~
- .k .
“mmﬁm .u

2m»;
u.

x.....

.13;—
gummy?
.1- ‘
. Mr.» mm.

é

q .

V .nr .. 23
askianﬂﬂm H...

. z. 8...“? . .

a5.

.

,_
w
m

"my—-._."r——r.

—u.-

"-

.157

v

 

{
!

 

TWEES3

iocﬁ3
’H C)l-| l j (a t" I.-.) ("‘1 "1

 

LIBRARY
Michigar: State
University

 

 

 

This is to certify that the

thesis entitled

Natural Products as Potential Herbicide Adjuvants:
Citric Acid Esters and Quercetin

presented by

HEATHER ENID JOHNSON

has been accepted towards fulﬁllment
of the requirements for

M.Sci. degree in Crop and Soil Sciences

 

 

 

Major professor

Date August 4 , 2000

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

 

Wig3l®l°r

— 1.1 v .—

 

 

 

 

 

 

 

 

 

 

 

 

6/01 cJCIFtCDateDue.p65~p.15

 

Natural Products as Potential Herbicide Adjuvants:

Citric Acid Esters and Quercetin

BY

HEATHER ENID JOHNSON

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

2000

Natural Products as Potential Herbicide Adjuvants:
Citric Acid Esters and Quercetin
HEATHER ENID JOHNSON
Abstract

With the addition of activator adjuvants, herbicides become more effective, whether the
adjuvant increases absorption, prevents photodegradation or facilitates wetting. Citric
acid esters have been shown to enhance herbicidal activity. Though the mode of action is
not yet known, the structure of the citric acid ester is known to be related to their
function. The structure-function relationship of citric acid esters, which vary in alkyl
chain length, ethylene oxide number and number of chains, was examined. Ethylene
oxide number, alkyl chain Aength and number of chains inﬂuenced adjuvant efﬁcacy as
well. Nineteen experimental adjuvants were evaluated in the greenhouse with ﬁve
commercial herbicides on various weed species. Adjuvant efﬁcacy was weed and
herbicide speciﬁc for both the citric acid esters and the 19 experimental adjuvants.

Two naturally occurring, known UV absorbing compounds, carotenoids and quercetin
were studied to determine if they could prevent photodegradation of cyclohexanediones
herbicides. The herbicides BAS 620 and clethodim were determined to be photolabile. In
addition, the UV absorbing compound quercetin was added to the spray solution, applied
to the plants, and irradiated in the UV light chamber for 0, 1, and 3 hrs. When quercetin
was added to the spray solution and subjected to UV irradiation, the rate of

phototransformation of clethodim was decreased.

ACKNOWLEDGMENTS

First and foremost I would like to thank Dr. Donald Penner for his support both
as a mentor and ﬁnancially. He saw my potential and never gave up on me. I
could not have done it without him. I would also like to thank the OK. Witco
Corp and James Hazen for their ﬁnancial support. James Hazen has been an
encouraging and supportive person throughout my research. He was always very
excited at the results we found and anxious to ﬁnd out more.

I could not have completed my research without the help of one student worker,
Amanda Borel. She was here through it all. There were days when she
encouraged me to keep going when I was frustrated and wanted to quit for the
day, and she was always willing to come in whenever I needed her.

I would also like to thank my parents. Without them I would not be where I am
today. They were my support system when things started to look down and I did
not think I would make it through the day. I would especially like to thank my
mom; she has given me strength and courage. I watched her go through college
late in life and succeed. She set goals and achieved them, giving me something to
strive for.

I cannot forget all of my friends who stuck by my side as they went off to get
jobs of there own; Kari, Tierney, Brandi, and Beth.

Last, but not least, I would like to thank my husband, Dan. He has listened to
every sob story I ever told. He has never let me down when I needed him. He
has even been known to help out with my research when I was in a bind. I owe

him a lot and appreciate all he done for me.

iii

TABLE OF CONTENTS

LIST OF TABLES ........................................... vi
LIST OF FIGURES .......................................... viii
INTRODUCTION ........................................... 1
CHAPTER 1.

Effect of Ethylene Oxide Number, Alkyl Chain Length and Number

on the Efﬁcacy of Citric Acid Esters with Four Herbicides .......... 2
Abstract .............................................. 2
INTRODUCTION ...................................... 4
MATERIALS AND METHODS ........................... 6

General ......................................... 6
Weed Species .................................... 6
Herbicide Application ............................. 6
Statistics ........................................ 7
RESULTS AND DISCUSSION ........................... g
Structure-Function Relationship of Citric Acid Esters to
Herbicide Efﬁcacy ..................................... 3
Ethylene Oxide Number ............................ 3
Alkyl Chain Length ........ ' ....................... 9
Number of Chains ................................ 10
Efﬁcacy of Citric Acid Esters as Herbicide Adjuvants ......... 11
Glyphosate ...................................... 12
Glufosinate ...................................... 12
Imazamox ....................................... 12
Nicosulfuron .................................... 1 3
LITERATURE CITED .................................. 14

CHAPTER 2.

Effect of 19 Adjuvants on the Efﬁcacy of Five Herbicides ........... 33
Abstract .............................................. 33
INTRODUCTION ...................................... 35
MATERIALS AND METHODS ........................... 36

General ......................................... 36

Weed Species .................................... 36
Herbicide Application ............................. 36
Statistics ........................................ 37
RESULTS AND DISCUSSION ........................... 38
Efﬁcacy of Citric Acid Esters as Herbicide Adjuvants ......... 38
Glyphosate ...................................... 38
Glufosinate ...................................... 38
Imazamox ....................................... 38
Nicosulfuron ..................................... 39

iv

Dicamba ....................................... 4O

LITERATURE CITED .................................. 42
CHAPTER 3.

The Effect of UV Light on BAS 620 and Clethodim Photodegradation and

the Efﬁcacy of Quercetin as a Potential UV Protectant ............. 47

Abstract ............................................. 47

INTRODUCTION ...................................... 49

MATERIALS AND METHODS ........................... 50

BAS 620 ............................................ 50

Spectrophotometry ................................ 50

Exposure to UV Light .............................. 50

UV Protectants ................................... 50

Carotenoids ................................ 50

Quercetin ................................. 51

Greenhouse Studies ............................... 51

Clethodim ........................................... 52

Irradiation->Herbicide Application ................... 52

Herbicide Application-)Irradiation ................... 53

RESULTS AND DISCUSSION ........................... 54

BAS 620 ............................................ 54

Spectrophotometry and Exposure to UV Light .......... 54

UV Protectants ................................... 54

Greenhouse Studies ............................... 55

Clethodim ........................................... 55

Irradiation-)Herbicide Application ................... 55

Herbicide Application-)Irradiation ................... 55

LITERATURE CITED .................................. 56

LIST OF TABLES

CHAPTER 1
Effect of Ethylene Oxide Number, Alkyl Chain Length and Number
of Chains on the Efﬁcacy of Four Herbicides ..................... 17

Table 1. Efﬁcacy of various esters of citric acid applied at 0.25% with
glyphosate on common lambsquarters (0.11 kg/ha) and giant foxtail
(0.406 kg/ha) .............................................. 17

Table 2 Efﬁcacy of various esters of citric acid applied at 0.25% with
glufosinate on common lambsquarters (0.067 kg/ha) and giant foxtail
(0.101 kg/ha) .............................................. 18

Table 3.Efﬁcacy of various esters of citric acid applied at 0.25% with
imazamox on common lambsquarters (0.015 kg/ha) and velvetleaf
(0.015 kg/ha) ............................................. 19

Table 4.Efﬁcacy of various esters of citric acid applied at 0.25% with
nicosulfuron on large crabgrass (0.0056kg/ha) and giant foxtail.
(0.0336 kg/ha) ............................................ 20

Table 5. Interpretation of statistically analyzed data by comparing the
effectiveness of varying carbon chain length, regardless of EO
number. ................................................. 21

Table 6. Interpretation of statistically analyzed data from comparing
the effectiveness of substitution number. Information obtained using

Figures 2-9 ............................................... 22
Table 7. Comparison of the chemistry of the adjuvants that most
increased the efﬁcacy of four herbicides on various weed species. . . . 23
CHAPTER 2.
Effect of 19 Adjuvants on the Efﬁcacy of Five Herbicides ........... 42

Table 1. Efﬁcacy of experimental adjuvants with glyphosate on
common lambsquarters and giant foxtail ........................ 42

Table 2 Efﬁcacy of experimental adjuvants with glufosinate on
common lambsquarters and giant foxtail ........................ 43

Table 3. Efﬁcacy of experimental adj uvants with imazamox on
common lambsquarters and velvetleaf ........................ 44

vi

List of Tables (cont.)

Table 4. Efﬁcacy of experimental adjuvants with nicosulfuron on
large crabgrass and giant foxtail ............................... 45

Table 5. Efﬁcacy of experimental adjuvants with dicamba on

common lambsquarters and velvetleaf .......................... 46
CHAPTER 3
The Effect of UV Light on Bas 620 and Clethodim Photodegradation
and the Efﬁcacy of Querciten as a Potential UV Protectant ......... 60

Table 1. The evaluation of carotenoids as a UV protectant for
BAS 620. Absorbency readings were taken at the peak wavelength,
of 274 nm ............................................... 60

Table 2. Evaluation of quercetin as a UV protectant for BAS 620.
Absorbency readings were taken at the peak wavelength, of 274nm. . .61

Table 3. Evaluation of quercetin (Q) as a UV protectant with
clethodim for control of giant foxtail ........................... 62

vii

LIST OF FIGURES

CHAPTER 1
Effect of Ethylene Oxide Number, Alkyl Chain Length and Number
of Chains on the Efﬁcacy of Four Herbicides .................... 24

Figure 1. Structures 3) citric acid ester, b) ethylene oxide and
c) alkyl chain ............................................. 24

Figure 2. The effect of substitution number on the efﬁcacy of
glyphosate on common lambsquarters. In the absence of any adjuvant the
weed control was 64% (7DAT) and 78%(14DAT) ................ 25

Figure 3. The effect of substitution number on the efﬁcacy of
glyphosate on giant foxtail. In the absence of any adjuvant the weed
control was 60% (7DAT) and 60% (14DAT) .................... 26

Figure 4. The effect of a substitution number on the efﬁcacy of
glufosinate on giant foxtail. In the absence of any adjuvant the weed
control was 20% (7DAT) and 14% (14DAT). .................. 27

Figure 5. The effect of substitution number on the efﬁcacy of
glufosinate on common lambsquarters. In the absence of any adjuvant the
weed control was 26% (7DAT) and 41%(14DAT) ............... 28

Figure 6. The effect of substitution number on the efﬁcacy of
imazamox on common lambsquarters. In the absence of any adjuvant
the weed control was 48% (7DAT) and 63% (14DAT) ............. 29

Figure 7. The effect of substitution number on the efﬁcacy of
imazamox on velvetleaf. In the absence of any adjuvant the weed
control was 9% (7DAT) and 29% (14DAT) ..................... 30

Figure 8. The effect of substitution number on the efﬁcacy of
nicosulfuron on giant foxtail. In the absence of any adjuvant the weed
control was 46% (7DAT) and 58% (14DAT) .................... 31

Figure 9. The effect of substitution number on the efﬁcacy of
nicosulfuron on large crabgrass. In the absence of any adjuvant the
weed control was 21% (7DAT) and 34% (14DAT) ............... 32

viii

List of Figures (cont.)

