased both absorption and translocation of ”C-imazethapyr in
redroot pigweed. Bentazon has also been observed to decrease absorption of
sethoxydim and acifluorfen (5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic
acid) in selected plant species (12, 15, 18). The decrease in absorption and
translocation of l“C-imazethapyr when tank-mixed with bentazon probably
contributed to decreased redroot pigweed control in greenhouse studies. Also, soil
interception of the spray solution may have played an important role in controlling

redroot pigweed in field studies.

10.

11.

12.

73
LITERATURE CITED

Cambell, J. R. and D. Penner. 1982. Compatibility of diclofop and BAS
9052 with bentazon. Weed Sci. 30:458-462.

Cantwell, J. R., R. A. Liebl, and F. W. Slife. 1989. Imazethapyr for weed
control in soybean (Glycine max). Weed Technol. 3:596-601.

Colby, S. R. 1967. Calculating synergistic and antagonistic responses of
herbicide combinations. Weeds 15:20-22.

Cole, T. A., G. R. Wehtje, J. W. Wilcut, and T. V. Hicks. 1989. Behavior
of imazethapyr in soybeans (Glycine max), peanuts (Arachis hypogaea), and
selected weeds. Weed Sci. 37:639-644.

Devine, M. D., H. D. Bestman, and W. H. Vanden Born. 1990.
Physiological basis for different phloem mobilities of chlorsulfuron and
chlopyralid. Weed Sci. 38:1-9.

Fuerst, E. P. and M. A. Norman. 1991. Interactions of herbicides with
photosynthetic electron transport. Weed Sci. 39:458-464.

Hartzler, K. K. and C. L. Foy. 1983. Compatibility of BAS 9052 OH with
acifluorfen and bentazon. Weed Sci. 31 :597-599.

Hatzios, K. K. and D. Penner. 1985. Interactions of herbicides with other
agrochemicals in higher plants. Rev. Weed Sci. 1:1-73.

Mahoney, M. D. and D. Penner. 1975. Bentazon translocation and
metabolism in soybean and navy bean. Weed Sci. 23:265-270.

Renner, K. A. and G. E. Powell. 1988. Dry edible bean tolerance to
postemergence herbicides. Proc. North Central Weed Cont. Conf. 43:36.

Rhodes, G. N. and H. D. Coble. 1984. Influence of application variables on
antagonism between sethoxydim and bentazon. Weed Sci. 32:436-441.

Rhodes, D. G. and H. D. Coble. 1984. Influence of bentazon on the
absorption and translocation of sethoxydim in goosegrass (Eleusine indica
L.). Weed Sci. 32:595-597.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

74

Riley, D. G. and D. R. Shaw. 1988. Influence of imazapyr on the control
of pitted morningglory (Ipomoea lacunosa) and johnsongrass (Sorghum
halepense) with chlorimuron, imazaquin, and imazethapyr. Weed Sci.
36:663-666.

Riley, D. G. and D. R. Shaw. 1989. Johnsongrass (Sorghum halepense) and
pitted morningglory (Ipomoea lacunosa) control with imazaquin and
imazethapyr. Weed Technol. 3:95-98.

Sorensen, V. M., W. F. Meggitt, and D. Penner. 1987 . The interaction of
acifluorfen and bentazon in herbicidal combinations. Weed Sci. 35:449-

456.

Suwanketnikon, R., K. K. Hatzios, and D. Penner. 1982. The site of
electron transport inhibition of bentazon (3-isopropyl-lH-2,1,3-
benzothiadiazin-(4)3H—one 2,2-dioxide) in isolated chloroplasts. Can. J.
Bot. 60:409-412.

Vencill, W. K., H. P. Wilson, T. E. Hines, and K. K. Hatzios. 1990.
Common lambsquarters (Chenopodium album) and rotational crop response
to imazethapyr in pea (Pisum sativum) and snap bean (Phaseolus vulgaris).
Weed Technol. 4:39-43.

Wanamarta, G., D. Penner, and J. J. Kells. 1989. The basis of bentazon
antagonism on sethoxydim absorption and activity. Weed Sci. 37:400-404.

Wills, G. D. and C. G. M°Whorter. 1987. Influence of inorganic salts and
imazapyr on control of pitted morningglory (Ipomoea lacunosa) with
imazaquin and imazethapyr. Weed Technol. 1:328-331.

Wilson, R. G. and S. D. Miller. 1991. Dry Edible bean (Phaseolus
vulgaris) response to imazethapyr. Weed Technol. 5:22-26.

Wilson, R. G. 1989. New herbicides for weed control in established alfalfa
(Medicago sativa). Weed Technol. 3:523-526.

WSSA Herbicide Handbook Committee. 1989. Herbicide Handbook. 6th ed.
Champaign, H..

 

75

 

Table 1.. Soil characteristics of field studies in 1991 and 1992.

 

 

Year

 

 

1991

1992

 

 

loamy sand

1.7 % OM pH 5 .5

82% sand 10% silt 8% clay
Capac loamy sand (Aeric
Ochraqualfs, fine-loamy,
mixed, mesic)

 

sandy clay loam

3.4% OM pH 7

55% sand 25 % silt 20% clay
Capac sandy clay loam (Aeric
Ochraqualfs, fine-loamy,
mixed, mesic)

 

 

.82 new .85 00 BO Z .53 2338262 688:2. we: Sausages: :8 8:8 835:: 05 2: EB we: :25:

.852: Man—om wEms cam—=28 2: 88558: E 3:225 .828, 88an on?

 

 

 

 

 

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77

Table 3. Response of redroot pigweed, velvetleaf, and common lambsquarters to
bentazon and imazethapyr applied alone and in combination in 1991 in the field.

Treatment Rate Visual control 14 DAT Dry weight 21 DAT

 

 

AMARE ABUTH CHEAL AMARE ABUTH

 

 

 

 

—-g ha"- % g plant"

Untreated - — 0 0 0 12. l 5 .6
Bentazon 420 8 18 73 16.5 5.3
Bentazon 840 38 78 90 6.7 l

Imazethapyr 53 99 75 60 1 .6 2.7
Imep +bent 53 +420 93 78 80 1.9 2. 1
Imep +bent 53 + 840 95 90 90 2.2 0.6
Imazethapyr 106 99 80 70 0.9 3 .0
Imep + bent 106 +420 98 80 80 0. 7 2.6
Imep+bent 106+840 95 90 88 0.5 0.4

LSD,_,,,, 13 20 13 2.1 1.7

 

78

Table 4. Response of redroot pigweed, velvetleaf, and common lambsquarters to
bentazon and imazethapyr applied alone and in combination in 1992 in the field.

