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THESfii

This is to certify that the
thesis entitled
FACTORS INFLUENCING SUGAR BEET RESPONSE
TO NICOSULFURON AND PRIMISULFURON

presented by

KAREN M. NOVOSEL

has been accepted towards fulfillment
of the requirements for

M.S. WEED SCIENCE

degree in

 

 

Major professor

Date March 1, 1994

 

0.7539 MSU is an Affirmative Action/Equal Opportunity Institution

 

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TO A ID FINES rotum on or bdoro duo duo.

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU Is An Nflrmotlvo Action/Equal Opportunity Instituion
fl 7 W

FACTORS INFLUENCING SUGAR BEET RESPONSE
TO NICOSULFURON AND PRIMISULFURON

BY

Karen M. Novosel

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

MASTER OF SCIENCE

Department of Crop and Soil Sciences

1994

ABSTRACT
FACTORS INFLUENCING SUGAR BEET RESPONSE TO
NICOSULFURON AND PRIMISULFURON
BY

Karen M. Novosel

Nicosulfuron and primisulfuron are two sulfonylurea
herbicides that may persist in the soil and injure sugarbeet.
Sugarbeet response was measured one and two years after
herbicide application at five sites. Nicosulfuron did not
injure sugarbeet at any site. Sugarbeet yield was reduced one
year following application of primisulfuron. IGso values for
primisulfuron were consistently lower than those of
nicosulfuron. Sugarbeet response was highly correlated to %
organic matter (R2: .88). Kd values for nicosulfuron were lower
than those of primisulfuron. In hydroponics, primisulfuron had
an IGso value of 1.9 ppb while nicosulfuron had an IGso value
of 8.9 ppb, regardless of solution.pH. Uptake of primisulfuron
was three times that of nicosulfuron. Nicosulfuron
translocation was more rapid, but there was no difference in
the total amount of herbicide translocated. Increased
susceptibility' of sugarbeet. to jprimisulfuron. was due to

increased sensitivity.

ACKNOWLEDGEMENTS

I would like to give my deepest thanks to Dr. Karen
Renner who has helped me, advised me and been my friend since
my arrival at Michigan State University. My sincerest thanks
are also extended to Dr. Jim Kells without whose guidance I
would have been lost on many occasions. I would also like to
thank Dr. Sharon Anderson.and.Dr. Matt Zabik for serving on my
committee and helping me overcome the various obstacles I have
run into over the past two years. Thank you all for bringing
to light the many different facets of my project. A special
thanks to Gary "now that’s a laugh!" Powell for bearing with
me through the process of learning about field work and all
that is involved in agriculture. I would also like to thank my
fellow grad students for all of their help : Troy "don’t hit
me with that truck again" Bauer, Aaron "the Baron" Hager,
Steve "the Hart man" Hart, Boyd "the Lure" Carey, Rick
"Schmenckanator" Schmenk, Bob Starke, and. Julie Lich. .A
special thanks to Kathy "we’ll only have one beer thank you"
Remus for the development of her soil isotherniprogram.and for
being my buddy. Pat Svec deserves special recognition for all
the lab work he did for me. Thank you as well to Sharon Grant,
Melody Davies, and all the others patience and help. Mark, I

love you and thanks aren’t enough!

TABLE OF CONTENTS

Chapter 1. Literature Review

Introduction ........................................ l
Sulfonylurea History and General Structure .......... l
Sorption ............................................ 2
Degradation ......................................... 5
Hydrolysis .......................................... 5
Persistence ......................................... 6
Movement and Metabolism ............................. 8
ALS Sensitivity, Uptake/Translocation, Metabolism ...9
Hydroponics ........................................ 12
Summary ............................................ 12
Literature Cited ................................... 14

Chapter 2. Sugar Beet Response to Nicosulfuron and

Primisulfuron
Abstract ........................................... 26
Introduction ....................................... 27
Materials and Methods .............................. 29
Field Studies ................................. 29
Growth Reduction Study ......................... 31
Sorption and Desorption Study ................. 32
Results and Discussion ............................. 34
Field Results ................................. 34
Greenhouse Results ............................ 35
Soil Sorption Results ......................... 37
Literature Cited ................................... 40

Chapter 3. Hydroponic Sugar Beet Response to Nicosulfuron
and Primisulfuron

Abstract ........................................... 50
Introduction ....................................... 51
Materials and methods .............................. 52
Hydroponic IGSO study .......................... 52
Uptake and Translocation study ................. 53
Results and Discussion ............................. S4
Hydroponic Results ............................. S4
Uptake and Translocation Results ........... -...55
Literature Cited ................................... 57

iv

LIST OF TABLES

Chapterz. Sugar Beet Response to Nicosulfuron and
Primisulfuron

Table 1. Characteristics of soils in field and greenhouse

Table
Table

Table
Table

Table

2.

3.

4.
5.

6.

Chapter 3.

studies ..................................... 42
Initial concentrations of :nicosulfuron. and
primisulfuron for sorption isotherms ........ 43
Sugar beet response to nicosulfuron and
primisulfuron at two Saginaw sites ....... 44
Campus site results ......................... 45
Correlation coefficients and Kd values for
nicosulfuron and primisulfuron ........... 46
Correlation coefficients for nicosulfuron and
primisulfuron on six soil types ........... 47

Hydroponic Sugar Beet Response to Nicosulfuron
and Primisulfuron

Table 1. Hydroponic sugar beet response

to nicosulfuron and
primisulfuron ............................... 58

Table 2. Sugar beet response at various pH values....59

LIST OF FIGURES

Chapter 1. Literature Review

Figure 1. General hydrolysis reactions of the

sulfonylurea class of herbicides ........... 21
Figure 2. Chlorimuron ethyl detoxification
reactions in soybeans ........................ 23
Figure 3. Metabolic deactivation pathways of
thifensulfuron methyl ..................... 25

Chapter 2. Sugar Beet Response to Nicosulfuron and
Primisulfuron

Figure 1. Correlation of sugar beet response to
primisulfuron as influenced by soil pH. . . .49

Chapter 3. Hydroponic Sugar Beet Response to Nicosulfuron
and Primisulfuron

Figure 1. Hyperbolic regression curves of hydroponic

sugar beet response .......................... 61
Figure 2. Translocation patterns of C“-labeled
nicosulfuron and primisulfuron ............ 63

vi

Chapter 1

LITERATURE REVIEW

Sulfonylureas are a herbicide family applied for
preemergence and postemergence weed control in many
agricultural systems. This group of chemicals is characterized
by low use rates and low mammalian toxicity (4,12,16). Typical
visual injury symptoms include interveinal chlorosis or
purpling of grasses, and similar discoloration as well as
stunting of broadleaf species. Soil factors influencing
sulfonylurea degradation, persistence and.bioavailability are
important because of the impact these compounds have on the
environment and sensitive rotational crops such as sugar
beets. The following review examines the history of this class
of herbicides, their soil interactions, the effect of
sulfonylurea soil residues on sensitive rotation crops, and
uptake, translocation, metabolism, and ALS sensitivity of

sulfonylureas.

History'and.Genera1 Structure. The discovery of the herbicidal
properties of the sulfonylureas occurred in 1966 in Germany.
The first compounds were derivatives of another class of
herbicides, the triazines (4) . The DuPont corporation patented
the earliest sulfonylurea herbicide in 1977 (5,11), and.it was
five years before any other company patented a pesticide in

this class. Chlorsulfuron, marketed under the trade name

Glean, was the first commercially available sulfonylurea, and
is still sold for weed control in a variety of cereal crops.
Since the discovery of this herbicide class, over fourteen
different companies have obtained sulfonylurea patents,
spanning hundreds of compounds.

Despite the wide variety' of sulfonylureas, a. basic
structure is common to the family. This common framework
consists of: an aryl portion, the sulfonylurea bridge, and a
nitrogen containing heterocycle (5,35). Breakdown in the soil
by chemical means usually occurs through hydrolysis of the
bridge portion of the molecule (12,33,47). Microbial
degradation pathways include bridge cleavage, methyl group
hydroxylation, demethylation followed by hydroxylation, and
deesterification resulting in free acid formation (5).
Metabolism in plants occurs predominantly by aryl
hydroxylation followed by glucose conjugation (12,29,35).

The literature on sulfonylurea herbicides is extensive.
This review will focus on the sorption, degradation, and
persistence of sulfonylureas in soil, the response of
rotational crops to sulfonylureas, and uptake, translocation

and metabolism of sulfonylureas in plants.

Sorption. The pH dependent ionization of the sulfonylurea
herbicides directly affects the sorptive properties of these
compounds. Chlorsulfuron has been the most thoroughly studied

member of this family because it was the first registered

compound in its class. Acidic conditions in the soil reduce
the water solubility of Chlorsulfuron and could reduce the
mobility of the compound in the soil (41).

