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THESIS

LIBRARY

Michigan State
University

 

ABSTRACT

THE INFLUENCE OF HERBICIDES
ON SELECTED GROUND COVER PLANTS

By Donald Bernard Carlson

Weed control in gromd cover plantings has been a problem, both
economically and aesthetically, to commercial nurserymen and home-
owners alike. Though the cost factor is more important to the former,
the labor involved for hand weeding practices, is just as tedious to the
latter. With this in mind, the following investigations were conducted
on the effectiveness of pre- and postemergence applications of herbicides
on new and established ground cover plantings. At the same time, studies
were made to gain a better understanding of triazine and phenylurea induced
chlorosis. An elucidation of this mechanism would eliminate potential
herbicide users fear of such injury.

Pre -emergence application of eight chemicals on new plantings, and
postemergence application of nine chemicals on simulated established
plantings were made, and subsequently rated for weed control, and the
occurrance of injury on the ground cover species.

Simazine, at two pounds per acre, diuron at two pounds per acre, and
simazine plus paraquat at two plus one ~eighth pound per acre, respectively,
gave the best results on new plantings. Postemergence applications of
linuron at two and four pounds per acre gave good weed control, but ground
cover burning was so severe that these treatments would be commercially
unacceptable.

Greenhouse experiments were conducted to study the chlorosis problem.
Treatments were made with herbicide solutions at concentrations ranging

from 0.25 to 40 ppm.

Donald Bernard Carlson - 2

There was no true correlation between the solubility of a herbicide
and the type of chlorosis caused. In general, herbicides of higher solubility
cause an interveinal chlorosis, whereas, those of lower solubility induce
veinal chlorosis. This leads to the hypothesis that the availability of a
herbicide, as influenced by its water solubility as well as the mode of

action, will influence the type of chlorotic injury induced.

THE INFLUENCE OF
HERBICIDES ON SELECTED
GROUND COVER PLANTS

By
Donald Bernard Carlson

A THESIS

Submitted to
the School for Advanced Graduate Studies of
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

1964

ACKNOWLEDGEMENTS

The author wishes to extend sincere appreciation to Dr. Harold
Davidson for his guidance throughout this investigation, and for his
encouragement during the Master's program.

Further appreciation is extended to Dr. Stanley K. Ries for his
suggestions throughout this study. Thanks is also extended to
Dr. Roy A. Mecklenburg for his advice pertaining to the results and

discussion portions of this thesis.

ii

TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS .......... . .......... ii
TABLEOFCONTENTS ......... iii
LIST OF TABLES O O O O O O O O O O O O O O O O O O O O O I 0 v
MRODUCTION O O O O O O ..... O O O O ...... O O 1
REVIEW OF LITERATURE .......... . . . . . . . 3
Herbicide History 3
Weed Damage 3
Herbicide Control and Associated Injury 4

Mode of Action of Chlorosis Inducing Herbicides 7
MATERMIS AND METHODS O O O O O O O O O O O O O O O O O 13
Field Experiments ‘ 13
General 13
Pre-emergence Studies 13
Postemergence Studies 13
MATERIALS AND METHODS O O O O O O O O O O O O O O O O O 16
Greenhouse Experiments 16
Experiment I - Toxicity Level Studies 16
Experiment 11 - Chlorotic Injury 17
Experiment HI - Chlorotic Injury 17
RESULTS 0 O O O O O O O O O O O O O O O ......... O O 19
Field Experiments l9
Pre-emergence Studies 19
Postemergence Studies 19
DISCUSSION AND CONCLUSIONS ...... . . . . . . . . . 22

Field Experiments 22

iii

RESULTS ..... O O O O O O O 0

Greenhouse Experiments

Experiment I

Experiment 11 and III

DISCUSSION AND CONCLUSIONS . . . . . . . . .

Greenhouse Experiments

LITERATURE CITED .

iv

Page
24
24
24
25
26
26
28

29

LIST OF TABLES

Tables Page
I. Effect of fall application of herbicides on
pre -emergence weed control in ground-
cover plantings O O O I O O O O O O O O I O O O O O 20
II. Effect of spring application of herbicides on
postemergence weed control in ground-
coverplantings................. 21

INTRODUCTION

"In the beginning God created the heavens and the earth. And God
said, 'Let the earth put forth vegetation, plants yielding seed, and
fruit trees bearing fruit in which is their seed, each according to its
kind, upon the earth. ' And it was so. The earth brought forth vegeta-
tion, plants yielding seed, each according to their own kinds. " (1)

And so it was that part of the vegetation was weeds, the curse of the
agrarian societies.