 

 

 

 

 

 

Treatment Rate Visual control 14 DAT Dry weight 21 DAT
AMARE ABUTH CHEAL AMARE ABUTH
-g ha"- % -----g plant"

Untreated - - 0 O 0 32.2 22.4
Bentazon 420 30 78 97 15.6 1 .7
Bentazon 840 33 92 98 10.4 0
Imazethapyr 27 88 60 45 6.3 8.3
Imep+bent 27+420 83 83 93 3.5 0.8
Imep+bent 27+840 83 93 93 2.3 0
Imazethapyr 53 98 63 65 5.3 6.5
Imep+bent 53 +420 93 90 83 2.6 0.5
Imep+bent 53+840 95 93 90 1.4 0.1
Imazethapyr 106 98 68 65 3.5 4.9
Imep+bent 106+420 99 88 83 1.4 1.9
Imep+bent 106+840 98 93 88 0.6 0.1
LSD“,05 8 10 15 2.9 1.5

 

79

Table 5. Redroot pigweed dry weight 21 DAT as influenced by
imazethapyr and bentazon with and without soil interception of the spray

solution.
Imazethapyr Bentazon No vermiculite Vermiculite LSD,,=0_05c

 

--g ha"-- --g ha"-- ----------- g plant" ----------
0 0 1.4 1.2
0 840 1.1 1.1 0.2
53 0 0.2 0.5
53 840 0.3 0.5
LSD,=O,,, 0.2

 

 

cA split plot LSD,,=0.05 was calculated for comparing values across soil treatment
(value at right) or comparing values across herbicide treatment (value at bottom).

 

80

Figure 1. l4C-Imazethapyr absorption when applied alone and tank-mixed with
bentazon in redroot pigweed. Regression equation for I“C-imazethapyr when
applied alone is Y = (784*X)/(1+(784/96)*X) (Rz=0.82) and when tank-mixed
with bentazon is Y = (738*X)/(l +(738/79)*X) (R2=0.75). LSD,,=0_05 bars are
centered over data points.

81

EVmEfi
mm mm vm Nu om 3 e: E a: or

w o

{v

 

—-———-—-u—-qd—--—u—u—uqq——qdflq__——

Eom + QOETOXXI aoE_-O:hr

——-ud—_

‘a-Io

 

 

 

 

ON

00..

(pendde Io %) uondiosqv

82

Figure 2. ”C-Imazethapyr translocation from the treated leaf when applied alone
and tank-mixed with bentazon in redroot pigweed. Regression equation for 1‘C-
imazethapyr when applied alone is Y = (6.5*X)/(1+(6.5/33)*X) (R2=0.86) and
when tank-mixed with bentazon is Y = (3.4*X/(1 +(3.4/ 18)*X) (R2=0.85).
LSDa=005 bars are centered over data points.

 

 

 

83

 

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on m: 9. mm on mm cm 3 S 6 oo
____.____.______.__.___.__....__._____.__.._._____
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0')

Pinto Bean (Phaseolus vulgaris) Varietal Tolerance to Postemergence

Imazethapyrl

T. A. BAUER, K. A. RENNER, D. PENNER, and J. D. KELLY2

Abstract. Preliminary greenhouse studies indicated pinto bean varietal tolerance
differences to postemergence imazethapyr. The objectives of this research were
to determine ( 1) if differences existed in pinto bean varietal tolerance to
postemergence imazethapyr under field conditions, (2) if tolerance differences were
due to differential acetolactate synthase enzyme sensitivity or differences in 1“C-
imazethapyr absorption, translocation, and/or metabolism, and (3) the number of
genes involved and the heritability of imazethapyr tolerance in pinto bean. All
rates of postemergence imazethapyr injured Olathe, Sierra, UIl l4, P89405, Aztec,
and P90570 pinto bean varieties 7 DAT in 1991 and 1992 except 53 g ha" of
imazethapyr applied to Sierra pinto bean in 1991. Olathe was injured more than
other varieties in 1991, and physiological maturity was delayed more than the

maturity of Sierra in both years. However, seed yields of all varieties were not

 

1Received for publication and in revised form

2Res. Asst., Assoc. Prof, Prof., and Assoc. Prof, Mich. St. Univ., East
Lansing, MI 48824-1325, respectively.

 

85
reduced in 1991, and only P90570 had reduced seed yields from 53 g ha" of

imazethapyr in 1992. Differential sensitivity of the ALS enzyme to imazethapyr
was not the mechanism of differential varietal response. Olathe pinto bean
absorbed and translocated more than 1.4 and 1.3 times, respectively, l“C-
imazethapyr as Sierra pinto bean 24 h after application. No differences in 14C-
imazethapyr metabolism were detected between Olathe and Sierra pinto beans.
Broad sense heritability of imazethapyr tolerance in pinto bean was calculated to
be 0.85. The number of genes controlling the inheritance of imazethapyr tolerance

in pinto beans was greater than one.

Nomenclature: Dry bean (Phaseolus vulgaris L.) #3 PHAVU, imazethapyr, 2-
[4,5-dihydro-4-methyl-4—methyl-4-(1-methylethyl)-5-oxo—1H-imidazol-2-yl]-5-ethyl-

3-pyridinecarboxylic acid.

Additional index words. Imidazolinone, acetolactate synthase, differential

tolerance, foliar absorption, translocation, metabolism, inheritance.

 

3Letters following this symbol are a WSSA-approved computer code from the
Composite List of Weeds, Weed Sci. 32, Suppl. 2. Available from WSSA, 309
West Clark Street, Champaign, H. 61820.