CHAPTER 3
Figure 1. a) Structure of clethodim b)Structure of BAS 620 ......... 63
Figure 2. Structure of Quercetin .............................. 64

Figure 3. Spectral scans for BAS 620 from 200 nm to 700 nm
a)Before exposure to UV light b) aﬁer exposure to UV light ........ 65

Figure 4. Conﬁrmation of photolability for BAS 620 and clethodim
O, 1, and 3hr after exposure to UV light ........................ 66

Figure 5. Evaluation of quercetin as a UV protectant for
clethodim 0 and 3hr after exposure to UV light .................. 67

ix

INTRODUCTION

Adjuvant research has been through many changes in the past 100 years. The focus
went from concentrating on the spreadability of an adjuvant to studying action and
searching for more effective adjuvants. Adjuvants are now screened in the greenhouse
with many herbicides and on difﬁcult to control weeds. Once potential adjuvants are
found they are compared to those already on the market.

Another focus of adjuvant research has been to ﬁnd natural materials that act as
adjuvants. Natural products are more easily accepted by the public as well as by a plant.
In this paper we looked at natural products in two ways; as activator adjuvants and
secondly as an adjuvant to prevent photodegradation of an herbicide.

Citric acid is a natural product obtained from cornstarch. Citric acid esters are readily
synthesized and have been found to have herbicidal activity.

Quercetin is also a natural product that is a yellow dye obtained from several different
plants. Not only is quercetin naturally occurring in plants, its function in plants is to
absorb UV light thereby preventing photodegradation. Therefore, since quercetin is
naturally occurring and acts as a UV absorbing compound, adding it to a photolabile
herbicide might prove to be beneﬁcial.

The overall objectives of this study were; evaluate citric acid esters for adjuvant
efﬁcacy and relate structure to function, to screen 19 experimental adjuvants with ﬁve
herbicides on several weed species for adjuvant efﬁcacy and to conﬁrm photolability of

BAS 620 and clethodim, and determine the effect of quercetin as a UV protectant.

CHAPTER 1
Effect of Ethylene Oxide Number, Alkyl Chain Length and Number on the Efﬁcacy

of Citric Acid Esters with Four Herbicidesl
HEATHER ENID JOHNSON

Abstract. Activator adjuvants may facilitate wetting, spreading, dispersal, decrease
phototransformation and/or increase absorption. The objective of this research was to
evaluate structure-function relationships of citric acid esters which vary in alkyl chain
number (mono-, di- and tri-), ethylene oxide number (EO 4,7,9,25,35,52), and alkyl chain
length (Cg, Clz/M, C1618). Adjuvant efﬁcacy was evaluated on two weed species for each
of four herbicides. The experimental adjuvants were applied with glyphosate and
glufosinate on giant foxtail and common lambsquarters, imazamox on velvetleaf and
common lambsquarters and nicosulfuron on giant foxtail and large crabgrass. Adjuvant
efﬁcacy was weed and herbicide speciﬁc. Ethylene oxide number, chain length and
number inﬂuenced adjuvant efﬁcacy with the effectiveness of various substitution
combinations dependent on both herbicide and weed species.

NOMENCLATURE: Glufosinate, 2-amino-4-(hydroxymethylphosphinyl)butanoic acid;
Glyphosate, N-(phosphonomethyl)glycine; Imazamox, 2-[4,5-dihydro-4—methyl-(1-
methylethyl)-5-oxo-1H-imidazol-Z-yl]-5-(methoxymethyl)-3-pyridinecarboxylic acid,

ammonium salt; Nicosulfuron, 2-[[[[(4,6-dimethoxy-2-

 

l Received for publication on and in revised form on

pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N—dimethyl-3-pyridinecarboxamide;
Common Lambsquarters, C lienopodium album L. #CHEAL; Giant Foxtail, Setariafaberi
Herrm. #SETFA; Large Crabgrass, Digitaria sanguinalis (L.) Scop. #DIGSA; Velvetleaf,
Abutilon theophrasti Medicus. #ABUTH.

ABBREVIATIONS: ANOVA; Analysis of Variance, DAT; Days Aﬁer Treatment, EO;

Ethylene Oxide, LSD; Least Signiﬁcant Difference

INTRODUCTION

Activator adjuvants increase the activity of a given herbicide. The most common
activator adjuvants are surfactants, which facilitate wetting, spreading, dispersal, decrease
phototransformation, and/or increase absorption (Penner 1999).

Speciﬁc surfactants can alter the solubility of a leaf surface, or perhaps the solubility of
the herbicide, increasing absorption. This allows polar herbicides to penetrate the non-
polar cuticle, as well as enhance penetration through the slightly polar pectin portion of
the leaf (McWhorter 1982). The herbicide is available for cellular uptake, translocation,
or action only after penetration through the cuticle, pectin, and cell wall (Koskinen 1982).

Citric acids (Figure l) have been shown to enhance herbicidal activity by chelating
various salts in hard water (Thelen 1995). They are natural products extracted from
cornstarch and are considered to be easily absorbed by a plant. Since citric acid is a tri-
carboxylic acid, esteriﬁcation can occur with any or all of the carboxylic groups (Figure
1). Ethoxylated alkyl chains can be readily conjugated with citric acid to form these
esters. The citric acid esters are potential spray adjuvants thereby adding value to
existing natural products.

Structure-function relationships for adjuvants have been studied (Green 1999; Gaskin
1992). However the information on ethylene oxide (EO) number appears directly
relevant to citric acid ester efﬁcacy. The efﬁcacy of citric acid esters with various
herbicides on speciﬁc weed species is unknown. Therefore the objective of this study
was to determine the relationship between structure of the adjuvants and their function.

The speciﬁc objectives were to determine the effect of variation in alkyl chain length,

ethylene oxide number and number of alkyl substitutions on efﬁcacy of the citric acid
esters as adjuvants to enhance the activity of four herbicides on several weed species.
The adjuvant structure-function relationships to herbicide and weed speciﬁcity was also

explored.

MATERIALS AND METHODS

General. The following studies were conducted in and between the greenhouses at
Michigan State University from May 1999 to March 2000. Plants applied with accent
and imazamox were placed outside between greenhouses ﬁom May to September of
1999, due to the occurrence of hot temperatures in the greenhouse. Plants were in an
enclosed area outside, leaving the plants undisturbed, yet subject to environmental
conditions such as rain or cloudy days. Plants applied with liberty and accord were kept
in the greenhouse from September 1999 to March 2000 and were exposed to less variable
conditions.

Weed Species. Four weed species, giant foxtail, common lambsquarters, velvetleaf, and
large crabgrass were used in this study. Seeds were placed in 945 ml plastic black pots,
using Baccto, a professional potting soil. Approximately 1 wk before herbicide
application, excess plants were removed from the pots, leaving 3-5 plants per pot, each
with a similar height and leaf stage to ensure a uniform stand for herbicide application.
When the plants reached the 3-5 leaf stage, they were thinned down to 1 plant per pot for
common lambsquarters, 3 plants per pot for giant foxtail, 1 plant per pot for velvetleaf,
and 2 plants per pot for large crabgrass for herbicide application.

Herbicide Application. A link belt sprayer was used with a ﬂat fan nozzle5 that
delivered 94 Lha'l spray volume at 138 kPa pressure and a boom height of 33 cm.

Distilled water was used for the herbicide carrier to avoid any interaction that might

 

5 TeeJet Flat Fan Nozzle SOOOSEV model Spraying Systems Co., Wheaton, IL 60188

occur between the herbicide and hard water. Formulated glyphosateb was evaluated on
giant foxtail (0.406 kg/ha) and common lambsquarters (0.11 kg/ha). Formulated
glufosinate7 was evaluated on giant foxtail (0.101 kg/ha) and common lambsquarters
(0.067 kg/ha). Formulated imazamox8 was evaluated on common lambsquarters
(0.015Kg/ha) and velvetleaf (0.015 kg/ha). Formulated nicosulﬁiron9 was evaluated on
giant foxtail (0.0056 kg/ha) and large crabgrass (0.0336 kg/ha). Adjuvants were applied
at 0.25% (v/v). There were a total of eight trials and each was repeated.

Statistics. Data presented are the means of two experiments with four replications each.
Plants and treatment sequences were selected at random. Treatments were applied in a
random sequence in a double blind study, which means that the chemistry of the
adjuvants was not known and the treatment sequence was randomly selected. Data were
subjected to AN OVA (SAS Institute, 1996) and means were separated using Fischer LSD

with a P value of 0.05.

 

6 Accord® Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO 63167

7 Liberty® AgrEvo USA Co., 2711 Centreville Rd. Wilmington, DE 19808

8 Raptor® American Cyanamid, One Campus Dr., Parsippany, NJ 07054

9 Accent® DF, DuPont Co., Walker’s Mill, Barley Plaza Wilmington, DE 19880-0038

RESULTS AND DISCUSSION

Structure-Function Relationship of Citric Acid Esters to Herbicide Efﬁcacy
Ethylene Oxide (E0) Number. lehosate. The application of glyphosate to giant
foxtail produced the same results as reported by Green (1999), as E0 number increased,
efﬁcacy of glyphosate increased. The data showed that as E0 number increased there
was an overall increase in efﬁcacy of the adjuvants with glyphosate (Table 1). With
mono- and di- substitutions there was an increase in efﬁcacy from E04 to E09 on
common lambsquarters. However results with the tri- substituted molecule were variable
(E09>E04>E012).

Glufosinate. As E0 number increased, efﬁcacy of the adjuvants with glufosinate
tended to increase for giant foxtail (Table 2). The greatest increase in efﬁcacy was with
E025, E035 and E052. The E0 number of seven was the most effective adjuvant with
glufosinate on common lambsquarters(E07>E09>EO4). E025, E035 and E052 showed
potential as well to be effective E0 chain lengths on common lambsquarters.

Imazamox. E0 chain length of 4 was the most efﬁcacious with imazamox on
velvetleaf, with efﬁcacy increasing from E09 to E04 (Table 3). The long E0 chains
were not as effective with imazamox, as was expected. The effectiveness of the
adjuvants with imazamox on common lambsquarters, with regards to E0 number was
variable, although the long E0 chains (25, 35, and 52) were very effective.

Nicosulfuron. There was a general increase in efﬁcacy of the adjuvants from E04 to
E09 with nicosulfuron on giant foxtail (Table 4). However adjuvants with an E0

number of 7 were the least effective whereas adjuvants with long E0 chains were very

effective adjuvants with imazamox on giant foxtail. Efﬁcacy trends for large crabgrass
with nicosulﬁiron were dependent upon substitution of the adjuvant. For mono and di
substitutions there was an increase in efﬁcacy of imazamox as E0 number increased
from E04 to E09. However for the tri-substituted esters, the opposite occurred; efﬁcacy
of imazamox decreased from E04 to E09. Adjuvants with long E0 chains enhanced
overall efﬁcacy of imazamox.