Weeds have plagued man since earliest time, and their control has
presented a challenge that often seems insurmountable. One area where
the control of weeds has attracted the interest of many people is in
ornamental plantings. Great progress has been made with the use of
herbicides in this area since 1955. But many plantsmen are still reluc-
tant to reap the harvest of advantages offered by this control method. One
of the major reasons for this hesitation has been the fear of injury that
can result from the misuse of herbicides. Increased research since 1959,
and publications of the results, has brought about a phenominal grth in
the number of users of chemical control measures, but still little has been
done to investigate the basis of herbicide induced injury. Unusual injury
symptoms such as veinal and interveinal chlorosis have been noted with the
use of herbicides having almost identical modes of action. In addition to
this, the area of weed control in new and established ground cover plantings
still presents a problem.

This study was undertaken to evaluate herbicides for weed control in
new and established ground cover plantings, to determine the tolerance of
various ground cover species to herbicides, and as a preliminary study

of herbicide induced chlorosis.

The names, terms and abbreviations used throughout this thesis
in reference to chemical materials are those adapted by the Weed
Society of America, as reported in Weeds, Volume 10, Number 3,

July, 1962 .

REVIEW OF LITERATURE

Herbicide History

 

Weed control has progressed through the ages from hands and
hoe to cultivator and plow. The present use of chemicals, however,
marks the outstanding technological advancement in this field. One
of the first records of the use of chemical materials to kill weeds was
around the latter 1890's, when Bonnett in France, Schultz in Germany,
and Bolley in the United States, all working independently, found that
solutions of copper salts would selectively kill broadleaved weeds in
cereals. 1 In 1908 Bolley found that table salt, iron sulfate, copper
and sodium arsenite would successfully control weeds in wheat. These
discoveries were followed by Pokorny's chemical synthesis techniques
for 2,4-dichlorophenoxyacetic acid, and its later application as a growth
regulator and selective herbicide by workers such as Zimmerman and
Hitchcock (30), Blackman (6), and Hamner and Tukey (15, 16).2

Though herbicides are a relatively new tool in man’s fight to control
plant competition in his environment, if used properly they can often do

the job better and more economically than other methods.

Weed Damage

 

Poor growth of ground cover plantings due to weeds is a factor worthy
of note when considering control. In new plantings that become infested
with weeds, the necessity for cultivation and hoeing reduces the nurseries'

efficiency since such practices increase cost. Furthermore, damage to the

 

1Excerpt from Klingman (18) page 9.
2Portions taken from Klingman (18) pages 9 and 10.

3

roots of wanted plants is always a risk associated with cultivation. Of
great importance is the fact that many ground cover plants at their
start do not effectively compete against heavy weed growth. One of

the major purposes of ground covers is to form a thick mat preventing
weed growth. Thus, the necessity for getting vigorously growing plants
as soon as possible is obvious. By eliminating weeds you eliminate
competition for factors, such as: soil moisture and soil nutrients, so
important for the growth of a plant.

In 1960 it was reported that good weed control had been obtained with
2-chloro-4, 6-bis(ethylamino)-s-triazine, (simazine), and 2-chloro-4 -
ethylamino-6-isopropy1aminofs-triazine, (atrazine), used on ornamentals
at rates up to ten pounds of active ingredient per acre (21). The results
of these experiments, conducted over a three year period from 1957 to
1959, showed that injury to most nursery crops was negligible, but
injury symptoms, including yellowing of the foliage, occurred in newly

planted and heavily watered Pachysandra and other ground covers. Light

 

infestations of quackgrass, (Agropyron repens), and seedlings of annual
weeds beyond the initial stage of grth occurred in the treated plots.
It is interesting to note that when these plants were fertilized weekly
throughout the summer, they regained their green color.