 

 

 

86

Introduction

The only postemergence broadleaf weed control option for Michigan dry edible
bean producers is bentazon [3—(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-(4(3H)-
one 2,2 dioxide] which does not control redroot pigweed or eastern black
nightshade (26). Imazethapyr controls these two weed species (3, 26) and many
legumes are tolerant of postemergence imazethapyr applications (3, 21, 24).
However, dry edible beans were susceptible to imazethapyr in previous research
(16, 23). Early season injury symptoms included bean stunting, leaf crinkling, and
interveinal chlorosis while late season injury was characterized by reduced plant
height and delayed maturity. Wilson and Miller (23) observed seed yield
reductions one year following the application of 100 g ha“1 of imazethapyr (a 2X
application rate). The authors noted bean cultivar by herbicide interactions, but
the interactions varied with year and location.

Imazethapyr is absorbed by both roots and shoots, and is translocated to the
meristematic tissues, characteristic of a phloem mobile herbicide (3, 18). The
primary site of imazethapyr action has been reported to be the inhibition of the
acetolactate synthase (ALS, also referred to as acetohydroxyacid synthase), the
first common enzyme in the synthesis of the branched chain amino acids valine,

leucine, and isoleucine (2, 12). The sulfonylurea herbicides have also been

87
reported to inhibit the ALS enzyme (8, 15).

Differential susceptibility of soybean (Glycine max L.), peanut (Arachis
hypogaea L.), and several weed species was attributed primarily to differential
metabolism (3). Soybean and corn (Zea mays L.) convert imazethapyr to 5-
hydroxyethyl-imazethapyr followed by glucose conjugation. The conversion to the
glucose conjugate is more rapid in soybean than in corn, which may result in the
reduced corn tolerance observed“. Some plants possess ALS isozymes which
are less sensitive to imidazolinone and sulfonylurea inhibition which increase their
tolerance ( 1, 6). Genetic studies of sulfonylurea herbicide resistance in soybean
(17) and Lactuca spp. (11), and imidazolinone resistance in com (13) indicated that
resistance was by a single nuclear gene inherited in a semidominant fashion.

The pinto bean class of dry beans appears to be particularly sensitive to
postemergence imazethapyr (5). Preliminary greenhouse studies indicated pinto
bean varietal tolerance differences following postemergence imazethapyr. The
objectives of this research were to (1) determine if differences in pinto bean
varietal tolerance to postemergence imazethapyr occurred under field conditions,

(2) determine if tolerance differences were due to differential ALS enzyme

 

‘Personal communication. Dale Shaner, American Cyanamid Co. , Princeton,
NJ 08540.

5AC-263-499 Technical Information Report. 1985. American Cyanamid Co. ,
Princeton, NJ 08540.

 

 

 

 

 

88

sensitivity or differences in l“C-imazethapyr absorption, translocation, and/or
metabolism, and (3) assess the number of genes involved and the heritability of

imazethapyr tolerance in pinto bean.

Materials and Methods

Field Research. Soil characteristics for 1991 and 1992 field experiments are
summarized in Table 1. Plots were maintained weed-free the entire season by
hand hoeing to eliminate the confounding factor of weed interference on pinto bean
maturity and yield.

Seedbed preparation consisted of fall moldboard plowing followed by two
passes with a Danish S-tine field cultivator6 in the spring, the second pass
perpendicular to the first. Pinto beans were planted on June 13, 1991 and June 9,
1992 at a seeding rate of 172,000 seeds ha" into plots 2.03 m by 4.57 m with crop
row spacings of 51 cm. Herbicide treatments were applied on July 3, 1991 and
July 6, 1992 when dry beans had reached the second trifoliolate growth stage.

Plots were visually evaluated 7 and 14 DAT to assess pinto bean injury.

Injury was measured on a scale ranging from 0 (no visible injury) to 100 (total

 

6Kongskilde. Kongskilde Corp. Bowling Green, OH 43402.

 

89

plant necrosis). TO quantitatively measure pinto bean chlorosis, three leaf discs,
6.5 mm in diameter, were harvested from the middle leaflet of the third trifoliolate
from three randomly selected bean plants in the middle two rows of each plot 7
DAT. Chlorophyll was extracted with 3 ml of N,N-dimethylformamide (7). Total
chlorophyll, chlorophyll a, and chlorophyll b levels were determined using UV-
VIS spectrophotometry as described by Inskeep and Bloom (1985). Through
statistical analysis, chlorophyll a levels were determined to be the most sensitive
indication of herbicide injury, so only chlorophyll a levels will be reported. The
number of growing days required to reach physiological maturity was recorded.
Plots were considered physiological mature when 90% of the pods had turned from
green to a golden-bronze (buck-skin) color. Yields were measured by hand
harvesting and threshing two, 3.05 m sections from the middle two rows of each
plot. Yields were adjusted to 18% moisture.

Imazethapyr was applied at 0, 53, and 106 g ha" to Olathe, Sierra, 1111 14,
Aztec, P89405, P90570 pinto beans. All postemergence herbicides were applied
with a tractor-mounted compressed air sprayer in a total volume of 205 L ha" at
a spray pressure of 210 kPa. The boom was equipped with 80027 flat fan nozzles

spaced 51 cm apart adjusted to 61 cm above the soil surface. Herbicide treatments

 

7Teejet flat fan tips. Spraying Systems CO., North Ave. and Schmale Road,
Wheaton, H. 60188.

 

90

were applied in a factorial arrangement with 1.4 % (v/v) NIS8. Treatments were
arranged in a randomized complete block design with four replications. All data
were subjected to AN OVA. Year by treatment interactions were present so 1991
and 1992 data are presented separately. Mean comparisons were made using
Fisher’s Protected LSDagom. Pinto bean seed yields were converted to a percent

Of the untreated control for mean separations. Values presented are actual seed

yields.

W. ALS enzyme activity was determined from the leaves of 21
to 28 day old Olathe and Sierra pinto beans. Pinto bean seed were planted in
BACCTO" greenhouse potting soil in 946 ml plastic pots. Environmental
conditions were maintained at 25 C i 4 C, and plants were grown in a 16 h
photoperiod of natural and supplemental metal halide lighting with a midday
photosynthetic photon flux density of 1000 aE In2 3". After emergence, plants
were thinned to one per pot. Plants were surface watered as needed and fertilized
weekly with 0.1 g of water soluble fertilizer solution (20% N, 20% P205, 20%
K20).