There have been several reports on the effect of E0 number on herbicidal activity
(Gaskin 1992; Kirkwood 1993; Riechers 1995; Green 1999). Much of this research was
done with glyphosate. Riechers (1995) found that glyphosate efﬁcacy increased with
increasing E0 number. We conﬁrmed these results with glyphosate and found the same
to be true with glufosinate and nicosulfuron but not with imazamox. Gaskin (1992)
found that an E0 content of 15-20 was the most effective number. Green (1999) looked
at the effect of E0 content on sulfonylureas and found that with an alkyl chain length of
16/18, the most effective E0 number was 12-30. We also found that the most effective

E0 number with the chain length of 16/18 was between 9 and 12.

Alkyl Chain Length. Table 5 shows the alkyl chain length that had the greatest effect on
increasing efﬁcacy of the four herbicides, regardless of E0 number. For all di-
substituted molecules, the most effective alkyl chain length was C16.

Glyphosate. The mono-substituted ester, with an alkyl chain length of 12, the di-
substituted ester with an alkyl chain length of 16, and the tri-substituted ester with an
alkyl chain length of 16 were the alkyl chain lengths that, when added to glyphosate and
applied to both common lambsquarters and giant foxtail were most effective.

Glufosinate. The mono-substituted ester with an alkyl chain length of 12 or 16, and the
(ii-substituted ester with an alkyl chain length of 16 were the alkyl chain lengths that,
when added to glufosinate and applied to both common lambsquarters and giant foxtail
were most effective. There was no efﬁcacy trends observed for the tri-substituted ester
with glufosinate.

Imazamox. There were no efﬁcacy trend observed for the mono-substituted ester for
either weed species. The (ii-substituted ester with an alkyl chain length of 16 for both
common lambsquarters and velvetleaf and the tri-substituted ester the alkyl chain length
of 12 on common lambsquarters and both the alkyl chain length of 12 and 16 on
velvetleaf were effective when added to imazamox.

Nicosulfuron. There were no efﬁcacy trends observed on giant foxtail since alkyl
chain length was dependent upon E0 number and number of chains. However, the
mono~substituted molecule with an alkyl chain length of 12, the (Ii-substituted ester with
an alkyl chain length of 16, and the tri-substituted molecule. with an alkyl chain length of

8 or 12, when added to nicosulfuron were the most effective for large crabgrass.

10

Though little work has been directed towards alkyl chain, Green (1999) found that
Clo/18 was the most effective alkyl chain length, which we conﬁrmed. Tarm (1995) also

reported that C18 was the most effective alkyl chain length.

Number of Chains. Figures 2 through 9 illustrate the effectiveness of the number of
chains for a given herbicide on a speciﬁc weed species. Results are summarized in Table
6. Effectiveness was dependent upon both weed species and herbicide. The tri-
substituted ester was found to be the least effective adjuvant.

Glyphosate. Both giant foxtail and common lambsquarters responded similarly to
glyphosate. The (ii-substituted ester increased efﬁcacy of glyphosate, followed by the
mono-ester and the tri-ester.

Glufosinate. The mono-ester was more effective than the di-ester for increasing the
efﬁcacy of glufosinate on giant foxtail and the di-ester was more effective than the mono
ester for increasing the efﬁcacy of glufosinate on common lambsquarters. The tri— ester
was the least effective for increasing efﬁcacy of glufosinate on both weed species.

Imazamox. The tri-ester was most effective for increasing efﬁcacy of imazamox on
velvetleaf, followed by the di-ester and the mono-ester. The di-ester was most effective
for increasing the efﬁcacy of imazamox on common lambsquarters, followed by the tri-
ester and the mono-ester.

Nicosulfuron. Both large crabgrass and giant foxtail responded similarly to

nicosulfuron. The mono-ester was the most effective with respect to the number of

11

chains on the efﬁcacy of nicosulfuron, followed by the di-ester. The least effective was
the tri-ester.

We found that when high E0 number was most effective, if E0 number was decreased
and alkyl chain length was increased, effectiveness remained the same. Green (1999)
described similar observations. He found that when the effective E0 number was 12
with an alkyl chain length of 16, by increasing the E0 number and equally decreasing the
alkyl chain length, efﬁcacy remained the same. Therefore there may be an optimum
molecular weight. There were adjuvant molecules evaluated that were larger than 4,500g
mol'1 and were very effective on herbicide activity, however little is known on the mode
of action of these large molecules. Can the plant even absorb molecules this large or do
they simply act on the surface of the plant?

Efﬁcacy of Citric Acid Esters as Herbicide Adjuvants.

No adjuvants increased the effectiveness of all four herbicides on all weed species.
However there were two adjuvants that increased the effectiveness of three out of the four
herbicides. Both the mono- and di- substituted molecules with an alkyl chain length of 8
and an E0 chain length of 12 increased the effectiveness of glyphosate, glufosinate, and
nicosulfuron compared to the herbicide alone treatment, on all weed species.

Glyphosate. The only adjuvant that increased the efﬁcacy of glyphosate, compared to
the herbicide alone treatment, on both common lambsquarters and giant foxtail was the
di- substituted ester with an alkyl chain length of 16 and an E0 chain length of 9 (Table
1). There were six adjuvants that increased the effectiveness of glyphosate, compared to

the herbicide alone treatment, on common lambsquarters and not on giant foxtail, mono-,

12

C12, E04, mono-, C16, E07; mono-, C16, E09; di-, C8, E04; tri-, C12, E09; and tri-,
C16, E04. There was only one adjuvant that increased effectiveness of glyphosate,
compared to the herbicide alone treatment, for giant foxtail and not for common
lambsquarters, the (11-, C16 E052 (Table 1).

Glufosinate. There were two adjuvants that increased the efﬁcacy of glufosinate,
compared to the herbicide alone treatment, on common lambsquarters and giant foxtail,
the mono- and (ii-substituted molecule with an alkyl chain length of 8 and E0 chain
length of 12 (Table 2). There was one adjuvant that increased effectiveness of
glufosinate, compared to the herbicide alone treatment, for common lambsquarters and
not giant foxtail, mono-, C16, E035. There were three adjuvants that increased the
effectiveness of glufosinate, compared to the herbicide alone treatment, for giant foxtail
and not common lambsquarters, mono-, C12, E09; mono-, C16, E09 and di-, C12, E04
(Table 2).

Imazamox. No adjuvants were evaluated that increased the effectiveness of imazamox,
compared to the herbicide alone treatment, on both common lambsquarters and velvetleaf
(Table 3). There was one adjuvant that increased effectiveness of imazamox, compared
to the herbicide alone treatment, for common lambsquarters and not on velvetleaf, the di-,
C8 E07. There was one adjuvant that increased the effectiveness of imazamox,
compared to the herbicide alone treatment, for velvetleaf and not for common
lambsquarters, the tri-, C16, E07 (Table 3).

Nicosulfuron. All of the adjuvants increased the effectiveness of nicosulfuron,

compared to the herbicide alone treatment, (Table 4). There was one adjuvant that

13

increased the effectiveness of nicosulfuron, compared to the herbicide alone treatment,
for giant foxtail and not on large crabgrass, the di-, C13, E025. There were two
adjuvants that increased the effectiveness of nicosulfuron, compared to the herbicide
alone treatment, for large crabgrass and not for giant foxtail: mono-, C8 E04 and mono-,
C16 E04 (Table 4).

Table 7 is a list of the adjuvants that were most effective with a given herbicide on a
speciﬁc weed species. From a commercial perspective it would be desirable to have one
very effective adjuvant that would be effective with all herbicides for all weed species.
The data presented indicates that this goal will remain elusive.

The mechanism that the spectrum of citric acid esters exert their efﬁcacy may vary with
the size of the adjuvant molecule. Since some of the citric acid esters had large numbers
of E0 units, thus having a large molecular weight it is appealing to conclude that they

exert their action on the surface of the leaf.

l4

LITERATURE CITED

Gaskin, R. E., and P. J. Holloway. 1992. Some physiochemical factors
inﬂuencing foliar uptake enhancement of glyphosate-mono-(isopropylammonium) by

polyoxyethylene surfactants. Pestic Sci. 34:195-206.

Green, J. M. 1999. Effect of nonylphenol ethoxylation on the biological activity

of three herbicides with different water solubilities. Weed Technol. 13:840-842.

Green, J. M. 1999. Optimizing alcohol ethoxylate surfactant activity at low

doses. Weed Technol. 13: 000-005

Kirkwood, R. C. 1993. Use and mode of action of adjuvants for herbicides; a

review of some current work. Pestic Sci. 38293-102.

Koskinen, W. C. and SS. Harper. 1984. Herbicide properties and processes
affecting application. Methods of Applying Herbicides. Champaign, IL Weed Science

Society of America. pp.9-l 7

McWhorter, C. G., 1982. The use of adjuvants. Adjuvants for Herbicides.

Champaign, IL. Weed Science Society of America. pp.10-21

15

Riechers, D., L. Wax, R. Liebl and D. Bullock. 1995. Surfactant effects on

glyphosate efﬁcacy. Weed Technol. 9:281-285

SAS Institute Inc. 1996. (v6.12) Cary, NC, USA

Tann, R. S., D Haggard and P. McMullan. 1995. Effect of various carbon chain
length methyl esters as agricultural tank mix adjuvants. Fourth International Symposium

on Adjuvants for Agrochemicals, Melbourne, Australia. pp.72-77

Thelen, K., E. P. Jackson and D. Penner. 1995. Utility of nuclear
magnetic resonance for determining the molecular inﬂuence of citric acid and an

organosilicone adjuvant on glyphosate activity. Weed Sci. 43:566-571.

16

Table 1. Efﬁcacy of various esters of citric acid applied at 0.25% with glyphosate on
common lambsquarters (0.11 kg/ha) and giant foxtail (0.406 kg/ha).

 

 

 

Trt R-Group Chain E0 Common lambsquarters Giant foxtail
number length number 7 DAT 14 DAT 7 DAT 14 DAT
4% Control) (% Control)
1 Mono 8 4 73 81 55 53
2 Mono 8 7 35 38 50 50
3 Mono 8 9 76* 93* 60 80*
4 Mono 8 12 85* 96* 60 81*
5 Mono 12 4 81* 91* 50 53
6 Mono 12 7 64 80 56 73*
7 Mono 12 9 81 * 94* 63 74*
8 Mono 16 4 75* 84 53 50
9 Mono l6 7 75* 89* 45 49
10 Mono l6 9 85* 94* 51 58
ll Di 8 4 86* 95* 50 58
12 D1 8 7 68 78 51 63
13 D1 8 9 66 83 61 73*
14 Di 8 12 80* 89* 65 79*
15 Di 12 4 76* 84 41 44
16 Di 12 7 70 81 64 70
17 Di 12 9 79* 86 64 83*
18 D1 16 4 66 78 54 59
19 D1 16 7 90* 99* 69 86*
20 D1 16 9 89* 93* 71* 85*
21 Tri 8 4 69 78 44 39
22 Tri 8 12 68 73 29 38
23 Tri 12 4 59 74 40 31
24 Tri 12 7 56 70 45 41
25 Tri 12 9 91 * 94* 58 63
26 Tri l6 4 85* 95* 44 55
27 Tri l6 7 73 85 55 64
28 Tri l6 9 76* 83 56 70
29 Di 13 25 64 83 66 83*
30 Di 16 52 71 86 68* 91*
31 Mono 16 52 69 85 65 89*
32 Mono 16 35 65 79 61 81*
33a 64 78 60 60
..... 340000
LSDOOS 11.3 98 89 112
2|Herbicide alone
bControl

’Values that were signiﬁcantly greater than herbicide alone

17

Table 2. Efﬁcacy of various esters of citric acid applied at 0.25% with glufosinate on
common lambsquarters (0.067 kg/ha) and giant foxtail (0.101 kg/ha).