In a study performed by Wehtje et al.(65), the pH
influence on sorption of sulfmeturon was demonstrated.
Sorption of the anionic species of sulfmeturon was dependent
on the iron and aluminum oxide content in weathered soils,
such as those found in the American southeast. The surface
charge of these soil minerals is pH dependent and is neutral
in a pH range of 6.0 to 8.5. Below 6.0, the charge is positive
due to a proton accumulation at the soil colloid surface.
Above the PZNC (Point of Zero Net Charge), OH- buildup imparts
a negative charge to the particles. In this study, as in
others, as the soil pH increased and the herbicide became more
negatively charged, the herbicide sorption decreased. This
resulted in an increase in availability and an increase in
plant uptake (2,3,42). Increased uptake could lead to
increased herbicide efficacy but also increases the potential
for injury to sensitive crops.

One of the most important factors in the sorption of any
herbicide is the organic matter content of the soil. The exact
mechanisms involved in sorption can only be postulated because
of the heterogeneous, amorphous nature of both the humic and
non-humic portions of the organic matter polymer (58). The
ability of organic matter to interact with organic compounds,

such as herbicides, stems from the oxygen containing

functional groups found in the humic components (58). Typical
bonding mechanisms for the adsorption of the sulfonylureas to
organic matter are: Van der Waals forces, hydrogen bonding,
and ligand exchange (58). The ionization of the functional
groups on the organic matter moiety depends on the pH of the
soil water with an acidic pH protonating many of the
functional groups resulting in a predominantly neutral
molecule. Past findings have indicated that herbicide sorption
may result.frtm1partitioning of the herbicide into hydrophobic
micelles (58). However, these claims have never been
confirmed, and evidence (41,42,61) suggests that there are
sorption sites where the herbicides bind. Until the structure
of organic matter and its various components is discerned the
pathways are conjectural.

Another experiment examining sulfonylurea sorption to
various soil components was performed by Borggaard and
Streibig in Denmark (10). They investigated Chlorsulfuron
sorption to humic acid, a variety of iron oxides, and a
montmorillonite clay by simulating field conditions at a pH
range of 4.0 to 8.0. The results were analogous to Stevenson’s
(58), i.e., that iron oxides adsorbed Chlorsulfuron over the
pH range of 4.0 to 8.0 and montmorillonite did not adsorb
Chlorsulfuron at any pH. Humic acid adsorbed Chlorsulfuron
below pH 8.0 and goethite (an iron oxide) adsorbed below pH
6.0 (10). Stevenson postulated that montmorillonite did not

sorb or affect herbicide mobility because the herbicide could

not enter the inner sites of the clay matrix causing a sieving
effect (58).

Degradation
Hydrolysis. Sulfonylureas are weakly acidic compounds having
a pKa range of 3.3 to 5.4. The pKa values of nicosulfuron and
primisulfuron are 4.3 and 4.5, respectively. These compounds
also have an alkaline pKa value which exceeds pH 10. Bulk soil
pH has a major effect on water solubility, K0... and the
chemical reactions these compounds undergo in the soil
(5,6,12). The most common reaction occurring in soil is a
hydrolysis reaction with the general form outlined in Figure
1. This reaction takes place at an increased rate as the soil
pH decreases because more of the herbicide is in the neutral
form. Under extremely alkaline conditions such as pH > 10, a
second ionization of the herbicides occur which also results
in increased hydrolysis (5,12,29). Controlling the process of
hydrolysis is the ionization of the sulfonylurea bridge. The
neutral molecule is lipophilic and is therefore 250 - 1000
times more likely to hydrolyze (12). Microbial degradation
occurs simultaneously through various mechanisms (4,31,39),
but the primary degradation pathway in soil is chemical.

Research performed by Bergstrom in Sweden (2,3) suggested
that though Chlorsulfuron and metsulfuron-methyl are mobile in
the soil, the rate of degradation limits movement of the
herbicides. Neither herbicides moved below the top 10 cm of

soil when applied at twice the normal use rate. Seven months

after application, less than 1% of either chemical applied at
twice the standard rate could be detected (2,3).

Soil moisture content and temperature also influenced the
rate of degradation in the soil (12,30). Fuesler and Hanafey
(30) concluded that degradation increased on air dry soil as
a function of temperature due to an increase in chemical
hydrolysis. The breakdown pathway of Chlorimuron they proposed
is shown in Figure 1. The degradation products suggested that
both microbial and chemical breakdown occurred in moist soils,
while only hydrolytic degradation occurred in air dry soil. A
reduction in the hydrolysis rate resulted from an increase in
soil pH, which. decreased. overall degradation (66), and,

therefore, increased soil persistence.

Persistence. Sulfonylurea persist in the soil long enough to
injure sensitive rotational crops such as sugar beets (52).
Tolerance to residual amounts of a herbicide is dependent on
the species of plant, the particular herbicide, and the amount
of chemical the plant intercepts. Problems that can occur as
a result from a long soil residual include rotation crop
injury and decreased crop yield. Rotation restrictions are
sometimes inadequate and labels are modified if persistence
problems arise.

Chlorsulfuron and metsulfuron-methyl were sold as a
formulated mixture in the United Kingdom but was removed from

the market because of the long soil persistence of

Chlorsulfuron. In response to this problem, a computer model
was developed.to predict sulfonylurea movement and.persistence
in the soil. Timing of application, spring vs. autumn, greatly
affected the accuracy of the model (6), as did the prediction
of herbicide fate under wet soil conditions. The program
tended to overestimate movement through the soil profile and,
therefore, underestimated the amount of herbicide the root
intercepted (6).

Brewster and Appleby (11) compared various rotation crop
responses to Chlorsulfuron. A reduction in sugar beet foliage
dry weight occurred for 26 months after application. Yields of
Italian.ryegrass, oilseed rape, and alfalfa.were reduced.up to
9 months after application. Snap bean and sweet corn were only
injured for 5 months following application, while wheat
exhibited no deleterious effects in that same time period.
Rahman (50) reported no detectable primisulfuron in a sandy
loam soil at pH 5.7 sampled 120 days after treatment using a
mustard bioassay.

Repeated applications of Chlorsulfuron did not lead to
increased persistence even when applied four times at twice
the normal use rate (66). The experiment was conducted under
dryland conditions, with a soil pH of 6.5 to 8.1. Not only was
there a lack of cumulative effect from repeated applications,
but there was no acceleration.in.breakdown (66). This data led
researchers to conclude that chemical hydrolysis is the

primary degradation pathway in dry soils although there are

primary degradation pathway in dry soils although there are
herbicides whose primary degradation pathway isrnicrobial that
do not exhibit accelerated breakdown in the presence of more
herbicide. The persistence of Chlorsulfuron was attributed to

the high pH more than the lack of rainfall.

Movement and Metabolism. Primisulfuron is absorbed primarily
through plant foliage but also possesses some soil activity
(50). After foliar uptake, the herbicide is translocated in
the phloem to the meristematic regions of the plant. Cessation
of cell division occurs immediately but total plant
desiccation takes approximately 10 to 20 days. Death occurs
due to an interruption in the synthesis of the branch chain
amino acids valine, leucine, and isoleucine (3,4,5).
Sulfonylureas inhibit the acetolactase synthase enzyme
(ALS). This enzyme catalyses the initial reactions in the
synthesis pathways of the branch chain amino acids (5,12,32).
In the formation of valine and leucine, two molecules of
pyruvate are condensed to form alpha-acetolactate + CO2 (55).
In the synthesis of isoleucine, the initial reaction is a:
condensation.reaction between one molecule of pyruvate and one
molecule of 1 alpha- ketobutyrate resulting in alpha-aceto—
alpha-hydroxybutyrate + CO2 (55). The interference of amino
acid synthesis results in a lengthy time period before injury

symptoms appear (15,24).

ALS Sensitivity, Uptake/Translocation and Metabolism. There
are three proposed mechanisms for observed differences in
plant species tolerance to sulfonylurea. These include 1) a
differenceein ALS sensitivity between tolerant and susceptible
species, 2) a difference in plant uptake and /or
translocation, and 3) differential metabolism.

Herbicides such as the aryloxyphenoxypropionates and the
cyclohexadiones show a difference in enzyme sensitivity as the
main factor influencing species response (12). However, ALS
enzyme isolated in tolerant and susceptible species of plants
had a limited range of sensitivity to any given sulfonylurea
(5). This indicated that differential enzyme sensitivity was
not the factor conferring tolerance. Research conducted on ten
corn genotypes expressing variable sensitivity to
thifensulfuron indicated that differences in response were a
result of relative efficiencies in metabolism and not in any
dissimilarity of the enzyme (25). Further evidence to support
this proposal was presented by Moberg (43). He concluded that
all cases of naturally occurring crop selectivity are not due
to ALS sensitivity but rather due to differences in metabolic
detoxification (43).

ALS sensitivity, however, has been reported to be the
cause of differential tolerance in genetically engineered
plants as well as in weed species that developed resistance
(16,34,44). Genetically engineered sugar beets tolerance to

primisulfuron and thifensulfuron was due to.altered ALS enzyme

sensitivity (34). The ALS enzyme isolated from resistant
varieties of chickweed (Stellaria media(L.)) was insensitive
to chlorsulfuron.with respect to the normal biotype (16). Some
cross resistance was noted but this alteration in enzyme
sensitivity did not confer cross resistance to all
sulfonylureas and imidazolinones (16).