ALS enzyme was extracted and activity levels measured in the presence of

 

8X-7 7 Non-Ionic Surfactant. A mixture of alkylarylpolyoxyethleneglycols, free
fatty acids and isopropanol. Valent U.S.A. Corp., Walnut Creek, CA 94956.

9Baccto is a product of Michigan Peat Co. Houston, TX 77098.

91
imazethapyr as outlined by Ray (15) and Shaner (18) with the following

modifications. All extraction, centrifugation, and column procedures were
conducted at 4 C. Forty to 50 g of plant leaves were homogenized in a volume
of cold buffer (0.1 M K2HPO4, pH 7.5, 1 mM sodium pyruvate, 0.5 mM MgCl,
0.5 mM thiamine pyrophosphate, 10 p.M flavin adenine dinucleotide (FAD), 10%
v/v glycerol) equivalent to twice the weight of the tissue.
Polyvinylpolypyrrolidone (2.5 g) was added for every 10 g of plant material
homogenized. The homogenate was filtered through eight layers of cheesecloth
and then centrifuged at 27,000 g for 20 min. Saturated cold (N H0280, solution
was added to the supernatant to bring the final (N H,,)2SO4 concentration to 50 %
saturated. The solution was centrifuged at 15,000 g for 15 min and the pellet
redissolved in resuspension buffer (0.1 M KZHPO4, pH 7.5, 20 mM sodium
pyruvate, 0.5 mM MgCl) and placed on a Sephadex G-25 PD-10lo column. The
desalted protein was immediately used for enzyme assays.

ALS enzyme activity was assayed by combining 0.5 ml of enzyme preparation
with 1 ml of reaction buffer (25 mM KZHPO4, pH 7.0, 0.625 mM MgCl, 25 mM
sodium pyruvate, 0.625 mM thiamine pyrophosphate, 1.25 EM FAD) and the
mixture incubated for 1 h at 35 C. Reaction tubes contained either 0, 1, 10, 100,

or 1000 EM of imazethapyr. The reaction was stOpped by the addition of 50 aL

 

loPD-lO column. Pharmacia, Inc., Piscataway, NJ 08855-1327.

92

of 6 N H2804 and the solutions were then heated at 60 C for 15 min. Following
termination of the reaction, 0.5 ml of 0.5% (w/v) creatine and 0.5 ml of 5 % (w/v)
oz-naphthol (freshly prepared in 2.5 N N aOH) were added. The solutions were
heated for an additional 15 min at 60 C and the acetoin content measured by the
Westerfield method (22). Protein concentration was determined by the Lowry
method (9).

The ALS enzyme assay was conducted twice with five replications of each
herbicide concentration per experiment. Enzyme activity is presented as a percent
of untreated control assays with the data subjected to AN OVA at each herbicide
concentration. Data were subjected to linear regression analysis to determine IsO

values (herbicide concentration required to inhibit enzyme activity by 50%).

l“C-Imazetha abso tion translocation and metabolism. l“C-Imazethapyr
(pyridine ring labelled, 6‘h position with specific activity = 784.4 MBq/g)

absorption, translocation, and metabolism was evaluated in Olathe and Sierra pinto
beans. Pinto beans were planted in BACCTO greenhouse soil in 946 ml plastic
pots. All experiments were conducted in growth chambers with day/night
temperatures of 26/22 C. Chambers were maintained at 68% relative humidity
with a 16 h photoperiod from fluorescent and incandescent lighting with a

photosynthetic photon flux density of 750 uE m'2 5". Plants were surfaced-watered

 

93
as needed.

The middle leaflet of the first trifoliolate was treated with l“C-imazethapyr.
Prior to spotting l4C-imazethapyr on the treated leaflet, plants were sprayed with
unlabelled herbicide to simulate a field application. The herbicide treatment was
applied with a continuous belt-link sprayer equipped with a single 8001 even flat
fan nozzle calibrated to deliver 205 L ha" at a spray pressure of 210 kPa.
Preliminary spray retention studies (data not presented) indicated the treated leaflet
intercepted approximately 24 ILL of spray solution. The treated leaflet was
covered with aluminum-foil prior to treatment with unlabelled herbicide so as to
avoid any spray interception. The covered leaflet was then spotted with 12, 2 pL
drops using a microsyringell containing a total of 5.83 kBq of l“C-imazethapyr.
Drops were not spotted on a leaf vein. The spotting solution contained 1“C-
imazethapyr with the appropriate amounts of formulation blank, unlabelled
commercial imazethapyr”, NIS, and water to simulate a spray solution containing
53 g ha" of imazethapyr, and NIS at % % (v/v) in a total volume of 205 L ha".

At 6, 24, 48, and 72 h after treatment (spotting), the treated leaflet was
excised and rinsed in a 20 ml glass scintillation vial containing 15 ml of methanol
: dd H20 (2:1 v/v) and swirled for 30 s. The leaflet was then rinsed with a

minimal amount of the rinsing solution. The total volume was divided into five,

 

“Hamilton microsyringe, Hamilton CO. Reno, NV 89520-0012.
l2Pursuit 2AS herbicide. American Cyanamide Co. Princeton, NJ 08540.

 

94

20 m1 glass scintillation vials and 15 ml of scintillator13 added to each vial. The
unabsorbed l“C-imazethapyr was quantified by liquid scintillation spectrometry
(LSS)l4 and absorption determined by subtracting the amount of l4C-imazethapyr
recovered in the washoff solution from the total amount of l4C-imazethapyr
applied.

The treated leaflet was frozen with dry ice and stored at -30 C for metabolism
analysis. The potting media was rinsed from the roots and the remainder of the
plant was then sectioned into four additional parts: above the treated leaflet,
lateral leaflet, below the treated leaflet, and roots. Fresh weight of each plant part
was recorded and the plant samples were combusted in a biological oxidizer”.
Radioactivity in each plant part was quantified by LSS.

Absorbed 1“C was extracted from the treated leaflet. The treated leaflet was
homogenated in 25 ml of methanol for 2 min in a stainless steel Sorvall
Omnimixer”. The inside of the mixer was washed with 15 ml of methanol and

the residue blended for an additional 2 min. The homogenate was filtered under

 

l3Safety-Solve. Research Products International Corp. Mount Prospect, IL
60056.