 

 

 

 

Trt R-Group Chain E0 C. lambsquarters Giant foxtail
number length number 7 DAT 14 DAT 7 DAT 14 DAT
(% Control) (% Control)
1 Mono 8 4 40* 46 32* 14
2 Mono 8 7 35 39 36* 21
3 Mono 8 9 45* 49 44* 36*
4 Mono 8 12 56* 54* 46* 29*
5 Mono 12 4 24 35 28 13
6 Mono 12 7 45* 41 38* 26*
7 Mono 12 9 20 40 48* 41*
8 Mono 16 4 34 35 39* 21
9 Mono l6 7 48* 47 37* 29*
10 Mono l6 9 29 33 42* 29*
11 Di 8 4 25 34 32* 14
12 Di 8 7 20 40 19 21
13 Di 8 9 25 44 19 21
14 Di 8 12 59* 60* 46* 33*
15 Di 12 4 23 42 33* 26*
16 D1 12 7 29 40 25 23*
17 Di 12 9 43* 51 33* 20
18 D1 16 4 31 44 34* l3
19 D1 16 7 43* 46 29* 19
20 D1 16 9 40* 40 41* 22
21 Tri 8 4 13 28 l9 14
22 Tri 8 12 39* 49 32* 22
23 Tri 12 4 14 33 23 ll
24 Tri 12 7 35 46 ‘ 14 19
25 Tri 12 9 24 33 17 11
26 Tri l6 4 21 36 19 17
27 Tri 16 7 26 38 18 14
28 Tri 16 9 24 36 26 15
29 Di 13 25 55* 58* 28 28*
30 D1 16 52 46* 51 26 25*
31 Mono 16 52 70* 63 * 22 24*
32 Mono 16 35 49* 58* 21 18
332| 26 41 20 14
_____ 3 40391812
LSDOOS 11.8 111 91 85
aHerbicide alone
bControl

‘Values that were signiﬁcantly greater than herbicide alone

18

Table 3. Efﬁcacy of various esters of citric acid applied at 0.25% with imazamox on
common lambsquarters (0.015 kg/ha) and velvetleaf(0.015 kg/ha).

 

 

 

 

Trt R-Group Chain E0 C. lambsquarters Velvetleaf
number length number 7 DAT 14 DAT 7 DAT 14 DAT
(% Control) (% Control)
1 Mono 8 4 46 64 8 31
2 Mono 8 7 48 68 15 23
3 Mono 8 9 51 7O 11 26
4 Mono 8 12 38 63 13 20
5 Mono 12 4 53 68 30* 21
6 Mono 12 7 48 65 6 21
7 Mono 12 9 53 76* 10 33
8 Mono 16 4 50 71 10 28
9 Mono l6 7 58* 81* 11 20
10 Mono 16 9 50 71 33* 33
11 D1 8 4 53 79* 10 38
12 D1 8 7 56* 84* 5 28
13 D1 8 9 54 79* 9 36
14 Di 8 12 48 78* 4 21
15 D1 12 4 51 76* 13 35
16 D1 12 7 51 74* 13 34
17 D1 12 9 55 83* 0 24
18 D1 16 4 50 86* 29* 44*
19 D1 16 7 49 81 * 28* 31
20 Di l6 9 65* 85* 29* 23
21 Tri 8 4 50 76* 29* 35
22 Tri 8 12 50 75* 26* 44*
23 Tri 12 4 54 78* 8 39*
24 Tri 12 7 56* 76* 26* 46
25 Tri 12 9 55 75* 0 6
26 Tri 16 4 50 75* 6 29
27 Tri l6 7 45 70 24* 39*
28 Tri 16 9 50 75* 10 41
29 D1 13 25 50 76* 20* 35
30 Di 16 52 53 76* 36* 65*
31 Mono 16 52 48 66 10 13
32 Mono 16 35 55 80* ll 9
33a 48 63 9 29
_---_3_4E’ ..................................................... 9 .............. 9 ____________ 9 ____________ 9 .......
LSDO 05 7.4 10 1 9 5 10 2
aHerbicide alone

bControl
‘Values that were signiﬁcantly greater than herbicide alone

19

Table 4. Efﬁcacy of various esters of citric acid applied at 0.25% with nicosulﬁiron
on giant foxtail (0.0056 kg/ha) and large crabgrass 0.0336 kg/ha).

 

 

 

Trt. R-Group Chain E0 Giant foxtail Large crabgrass
number length number 7 DAT 14 DAT 7 DAT 14 DAT
(% Control) (% Control)
1 Mono 8 4 61* 78* 40* 23
2 Mono 8 7 53 70* 43* 56*
3 Mono 8 9 63 * 79* 51* 60*
4 Mono 8 12 65* 91* ' 55* 75*
5 Mono 12 4 63* 74* 50* 48*
6 Mono 12 7 55* 76* 53* 63*
7 Mono 12 9 55* 73* 51* 70*
8 Mono l6 4 60* 78* 39* 35
9 Mono l6 7 59* 74* 43* 58*
10 Mono 16 9 59* 73* 48* 50*
11 D1 8 4 50 71 * 54* 71*
12 Di 8 7 58* 70* 58* 71*
13 Di 8 9 66* 83* 53* 63*
14 D1 8 12 61 * 78* 44* 56*
15 Di 12 4 56* 74* 58* 79*
16 Di 12 7 55* 74* 53* 73*
17 Di 12 9 59* 76* 58* 74*
18 Di 16 4 60* 78* 53* 79*
19 Di l6 7 50 69* 58* 79*
20 Di 16 9 65* 80* 58* 76*
21 Tri 8 4 63* 79* 60* 81*
22 Tri 8 12 69* 83* 53* 68*
23 Tri 12 4 60* 78* 55* 66*
24 Tri 12 7 61* 79* 59* 83*
25 Tri 12 9 55* 78* 63* 88*
26 Tri l6 4 68* 74* 65* 74*
27 Tri l6 7 55* 73* 58* 73*
28 Tri l6 9 58* 75* 55* 81*
29 D1 13 25 33 40 55* 70*
30 Di 16 52 68* 81* 56* 79*
31 Mono 16 52 65* 81* 54* 71*
32 Mono 16 35 60* 80* 56* 76*
33“ 46 58 21 34
340 ............ Q ............ 9. ............ 9 ......
LSDO 05 8.7 7 4 7 2 ll 7
“Herbicide alone

bControl
Values that were signiﬁcantly greater than herbicide alone

20

Table 5. Interpretation of statistically analyzed data by comparing the effectiveness of
varying carbon chain length, regardless of E0 number.

 

 

 

Glyphosate Glufosinate Imazamox Nicosulfuron
a... ,(Cerben.length)__. m.---_(Carbon,1eng_th).-WW(Cnrben.Length) (Carbomeng_th)_____
SETFA“ CH EAL“) SETFA CHEAL ABUTHc CHEAL DIGSA“ SETF A
Mono 12 12 12/16 8 NT“ NT 12 NT
Di 1 6 l 6 l 6 l 6 l6 16 16 NT
Tri 16 16 NT NT 12/16 12 8/12 NT

 

“ Giant foxtail

b Common lambsquarters
c Velvetleaf

“ Large crabgrass

e No trend

21

Table 6. Interpretation of statistically analyzed data from comparing the effectiveness of
substitution number. Information obtained using Figures 2-9.

 

 

 

W . -Qlyphesate . _ _ W ﬁlyfesinate . . W..- .. .. Imazamox Meringue...“
SETFA“ CHEAL“ SETFA CHEAL ABUTHc CHEAL DIGSA“ SETFA
Mono 2 2 l 2 3 3 l 1
Di . 1 1 2 1 2 1 2 2
Tri 3 3 3 3 1 2 3 3

 

1 = Most effective number of chains
2 = Moderately effective number of chains
3 = Least effective number of chains

22

Table 7. Comparison of the chemistry of the adj uvants that most increased the efﬁcacy
of four herbicides on various weed species

 

 

 

 

 

 

 

 

 

 

Herbicide Weed species Alkyl chain E0 number Number of
length substitutions
Glyphosate Common 1 6 7 di-
Iambsquarters
Giant foxtail 16 52 di-
Glufosinate Common 8 12 di-
....1.arnb§quener§--1..._....._._....__...
Giant foxtail 12 9 mono-
Imazamox Common 16 9 di-
-.lan3.b,§qn§n,er§__.._.._ _ WW
Velvetleaf 16 52 di-
Nicosulfuron -9911}.f9§£iii.L------1-.--.-.. 8 12 mono—
Large crabgrass 12 9 tri-

 

23

 

 

 

 

 

 

 

 

 

 

 

 

A. 0
H2 C 0R1
R = H (Citric Acid)
0 or
I 1 R = Alkyl Chain + Ethylene Oxide
H O C 0R2 Chain
0 (R-Group Substiturion = mono, di or
‘ I tri)
H2 C 0R3
B.
C C _—
Ethylene Oxide (E0)
Number = 4,7,9,25,35,52
0
C.
—— C C — Alkyl Chain Length = 8,12,
or16

 

 

 

Figure 1. Structures 3) Citric Acid Ester b) ethylene oxide and c)alky| chain

24

A. 7 DAT, MONO LSD 0105:1113 D. 14 DAT. MONO LSD 0.05:9.8

.‘ 111. w"

‘- ”101

thallllmim

   

7
EONumber 9 12 EONumber 9 12

: LSD 0.05:9.8
B. 7 DAT. DI LSD 0'05 “'3 E. 14 DAT, DI

   

so Number 9 12 to Number ‘2

C. 7 DAT. TRI LSD o.os=11.3 F. 14 DAT. TRI
1 .. .. . LSD0.05=9.8

Al
iii. 1

   

7
E0 Number 9 12 E0 Number

Figure 2. The effect of substitution number on the efﬁcacy of glyphosate on common lambsquaters
In the absence of any adjuvant the weed control was 64% (7DAT) and 78% (14DAT)

25

LSD 0.05=11.2

A. 7 DAT. MONO D. 14 DAT. MONO
LSD 0.05:8.9

11' Ill” , II
11111” I'

I II“

11114”

"I'M. 1 “IBM

IIIIIW' III

IIIIII'

   

EC Number

B. 7 DAT, DI E. 14 DAT. DI
LSD 0.05:8. 9 LSD 0.05=11.2

I'IIIII IIIIIIIIIIII1I II“
- III?IIIIIIIIIIIIIIIIIIIIII

   

9
EC Number 12

c. 7 DAT. TRI LSD 0.0543 F- 1‘ 0111,7111 LSD o.os=11.2

11111 ' ‘
‘ ill” ”“1,“

.11“. . I ll 1
‘11.. Ilium Ii I;I1l1
"'Ull ‘

   

EC Number 9 12 EC Number

Figure 3. The effect of substitution number on the efﬁcacy of glyphosate on giant foxtail
In the absence of any adjuvant the weed control was 64% (7DAT) and 78% (14DAT)

26

A. 7 DAT. MONO

 

LSDO.=05 9.1

‘ 1111":

111111111II1I‘III
1.111.1111.1111111“: 501111111111-III 1 1
1.11111... 1..