Small variations in uptake, expressed as a percent of
control, could not account for differences in barnyardgrass
(Echinochloa crus-galli) response to primisulfuron (14, 28, 60) .
The tolerant variety translocated more herbicide than the
sensitive biotype. This excluded the possibility that reduced
uptake and/or translocation was the mechanism of tolerance.

Sweester, Schow, and Hutchinson were the first to report
the mechanism of differential tolerance as metabolic
deactivation (60). Specifically, they characterized the
metabolites of Chlorsulfuron through the use of mass
spectroscopy, nuclear magnetic resonance spectroscopy, and
high performance liquid chromatography and found a dramatic
increase in the formation rate of the metabolic products in
tolerant grass species (60). No differences were found in the
rate of uptake and translocation but there was a high
correlation with the rate of metabolism and plant tolerance.
The metabolites that were formed were identified as the 5-OH
derivative of Chlorsulfuron and the S-glycoside conjugate of
Chlorsulfuron (60). It was also noted that the conversion of

the hydroxylated moiety to the glucose conjugated entity was

10

a very rapid process.

Hydroxylation followed.bnglucose conjugation is also the
detoxification mechanism of primisulfuron. In barnyardgrass,
the conversion takes place on the pyrimidinyl ring as opposed
to the phenyl ring (44). Tolerance in broadleaf species is
attributed to rapid inactivation by the same mechanisms but
the reactions take place on either the phenyl or the
heterocyclic ring non-preferentially (28) with.a1ninor pathway
being hydrolytic bridge cleavage. Removal of NADPH or 02
caused.a cessation of hydroxylation indicating the presence of
a mixed function oxidase in the early stages of the metabolic
pathway. The actual positions of the hydoxylations have not
yet been determined but it is known that a cytochrome P-450
monooxygenase acts as the catalyst for this reaction (28).

Chlorimuron ethyl detoxification in soybeans (Figure 2)
is due to a displacement of the pyrimidinyl chlorine by
homoglutathione that has been conjugated with a sulfhydryl
group (14). This was proven to be the major metabolite in
broadleaf species with a ndnor metabolite being the
deesterified molecule, Chlorimuron. Increased broadleaf
tolerance was due to increased metabolism (14).

Thifensulfuron methyl has the most metabolic pathways of
all the sulfonylurea characterized to date (Figure 3).
Thifensulfuron methyl is rapidly metabolized in soybean into
a herbicidally inactive deesterified acid, thifensulfuron

(14). There was no correlation between foliar uptake (as a

ll

percent of applied) and species sensitivity which further
discounted the possibility of uptake being the basis of
tolerance. Sulfonylurea uptake and.translocation.depends on an
acid trapping mechanism (14) and research (12,29,60)indicates
that this cannot be solely responsible for differences in

plant response.

Hydroponics. The technique for growing plants in the absence
of soil is known as hydroponics. This type of growth system is
utilized in the commercial production of vegetable crops such
as lettuce, tomatoes, and cucumbers. Hydroponics can also be
a useful scientific procedure, providing more uniform plant
growth for use in experimentation. The literature on
hydroponics in the determination of herbicide-plant
interactions is limited (15,20,54), although it is a viable
tool for the investigation of metabolism and the role that
soil factors play in plant response to herbicides.

Atrazine uptake in cats decreased over time due to
atrazines interference with carbohydrate production in the
root (54). This reduced carbohydrate concentration.in the root
caused root necrosis. No information was found on plant
response to sulfonylurea herbicides utilizing hydroponic
experimentation.

Summary. A plethora of papers are available on the
sulfonylurea herbicides, particularly Chlorsulfuron. Soil pH

greatly affects the behavior of these compounds. As the pH

12

increases, the rate of chemical hydrolysis decreases and thus
persistence increases. Adsorption to soil decreases as the
soil pH increases. Organic matter content increases sorption
and persistence due to herbicide binding to various functional
groups. Clay content has little effect on sulfonylurea
sorption. Since all plants contain an ALS pathway, potential
for plant injury existsknnzis species dependent. Tolerance is
a result of differential metabolism of the herbicides with
susceptible species metabolizing the compounds at a much

slower rate.

13

LITERATURE CITED

1. Beckie, H.J., R.B. McKercher. 1990. Mobility' of two
sulfonylurea herbicides in soil. J. Agric. Food Chem. 38 310-
315.

2. Bergstrom, L. 1990. Leaching of Chlorsulfuron and
metsulfuron methyl in three Swedish soils measured in field
lysimeters. J. Environ. Qual. 19:701-706.

3. Bergstrom, L. 1989. Field observation of soil movement and
residues of sulfonylureas in Sweden. Brighton Crop Protection
Conference. Vol. 9 pp. 1127-1132.

4.Beyer, E.M., H.M. Brown, M.J. Duffy. 1987. Sulfonylurea
herbicides in soil. British Crop Protection Conference. Vol.
6 pp. 531-540.

5. Beyer, E.M., M.J. Duffy, J.V. Hay, D.D.Schlueter. 1987.
Sulfonylurea Herbicides. Reprinted from Herbicides: Chemistry,
Degradation, and Mode of Action Vol. 3 pp. 119-189. Marcel
Dekker, Inc.

6. Blair, A.M., T.D. Martin, A. Walker, S.J. Welch. 1989.
Measurement and prediction of Chlorsulfuron persistence in
soil following autumn and spring application. Brighton Crop
Protection Conference. Vol. 9 pp. 1121-1126.

7. Blair, A.M., T.D. Martin. 1988. A review of the activity
fate and mode of action of sulfonylurea herbicides. Pestic.
Sci. 22: 195-219.

8. Blankendaal, M., R.H. Hodgson, D.G. Davis, R.A. Hoerauf,
R.H. Shimabukuro. 1972. Growing' plants without soil for
experimental use. Miscellaneous Publication No. 1251, U.S.
Dept. of Agriculture.

9. Borggaard, O.K., J.C. Streibig. 1989. Chlorsulfuron
adsorption by selected soil samples. Acta. Agric. Scand.
39:351-360.

10. Borggaard, O.K., J.C. Streibig. 1988. Chlorsulfuron
adsorption by humic acid, iron oxides, and montmorillonite.
Weed Sci. 36:530-534.

11. Brewster, B.D., A.P. Appleby. 1983. Response of wheat

(Triticum aestivum) and rotational crops to Chlorsulfuron.
Weed Sci. 31:861-865.

14

12. Brown, H.M. 1990. Mode of action, crop selectivity, and
soil relations of the sulfonylurea herbicides. Pestic. Sci.
29:263-281.

13. Brown, H.M., S.M. Neighbors. 1987. Soybean metabolism of
Chlorimuron ethyl: physiological basis for soybean
selectivity. Pestic. Bio. Phys. 29: 112-120.

14. Brown, H.M., et al. 1990. Basis for soybean tolerance to
thifensulfuron methyl. Pestic. Bio. Phys. 37: 303-313

15. Burt, M.E., F.T. Corbin. 1978. Uptake, translocation, and
metabolisniof prophaniby wheat (Triticuniaestivum), sugar beet
(Beta vulgaris), and alfalfa (Medicago sativa). Weed Sci.
26:296-303

16. CIBA-GEIGY Ltd. 1988. Beacon technical release. Issued
January 1988.

17. Contos, D.A., L.E. Slivon. 1989. Liquid chromatography/
mass spectrometry of pesticides in agricultural matrices:
technology assessment. Brighton Crop Protection Conference.
Vol.3 pp. 273-275.

18. Corbin, F.T. 1986. Radioisotope techniques. Research
Methods in Weed Science 3rd Edition, South. Weed Sci. Society.
Chapter 13.

19. Devine, M.D., M.A.S. Marles, L.M. Hall. 1991. Inhibition
of acetolactate synthase in susceptible and resistant biotypes
of Stellaria media. Pestic. Sci. 31:273-280.

20. Devlin, R.M., I.I. Zbiec, S.J. Karczmarczyk. 1982.
Influence of .napropamide on ‘uptake and translocation. of
mineral nutrients. Weed Sci. 30:503-506

21. Dexter, A.G., J.D. Nalewaja, D. Peterson. 1988. Injury to
sugarbeets and other crops from herbicide carryover. North
Dakota Research Report, 1988 pp. 57-58.

22. Dexter, S.T., M.G. Frakes, F.W. Snyder. 1967. A rapid and
practical method.of determining extractable white sugar as may
be applied to the evaluation.of agronomic practices and grower
deliveries in the sugarbeet industry. Journal of the
Assoc.Soc.Sugar Beet Tech. Vol.14 No.5 pp. 434-454.

23. Duffy, M.J., M.K. Hanafey. 1987. Predicting sulfonylurea
herbicide behavior under field conditions. British Crop
Protection Conference. Vol.6. pp 541-547.