1“Model 1500. Packard Instrument Corp. Downers Grove, H. 60515.
15OX-300. R. J. Harvey Instrument Corp. Patterson, NJ 07642.
“Sorvall Omni-Mixer. Omni International, Inc. Waterbury, CT 06704.

95

vacuum through filter paper”, and the homogenizer vessel thoroughly rinsed with
methanol and filtered. The entire filtrate volume was recorded. Two, 0.5 ml
aliquots were sampled from the filtrate, and radioactivity was quantified with LSS.
The filter paper and extracted tissue were allowed to air dry and then oxidized to
determine unextracted radioactivity. The filtrate was concentrated to 1 to 5 ml
under a vacuum at 39 C using a rotary evaporator”. The flask was rinsed twice
with methanol at a total volume of 3 ml and combined with the concentrated plant
extract. The remaining extract was filtered through a polysulfone membrane
filter19 with a mean pore size of 0.45 pm following evaporation under a stream
of nitrogen in a water bath at 35 C. The filter housing was then rinsed with 1 ml
methanol, and added to the filtrate. The total volume was then reduced to 1 ml
and 50 [LL of concentrated extract was chromatographed using thin-layer
chromatography (TLC) silica gel plates”. As a standard, 370 Bq of ‘4C-
irnazethapyr was also spotted on each plate. TLC plates were developed in a
system of n-propanol : methylene chloride : formic acid (4:5: 1, v/v/v) which

provided a clear separation of metabolites. Radioactivity was located and

 

1"Whatrnan #1. Whatrnan International Ltd. Maidstone, England.
18BI'ichi R110. Brinkrnann Instruments, Inc. Westbury, NY 11590.
19Supor 200 Membrane Filter. Gelman Sciences Inc., Ann Arbor, NH 48106.

2OWhannan Silica Gel 150 A LKSDF, Whatrnan International, Ltd, Maidstone,
England.

96

quantified by a plate scanner“. The amount of 1“C in the treated leaflet was
calculated by adding the extractable and unextractable 1“C. To calculate the
amount of 1“C translocated from the treated leaflet, the amount of 1“C recovered
in the treated leaflet was subtracted from the amount absorbed. This value was
then converted to a percentage and subtracted from 100 %.

All pots for the ALS enzyme assay, absorption, translocation, and metabolism
studies were arranged in a completely randomized design with four replications.
Absorption, translocation, and metabolism experiments were repeated. All data
were subjected to AN OVA and data were combined over time. Mean comparisons
were made by LSDMM,5 within each time period.

I“C-Imazethapyr absorption and translocation from the treated leaf studies were
subjected to curvilinear regression analysis and coefficient values determined (19).
The absorption and translocation data were fit to the curvilinear equation Y =
(I*X)/(1+(I/A)*X), where Y and X are the Y - axis and X - axis coordinates, I
is the percentage absorption as time approaches 0, and A, the asymptotic value,

is the percentage absorption as time approaches infinity.

Inheritance of imazethapyp tolerance in pintp bean. F2 crosses of Olathe (least

tolerant) x Sierra (most tolerant) pinto beans were evaluated for inheritance of

 

21Radioactivity Detecting Plate Scanner. AMBIS Inc., San Diego, CA 92123.

 

97

imazethapyr tolerance. The F 1 generation was assayed with a diaphorase isozyme
to ensure they were true crosses (data not presented) using a method modified by
Malburg (10). Approximately 440 F2 seeds and 20 F1 seeds were planted on June
22, 1992 at a 20 cm spacing within rows and 51 cm spacing between rows.
Where emergence was poor and to fill the ends of rows, the parental line Sierra
was hand planted 1 week later to ensure uniform interplant competition. Parental
lines were included as controls on each side of the F2 population. Imazethapyr
was applied at 106 g ha" with % % (v/v) NIS as previously described when beans
were at the second trifoliolate stage. Visual injury to each pinto bean was assessed
14 DAT. Injury was measured on a scale ranging from 0 (no visible injury) to
100 (total plant necrosis). Broad sense heritability of imazethapyr tolerance was

calculated using the following formula:

 

Ozrz'vlaznl (02131) (02192)

02:2

H-

 

where 02“, 021:2, 021:1, and 02F2 are variances of parent 1, parent 2, F1, and F2
generations, respectively (4). Additionally, the number of factors (genes)
controlling the inheritance of imazethapyr tolerance was calculated using the

equation:

A2
8 (029-02,.1)

 

98

where N and A are the number of factors and the difference between the parental

strains, respectively (14, 25). The symbols 0%, and 021.2 are as described above.

Results and Discussion

_F_iel_d___Resear_c_h. All pinto bean varieties except Sierra exhibited injury from 53
g ha" of imazethapyr 7 DAT in 1991 (Table 2). All varieties were injured from
106 g ha" of imazethapyr, and Olathe was injured more than other varieties. By
14 DAT, injury to any variety was no longer evident from 53 g ha" of
imazethapyr. Injury persisted at 106 g ha" of imazethapyr on Olathe, UIl 14,
P89405, and P90570. Chlorophyll a levels decreased in [H1 14 and Aztec from
106 g ha" of imazethapyr. Maturity of all varieties was delayed except for Sierra
and U1114 treated with 53 g ha" of imazethapyr. Olathe maturity was delayed
more than all varieties except Aztec from 106 g ha" of imazethapyr. However,
pinto bean seed yields were not reduced by any imazethapyr application.

In 1992, imazethapyr injured all pinto bean varieties at 7 and 14 DAT (Table
3). Olathe displayed more injury than either Sierra or Aztec 7 DAT. By 14
DAT, Olathe stilled showed more injury from 53 g ha" of imazethapyr, and more
injury than all varieties except Aztec from 106 g ha" of imazethapyr. Chlorophyll

a levels were reduced in Olathe and Aztec from 106 g ha" of imazethapyr.

99

Physiological maturity of all varieties was delayed from both rates of imazethapyr.
Olathe and Aztec were delayed more than P89405 and Sierra. P90570 seed yields
were reduced by 53 and 106 g ha" of imazethapyr while U11 l4 and Aztec seed
yields were reduced from 106 g ha" of imazethapyr.