E0 Number

LSD 0.05:9.1

  

Carbon

 

E0 Number

LSD 0. 05=9. 1

 

E0 Number

 

D. 14 DAT. MONO LSD 0 05=8. 5
1 1

IIIIIIIIIIIIIIIIIIII1111111
HIIIIIIIIIIIIIIIIIIIIIIIII

I IIIIIIIIIIIIIIIIIIIII
1.1.1.1111

I”.II1I_IIIIIIIIII1I_L 1

1 11.111111111111IIIIII II
1111111|II

111.11. 1'-

% Effmcy

   
 

Carbon
Number

E0 Number

LSD 0 05:8. 5
5149111111111111111111111.1111"' IIIII ,‘ ‘
IIIIIIIIIIIIIIIIIIIIIIIII III II II

, 1.111111II1IIIIIIIII I1IIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIII . i U

% Efﬁcacy

LSD 0. 05=8. 5

, 1111111 _
II . IIIII11I'1II
11111111:IIIIIIIIIIIIIIII‘WI IIIIIIIIIIII“I.““M"IIIIIIIIIIIIIl I. i i ‘

'IIIIIIIIIIII I 111111 1
1 IIII..1,1111111 . III.111luliiii........1.11111I.Ii.i.........I..
i 1.1“... 1111“”1111111111111

1 II‘IIIII 1"”
I “I ” M II...IIIIII1IIIII1I ‘

% Efﬁcacy

 

E0 Number

Figure 4. The effect of substitution number on the efﬁcacy of glufosinate on giant foxtail
In the absence of any adjuvant the weed control was 20% (7DAT) and 14% (14DAT)

27

  

LSD 0.05=11.1

 

D. 14 DAT ‘." .

  
    
    

A. 7 DAT MONO LSD 00541.8
l ‘ mI-HW' “I
t n

g- 40 In .I 5.40 ﬂ"Ml

g E 30 W”

a 3‘ 20

16 16
Carbon Carbon
8Number 8 Number
50 Number ‘2 50 Number 12
B. 7 DAT, DI E. 14 DAT, DI
LSD 0.05=11.1

   

6‘
23
2:
Lu
32
16
Carbon
7 9 5 Number
12
E0 Number
C. 7 DAT, TRI LSD 0.05=11,8

   

5‘
E
Lu
32
16
Carbon
7 9 8 Number
12
EC Number

EC Number

Frgure 5 The effect of substitution number on the efﬁcacy of glufosinate on common lambsquarters
In the absence of any adjuvant the weed control was 20% (7DAT) and 14% (14DAT)

28

AJDAT, MONO LSD °~°5=7-4 o, 14 DAT, MONO LSD o.os=1o.1
I|| IIIIIIIIIII IIII IIIIIIIII
IIIII ‘ I I W II
II WIIIIII IIIIIIIII
IIIII -IJI

'I‘IIIIIIIIIIIII ,. IIIIIIIII
"IIIIII ‘II'IIIIIIIIIIIIIIIII

IIIIIIIIIII‘
" IIIII

g3}

IIIIIIII

Pg:

I ‘ II II II

   

9
E0 Number ‘2 so Number 12

B. 7 DAT. DI LSD 0.05=7.4 EI 14 DAT. DI LSD 0.05=10.1

 

9 9
E0 Number 12 E0 Numb“ 12

   

LSD 0 05-7 4 F. 14 DAT, TRI
C.7DATTRI .I - ‘-I ,

 

E0 Number 9 ‘2 EC Number

Figure 6. The effect of substitution number on the efﬁcacy of imazamox on common lambsquarters
In the absence of any adjuvant the weed control was 48% (7DAT) and 63% (14DAT)

29

LSD 0‘05=9,5 LSD 0.05=10.2
o

“ IIIIIIIIIIIIIIIIIIIIII , .I I.
"III. II

      

    

  
  

A. 7 DAT MON III, III ,
0 .I.III|II _IIIIIII IIIIIIII'"I
Ir-III I I IIIIIIIIIIIIIIIII- IIIIIIIIIIII

II ‘
II' III IIIIII IJJ‘ IIIIIIIIIIIIIIIIII, IIIIIIIIIIIIIIIIIII IIIIIIIIIaalI

  

    

IIIIIIIIIIII “I‘m W II“"II|’ I“. WIIIIIIIIIIII

I
'"I ll IIIIIIIIIIIII

      

  
   
    
   
  

      
   
  
 
 
 

    
 

    

            
  

4o III‘IIIIIIIIIIIIN'I ‘ IIIIIII IIIIII III IIIIII IIIII'I"" IllII
3 30 I IIIII .IIIIIIII'I" III'I" ,wIIII
g I IIILi‘dIIII'I'II IIIIIII'1III:IIIII IIIIIIIIIIIIIIIIIIIIII
LU < I II .

20 - 1t IIIII I.IIII'II'I’I“I‘
a2 6 1“ I IIIIIII

     

16
0 Carbon
8Number 12
E0 Number 12 EC Number
LSD 005:9.5
E. 14 DAT. DI LSD 0.05=10.2

B. 7 DAT, DI

  
     

 

 

 

 

 

32
16
Carbon
8 Number
E0 Number 12
LSD 0.05=9.5
LSD 0.05=10.2

C. 7 DAT, TRI F. 14 DAT, TRI

“In Efﬁcacy

16
Carbon 9
4 7 ”umber E0 Number ‘2

 

EO Number

Figure 7. The effect of substitution number on the efﬁcacy of imazamox on velvetleaf
In the absence of any adjuvant the weed control was 48% (7DAT) and 63% (14DAT)

30

LSD 0.05=8J
A. 7 DAT. MONO

”u" i‘ N" ,u‘, m.
mitil Wlilnll'ilW' "“W L

I llhlilil[HIIIIW'HH
lililillill‘iliiillil
n .mnnlillillili

 

 

 

 

 

 

  

5
LU
:2
E0 Number 12
LSD 0.05:8]
B. 7 DAT. DI
5
LL]
31
16
Carbon
8 Number
12
E0 Number
c. 7 DAT. TRI LSD 005:8]

um.
L “H I‘liilml “Wm

_ 0' ill ml ,1]

‘ N

H

"""miuhnf I Indium,“ i
55 ”i

”ii ii

% Efﬁcacy

  

 

 

LSD 0.05=7.4

 

E0 Number

LSD0.05= 7.4

E0 Number

  

F. 14 DAT. TRI ‘ LSD 0. 05: 7 4
, i ‘ W ‘ 1:

E0 Number

Figure 8. The effect of substitution number on the efﬁcacy of nicosulfuron on giant foxtail
In the absence of any adjuvant the weed conhoi was 46% (7DAT) and 58% (14DAT)

D. 14 DAT MONO LSD 0.05=11J

A. 7 DAT. MONO

LSD 0.05:7.2

   

  
  

 

 

5'
.2
Lu
32
7 so N
E0 Number 9 12 umber
LSD 0 05:7 2 LSD 0.05=11.7
B. 7 DAT, DI . I ‘ E. 14 DAT. DI
iii ‘_ minim WHHMH M ‘m i‘
‘ ’ | r
6‘
g
a?
16
Carbon
Number
9 12
E0 Number E0 Number 12
LSD 0.05:7.2 LSD 0.05=11.7
C. 7 DAT, TRI
6‘
E
a?
16
Carbon
8Number
12

 

g 7
E0 Number E0 Number

Figure 9 The effect of substitution number on the efﬁcacy of nicosulfuron on large crabgrass
In the absence of any adjuvant the weed control was 46% (7DAT) and 58% (14DAT)

32

CHAPTER 2

Effect of 19 Adjuvants on the Efficacy of Five Herbicidesl

HEATHER ENID JOHNSON

Abstract. Adjuvant screening with popular herbicides against difﬁcult to control weeds
is a powerful pragmatic way to identify effective adjuvants. The objective of this study
was to screen 19 experimental adjuvants with ﬁve herbicides on two weed species each to
determine the effectiveness of these experimental adjuvants. Experimental adjuvants
were applied with glyphosate and glufosinate on giant foxtail and common
lambsquarters, with imazamox and dicamba on common lambsquarters and velvetleaf
and with nicosulfuron on giant foxtail and large crabgrass. Herbicide applications were
made when weeds reached the 3 to 5 leaf stage. Adjuvant efﬁcacy was dependent both
on herbicide and weed species. Therefore screening adjuvants is very important in
identifying the most effective adjuvant, whether it be broad spectrum or on a single weed
with a speciﬁc herbicide.

NOMENCLATURE: Dicamba, 2-methoxy-3,6-dichlorobenzoic acid; Glufosinate, 2-
amino-4-(hydroxymethylphosphinyl)butanoic acid; Glyphosate, N-
(phosphonomethyl)g1ycine; Nicosulfuron, 2-[[[[(4,6-dimethoxy-2-

pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N, N-dimethyl-3-pyridinecarboxamide;

 

' Received for publication on Date, and in revised form on Date

33

Imazamox, 2- [4,5 -dihydro-4-methyl-(1—methy1ethyl)-5-oxo-1H—imidazol-2-yl]-5-
(methoxymethyl)-3-pyridinecarboxy1ic acid, ammonium salt; Common Lambsquarters,
Chenopodium album L. #CHEAL; Giant Foxtail, Setaria faberi Herrm. #SETFA; Large
Crabgrass, Digitaria sanguinalis (L.) Scop. #DIGSA; Velvetleaf, Abutilon theophrasti
Medicus. #ABUTH.

ABBREVIATIONS: ANOVA; analysis of variance, DAT; days after treatment, LSD;

least signiﬁcant difference.

34

INTRODUCTION

Adjuvant research had reached an all time high by the 1960’s. There were thousands of
adjuvants being discovered and used, although very little research was being directed
towards the efﬁcacy of the adjuvants (Grondin 1985). Up until very recently, adjuvant
research was directed towards spray droplet contact angle, surface tension and
spreadability (McWhorter 1982).

It was believed that decreasing the surface tension of a spray solution increases
spreadability and therefore increasing activity of an herbicide (Penner 1984). Under this
assumption, the method of evaluating adjuvants consisted of screening materials that
increased spreadability of a spray solution on artiﬁcial surfaces. They soon found out
that their method of evaluation was not only ﬂawed, but it had little value in identifying
effective adjuvants. They found that spreadability depended completely upon the type of
artiﬁcial surface that was used for testing (Penner 1984). There were adjuvants that
showed great potential on a glass surface, yet when tested on a leaf surface they did
poorly.

Today, adj uvant research has a very different focus. Screening of adjuvants by testing
with herbicides on plants is used to identify the most effective adjuvants. Effective
adjuvants are now found by screening in the greenhouse and ﬁeld studies with herbicides
that need adjuvants on weeds that are difﬁcult to control.

The objective of this study was to screen 19 experimental adjuvants with ﬁve
herbicides on various weed species to identify the most effective herbicide for a given

situation.

35

MATERIALS AND METHODS

General. The following studies were carried done between the greenhouses at Michigan
State University from May 1999 to March 2000. Plants applied with imazamox,
nicosulfuron and dicamba, were placed outside between greenhouses from May to
September of 1999, due to the very hot temperatures of the greenhouse. The area was
enclosed thereby leaving the plants undisturbed, however they were subject to
environmental conditions such as rain and cloudy days. Plants applied with glyphosate
and glufosinate were kept in the greenhouse from September 1999 to March 2000 and
were exposed to less variable conditions.