24. DuPont Co. 1988. Accent technical bulletin.

15

25. Eberlein, C.V ,K M. Rosow,J.L. Geldelmann,S.J. Openshaw.
1989. Differential tolerance of corn genotypes to DPX-M6316.
Weed Sci. 37: 651-657.

26. Efthimidiadis, P., E.A. Skorda, T.H. Adamidis. 1989. The
persistence of sulfonylurea herbicides alone or in mixtures
with graminicides. Brighton Crop Protection Conference. Vol.4
pp. 383-388.

27. Fielding, R.J., E.W. Stoller. 1990. Effects of additives
on efficacy, uptake, and translocation of Chlorimuron ethyl
ester. Weed Tech. 4: 264-271.

28. Fonne-Pfister,R., J. Gaudin, K. Kreuz, K. Ramsteiner,E.
Ebert. 1990. Hydroxylation of primisulfuron by an inducible
cytochrome P450-dependent monooxygenase system from maize.
Pestic. Bio. Phys. 37:658-664

29. Fredrickson, D.R., P.J. Shea. 1986. Effect of soil pH on
degradation, movement, and plant uptake of Chlorsulfuron. Weed
Sci. 34:328-332.

30. Fuesler, T.P., M.K. Hanafey. 1990. Effect of moisture on
Chlorimuron degradation in soil. Weed Sci. 38:256-261.

31. Grover, R. 1988. Environmental Chemistry of Herbicides.
Vol.1. CRC Press.

32. Grover, R., A.J. Cessna. 1991. Environmental Chemistry of
Herbicides. Vol.2. CRC Press.

33. Harvey, J.Jr., J.J. Dulka, J.J. Anderson. 1985.
Properties of sulfometuron methyl affecting its environmental
fate: Aqueous hydrolysis and photolysis, mobility, and
adsorption on soils, and bioaccumulation potential. J. Agri.
Food Chem. 33:590-596.

34. Hart, S.E., R.A. Renner, J.W. Saunders, D. Penner. 1992.
Field evaluations of sulfonylurea resistant sugarbeet. Weed
Sci. 41:317-325

35. Hay, J.V. 1990. Chemistry of sulfonylurea herbicides.
Pestic. Sci. 29:247-261.

36. Helling, C.S. 1971. Pesticide mobility in soils 1.
Parameters of thin-layer chromatography. Soil Science Society
of America Proceedings. Vol. 35:732-737.

37. Hutson, J.L., R.J. Wagenet. 1989. Predicting the fate of
herbicides in the soil environment. Brighton Crop Protection
Conference. Vol.9 pp. 1111-1120.

16

38. Iwanzik, W., H. Egli. 1989. Comparison of bioassay and
chemical analysis for triasulfuron quantification in soil
samples. Brighton Crop Protection Conference. Vol.9 pp. 1145-
1150.

39. Joshi, M.M., H.M. Brown, J.A. Romesser. 1985. Degradation
of chlorsulfurtuiby'soil microorganisms. Weed Sci. 33:888-893.

40. Maurer, W., H.R. Gebber, J. Rufener. 1987. A new
postemergence herbicide for the control of Sorghum spp. and
Elymus repens in maize. British Crop Protection Conference
Vol.2 pp. 41-48.

41. Mersie, W., C.L. Foy. 1986. Adsorption, desorption, and
mobility of Chlorsulfuron. J. Agri. Food Chem. 34:89-92.

42. Mersie, W., C.L. Foy. 1985. Phytotoxicity and adsorption
of Chlorsulfuron as affected by soil properties. Weed Sci.
33:564-568.

43. Moberg, W.K. 1990. Herbicide inhibiting branched-chain
amino acid biosynthesis. Pestic. Sci. 29:241-246.

44. Neighbors, S., L.S. Privalle. 1990. Metabolism of
primisulfuron by barnyardgrass. Pestic. Bio. Phys.
37:377-383

45. Nicholls, P.H., A.A. Evans. 1987. The behavior of
Chlorsulfuron and metsulfuron in soils in relation to
incidents of injury to sugarbeets. British Crop Protection
Conference. Vol 6 pp. 549-556.

46. Nicholls, P.H.,.A.A. Evans. 1985. Adsorption.and movement
in soils of Chlorsulfuron and other weak acids. British Crop
Protection Conference. Vol 3. pp 333-339.

47. Okajima, N., I. Aoki, Y. Okada. 1991. Hydrolytic
activation/ decomposition pathways of herbicidally active
ethyl 5-[N-(5,7-dimthoxy-2H-1,2,4-thiadiazolo[2,3-a]pyrimidin-
2-ylidene)sulfamoyl]-1,3-dimethylpyrazole-4-carboxylate.
Pestic. Sci. 32:265-273.

48. Peter, C.J. 1989. Analytical methods for" detecting
Chlorsulfuron and metsulfuron methyl . Brighton Crop Protection
Conference. Vol.9 pp. 1139-1144.

49. Peterson, M.Au, W.E. Arnold. 1985. Response of rotational
crops to soil residues of Chlorsulfuron. Weed Sci.34:131-136.

17

50. Rahman, A., T.K. James, T.M. Patterson. 1990. Soil
activity and persistence of the sulfonylurea herbicide
primisulfuron. Proceedings of the 43rd New Zealand Weed and
Pest Control Conference. Vol.43. pp. 142-145.

51. Rahman, A. 1989. Sensitive bioassays for determining
residues of sulfonylurea herbicides in soil and their
availability to crOp plants. Hydrobiologia. 188/189: 367-375.

52. Renner, K.A., G.E. Powell. 1991. Response of sugarbeet to
herbicide residues in soil. Weed Tech. 5:622-627.

53. Shea, P.J. 1986. Chlorsulfuron dissociation and
adsorption on selected adsorbents and soil. Weed Sci. 34:474-
478.

54. Shimaburkuro, R.H., A.J. Linck. 1967. Root absorption and
translocation of atrazine in oats. Weed Sci. 15:175-178.

55. Scloss, J.V. 1990. Acetolactate synthase, mechanism of
action.and.its herbicide binding site. Pestic. Sci.29:283-292.

56. Smith, A.E., A.I. Hsiao. 1985. Transformation and
persistence of chlorsulfuron.in prairie field soils. Weed Sci.
33:555-557.

57. Stehhouwer, R.C., W.A” Dick, S.J.‘Trainia. 1992. Sorption
and retention of herbicides in earthworniburrows. Ohio Ag. R&D
Center.

58. Stevenson, F.J. 1972. Organic matter reactions involving
herbicides in soil. J. Envir. Qual. 1:333-343.

59. Streck, H.J. 1989. Use of bioassays to characterize the
risk of injury to follow crops by sulfonylurea herbicides.
Brighton Crop Protection Conference. Vol.3 pp. 245-250.

60. Sweester, P.B., G.S. Schow, J.M. Hutchison. 1982.
Metabolism of chlorsulfuron by plants: Biological basis for
selectivity of a new herbicide for cereals. Pestic. Bio. Phys.
17:18-23.

61. Thirunarayanan, K., R.L. Zimdahl, D.E. Smika. 1985.
Chlorsulfuron adsorption and degradation in soil. Weed Sci.
33:558-563.

62. Wadd, D.J., D.S.H. Drennan. 1989. A field study a: the
persistence and leaching of chlorsulfuron and metsulfuron
methyl. Brighton Crop Protection Conference. Vol.9 pp. 1133-
1138.

18

63. Walker, A., E.G. Cotterelli, S.J. Welch. 1989. Adsorption
and degradation of chlorsulfuron and metsulfuron-methyl in
soils from different depths. Weed Res. 29:281-287.

64. Walker, A., S.J. Welch. 1989. The relative movement and
persistence in soils of chlorsulfuron, metsulfuron-methyl, and
triasulfuron. Weed Res. 29:375-383.

65. Wehtje, G., R. Dickens, J.W. Wilcut, B.F. Hajek. 1987.
Sorption mobility of sulfometuron and imazethapyr in five
Alabama soils. Weed Sci. 35:858-864.

66. Wiese, A.P., M.L. Wood, E.W. Chenault. 1988. Persistence
of sulfonylureas in Pullman clay loam. Weed Sci. 2:251-256.

19

 

Figure l. Generalized hydrolysis reactions of the
sulfonylurea class of herbicides.

20

 

N__/R2

0:0fi NCNH—QQ 3W) +

O’R‘Hoi

\R

pKa= 3.3-5.2

/R2

so NHCNH_<\N N>(N)

\R

3

H

Figure 2. Chlorimuron ethyl detoxification reactions
in soybeans.

22

 

 

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2 O
/Vlz.r :z\m
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.0 o
.100 a a
z :2 cm \
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:00
III—“VI: 120:2 Om
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Figure 3. Metabolic deactivation pathways of
thifensulfuron methyl.