Birdsell, et. al. (5) did evaluation tests on five herbicides for weed
control and toxicity to nursery plants. Included among the plants treated

were two ground covers, Vinca minor (Myrtle) and Hedera helix baltica

 

 

(Baltic Ivy). The chemicals used were l-n-butyl-3-(3,4-dichlorophenyl)-l-
methylurea, (neburon), at two pounds per acre; 2, 4-dichlorophenoxyacetic
amide, (2,4-D amide), at two pounds per acre; 2-chloro-4, 6-bis(diethylamino)-
s-triazine, (chlorazine), at eight pounds per acre; 2, 3, 6-trichlorobenzoic

acid, (2, 3, 6-TBA), at two pounds per acre; and 2-(2, 4, 5-trichlorophenoxy)

ethyl-2,2-dichloropropionate, (erbon), applied at the rate of eighty
pounds per acre. Though chlorotic injury due to 2,4-D amide appeared

on some larger ornamentals, neither ground cover suffered from this
type of symptom. Both, however, exhibited epinasty with the Myrtle
recovering after approximately three months. In contrast, most of the
Ivy plants were dead after eleven weeks. Chlorazine, on the other hand,
caused moderate to severe chlorosis on Ivy, but the Myrtle was uninjured.
The Ivy remained in poor condition even after eleven weeks. Neburon
caused slight chlorosis on Ivy, but no other injury was particularly evident.
2, 3, 6-TBA showed unfavorable responses on both Myrtle and Ivy. The
former showed epinasty, and either chlorosis or necrosis of the leaves
and dieback of the tips, while the latter exhibited slight chlorosis and
necrosis of the leaves. Erbon injury to both ground covers was very
severe, eventually causing the death of all the Ivy plants.

Control of broadleaved weeds by four of the herbicides, (2, 4-D amide,
chlorazine, neburon and 2, 3, 6-TBA), was good to excellent after one
months time, but grass weed control varied. 2,4-D amide, chlorazine
and neburon gave fair grass weed control, but the use of 2,3, 6-TBA re-
sulted in only poor grass weed control. After two months only chlorazine
continued to show excellent control of broadleaved weeds, and improved
control of grasses. 2, 4-D amide, neburon, and 2, 3, 6-TBA all showed
poor control of grass weeds. Neburon's good control of broadleaved
weeds remained unchanged, while all others decreased.

Rewarding results in field tests conducted by Ries, Grigsby and
Davidson (22) during 1957 paved the way for further greenhouse tests.
Ground covers included among the plants that were treated were:

Hedera helix baltica, Pachysandra terminalis and Euonmus fortunei

 

vegeta. The poor growth of weed seeds planted in the pots did not permit

their use as an index of weed control, but an evaluation of injury was
possible. Euonymus exhibited severe chlorosis with the use of
2-chloro-4,6-bis(isopropylamino)-s-triazine, (propazine), at four
pounds per acre, and slight chlorosis with a combination treatment

of simazine and 2, 2-dichloropropionic acid, (dalapon), at four and

ten pounds per acre. Dalapon on Pachysandra at the rate of ten and
twenty pounds per acre showed chlorotic injury, increasing respectively.

The use of various soil fumigants as a preplanting measure to control
weeds in ground covers has been reported by different workers (21, 22).
Efficient weed control was achieved in most cases. If planting was de-
layed, little or no injury resulted. But such measures usually require
the use of a water seal following application of the various chemicals,
which is not always feasible.

The foliage in Euonymus on median strip plantings has been repa: ted
to become 10% chlorotic when 3-amino-l,2,4-triazole, (amitrole), was
used at two pounds per acre. At this rate only 30% weed control was
obtained (2).

Other tests made to determine herbicide toxicities as well as seedling
weed control ability of various chemicals have given fair to good results
(9, 20).

Chlorotic injury symptoms have been found in plants other than ground
covers (23). On grapes, Hemphill (16), reported that 3-(p-chloropheny1)l,
l-dimethylurea, (monuron), caused chlorosis of young transplants,
whereas, 3-(3,4-dichlorophenyl)-l, l-dimethylurea, (diuron), did not.
Carlson (8) reported similar symptoms when monuron was used on
light soils. Doll (12) on the other hand, found that diuron in addition
to simazine caused mottled chlorosis of grape leaves, with the

injury disappearing by the end of the season at lower rates. Plants

treated at higher rates continued to show symptoms throughout the
season, with the higher rates producing consecutively more severe
symptoms.

Apple trees, treated with sixteen pounds per acre of simazine,
showed interveinal chlorosis and necrosis, which was followed by
defoliation. Diuron injury, on the other hand, was characterized
by faint veinal chlorosis on trees treated with eight pounds per acre.
and extremely severe veinal chlorosis when used at sixteen pounds
per acre. The chlorosis on the leaves of these trees rapidly advanced
and changed to necrosis, ultimately causing complete defoliation of
the tree (26).