Weed Species. Four weed species, giant foxtail, common lambsquarters, velvetleaf, and
large crabgrass were used in this study. Seeds were placed in 945 ml plastic black pots,
using Baccto professional potting soil. Approximately 1 wk before herbicide application,
excess plants were removed from the pots, leaving 3-5 plants per pot, each with a similar
height and leaf stage to ensure a uniform stand for herbicide application. When plants
reached the 3-5 leaf stage, they were thinned down to 1 plant per pot for common
lambsquarters, 3 plants per pot for giant foxtail, 1 plant per pot for velvetleaf and 2 plants
per pot for large crabgrass.

Herbicide Application. A link belt sprayer was used with a ﬂat fan nozzle5 that
delivered 94 Lha'l spray volume at 138 kPa pressure and a boom height of 33 cm. We
used distilled water for the herbicide carrier to avoid any interaction that might occur

between the herbicide and hard water. Formulated glyphosate6 was tested on giant foxtail

 

5 TeeJet Flat Fan Nozzle SOOOSEV model Spraying Systems Co., Wheaton, IL 60188
6 Accord® Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO 63167

36

(0.406 kg/ha) and common lambsquarters (0.11 kg/ha). Formulated glufosinate7 was
tested on giant foxtail (0.101 kg/ha) and common lambsquarters (0.067 kg/ha).
Formulated imazamox8 was tested on common lambsquarters (0.015 kg/ha) and
velvetleaf (0.015 kg/ha). Formulated nicosulfuron9 was tested on giant foxtail (0.0056
kg/ha) and large crabgrass (0.0336 kg/ha). Formulated dicambalo was tested on
velvetleaf and common lambsquarters. Adjuvants were added to the spray solution at
0.25% (v/v). There were a total of ten trials and each trial was repeated.

Statistics. Data presented are the means of two experiments with four replications each.
Plants and treatment sequences were selected at random. Treatments were applied in a
random sequence in a double blind study, which means that the chemistry of the adjuvant
was not known nor was the sequence of treatment application known. Data were
subjected to ANOVA (SAS Institute 1996) and means were separated using Fisher LSD

with a P value of 0.05.

 

7 Liberty® AgrEvo USA Co., 2711 Centreville Rd. Wilmington, DE 19808

8 Raptor® American Cyanamid, One Campus Dr., Parsippany, NJ 07054

9 Accent® DF, DuPont C0,, Walker’s Mill, Barley Plaza Wilmington, DE 19898
'0 Banvel® Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO 63167

37

RESULTS AND DISCUSSION
Efﬁcacy of Citric Acid Esters as Herbicide Adjuvants

There were no adjuvants that increased the effectiveness of all ﬁve herbicides on all
weed species, which is consistent with adjuvant research today. However there was one
adjuvant that increased the effectiveness of three out of the ﬁve herbicides: adjuvant 18
increased the herbicidal activity of glufosinate, imazamox and nicosulfuron on all weed
species. Adjuvant 8 increased efﬁcacy of imazamox, nicosulfuron and dicamba but not
of glyphosate or glufosinate on all weed species tested.

Glyphosate. The only adjuvant that increased the efﬁcacy of glyphosate on both
common lambsquarters and giant foxtail was adjuvant 7 (Table 1). However treatment
number 8 was most effective for increasing glyphosate efﬁcacy on common
lambsquarters and treatment number 10 for giant foxtail. There were no adjuvants that
increased the effectiveness of glyphosate compared to the herbicide alone treatment for
common lambsquarters and not on giant foxtail. There were two adjuvants that increased
the effectiveness of glyphosate compared to the herbicide alone for giant foxtail but not
for common lambsquarters, treatments 3 and 17 (Table 1).

Glufosinate. There were three adjuvants that increased efﬁcacy of glufosinate on both
common lambsquarters and giant foxtail, adjuvant 4, 10 and 18(Table 2). However
adjuvant number 4 was the most effective for both weed species. There was only one
adjuvant that increased the effectiveness of glufosinate signiﬁcantly compared to the

herbicide alone for common lambsquarters and not on giant foxtail, adjuvant 19. There

38

were four adjuvants that increased the effectiveness of glufosinate signiﬁcantly compared
to herbicide alone for giant foxtail and not for common lambsquarters, adjuvants 11, 12,
13 and 15. However adjuvant number 11 was the most effective (Table 2).

Imazamox. There were ﬁve adjuvants that increased the effectiveness of imazamox on
both common lambsquarters and velvet leaf, 2, 6, 8, 11, and 18, however adjuvant
number 6 was the most effective for both weed species (Table 3). There were two
adjuvants that increased the effectiveness of imazamox signiﬁcantly compared to the
herbicide alone for common lambsquarters and not on velvetleaf, adjuvant 5 and 13.
There were no adjuvants that increased the effectiveness of imazamox signiﬁcantly
compared to herbicide alone for velvetleaf and not for common lambsquarters (Table 3).

Nicosulfuron. There were several adjuvants that increased the effectiveness of
nicosulfuron compared to the herbicide alone treatment, 3, 7 through 10, 14 and 18
(Table 4). However the adjuvant that was the most signiﬁcant was number 10. Adjuvant
number 5 was most effective for glyphosate control on giant foxtail and adjuvant number
10 on large crabgrass. There were several adjuvants that increased the effectiveness of
nicosulfuron signiﬁcantly compared to the herbicide alone for giant foxtail and not on
large crabgrass, 2, 4, 6, 11, 12, 13, 15, 16, 17, and 19, however adjuvant number 11 was
the most effective. There were no adjuvants that increased the effectiveness of
nicosulfuron signiﬁcantly compared to herbicide alone for large crabgrass and not for
giant foxtail; however the most effective adjuvant compared to herbicide alone was
adjuvant number 10 (Table 4).

Dicamba. There was only one adjuvant that increased the effectiveness on both

common lambsquarters and velvetleaf, adjuvant 8 (Table 5). However, adjuvant number

39

11 was the most effective for control with dicamba on common lambsquarters and
treatment number 7 on velvetleaf. There were two adjuvants that increased the
effectiveness of dicamba significantly compared to herbicide alone for common
lambsquarters and not giant foxtail, adjuvant 11 and 14. There were no adjuvants that
that increased the effectiveness of dicamba signiﬁcantly compared to the herbicide alone
only on giant foxtail (Table 5).

Adjuvant screening can take on many different goals. For example, adjuvants can be
screened against several different herbicides to determine which herbicide with which the
adjuvants are most effective. We evaluated whether the adjuvants worked with all
herbicides on all weed species. Some adjuvants are weed species speciﬁc whereas others
are simply herbicide speciﬁc and some are both. All this information is very important
when identifying the most effective adjuvant to use for a speciﬁc situation. Information
on weed speciﬁc adjuvants may prove to be very useful in today’s market, especially
with the invention of glyphosate resistant crops. For example those adjuvants that are
effective only on monocots may prove to be very useful on glyphosate resistant corn.
Whereas those adjuvants that were effective only on dicots would be useful for
glyphosate resistant soybeans. Although conclusions on the efﬁcacy of the adjuvants can
be drawn, all potentially effective adjuvants need to be compared with those already on

the market.

40

LITERATURE CITED
Grondin, B. 1985. Working through the confusion of adjuvants.
Agrichemical Age. pp. 6-8.
McWhorter, C. G. 1982. The use of adjuvants. Adjuvants for Herbicides.
Champaign, IL Weed Science Society of America.
Penner, D., K. VanFleteren, and F. Roggenback. 1984. Evaluation of soybean oil
concentrates as a substitute for petroleum oil based crop oil concentrates. Proceedings:

Ag-Chem Uses of Soybean Oil. Workshop: American Soybean Association. pp. 26-29.

41

Table 1. Efﬁcacy of experimental adjuvants with glyphosate on common
lambsquarters and giant foxtail.

 

 

 

Adjuvant Common lambsquarters Giant foxtail
_______ z DAT14DAT7DAT14DAT
(% Control) (% Control)
1 54 69 71 5
2 61 71 71 71*
3 59 60 75* 74*
4 78* 73 70 64*
5 68* 83* 7O 78*
6 59 89* 71 69*
7 68* 93* 74* 75*
8 83* 95* 71 66*
9 55 64 74* 70*
10 68* 90* 71 85*
11 6O 71 71 70*
12 55 78* 70 64*
13 51 79* 70 65*
14 68* 93* 73 75*
15 66* 74 71 66*
16 54 84* 71 66*
17 61 84 74* 66*
18 53 74 71 69*
19 6O 76* 71 63*
20‘!l 56 64 7O 26
21b 0 o 0 0
LSDoos 8.0 12.8 3.7 10.5
aHerbicide alone
bControl

tValues that were signiﬁcantly greater from the herbicide alone treatment

42

Table 2. Efﬁcacy of experimental adjuvants with glufosinate on common
lambsquarters and giant foxtail

 

 

 

Adjuvant Common lambsquarters Giant foxtail
...... 7 .QAI.-._._._-_.1_4.DAI_._--.---.7_DAI_.-.-._.-.l.‘1.1_3.A_T._._-_
(% Control) (% Control)
1 22 16 33* 25
2 98* 95* 36* 21
3 81* 68 51* 33*
4 86* 78* 58* 48*
5 84* 58 35* 25
6 84* 68 28* 19
7 65 49 25* 21
8 81* 66 21* 11
9 53 21 25* 15
10 95* 90* 43* 31*
11 15 6 41* 35*
12 64 30 29* 30*
13 54 3O 41* 29*
14 74* 43 26* 24
15 19 8 43* 38*
16 35 29 25* 23
17 56 26 20* 23
18 90* 78* 26* 30*
19 88* 76* 8 20
20a 59 50 6 15
21b 0 0 o 0
LSDo.os 14.1 18.5 11.9 11.9
“Herbicide alone
bControl

'Values that were signiﬁcantly greater from the herbicide alone treatment

43

Table 3. Efﬁcacy of experimental adjuvants with imazamox on common
- lambsquarters and velvetleaf.

 

 

 

Adjuvant Common lambsquarters Velvetleaf
7DAT14DAT7DAT14DAT
(% Control) (% Control)
1 15 5 15 4
2 26* 70* 26* 50*
3 31* 69* 19* 36
4 23* 61 13 46
5 30* 76* 16 43
6 34* 78* 25* 56*
7 33* 68* 16 55*
8 31* 79* 20* 55*
9 28* 71* 13 50*
10 20* 61 16 41
11 24* 73* 21* 55*
12 25* 65 11 20
13 20* 70* 11 36
14 16 63 9 40
15 26* 61 10 40
16 19* 64 6 9
17 21* 63 10 35
18 24* 69* 19* 51*
19 19* 64 15 50*
20a 13 55 10 38
21b 0 0 0 o
LSDo.os 5.6 10.5 6.6 11.2
aHerbicide alone
bControl

'Values that were signiﬁcantly greater from the herbicide alone treatment

44

Table 4. Efﬁcacy of experimental adjuvants with nicosulfuron on large crabgrass
and giant foxtail.