24

 

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Chapter 2

Influence of Soil on Sugar beet Response to
Nicosulfuron and Primisulfuron

ABSTRACT

Nicosulfuron and primisulfuron are two sulfonylurea
herbicides that have been observed to persist in the soil and
injure sensitive rotational crops such as sugar beet (Beta
vulgaris L.). Field and greenhouse studies were conducted to
determine sugar beet response to these two compounds. Studies
were initiated at four field sites to measure sugar beet
response one and two years after nicosulfuron and
primisulfuron.application” Nicosulfuxtmiat 70 and 140 g/ha and
primisulfuron at 40 and 80 g/ha were applied postemergence to
corn (Zea mays L.). At a fifth field site, 35 g/ha of
nicosulfuron was applied to corn and sugar beet response
observed.one and two years after application” Nicosulfuron did
not injure sugar beet at any site one or two years after
application. In contrast, sugar beet yield was reduced one
year after application of 40 and 80 g/ha of primisulfuron at
both of the Saginaw sites. Visual injury was observed two
years after application of 80 g/ha primisulfuron but this was
not reflected in a yield reduction. Greenhouse studies
determined sugar beet IGso (inhibit growth by 50%) values for
nicosulfuron and primisulfuron on four field soils, a muck,
and a sand. IGso values for primisulfuron were three times

26

 

lower than those of nicosulfuron for four soils indicating
greater potential for sugar beet injury from primisulfuron.
Sugar beet response was highly correlated to organic matter
content (R3: .88) and not correlated to soil rfii CpH range:
6.4-7.9) . K,l values for nicosulfuron were lower than Kg1 values
for primisulfuron for four of five soils indicating stronger
affinity of primisulfuron for soil sorptive sites. K; values
for mineral soils were between .299 and .866 indicating a low
sorptivity of both herbicides. Nomenclature: nicosulfuron, 2-
[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyIJamino]
sulfonyl]-N,N-dimethyl-3-pyridinecarboxamine; primisulfuron,
2-[[[[[4,6-bis (difluromethoxy)-2-pyrimidinyl]amino]caronyl]

amino]sulfonyl] benzoic acid.

INTRODUCTION

Nicosulfuron and primisulfuron are two members of the
sulfonylurea herbicide family. These compounds applied
postemergence control perennial grasses such as johnsongrass
(Sorghum halapense L.), quackgrass (Elytrigia repens L.) and
some annual grasses and broadleaf weeds in field corn (zed
may§_L.) (7,9). The sulfonylureas inhibit branched.chain.amino
acid synthesis by interfering with the enzyme acetolactate
synthase, commonly called ALS or acetohydroxyacid synthase
(AHAS)(2,10).

Although these herbicides are degraded rapidly in soil,

27

residual amounts can persist and injure sensitive crops such
as sugar beet. According to herbicide labels, sugar beets can
be safely planted 10 months after nicosulfuron application if
soil pH is less than 6.5 and after 18 months if soil pH
exceeds 6.5 (7). Sugar beets may be planted 18 months after
primisulfuron application regardless of soil pH (9). This may
preclude the inclusion of sugar beet into a rotation the year
following corn, but, more importantly, these herbicide labels
are based on limited field studies. Soil factors, including
soil pH, may play a role in the persistence and
bioavailability of these two herbicides (11,12). As the pH
increases, sorption to soil components decreases (3). The rate
of chemical hydrolysis is therefore decreased and thus
persistence increases (1). An understanding of soil-herbicide
interactions and the role individual soil factors have on
sorption, persistence, and.bioavailability of these compounds
is critical to predicting herbicide carryover and
recommendations in sugar beet production areas.

Experiments were initiated to determine the response of
sugar beet to nicosulfuron and primisulfuron at field sites
and in the greenhouse. Soil sorption and desorption isotherms
were constructed to determine if a difference in the sorptive
properties of nicosulfuron and primisulfuron is a factor in

sugar beet response.

28

 

MATERIALS AND METHODS
Field Studies. Characteristics of field site soils are given
in Table 1.

Freeland sites. Nicosulfuron at 70 and 140 g/ha and
primisulfuron at 40 and 80 g/ha were applied in a
postemergence broadcast treatment in 1990 (site 1) and 1991
(site 2) to 13-25 cm corn. Plot size was 3 altar 10 m and
applications were made with a tractor mounted compressed air
sprayer in 206 L/ha of water at 208 kPa. In the year following
herbicide application, dry beans, sugar beets, and alfalfa
were planted in a randomized complete block design to
determine rotational crop response. Field maintenance in 1991
included spring moldboard plow followed by a cultipacker. In
1992 the field site was fall chisel plowed and followed by a
spring culti-mulch, field cultivation with a Triple K? at 8
cnidepth, and was cultipacked. Visual injury was rated 60 days
after planting (with 0 indicating no injury and 100%
representing total plant death) and sugar beet stand counted
44 days after planting at both sites. Sugar beets were not
harvested due to significant variations within replications as
a result of soil pH.

Saginaw'sites. Studies were conducted at two sites at the
Saginaw valley research facility. The first experiment was

initiated in 1990 and the second in 1991. Nicosulfuron was

 

1 Made by Kong Skilde. Kong Skilde Corporation, Bowling Green,
OH 43402. '

29

applied broadcast (POST) at 70 and 140 g/ha and primisulfuron
was applied broadcast (POST) at 40 and 80 g/ha using a tractor
mounted compressed air sprayer in 206 L/ha of water at 208 kPa
to 28-35 cm corn. The year after herbicide application, dry
beans, sugar beet, and alfalfa were planted in a randomized
complete block design with six replications and in the second
year after application the entire site was planted to sugar
beet. Plot size was 3 m by 10 m. Field maintenance included
fall moldboard.plowing followed by spring field cultivation to
a 10 cm depth. Prior to the second year of each study, the
site was fall chisel plowing and.spring culti-mulched followed
by one pass with a Triple K to an 8 cm depth and cultipacked.
Sugar beet plant density and visual injury were evaluated 60
days after planting. All plots were maintained weed free by a
common herbicide program, cultivation and handweeding. Yield
was determined by harvest of the center two rows of each plot
after 1 m of border plants from each end were removed. Sugar
beets were mechanically harvested and processed to determine
sugar quality and recoverable white sugar per acre (8).
Treatment means were computed using ANOVA and LSDs at the 5 %
level of significance and data was not combined over year and
location.

Campus site. A.two year plant back study was initiated at
the agronomy farm at Michigan State University in_1991.
Nicosulfuron at 35 g/ha was applied to 25 cm corn with a

tractor mounted compressed air sprayer delivering 206 L/ha of

30

water at 208 kPa. The year following herbicide application
half the field was planted to corn and half to sugar beets.
Two years after herbicide application, the field was planted
entirely to sugar beets. Plot size was 3 m by 10 m and sugar
beets were harvested by hand. Yields were taken from the
center two rows after 1 m of border plants were removed from
each end. Following herbicide application and harvest, the
field was fall chisel plowed, and field cultivated twice to an
8 cm before corn and sugar beet planting. Prior to planting
sugar beets in 1993, the field was disked once to a 10 cm1
depth, chisel plowed, and then field cultivated.using a'Iriple
"K" to an 8 cm depth. Data was subjected to ANOVA and LSD at

the 5 % level of significance.

Greenhouse studies.

Growth reduction study. Characteristics of the soils used in
this experiment are presented in Table 1. These soils were
chosen from untreated areas of the previously described field
sites. All soils except the washed sand were air dried and
sieved through a 2.0 mm sieve. Large soil aggregates were
either hand ground or ground by a hammer mill. Four hundred g
of the non-organic soil and 200 g of organic soil were placed
in 0.5 L plastic containers. Drainage holes were punched in
the pots to prevent standing water from accumulating.
Nicosulfuron or primisulfuron was applied using an over the

top drench method and the soils were then brought to field

31

capacity. Application rates for both compounds were 1, 5, and
25 ppb. Each treatment was replicated three times including
the untreated controls. Four Monohybrid E-4 variety sugar
beets were planted in each pot in a Conviron? growth chamber
for 37 days. The chamber diurnal settings were 11 hr D/ 13 hr
N at 24°C with 90% relative humidity. Root and shoot fresh and
dry weights were taken at harvest 37 days after planting. Two
runs of the experiment were performed and combined for
analysis and converted to percent of control.

Regression and correlation analyses were performed using
the MSTAT3 statistical analysis program. Hyperbolic regression
analysis was used to determine the IGso values. Results are
presented for shoot dry weight only since all measurements
showed the same trends.