Imazethapyr injured all pinto beans 7 DAT in 1991 and 1992 except in 1991
when applied to Sierra at 53 g ha". However, Olathe was injured more than other
varieties in 1991 and 1992, and chlorophyll a levels were reduced in 1991. Olathe
maturity was delayed more than the maturity of Sierra in both years, although seed
yields of Olathe and Sierra were not reduced. Sierra appears to be more tolerant
than Olathe to postemergence imazethapyr and these two varieties were therefore
used in subsequent research determining the basis of differential response to

imazethapyr.

ALS ewe assay. ALS enzyme was assayed from leaves of Olathe and Sierra
pinto bean (Figure 1). Activity was measured in the presence Of imazethapyr at
concentrations ranging from 1 to 1000 EM. ALS activity for the untreated
controls averaged 414 and 339 nM acetoin h" mg" for Sierra and Olathe,
respectively. AN OVA,,,=O.05 revealed no differences in ALS activity between the
two varieties for any imazethapyr concentration. Therefore, differential sensitivity
of the ALS enzyme to imazethapyr is not the mechanism of differential varietal

response.

100

To determine the I50 values, the data were combined over varieties and
subjected to linear regression (Y = 84.1 - 13*ln(X) R2 = 0.98). The herbicide
concentration required to inhibit enzyme activity by 50% for pinto bean was 16

uM. This Is() value correspond closely with the 150 values reported for lima bean,

18.4, and other plant species (20).

l"C-Imazetha abso tion translocation and metabolism. At 6, 24, 48, and
72 h after treatment, Olathe absorbed more l“C-irnazethapyr than Sierra (Figure

2). By 24 h after treatment, Olathe absorbed 74% of the applied l“C—imazethapyr
while Sierra absorbed only 48 %. The asymptotic value for l“C-imazethapyr
absorption on Olathe and Sierra was 76% and 53 % of the applied, respectively.
At 24 h or greater, Olathe absorbed 1.4 times more l“C-imazethapyr than Sierra.

At 24, 48, and 72 h after treatment, Olathe translocated more 14C from the
treated leaflet than Sierra (Figure 3). The asymptotic value for 1“C translocation
from the treated leaflet of Olathe and Sierra was 41% and 30%, respectively.
This indicates 1.3 times more 1“C translocation by Olathe than by Sierra.

At 24, 48, and 72 h after treatment, Sierra retained more “C in the treated
leaflet than Olathe (Table 4), indicating Olathe translocated more 1"C from the
treated leaflet than Sierra. At all times measured, Olathe had accumulated more
1“C above the treated leaflet than Sierra. By 72 h, Olathe had accumulated more

than twice as much l4C above the treated leaflet as Sierra. Recovery of applied

101
1“C averaged greater than 95 %.

N o differences in l“C-imazethapyr metabolism were detected (Table 5). The
14C which migrated to an Rf value of 0.75 co-chromatographed with the 1“C-
imazethapyr standards, and was identified as parent imazethapyr. Technical grade
5-hydroxyethyl-imazethapyr was obtained22 and was chromatographed using the
same solvent system as described above and had an Rf value of 0.57 . Since the
least polar metabolite also chromatographed at 0.57, this metabolite was identified
as 5-hydroxyethyl-imazethapyr. TLC plates with metabolite migrating to an Rf
value of 0.22 were scraped and incubated with B—glucosidase23 at pH 5. The
sample was then spotted on a TLC plate and developed as described above. The
resulting Rf value was 0.57, indicating that the metabolite at an Rf value of 0.22
is the glucose conjugate of 5-hydroxyethyl-imazethapyr.

To determine the half-life of l“C-imazethapyr within the plant, the data were
combined over varieties and subjected to curvilinear regression (Y = 100 -
(13.3*X)/(1 + 0.133*X) R2 = 0.85). The calculated half-life for 1“C-
imazethapyr in pinto bean was determined to be 7 .5 h.

Soybean and dry edible bean first convert imazethapyr to 5-hydroxyethyl-

 

22American Cyanamid CO., Princeton, NJ 08543-0400.

23Sigma B-glucosidase from almonds. Sigma Chemical CO., St. Louis, MO
63178.

102

imazethapyr followed by glucose conjugation“. The conversion to the glucose
conjugate is faster in soybean” than in pinto bean as shown in the previously
described studies. The 5-hydroxyethyl-imazethapyr molecule maintains herbicidal
activity, however, it is five times less active than imazethapyr". Because 5-
hydroxyethyl-imazethapyr persists longer in dry bean than in soybean, its

herbicidal activity may render dry bean less tolerant to imazethapyr than soybean.

Inheritance of imazetham tolerance in pinto bean. The percent injury, sample

size, and predicted variances of the parent, F1, and F2 populations are listed in
Table 6. Broad sense heritability was calculated to be 0.85, indicating that
imazethapyr tolerance in pinto bean is a highly heritable trait, and selection for
tolerance is possible. F2 data indicates that dominance effects may be skewing
distribution towards the susceptible parent. Dominance effects are genetic but not
necessarily fixable in the pure breeding variety whereas additive effects are
fixable. It is often useful to estimate the number of factors (genes) controlling the
inheritance Of a factor. Using an equation proposed by Wright (1934) and

modified by Poehlman (1987), the minimum number of factors controlling the

 

24AC-263-499 Technical Information Report. 1985. American Cyanamid Co. ,
Princeton, NJ 08540.

25Personal communication. Dale Shaner, American Cyanamid Co. , Princeton,
NJ 08540.

103

inheritance of imazethapyr tolerance in pinto bean is greater than 1. However, this
method of estimating the number of genes is based on the assumptions that the
genes have equal effect, without dominance or epistasis, and that no linkage exists.
If these assumptions do not hold true, the number of factors would be higher than
estimated.

The inheritance of imazethapyr tolerance in pinto beans appears to be a highly
heritable trait controlled by more than a single gene. However, ratings are
somewhat arbitrary making individual plant rating difficult and imprecise. Since
this trait is not inherited qualitatively (controlled by one major gene), it would be
impractible for dry bean breeders to select for this trait in early segregating
generations. Additionally, imazethapyr tolerance was difficult to evaluate on a
single plant basis (personal observation) making this trait even more difficult to
select in an F2 generation. Data would suggest that selection for tolerance be
delayed to a later generation when tolerance can be better accessed using replicated
plots. The intermediate reaction of F1 generation to imazethapyr would suggest
the additive nature of the inheritance and support selection for tolerance in later
generations when such traits are fixed.