 

 

 

Adjuvants Large crabgrass Giant foxtail
- _____ 7.12.4: ........... 1 3.1.3.24: __________ 7.12.41? ........... 1 -4.par_-_._
(% Control) (% Control)
1 - 21 25 5
2 - 58 50* 71*
3 - 70* 51* 74*
4 - 53 50* 64*
5 - 58 51* 78*
6 - 58 56* 69*
7 - 80* 51* 75*
8 - 61* 50* 66*
9 - 69* 53* 70*
10 - 84* 54* 75*
1 1 - 48 51* 70*
12 - 49 53* 64*
13 - 48 55* 65*
14 - 64* 54* 75*
15 - 58 50* 66*
16 - 39 53* 66*
17 - 55 53* 66*
18 - 69* 54* 69*
19 - 48 53* 63*
20a - 48 3O 26
21b - 0 0 0
LSDo.os - 10.7 3.4 10.5
aHerbicide alone
bControl

‘Values that were signiﬁcantly greater from the herbicide alone treatment

45

Table 5. Efﬁcacy of experimental adj uvants with dicamba on common
lambsquarters and velvetleaf.

 

 

 

Adjuvant Common lambsquarters Velvetleaf
_______ 7 DAT14DAT7DAT14DAT
(% Control) (% Control)

1 43 75* 14 3O

2 59 74* 20 30
3 59 74* 30 40*

4 44 85* 26 39
5 55 85* 31 _ 49*
6 56 69* 35* 51*
7 55 76* 34* 54*
8 66* 81* 34* 44*

9 60 78* 29 30

10 59 83* 29 36

11 69* 85* 16 28

12 51 70* 25 36

13 6O 79* 30 35

14 68* 76* 24 29

15 51 76* 23 28

16 50 76* 25 21

17 51 74* 25 25

18 51 78* 28 39

19 55 70* 18 29

20a 45 53 26 31
21b 0 0 0 0
LSDo.os 17.2 10.9 8.0 9.4

aHerbicide alone
bControl

‘Values that were signiﬁcantly greater from the herbicide alone treatment

46

 

CHAPTER 3
The Effect of UV Light on Bas 620 and Clethodim Photodegradation and the

Efﬁcacy of Querciten as a Potential UV Protectantl

HEATHER ENID JOHNSON

Abstract. Various cyclohexanediones are known to be vulnerable to
phototransformation. Plants produce compounds that protect themselves from
phototransformation; two such compounds are carotenoids and quercetin. Upon
conﬁrmation of the photolability of BAS620 (spectrophotometrically and in the
greenhouse) and clethodim (in the greenhouse), carotenoids and quercetin were
evaluated for their ability to prevent phototransformation of the two herbicides.
Giant foxtail plants were grown in the greenhouse and thinned down to 2 to 3
plants per pot. The herbicides were applied when plants reached the 3 to 5 leaf
stage. Formulated clethodim (Select 2EC) was applied at 0.007 kg/ha. Following
herbicide application, plants were exposed to UV light in a UV chamber where
plants were continually rotated to assure uniform exposure to the UV light. Plants
were exposed for O, 1, and 3 hours and returned to the greenhouse where they were
evaluated at 7 and 14 DAT. Tests showed that BAS 620 was labile when exposed

to UV light, and evaluated spectrophotometrically. Greenhouse studies also

 

' Received for publication on , and in revised for on

47

conﬁrmed photolability of BAS 620. Upon conﬁrmation of the photolability of
BAS 620, both carotenoids and quercetin were evaluated for their potential as UV
protectants. At the carotenoid concentrations tested, they were ineffective at
preventing photodegradation. However quercetin appeared to be effective both
spectrophotometrically and in greenhouse evaluations.

KEY WORDS: Quercetin, Carotenoids, UV Protectant, and Clethodim
NOMENCLATURE: BAS 620 C17H24CINO4; Clethodim (i)-2-[(E)-1-[(E)—3-
Chloro-allyloxyimino]propyl]-5-[2-(ethylthio)propyl]—3-hydroxy-2-cyclohexen-l-
one; Quercetin, 2-(3,4-Dihydroxyphenyl)-3,5,7-trihydroxy-4H-1-benxopyran-4-
one; Giant Foxtail, Setariafaberi Herrm. #SETFA;

ABBREVIATIONS: DAT, days after treatment; EC, emulsiﬁable concentrate

48

INTRODUCTION

Various cyclohexanediones are known to be vulnerable to phototransformation
such as clethodim (Figure 1a) (McMullan 1996; Falb 1990) and sethoxydim
(Matysiak 1999; Campbell 1985). As a result, herbicides may either lose or gain
activity, depending on the activity of the breakdown product. For those
compounds that lose activity upon phototransformation, a material that could
prevent transformation would prove to be beneﬁcial.

There are many known compounds that naturally protect a plant from
phototransformation. Plant systems contain natural defense mechanisms, which
absorb UV light thereby preventing photodegradation. Two such mechanisms
involve carotenoids and/or quercetin.

Carotenoids are known to absorb UV light in both plants (Cen 1990; DeChazal
1994; Gerber 1994; Middleton 1993) and animals (Black 1998; Cuadra 1997; Gotz
1999; Harbome 1984; Krinsky 1989; and Savoure 1995). Quercetin has also been
shown to absorb UV light in plants (Harbome 1984; Mohle 1985; Olsson 1998;
Steerenberg 1998; Takahama 1984; Zhestkova 1984). Since carotenoids and
quercetin are naturally occurring compounds and easy to obtain both were tested
for their ability to protect herbicides from UV light, or phototransformation.

The ﬁrst objective of this study was to determine the photolability of BAS 620
(Figure 1b) spectrophotometrically and in the greenhouse, and to evaluate
carotenoids as a UV protectant for BAS 620. The second objective was to conﬁrm
the photolability of formulated clethodim (Select 2EC) and evaluate quercetin

(Figure 2) as a UV protectant.

49

MATERIALS AND METHODS
BAS 620
Spectrophotometry. A spectral analysis of BAS 620 was obtained using the
Spectronic Genesys 5. Solutions of BAS 620 diluted with methanol were prepared
at four concentrations 0.06, 0.25, 0.5 and 1 mg ml'l. An absorption spectrum was
created using a program for spectral scans on the spectrophotometer from 200 nm
to 700 nm. The peak absorbencies were labeled and printouts were obtained.
Exposure to UV Light. Photolability of BAS 620 was conﬁrmed by exposing the
herbicide to UV light followed by a spectral analysis. The same four
concentrations were used to determine the effect of UV light on BAS 620. A
system was devised to expose an herbicide to UV light in a consistent manner.
The UV light source was an enclosed system with bulbs emitting 300 nm
surrounding the opening in the center of the system. A rotating test tube rack in
the center of the chamber allowed each test tube to be exposed to the same
intensity of light. In replicates of four, the herbicide was monitored at its peak
absorbency for degradation using the spectrophotometer. Recordings of the peak
absorbance were monitored for change (increase or decrease in peak absorbance).
A spectral scan was performed before UV exposure and after 6 hr to determine if
photodegradation had occurred.
UV Protectants. Breakdown of an herbicide molecule may result in loss of
activity, therefore, if a compound could prevent phototransformation, no activity
would be lost. Both carotenoids and quercetin are known to absorb UV light in

plant systems, thereby preventing negative effects from the UV light

50

 

 

Carotenoids were extracted from carrots (baby carrots from Mann’s Sunny
Shores). Several methods of carotenoid extraction were attempted but only one
method was compatible with the spectrophotometer.

One gram of freeze-dried carrots was added to 75-ml acetone and blended for
approximately 3-5 min supernatant was collected and centrifuged for 10 minutes.
The supernatant was again collected and the volume was reduced under vacuum,
leaving behind only the carotenoids which were then re-dissolved in hexane (1 mg
ml") (hexane was the only solvent that could be used other than acetonitrile).

Once the carotenoids were extracted, they were added to BAS 620 and exposed
to UV light for 0, 2, 8, 10 and 12 hr to determine if the carotenoids prevented
phototransformation of BAS 620. There were ﬁve concentrations of carotenoids
tested; 0, 0.625, 0.25, 0.5 and 1mg ml". BAS 620 concentration was 0.00025 mg
ml'1 with hexane as the solvent. In order to determine the effect of BAS 620 alone,
a control was included which contained hexane and carotenoids at each carotenoid
concentration. Evaluations were made by taking absorbency readings at the peak
absorbance for BAS 6200f 274 nm at each time interval.

Quercetin is easily dissolved by methanol and acetone (unfortunately acetone
could not be used due to interference with the spectrophotometer readings). BAS
620 was diluted with methanol to 0.000625 mg ml’1 and quercetin was added to
BAS 620 at a concentration of 0, 0.2 and 0. 4 mg ml'l. Methanol plus quercetin, at
each concentration, was used as a blank, thereby analyzing the effects of UV light

on BAS 620 in the presence of quercetin.

51

 

Greenhouse Studies. Giant foxtail plants were grown in 945-ml black pots in the
greenhouse, using Baccto (Professional potting soil) potting soil. Approximately 1
wk before herbicide application, excess plants were removed from the pots,
leaving 3-5 plants per pot each with a similar height and leaf stage. When the
plants reached the 3-5 leaf stage, the plants were thinned to 3 plants per pot for
herbicide application.

BAS 620 was subjected to UV irradiation in the UV light chamber (previously
described), for 0, 1, and 3 hours. Upon completion of UV irradiation, BAS 620
was applied to giant foxtail at a rate of 0.007 kg ha'1 using a link belt sprayer with
a ﬂat fan nozzle4 that delivered 94 Lha’l spray volume at 138 kPa pressure and a
boom height of 33 cm. The commercial adjuvant, Scoil, was included at 0.5%
(v/v). Data presented are the means of the two experiments with three replications

each.

CLETHODIM
Clethodim is known to be a photolabile compound (Falb 1990). To conﬁrm

5, the herbicide was subjected to UV

photolability of formulated clethodim
irradiation and sprayed on giant foxtail.
Irradiation-)Herbicide Application. Plants were grown in 945-ml black pots as

previously described. Select 2EC was placed in test tubes and into the UV

chamber, previously described, for 0, 1, and 3 hr.

 

4 TeeJet Flat Fan Nozzle 80005EV model Spraying Systems Co., Wheaton, IL 60188
5 Formulath as Select 2EC

52

Herbicide Application. Irradiated and non-irradiated clethodim was sprayed on
giant foxtail at a rate of 0.007kg ha’1 using a link belt sprayer with a ﬂat fan
nozzle6 at 94 Lha'l spray volume, 138 kPa pressure and a boom height of 33 cm.
The adjuvant Scoil was applied with clethodim at 0.5% (v/v). Data presented are
the means of two experiments with three replicates of each treatment.

Herbicide Application-)Irradiation. For the second part of the greenhouse
study, giant foxtail seeds were planted in yellow cone pots, 15 cm tall and 2.5 cm
wide. Plants were kept in the greenhouse and watered daily and as needed. When
the plants reached the 3-5 leaf stage, plants were thinned down so that only one
giant foxtail plant remained for herbicide application.

A holder was made to carry the yellow cone pots that ﬁt inside the UV chamber
on the rotating stand. The holder was constructed out of Styrofoam and covered
with aluminum foil to prevent melting by the UV light. Nine slots were made on
the perimeter of the holder. The holder was used both in the herbicide application
and in the UV chamber.