Sorption/desorption study. These experiments utilized 1“C
labeled primisulfuron and nicosulfuron. Nicosulfuron was
uniformly ring labeled on the phenyl ring and had a specific
activity of 62.2 pCi/mg..A stock solution with a concentration
of 100 ppm was made by dissolving the compound in
tetrahydrofuran. Primisulfuron was uniformly labeled on the
pyrimidine ring and had a specific activity of 57.9 uCi/mg. A
100 ppm stock solution was made by dissolving the compound in

methanol. Five 9 of soil plus 10 ml of .01 M Cacl2 was placed

 

2 Conviron Corporation 3244 controller. Conviron Products of
America, Pembria, ND 58271

3 Developed by the MSTAT Devlopment Team at Michigan State
University, East Lansing, MI 48824

32

in 25 ml glass centrifuge tubes. Soils used were the same as
those used in the growth reduction study excluding the 100%
sand. Five ul of labeled stock solution was added to each
tube. Various amounts of cold stock solutions were added to
each tube in order to achieve total herbicide concentrations
ranging from .05 ppm to 5 ppm. The range of herbicide
concentration was dictated by as prior sorption isotherm
trials and were below the solubility of the compounds to
prevent precipitation. Sorption isotherm initial
concentrations are presented on Table 2. Tubes were then
capped and equilibrated on a shaker for 24 h and then
centrifuged at 10,000 rpm for 10 m for the sandy loam (Campus
and Freeland) and organic soils (Rose Lake) and 3,000 rpm for
5 m for the clay soils (Saginaw and Frahm). Three 1.0 ml
aliquots of the supernatant were taken for liquid
scintillation analysis and the rest of the liquid decanted
off. These aliquots were radioassayed. in. a jliquid
scintillation spectrometer and differences between standards
and supernatant were assumed to be due to soil sorption. The
solution was then replaced with freSh .01 M CaCl2 and the
system was equilibrated for 24 h. Centrifuge and sampling
procedures for the desorption experiment were the same as in
the sorption study. Each sorption point was replicated three
times.

An isotherm analysis program was developed at Michigan

33

State University4 ‘utilizing a spreadsheet program. This
program constructs Freundlich or Langmuir sorption and
desorption isotherni curves on. a logarithmic scale using
initial and final solution concentrations of ions or
radiolabeled compounds. The program also calculates RP'values
for the curves generated by the program. Kd values were
calculated from sorption isotherms to express the sorptive

capacity of the herbicides at equilibrium.

RESULTS AND DISCUSSION
Field Results. Visual injury ratings taken 60 days after
planting the year following application were similar at the
two Saginaw sites (Table 3). No injury was observed at the 70
g/ha rate of nicosulfuron and less than 10% injury was noted
for 140 g/ha nicosulfuron. In contrast, sugar beets in the 40
g/ha primisulfuron plots exhibited 59 to 66% visual injury and
the 80 g/ha plots a 73 to 90% reduction in above ground sugar
beet growth. Primisulfuron at 80 g/ha reduced RWSS from 3496
kg and 4273 kg/ha to 879 and 2175 kg/ha at the two Saginaw
sites respectively. Yield, expressed as RWS, was reduced at
the 40 g/ha rate of primisulfuron from 4273 to 3445 kg at one
Saginaw site. No loss in yield or sugar quality occurred with

any nicosulfuron treatment. By two years after application,

 

‘Kathleen Remus and Boyd Ellis. Crop and Soil Sciences Dept.,
Michigan State University. East Lansing, MI 48824.

5 RWS: Recoverable White Sugar expressed in kg/ha.

34

there was still up to 16 % visual injury from 80 g/ha of
primisulfuron but this did not affect sugar beet yield or
quality.

Sugar beet response at the Freeland sites one year after
application was extremely variable and, therefore, the data is
not presented. No injury occurred following nicosulfuron
application, however, sugar beet response in the primisulfuron
treated plots was variable. Soil cores to 14 cm depth were
taken adjacent to sugar beets across a range of injury levels
and compared to unaffected areas within the same plots. A
strong correlation was observed between sugar beet response to
primisulfuron one year after application and pH (Figure 1).
The marked difference in regression lines, which represent the
different sites, could be attributed to dissimilarities in
weather conditions between years or in site variations.

Sugar beet yield 1 year after application was not
significantly reduced at the Campus site with the nicosulfuron
treatment compared to the alachlor control (Table 4) . In 1993,
two years after nicosulfuron application, sugar beet yield was
not reduced by nicosulfuron regardless of whether corn or

sugar beets were planted in 1992.

Growth Reduction Results. Sugar beet response to nicosulfuron
and primisulfuron for the various soils is shown in Table 5.
IGso (inhibit growth by 50%) values ranged from 0.8 to over 150

ppb ai for nicosulfuron and from 0.5 to 40 ppb ai for

35

primisulfuron. On each soil, the IGSD value for nicosulfuron
was greater than that of primisulfuron, showing primisulfuron
to be more injurious to sugar beet than nicosulfuron.
Researchers at the University of Nebraska found primisulfuron
to ihave (greater' soil activity' than. nicosulfuron. using' a
shattercane bioassays. Correlation coefficients of soil
organic matter content with respect to sugar beet injury were
0.8 for nicosulfuron and 0.69 for primisulfuron (Table 6).
This indicates that organic matter may be the primary binding
factor in a soil system thereby reducing'bioavailibilityu The
ability of organic matter to interact with organic compounds,
such as herbicides, stems from the oxygen containing
functional groups found in the humic components. Soil organic
matter content has been positively correlated to sulfonylurea
sorption (15).

There was no correlation of sugar beet response to pH in
the range of this experiment (pH 6.4 to 7.9). This data is
seemingly in conflict with. previous field findings that
correlate soil pH to carryover potential and soil persistence
(13,14,17). In this greenhouse study, herbicides were applied
to the soil immediately prior to sugar beet planting. Our data
indicates that although soil pH may influence the persistence
of these herbicides, it does not play a major role in

bioavailability.

 

6Schluefer, Personal communication. University of Nebraska.
Lincoln, NE

36

IGso values for nicosulfuron and primisulfuron were

similar for the Sand, Campus and Frahm soils but there were
very large differences in the IGso values on the Saginaw,
Freeland, and muck soils. There appears to be no single factor
to which these differences can be attributed. Multiple
regression analysis did not improve the correlation of sugar
beet response to % organic matter. Since 1 ppb of
primisulfuron and nicosulfuron would.be equal to 0.22 g/ha in
the top 15 cm of the soil profile, at least 99 % degradation
and/or dilution is needed to reach the IGso concentration in
the soil on some soil types. Sugar beet injury that results in
yield loss, however, may still occur on field sites when
herbicide concentrations are equal to 1 ppb.
Sorption studies. The sorptive and desorptive isotherms
differed for nicosulfuron and primisulfuron. All non-organic
soil sorption Ka'values were between .299 and .866. K; values
for chlorsulfuron have been measured at 0.23—1.23 (3,4,6).
Desorption 2K. values for nicosulfuron are close to the
sorption values although not identical. There is a larger
discrepancy between sorptive and desorptive Kd values for
primisulfuron. This data suggests that hysterisis occurs with
both compounds but to a greater extent with primisulfuron.

Freundlich sorption and desorption isotherms were
performed with the resulting R2 values of .99 and} also
indicated.a linear relationship of the data. The Ka'value for

primisulfuron was two to three times higher than that of

37

nicosulfuron (Table 5). The pKa values of nicosulfuron and
primisulfuron are 4.3 and 4.5, respectively (9, personal
communication Dr.Ron Ross,Ciba). This small difference in pKa
values precludes the possibility that differences in
ionization of the sulfonylurea bridge is the key factor in
differential sorption.

Although primisulfuron appeared to have greater soil
activity in our field and greenhouse studies compared to
nicosulfuron, primisulfuron bound more tightly to soil
particles, thereby becoming less available to the sugar beet.
The greatest amount of sorption.for both compounds occurred on
the 82% organic matter soil (muck), which.was reflected in the
high IGso values for both herbicides on the muck soil. Kd
values and IGso data for nicosulfuron are supportive with the
exception of the Campus soil. The IGso value for nicosulfuron
and primisulfuron on the Campus soil would be predicted to be
between 16 - 24 ppb, and 1.2 - 15.1 ppb, respectively using
the equations determined by hyperbolic analysis. Findings in
the Campus soil also do not support primisulfuron sorption
trends. The untreated controls grew well so the possibility of
site contamination with another ALS inhibiting herbicide is
remote. Organic matter content and pH of the Campus soil are
comparable to that of the Freeland soil so the reasons for the
anomalous data from this site are still unclear.

The Kd values, and soil activity of, primisulfuron are

greater than that of nicosulfuron. Therefore, increased

38

sensitivity of sugar beet to primisulfuron is not due to
decreased sorption of primisulfuron to soil but rather the

data is indicative of an inherent sensitivity of sugar beet to

primisulfuron.

39

LITERATURE CITED

1. Beckie, H.J., R.Bn McKercher. 1990. Mobility' of two
sulfonylurea herbicides in soil. J. Agric. Food Chem. 38:310-
315.

2. Beyer, E.M., M.J. Duffy, J.V. Hay, D.D.Schlueter. 1987.
Sulfonylurea Herbicides. Reprinted from Herbicides: Chemistry,
Degradation, and Mode of Action Vol. 3 pp. 119-189. Marcel
Dekker, Inc.

3. Blair, A.M., T.D. Martin, A. Walker, S.J. Welch. 1989.
Measurement and prediction of chlorsulfuron persistence in
soil following autumn and spring application. Brighton Crop
Protection Conference. Vol. 9 pp. 1121-1126.

4. Borggaard, O.K., J.C. Streibig. 1989. Chlorsulfuron
adsorption by selected soil samples. Acta. Agric. Scand.
39:351-360.