Imazethapyr can cause early season visual injury as well as a delay in pinto
bean maturity. Pinto bean varieties vary in response to postemergence
imazethapyr, with Sierra being more tolerant than Olathe. Differential ALS

enzyme sensitivity did not account for this tolerance difference nor did

104

imazethapyr metabolism differ between varieties. However, Olathe absorbed and
translocated more l“C-imazethapyr than Sierra, possibly accounting for the reduced
tolerance exhibited by Olathe pinto bean. Imazethapyr tolerance in pinto bean
appears to be a relatively highly heritable trait but under quantitative control which

would suggest that individual plant selection would not be feasible.

105

LITERATURE CITED

Anderson, P. C. and M. Georgson. 1986. Selection of an imidazolinone
tolerant mutant corn. Page 437 in D. A. Somers, B. G. Gengenback, D.
D. Biesboer, W. P. Hackett, and C. E. Green, eds. VI International
Congress of Plant Tissue and Cell Culture Abstracts, Univ. Minnesota,

Minneapolis.

Anderson, P. C. and K. A. Hibberd. 1985. Evidence for the interaction of
an imidazolinone herbicide with leucine, valine, and isoleucine metabolism.
Weed Sci. 33:479-483.

Cole, T. A., G. R. Wehtje, J. W. Wilcut, and T. V. Hicks. 1989. Behavior
of imazethapyr in soybeans (Glycine max), peanuts (Arachis hypogaea), and
selected weeds. Weed Sci. 37:639-644.

Fehr, W. R. 1987. Principles of cultivar development, Vol 1, theory and
technique. pp 95-105 McGraw-Hill, Inc. , New York.

Hart, R., E. Lignowski, and F. Taylor. 1991. Imazethapyr herbicide. pp.
247-259 in D. L. Shaner and S. L. Conner, ed. The Imidazolinone
Herbicides. CRC Press, Inc. Boca Raton, Florida.

Hart, S. E., J. W. Saunders, and D. Penner. 1993. Semi-dominant nature
of monogenic sulfonylurea herbicide resistance in sugarbeet (Beta vulgaris).
Weed Sci. (in press)

Inskeep, W. P. and P. R. Bloom 1985. Extinction coefficients of chlorophyll
a and b in N,N-dimethylformamide and 80% acetone. Plant Physiol.
77:483-485.

LaRossa, R. A. and J. V. Schloss. 1984. The sulfonylurea herbicide
sulfometuron methyl is an extremely potent and selective inhibitor of

acetolactate synthase in Salmonella typhimuriom. J. Biol. Chem. 259:8753-
8757.

10.

11.

14.

15.

106

Lowry, O. H., N. S. Rosebrough, A. L. Farr, and R. S. Randall. 1951.
Protein measurement with the folin phenol reagent. J. Biol. Chem.
193:265-275.

Malburg, M. E. 1992. Genetic relationships between plant architecture, seed
size and allozymes in common bean (Phaseolus vulgaris L.). Mich. St.
Univ., MS Thesis. pp 49-52.

Mallory-Smith, C. A., D. C. Thill, M. J. Dial, and R. S. Zemetra. 1990.
Inheritance of sulfonylurea herbicide resistance in Lactuca spp. Weed
Technol. 4:787-790.

. Muhitch, M. J ., D. L. Shaner, and M. A. Stidham. 1987. Imidazolinones

and acetohydroxyacid synthase from higher plants. Plant Physiol. 83:451-
456.

. Newhouse, K. E., T. Wang, and P. C. Anderson. 1991. Imidazolinone

resistant crops. pp. 139-150 in D. L. Shaner and S. L. Conner, ed. The
Imidazolinone Herbicides. CRC Press, Inc. Boca Raton, Florida.

Poehlman, J. M. 1987. Quantitative inheritance in plant breeding. pp. 70-
81 in Breeding Field Crops. 3rd ed. AVI Publishing Co. Inc., Westport,
Conn.

Ray, T. B. 1984. Site of action of chlorsulfuron. Plant Physiol. 75:827-
831.

. Renner, K. A. and G. E. Powell. 1988. Dry edible bean tolerance to

postemergence herbicides. NCWCC Proc. 43:36.

. Sebastian, S. A., G. M. Fader, J. F. Ulrich, D. R. Fomey, and R. S.

Chaleff. 1989. Semidominant soybean mutation for resistance to
sulfonylurea herbicides. Crop Sci. 29:1403-1408.

. Shaner, D. L., P. C. Anderson, and M. A. Stidham. 1984. Imidazolinones -

potent inhibitors of acetohydroxyacid synthase. Plant Physiol. 76:545-546.

. Steel, R. G. D. and J. H. Torrie. 1980. Principles and procedures of

statistics: A biometrical approach. 2“‘l ed. p. 341.

20.

21.

22.

23.

24.

25.

26.

107

Stidham, M. A. and B. K. Singh. 1991. Imidazolinone-acetohydroxyacid
synthase interactions. pp 71-90 in D. L. Shaner and S. L. Conner, ed. The
Imidazolinone Herbicides. CRC Press, Inc. Boca Raton, Florida.

Vencill, W. K., H. P. Wilson, T. E. Hines, and K. K. Hatzios. 1990.
Common lambsquarters (Chenopodium album) and rotational crop response
to imazethapyr in pea (Pisum sativum) and snap bean (Phaseolus vulgaris).
Weed Technol. 4239-43.

Westerfield, W. W. 1945. A colorimetric determination of blood acetoin.
J. Biol. Chem. 161:495—502.

Wilson, R. G. and S. D. Miller. 1991. Dry edible bean (Phaseolus vulgaris)
response to imazethapyr. Weed Technol. 5:22-26.

Wilson, R. G. 1989. New herbicides for weed control in established alfalfa
(Medicago sativa). Weed Technol 32523-526.

Wright, S. 1934. The results of crosses between inbred strains of guinea
pigs, differing in number of digits. Genetics 19:537—551.

WSSA Herbicide Handbook Committee. 1989. Herbicide Handbook. 6‘h ed.
Champaign, IL.