Herbicide Application. In the ﬁrst application, clethodim was applied at a rate of
0.007 kg ha'1 using a link belt sprayer with a ﬂat fan nozzle7 delivered at 94 Lha'1
spray volume at 138 kPa pressure and a boom height of 33 cm. Tap water was the
spray solution carrier. In addition to the tap water, 5% acetone was included since
it was included in the spray solution including quercetin. In the second application,
quercetin was added to the spray solution at 0.4 mg ml'1 (quercetin was dissolved

in 5% acetone).

 

5 TeeJet Flat Fan Nozzle 80005EV model Spraying Systems Co., Wheaton, IL 60188
5 TeeJet Flat Fan Nozzle 80005EV model Spraying Systems Co., Wheaton, IL 60188

53

UV Exposure. Plants were then placed into a dark box and transported to the UV
chamber for irradiation. Each yellow cone pot holder contained 3 pots that were
sprayed with herbicide alone, 3 pots that were sprayed with herbicide plus
quercetin and 3 pots that were controls. The holder was placed on the rotating rack
in the UV chamber and exposed for 0, 1 and 3 hr (at 4 hr the control plants
suffered damage from UV light) and returned to the greenhouse. The experiment

was repeated.

RESULTS AND DISCUSSION
BAS 620
Spectrophotometry and Exposure to UV Light. A spectral scan was obtained
ranging from 200 nm-700 nm. The spectral scan of BAS 620 had two peaks, one
that tended to go off the scale at extremely low concentrations and another peak at
274 nm. (Therefore all readings done on the spectrophotometer with BAS 620
were read at 274 nm). Another clue to the phototransformation of BAS 620 was
the reduction of absorbance at 274 nm, an indication that the parent product
increased (Figure 3a). When BAS 620 was exposed to UV light, a third peak
appeared on the spectral scan, suggesting that UV light had indeed
phototransforrned BAS 620 (Figure 3b).
UV Protectants.
Carotenoids. Table 1 shows that BAS 620 behaved similarly with and without

carotenoids. An increase in the absorbance at 274 nm occurred regardless of the

54

presence of carotenoids. Since the absorbance increased regardless of the presence
of carotenoids, they did not act to protect BAS 620 from the effects of UV light.
Carotenoids should be effective at preventing herbicidal breakdown since they
absorb light in the UV portion of the light spectrum. It may be that the carotenoids
were not pure enough or the concentration was too low.

Quercetin. Table 2 compares the effects of UV light on BAS 620 absorbance
spectrum with and without quercetin. Unlike the results found using carotenoids,
the absorbance for BAS 620 plus quercetin remained constant. The effect of UV
light on BAS 620, as seen in both Tables 1 and 2, was a steady increase in
absorbance at the peak absorbance (274 nm) suggesting that was preventing
phototransformation.

Greenhouse Studies. Greenhouse studies conﬁrmed that after exposure to UV
light there was a decrease in biological activity of BAS 620 at 7 DAT (Figure 4).
However since there were no statistical differences at 14 DAT between 0, 1 and 3
hr of UV irradiation, an herbicide known to be photolabile, clethodim, was used

for the remainder of the research.

Clethodim

Irradiation 9Herbicide Application.

Photolability of commercially formulated clethodim was conﬁrmed in the
greenhouse (Figure 4). Figure 3b showed that non-irradiated clethodim was more
active than if it were irradiated for 1 and 3hrs. Therefore, since photolability was

conﬁrmed, a protectant would be a useful addition to clethodim.

55

Herbicide Applicationélrradiation.
After quercetin was added to the spray solution and plants were irradiated in the
UV chamber for 0, 1, and 3 hr (Table 3), there was a signiﬁcant difference between
those with quercetin added to the spray solution and those without quercetin at 3
hours after irradiation (Figure 5). Spraying the plants with the herbicide plus
quercetin ﬁrst and then irradiating the plants in the UV chamber proved to be an
effective way to determine both photolability and the efﬁcacy of a given UV
protectant under for more realistic conditions than irradiated spray droplets on a
glass slide or spray solution in a test tube.

Interestingly, the formulated clethodim still appears to be subject to
phototransformation and increased herbicide efﬁciency should be possible with

more effective UV protectants.

56

LITERATURE CITED

Black, HS. 1998. Radical Interception by Carotenoids and Effects on

UV Carcinogenesis. Nutr—cancer. 31(3):212-217.

Campbell, JR. and D. Penner. 1985. Abiotic transformation of

sethoxydim. Weed Sci. 33:435-439

Cen, Y.P. and IF. Bomman. 1990. The response of bean plants to UV-B

radiation under irradiances of background visible light. J-Exp-Bot. 41 : 1489-1495.

Cuadra, P., J.B. Harboume, and PG. Waterman. 1997. Increases in
surface ﬂavonols and photosynthetic pigments in gnaphalium luteo-album in

response to UV-B radiation. Phytochem. 45:1377-1383.

De-Chazal N. M. 1994. Characterization of a brown nostoc species from

java that is resistant to high light intensity and UV. Society for

General Microbiology. 140:3183-3189.

Falb, L., D. Bridges and A. Smith. 1990. Effects of pH and adjuvants on

clethodim photodegradation. J. Agric. Food Chem. 38:875-878.

57

Gerber, S, and DP. Hader. 1994. Effects of enhanced UV-B irradiation on
the red coloured freshwater ﬂagellate Euglena sanguinea. FEMS-Micorbioal-

Ecol. 13:177-184.

Gotz, T., U. Windhovel, P. Boger and G. Sandmann. 1999. Protection of
photosynthesis against UV-B radiation by carotenoids in transforrnants of the

Cyanobacteriu synechococcus PCC7492. Plant Physiol. 120:599-604.

Krinsky, NI. 1989. Carotenoids and cancer in animal models. J-Nutr. 119:123-

126.

Matysiak, R. and J. Nalewaja. 1999. Temperature, adjuvants and UV light

affect sethoxydim phytotoxicity. Weed Techol. 13:94—99.

McMullan, RM. 1996. Grass herbicide efﬁcacy as inﬂuenced by adjuvant, spray

solution pH, and ultraviolet light. Weed Technol. 10:72-77.

Middleton, EM. and AH. Teramura. 1993. The role of ﬂavonol glycosides and

carotenoids in protecting soybean from ultraviolet-B damage” Plant Physiol.

103:741-752.

58

Olsson, L.C., M. Veit, G. Weissenbock, and IF. Bomman. 1998. Differential
flavonoid response to enhanced to UV-B radiation in Brassica napus” Phytochem.

49:1021-1028.

Savoure, N., G. Briand, et al. 1995. Vitamin A status and metabolism of
cutaneous plyamines in the hairless mouse after UV irradiation; action of beta-carotene

and astaxanthin. Int-j-vitam-nutr-res. 65:79-86

Steerenberg, P.A., J. Garssen et al. 1998. Protection of UV-induced suppression

of skin contact hypersensitivity: a common feature of ﬂavonoids after oral administration.

Photochem Photobiol. 67:456-461.

59

Table 1.

Absorbency readings were taken at the peak wavelength of 274nm.

The evaluation of carotenoids as a UV protectant for BAS 620.

 

 

 

 

 

 

 

 

 

 

 

 

Length of Irradiation
Herbicide + Calculations 0 hr 2 hr 8 hr 10 hr 12 hr
Carotenoids (O.D.) 3 (OD) (O.D.) (O.D.) (O.D)
BAS 620 + Mean 2.079 2.001 2.408 2.566 2.808
0 mg ml“
Difference -0.078 0.329 0.487 0.729
BAS 620 + Mean 1.719 1.661 1.988 2.126 2.298
1 mg ml'1
Difference -0.058 0.269 0.407 0.579
(Asa-before) 2,.
BAS 620 + Mean 1.753 1.681 1.998 2.146 2.331
0.5 mg ml'1
Difference -0.072 0.245 0.393 0.578
(After-before) ..__ __
BAS 620 + Mean 1.774 1.739 2.062 2.224 2.416
0.25 mg ml'1
Difference -0.035 0.288 0.466 0.642
(After-before)
BAS 620 + Mean 1.749 1.682 1.983 2.187 2.350
0.06 mg ml'1
Difference -0.067 0.234 0.438 0.601
(After-before)
8 Optical Density

*Herbicide concentration = 0.00625 mg ml”1

60

Table 2. Evaluation of quercetin as a UV protectant for BAS 620. Absorbency
readings were taking at the peak wavelength of 274 nm.

 

 

 

 

 

 

____ Length of Irradiation
Treatment 0 hr 2 hr 5 hr
(O.D.) (O.D.) (O.D.)
BAS 620 + 2.358 2.836 2.947
0 mg ml" -
BAS 620 + 2.241 2.274 2.402
02mgmlif-.-
BAS 620 + 2.363 2.388 2.277
0.4 mg ml'I

 

 

*Herbicide concentration = 0.00625 mg ml“1

61

Table 3. Evaluation of quercetin (Q) as a UV protectant with clethodim for
control of giant foxtail.

 

 

 

 

 

 

 

Treatment Time Irradiated 7 DAT 14 DAT
(hr) (% Control)
Clethodim + Q 0 52d 53c
Clethodim - Q 0 55c 550
___Control ___0 _____________ 06 0d
Clethodim + Q 1 58b 53c
Clethodim - Q 1 53cd 56c
.__.C_.ontrol - .......... I. ............................ 0e .- 0d
Clethodim + Q 3 78a 75a
Clethodim - Q 3 60b 68b
Control 3 0c 0d

 

*Herbicide Rate = 0.007 kg/ha

62

 

 

 

 

 

 

CH3
I
CH3-CH2-S-CH-H2C
\
:0
O? \(‘\=N-O-CH2-CH=CH-Cl
CHrCH3
B.
/
o / N O W0
\on

Figure 1. A) Structure of clethodim B) Structure of BAS 620

63

 

Figure 2. Structure of quercetin

64

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.374
274nm
2009
ABS
0.002
200 nm 700 nm
B.
4.00
274nm
2.764
ABS
0.002
200 nm 700 nm

Figure 3. Spectral scans for BAS 620 from 200nm to 700nm a) Before exposure
to UV light b) After exposure to UV light

65

 

 

 

Photolability of BAS 620

 

_l
O
O

    
 
 
 
 
 
 

 

 

 

80 -
g 50 . 0hr
0 I 1 hr
5
"3, 40- u 3hr
.\ El Control

 

N
O
I

 

 

0-

 

7DAT 1 4DAT

 

 

Photolability of Clethodim

 

_l
O
O

    
 
 
 
 
 
 

 

 

 

80*
>.
g 60‘ IEOhr
E I1hr
"J 40_ U3hr
°\ DControl

 

N
O

 

7DAT 1 4DAT

 

 

 

Figure 4. Conﬁrmation of photolability for BAS 620 and clethodim 0, l, and 3 hr after
exposure to UV light

66

 

Quercetin as a UV Protectant
(UV Exposure = 3hr)

 

illllllil||iililii|“,lz
”lllllilllli!ll!gilu;
’l‘lllitilllumlmm
11111111111
llllfllillliilllﬁliyl

% Efficacy

1111110

 

 

 

 

 

 

Figure 5. Evaluation of quercetin as a UV protectant for clethodim O and 3 hr aﬁer

exposure to UV light.

67