5. Borggaard, O.K., J.C. Streibig. 1988. Chlorsulfuron
adsorption by humic acid, iron oxides, and montmorillonite.
Weed Sci. 36:530-534.

6. Brown, H.M. 1990. Mode of action, crop selectivity, and
soil relations of the sulfonylurea herbicides. Pestic. Sci.
29:263-281.

7. CIBA-GEIGY Ltd. 1988. Beacon technical release. Issued
January 1988.

8. Dexter, S.T., M.G. Frakes, F.W. Snyder. 1967. A rapid and
practical method ofidetermining extractable white sugar as may
be applied to the evaluation of agronomic practices and.grower
deliveries in the sugarbeet industry. Journal of the
A.S.S.B.T. Vol.14 No.5 pp. 434-454.

9. DuPont Co. 1988. Accent technical bulletin.

10. Harvey, J.Jr., J.J. Dulka, J.J. Anderson. 1985.
Properties of sulfometuron methyl affecting its environmental
fate: Aqueous hydrolysis and photolysis, mobility, and
adsorption on soils, and bioaccumulation potential. J. Agri.
Food Chem. 33:590-596.

11. Mersie, W., C.L. Foy. 1985. Phytotoxicity and adsorption

of chlorsulfuron as affected by soil properties. Weed Sci.
33:564-568.

40

12. Nicholls, P.H., A.A. Evans. 1987. The behavior of
chlorsulfuron and metsulfuron in soils in relation to
incidents of injury to sugarbeets. British Crop Protection
Conference. Vol.6 pp. 549-556.

13. Shea, P.J. 1986. Chlorsulfuron dissociation and
adsorption on selected adsorbents and soil. Weed Sci. 34:474-
478.

14. Smith, A.E., A.I. Hsiao. 1985. Transformation and
persistence of chlorsulfuron.in prairie field soils. Weed Sci.
33:555-557.

15. Stevenson, F.J. 1972. Organic matter reactions involving
herbicides in soil. J. Envir. Qual. 1:333-343.

16. Thirunarayanan, K., R.L. Zimdahl, D.E. Smika. 1985.
Chlorsulfuron adsorption and degradation in soil. Weed Sci.
33:558-563.

17. Wiese, A.F., M.L. Wood, E.W. Chenault. 1988. Persistence
of sulfonylureas in Pullman clay loam. Weed Sci. 2:251-256.

41

 

TABLE 1.

Characteristics of soils used in field and

greenhouse studies.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SITE %Clay %Silt %Sand %OM pH Series

Saginaw Mistequay

(Site 1) 60 23 17 2.9 6. silty clay

(Site 2) 58 23 19 3.1 7.

Frahm 52 21 27 3.8 6. Tappan-
londo clay

Campus 26 24 49 2.9 7. Capac
sandy loam

Freeland 28 12 59 2.8 7. Kawkawlin
fine sandy
loam

Rose Lake — - - 82. 6. Carlisle
Muck

Sand' 0 0 100 0 6. _

* - Sand in this experiment was obtained from bottled

washed sand treated with nutrient solution.

42

 

TABLE 2. Initial concentrations of herbicide for sorption

 

 

 

 

 

 

 

 

 

isotherms.
Amount of 1000 ppm Amount of 100 ppm Total
(unlabeled material) (labeled material) Herbicide
(ul) (ul) (ppm)
0 5 .05
1 5 .15
2 5 .25
4 5 5 5
9 5 5 1
24.5 5 2 5
34 5 5 3 5
49.5 5 5

 

 

 

 

 

43

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mbvm om m bmmv N¢ m oamm av o mmwm mm o or
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TABLE 4. Sugar beet response in 1992 and 1993 to nicosulfuron

applied in 1991 at a Campus site. Ratings were combined over

previous crop.

 

 

 

 

 

 

 

 

 

Herbicide Bate %Injury 3313 %Injury* Yield'
(g/ha) 6/22/92 (Kg/ha) 6/23/93 (Kg/ha)
Nicosulfuron 35 15 43.5 0 52.9
Imazethapyr 71 40 42.8 5 51.5
Alachlor 2400 0 45.2 0 50.4
LSD.05= 11 NS NS NS
* = Combined over corn and sugar beet as previous

crop from 1992.

45

TABLE 5. Sugar beet response to nicosulfuron and primisulfuron

in greenhouse and sorption experiments.

 

PRIMISULFURON NICOSULFURON
IGso (ppb) Kd IG.50 (ppb) Kc1
82 % OM 40 3.47 >150 2.58
Saginaw 2 .812 >25 .359
Frahm 15 .866 24 .523
Freeland 1 .757 16 .429
Campus 0.62 .840 1' .299
Sand 0.5 - 0.8 -

46

TABLE

6 .

Correlation Coefficients for nicosulfuron

and

primisulfuron at the five ppb rate analyzed over six soil

 

 

 

 

 

types.
Nicosulfuron Primisulfuron
R2 R2
J

% Clay -0.05 0.20

% Sand -0.81 -0.88

% OM 0.80 0.69

pH -0.11 -0.21

 

 

 

 

 

47

Figure 1. Sugar beet response to primisulfuron one year
after application as influenced by soil pH. Each regression
line represents a different site. Regression analysis on the
data gave 1R2 values of 0.93 and 0.96 in 1991 and 1992
respectively.

48

 

 

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49

Chapter 3

Sugar Beet Root Uptake and Translocation of
Nicosulfuron and Primisulfuron.

ABSTRACT

Field studies have shown primisulfuron to be more
injurious to sugar beet than nicosulfuron. Experiments were
initiated to determine if primisulfuron is more injurious to
sugar beet in the absence of soil and secondly to determine if
the difference in sugar beet response is a result of greater
uptake and translocation of primisulfuron. Hydroponic growth
reduction curves were established using a modified full
strength Hoagland’s solution with adjusted pH values of 4.0,
5.0, 6.5 and 8.0. IGSO (inhibit growth by 50%) values were
determined for both compounds. Primisulfuron and nicosulfuron
IGso values were 1.9 and 8.9 ppb, respectively, at pH 6.5. The
pH of the nutrient solution did not influence sugar beet
response to either herbicide. Uptake of primisulfuron was
slightly greater (3%) than that of nicosulfuron (1%).
Translocation (expressed as a percent of uptake) of
nicosulfuron was much more rapid compared to primisulfuron.
Fifty seven percent of the nicosulfuron translocated from the
root by 0 hr while 48 hours were required for 60% of the
primisulfuron to translocate out of the root. However, the
actual amount of herbicide translocated, total ppb ai, was

double for' primisulfuron. 'The total amount of nutrient

50

solution taken up by sugar beet in the 12 h pulse period was
41% lower when either herbicide was present in the system
compared.tx> untreated controls. Therefore nicosulfuron and
primisulfuron. inhibited transpiration. in sugar" beet.
Nomenclature: nicosulfuron, 2-[[[[(4,6-dimethoxy-2-
pyrimidinyl)amino]carbonleamino] sulfonyl]-N,N-dimethyl-3-
pyridinecarboxamine; primisulfuron, 2-[[[[[4,6-bis
(difluromethoxy)-2-pyrimidinyl]amino]caronyl]amino]sulfonyl]

benzoic acid.

INTRODUCTION

Field research indicated that Vprimisulfuron,but not
nicosulfuron, persisted in soil and injured sugar' beets
planted one year after application (6) . The difference in
response of sugar beet to nicosulfuron and primisulfuron, two
sulfonylurea herbicides, may be due to differences in soil
persistence or to differences in sugar beet tolerance to these
two herbicides.

Soil pH: influences crop response: to sulfonylureas.
Persistence increases due to a decrease in chemical hydrolysis
as soil pH is increased (8,9). Sugar“ beet response to
primisulfuron has been observed in the field to be directly
related to pH (6).

Tolerance of johnsongrass (Sorghum halapense L.),
Eastern black nightshade (Solanum ptygantum L.) , barnyardgrass

(Echinoghlga grus-galli Beav.), and giant foxtail (Setaria

51

faberi Herrm.) to nicosulfuron and primisulfuron varies by
species and herbicide (5). Both metabolism and variations in
ALS site sensitivity have been implicated in the differences
in response of these species to nicosulfuron and
primisulfuron.