 

108

 

Table 1. Soil characteristics of field studies conducted in 1991 and 1992.

 

 

 

 

 

 

Year
Study 1991 1992
Pinto Bean sandy clay loam clay
Herbicide Tolerance 2.9% OM pH 7.1 2.4% OM pH 6.5

51% sand 19% silt 30% clay 23% sand 16% silt 60%
Parkhill sandy clay loam (Mollie clay

Haplaquept, fine-loamy, mixed, Misteguay clay (Aerie
mesic) Haplequept, fine-loamy,
mixed, mesic)

 

 

 

 

109

Table 2. Pinto bean varietal tolerance differences to postemergence imazethapyr
applications in 1991.

Imazethapyr Injury 7 Injury Chlorophyll Maturity

 

 

Variety rate DAT 14 DAT a delay Yield
-g ha"- % - % of control- -days- kg ha"
Olathe 0 0 0 100 O 3680
Sierra 0 0 0 100 0 3830
UN 14 0 0 0 100 0 3200
P89405 0 0 0 100 0 3150
Aztec 0 0 0 100 0 3170
P90570 0 0 0 100 0 2600
Olathe 53 13 3 90 4 3300
Sierra 53 3 0 102 0 3450
[H1 14 53 5 3 88 2 3220
P89405 53 8 3 102 4 2970
Aztec 53 5 3 88 3 3260
P90570 53 5 3 103 3 2390
Olathe 106 23 5 91 7 3550
Sierra 106 10 3 103 4 3420
U11 14 106 8 5 83 4 3040
P89405 106 10 5 93 4 3280
Aztec 106 10 3 80 6 3170
P90570 106 8 5 95 3 3060

LSD,,_,,_,,5 3 3 17 2 NS

 

110

Table 3. Pinto bean varietal tolerance differences to postemergence imazethapyr
applications in 1992.

Imazethapyr Injury Injury Chlorophyll Maturity

 

 

Variety rate 7 DAT l4 DAT a delay Yield'

-g ha"- % -% of control- -days- ---kg ha"--
Olathe 0 0 0 100 0 2570 a
Sierra 0 0 0 100 0 3120 a
U1114 0 0 0 100 0 2420 a
P89405 0 0 0 100 0 2770 a
Aztec 0 0 0 100 0 2640 a
P90570 0 0 0 100 0 2180 a
Olathe 53 18 18 85 14 2330 a
Sierra 53 10 10 88 8 2900 a
UIll4 53 13 13 101 12 1880 abc
P89405 53 13 13 90 7 2280 ab
Aztec 53 10 13 96 15 2110 abc
P90570 53 13 13 107 9 1480 bcd
Olathe 106 28 33 77 18 2090 abc
Sierra 106 20 23 79 14 2940 a
Ulll4 106 23 25 90 15 1450 cd
P89405 106 25 25 97 11 2300 ab
Aztec 106 20 28 67 19 1690 bed
P90570 106 23 25 97 15 1200 d
LSDa-o.os 5 5 22 3

 

 

aMeans followed by the same letter are not significantly different when
compared using Fisher’s protected LSDMW.

111

Table 4. Partitioning of 1“C applied as l“C-imazethapyr in Olathe and Sierra pinto bean.

 

 

 

 

Time Above the Below the

after Treated treated Lateral treated

trt Variety leaflet leaflet leaflets leaflet Roots Recovery

% of recovered % of
applied

6 h Olathe 92 2 2 2 2 89
Sierra 95 1 1 1 2 94

24 h Olathe 83 5 3 5 4 95
Sierra 89 3 2 3 4 94

48 h Olathe 80 7 4 6 4 100
Sierra 86 5 3 3 4 98

72 h Olathe 80 7 3 6 5 98
Sierra 86 4 3 3 3 95

LSD ”om 5 1 N 8 NS NS

within time

across variety

LSD a- 0.05 7 3 3 3 3

within variety

across time

 

 

112

Table 5. Metabolism of l“C-imazethapyr in Olathe and Sierra pinto bean.

 

 

 

 

Time after Rf values Total
treatment Variety 0.75 0.57 0.22 accounted
% of extractable "C-—---- --%--

6 h Olathe 69 28 1 98
Sierra 68 30 1 99

24 h Olathe 15 72 12 99
Sierra 14 75 l 1 100

48 h Olathe 6 68 23 97
Sierra 6 71 22 99

72 h Olathe 5 62 31 98
Sierra 3 65 31 99

LSDa_o_05 NS NS NS

within time across

variety

LSD a-0.05 8 6 6

within variety across
time

 

113

Table 6. The injury, sample size, and variance of parent, FI, and F2 populations.

 

 

 

 

Population Injury 14 DAT n 02
%

Olathe 15 20 0.34

Sierra 10 20 0.2 1

Fl 13 18 0_42

1:, 14 422 2.05

 

114

Figure 1. Olathe and Sierra pinto bean ALS enzyme activity in the presence of
imazethapyr.

 

 

100

.“A.
I
1

I--|
h—fi

5

1000

* Olathe
1‘ Sierra

A
l
100

10
Imazethapyr Conc. (uM)

 

l
O O O O O

(mum to %) AIIAIIoe ew/lzue 31v

116

Figure 2. l4C-Imazethapyr absorption in Olathe and Sierra pinto bean varieties.
Regression equation for 14C-irnazethapyr when applied to Olathe was Y =
(51*X)/(1+(51/76)*X) (R2=0.9l) and when tank-mixed with bentazon is Y =
(36*X)/(1+(36/53)*X) (R2=0.91). LSD,,=0.05 bars are centered over data points.

117

 

* Olathe ‘0' Sierra

1

l l l l l I

 

 

 

(pendde IO %) uondiosqv

20 30 4o 50 60 70
Time (h)

10

 

 

118

Figure 3. l4C-Imazethapyr translocation from the treated leaflet in Olathe and
Sierra pinto bean varieties. Regression equation for 14C-irnazethapyr when applied
alone is Y = (10*X)/(1+(10/41)*X) (R2=0.93) and when tank-mixed with
bentazon is Y = (15*X/(1+(15/30)*X) (R2=0.96). LSD,,=0_05 bars are centered
over data points.

119

 

 

 

 

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