Hydroponic experiments were conducted to determine if
solution pH influenced sugar beet response to primisulfuron
and nicosulfuron and if differences occurred in sugar beet
response to these two herbicides in the absence of soil.
Uptake and translocation of nicosulfuron and primisulfuron in
sugar beet were measured to determine if increased sugar beet
sensitivity was related to greater uptake and/or

translocation.
MATERIALS AND METHODS

IGso studies at various pH. Mono-hybrid E-4 variety sugar beets
were germinated for 7-10 days in a washed sand medium spiked
with 250 ml of a modified Hoagland’s solution (2). When
seedlings reached cotyledon to first leaf pair, plants were
transferred to 125 ml glass jars wrapped in aluminum foil
containing 120 ml of full strength modified Hoagland’s
solution. Jars were placed in a growth chamber with diurnal
settings of 11 hr day/ 13 hr night at 24°C with 90% relative
humidity. Nutrient solution pH was either 4.0, 5.0, 6.0, 6.5

or 8.0. Since this was a non-aerated system” nutrient solution

52

was changed every two to three days. Seedlings were supported
by glass wool. After a 10 day acclimation period in an
untreated system, sugar beet roots were exposed to 5 or 25 ppb
ai of either nicosulfuron or primisulfuron. Plants at pH 6.5
were also exposed to 1 ppb ai. Fourteen days after treatment
plants were harvested. Root and shoot fresh and dry weights
were measured and hyperbolic regression analysis performed on
the root dry weight data only since trends were similar for
all measurements. The MSTATa statistical program was used for
correlation and separation of treatment means at the S %
significance level using Fisher’s protected LSD. The
experiment consisted of 4 replications of each concentration
of nicosulfuron and primisulfuron plus four control vials
containing no herbicide. Two runs of the experiment were
performed and data was combined for analysis.
Uptake and translocation study. The experimental procedure was
the same as the IGso experiment with the following exceptions:
Plants were transferred to vials containing 100 ml of
nutrient solution with a pH of 6.8. Twenty-one days after
transfer, plant roots were exposed to 5 or 25 ppb ai of 1“C-
labeled nicosulfuron or primisulfuron for 12 h (7).
Nicosulfuron was uniformly ring labeled on the phenyl ring and
had a specific activity of 62.2 uCi/mg. Primisulfuron was

uniformly labeled on the pyrimidine ring and had a specific

 

8Program developed by the MSTAT Development Team at Michigan
State University East Lansing, MI 48824

53

activity of 57.9 uCi/mg. After the 12 h pulse period, plant
roots were rinsed and transferred to vials containing 100 ml
of untreated solution. Four sugar beets at each time interval
were harvested. Sample times were 0, 4, 8, 12, 24, 48, and 144
h after pulsing. Root and shoot fresh weights were taken at
harvest and. plant parts were combusted in a ibiological
oxidizer. Data.were combined.over experiment and ANOVA and LSD
at the 5 % significance level were performed. Regression and
correlation analysis were also executed on the untransformed
data. Radioactivity in the system was quantified using liquid
scintillation.
RESULTS AND DISCUSSION

Hydroponic Studies. Primisulfuron concentrations of 1, 5 and
25 ppb reduced sugar beet root and shoot dry weight more than
comparable concentrations of nicosulfuron (Table 1). Varying
the pH of the nutrient solution did not influence sugar beet
response (Table 2). The predominant species of both
nicosulfuron and primisulfuron at pH 4.0 would be the neutral
species while at pH 8.0 both compounds would be mostly
ionized. Ion or acid trapping mechanisms have been suggested
to be the method through which sulfonylureas enter the root of
plants (4). If this were the sole method of entry, then more
herbicide should enter the plant at a lower pH. The data
indicates that another method of entry, such as passive
uptake, occurs in conjunction with the ion trapping mechanism.

Increased sugar beet injury has been noted at high soil pH

54

(6,8,9) when the molecule would predominantly exist in
negative state (1,3) and in the absence of soil pH did not
affect sugar beet response. This shows the effect of pH to be
related to the persitence of nicosulfuron and primisulfuron.
Hyperbolic regression analysis was performed on the data
and equations for each line determined (Figure 1). Estimated
IGso (inhibit growth by 50%) values for nicosulfuron and
primisulfuron are 8.9 and 1.9 ppb ai, respectively. This data
indicates that differential tolerance in sugar beet may play
a significant role in greater sugar beet response to
primisulfuron in the field.
Uptake and translocation. Only 1.5% of the total amount of
nicosulfuron was taken up by sugar beet roots, while roots
exposed to primisulfuron took up 3 % of the herbicide at the
25 ppb rate. Sugar beet uptake at a concentration of 5ppb was
.9% for nicosulfuron and 2.5% for primisulfuron. Sugar beets
exposed to a 25 ppb concentration of primisulfuron were
visibly injured within 48 hours of pulsing. Injury symptoms
also appeared with primisulfuron concentrations of 5 ppb but
the injury did not become apparent until six days after
treatment. Nicosulfuron treated plants showed slight injury
six days after pulsing at 25 ppb, but the extent of the injury
was not as severe as that of primisulfuron. The slight
difference in uptake between these compounds did not account
for the observed differences in sugar beet response when

subjected to ANOVA.

55

The translocation patterns of these two herbicides were
dissimilar (Figure 2). Although there was no significant
difference in the total amount of herbicide translocated
(expressed as a percent of uptake) after 144 hours,
nicosulfuron translocated 57 % out of the treated root at the
0 hour sampling time. A similar amount of primisulfuron was
not translocated until 48 hours after pulsing. The actual
total amount of nicosulfuron that moved to the site of action
was .20 ppb ai. Sugar beet translocated a total of .43 ppb ai
of primisulfuron. in the same time interval. Statistical
analysis determined that there was no significant correlation
of sugar beet response to uptake and/or translocation.

Transpiration rates of sugar beet, as calculated by the
amount of nutrient solution taken up during the pulse period,
were similar for both compounds. Nutrient solution taken up by
sugar beet was 41 % less (3.4 ml and 3.5 ml) than that of the
untreated control (8.6 ml) in the presence of herbicide. This
indicates that both nicosulfuron and primisulfuron inhibited
transpiration which may account for the lack of uptake of
either herbicide, regardless of concentration. Nicosulfuron
should have reduced transpiration more quickly than
primisulfuron since translocation was much more rapid. Since
this was not the case, another mechanisulmust confer tolerance
of nicosulfuron to sugar beet, such as more rapid metabolism

and/or reduced ALS sensitivity compared to primisulfuron.

56

LITERATURE CITED

1. Beyer, E.M., H.M. Brown, M.J. Duffy. 1987. Sulfonylurea
herbicides in soil. British Crop Protection Conference. Vol.
6 pp. 531-540.

2. Blankendaal, M., R.H. Hodgson, D.G. Davis, R.A. Hoerauf,
R.H. Shimabukuro. 1972. Growing' plants without soil for
experimental use. NHscellaneous Publication PkL. 1251, U.S.
Dept. of Agriculture.

3. Brown, H.M., et al. 1990. Basis for soybean tolerance to
thifensulfuron methyl. Pestic. Bio. Phys. 37: 303-313

4. Burt, M E., F.T. Corbin. 1978. Uptake, translocation and
metabolism of propham.by wheat (Tritcum aestivum), sugar beet
(Beta vulgaris), and alfalfa (Medicago sativa). Weed Sci.
26:296-303

5. Carey, J.B., J.J. Kells. 1993. Absorption, translocation
and metabolisntof nicosulfuron.and.primisulfuron in five plant
species. North.Central Weed Science Society proceeedings. Vol.
48, 1993.

6. Chomas, A.J., J.J. Kells. 1993. Response of rotation crops
to nicosulfuron or primisulfuron following application in
corn. WSSA Abstracts. p88 Vol 33,1993.

7. Corbin, F.T. 1986. ‘Radioisotope techniques. Research
Methods in Weed Science 3rd Edition, South. Weed Sci. Society.
Chapter 13.

8. Duffy, M.J , M.K. Hanafey. 1987. Predicting sulfonylurea
herbicide behavior under field conditions. British Crop
Protection Conference. Vol.6. pp 541-547.

9. Fredrickson, D.R , P.J. Shea. 1986. Effect of soil pH on

degradation, movement, and plant uptake of chlorsulfuron. Weed
Sci. 34:328-332.

57

Table 1. Sugar'beet response to:nicosulfuron
in hydroponics at pH 6.5.

and.primisulfuron

 

 

 

 

 

 

 

 

 

 

 

 

 

Herbicide Rate Root dry Shoot dry
(ppb) weight weight
(% of Control) (% of Control)
Nicosulfuron l 75 95
5 62 88
25 4O 52
Primisulfuron 1 66 75
5 29 38
25 15 25
LSD (.05) 27 22

58

Table 2. Sugar'beet response to:nicosulfuron.and.primisulfuron

at various pH values.

 

 

 

 

 

 

 

 

 

 

 

 

Herbicide Rate pH 4.0 pH 5.0 pH 6.0 pH 8.0
Shoot Shoot Shoot Shoot
ppb dry dry dry dry
weight weight weight weight
as a as a as a as a
% of % of % of % of
control control control control
Nicosulfuron 5 98 100 95 100
25 91 77 100 88
Primisulfuron 5 79 75 88 71
25 40 50 55 53
LSD .05 = 22 20 18 21

59

 

Figureel. Hyperbolic regression curves showing sugar beet
response to nicosulfuron.and.primisulfuron.at pH 6.5. Analysis
was performed on root dry weight data since trends for all
measurements were similar.

60

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catarawgcn ............................................ W cm
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Figure 2. Translocation of 1“C—labeled nicosulfuron and
primisulfuron in sugar beet at pH 6.8. Translocation is
presented as a percent of control.

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