In a study designed specifically to study the response of plants to
monuron, Christoph and Fisk (10) founi that soybeans developed
chlorotic areas followed by red-brown spots, at rates as low as one
pound per acre. An interesting observation was the fact that there was
a marked reduction in the amount of mature xylem tissue, compression
and collapse of the cambium, and disorganization of the phloem in the
stems. Following cellular breakdown the xylem vessels in the leaves
became plugged, thus, in the leaves this plugging was probably a secon-
dary effect of the herbicide. Whether or not these conditions aggravated

the chlorosis was not hypothesized.

Mode of Action of Chlorosis Inducing Herbicides

 

The actual cause of herbicide induced chlorosis is not known. The
steps to a clear understanding could not even be started without having
some knowledge of the mode of action of the herbicides causing such
injury. The substituted urea (phenylurea) herbicides and the triazines

have been referred to as causing chlorotic injury. The mechanism of

both groups has a common physiological action, that of upsetting
photosynthesis (4). A detailed description of photosynthesis is
unnecessary, but a review with emphasis on the phases affected by
herbicides, and in particular those places where the effect could
be causing chlorosis, may be helpful.

Chlorophyll, the wonder pigment in the plant which absorbs the
light, is found in association with protein, forming chlorophyll-protein
molecules that are arranged in layers. These layers of molecules form
the functional units which trap the light. When photons of light strike
this chlorophyll unit they throw electrons out of their track, leaving
holes behind them. A certain number of these electrons will fall back
into the holes, and as a result the chlorophyll emits light in the form
of red fluorescence. There are some electrons that escape and are
attracted by electron acceptors; these are finally returned to the
chlorophyll where they came from by means of electron carriers such
as cytochromes (19). Before they are returned, however, they transfer
some of their energy for the creation of high energy phosphate bonds.
As a result there is the formation of ATP with its high chemical bond
energy. Here the electrons from the chlorophyll are returned to it
by a seemingly closed circuit, or cyclic system, and ATP generation
by this means is therefore known as cyclic phosphorylation. In a
second case, the electrons do not flow back into the chlorophyll, but
after being shot out are captured by triphosphopyridine nucleotide or TPN.
(This process is referred to as non-cyclic phsophorylation). The TPN
molecule with an extra electron now has a negative charge and as a re-
sult attracts a proton (HI) from water forming TPNH (reduction). It
is TPNH and ATP that store the energy of light for future use in plant

processes. The holes left in the chlorophyll by the electrons captured

by TPN are refilled with electrons from the hydroxyl ion (OI-1'), left
behind from the water after a proton was removed by TPN forming TPNH.
In the process oxygen, along with water, is generated as a product.
Evidence seems to indicate that the substitute urea and triazine herbicides
interfere at this point where electrons are required to refill the holes in
the chlorophyll molecule. As a result the holes left behind are not refilled
since the supply of electrons is blocked by the herbicide. The higher the
light intensity the more electrons that are shot out, and the more holes
that are not refilled. Eventually the molecule has so many holes it is
severely damaged. Van Overbeek (28) cites the following backing up this
hypothesis. Remitted light in the form of red fluorescence is given off

by all photosynthetic organisms after illumination. This reemission of
light, as stated previously, is probably due to electrons refilling the holes
in the chlorophyll. It has been shown that the substitute urea monuron,
strongly inhibits this reemission of light.

A somewhat similar accomt of this phase of photosynthesis is given by
Good (14). However, he does not commit himself as to whether it is the
chlorophyll molecule that looses the electrons upon exposure to light, and
then gains them back, except those lost to TPN. He states that the Slm's
energy is passed to a molecule of chlorophyll A, which is associated with
two unidentified carrier substances designated as X and Y. "The reactivity
of the light activated chlorophyll is such that Y is oxidized by loosing electrons
or hydrogen atoms and X is reduced by gaining electrons or hydrogen atoms.
Light energy is thus converted into potential chemical energy. It should be
noted that either X or Y may, or may not, be a part of the chlorophyll mole-
cule itself. " The reduced carrier X can transfer its excess electrons or

hydrogen atoms to a number of electron acceptors, the normal acceptor in

10

intact plant cells being TPN. The oxidized Y must be reduced again

by some donar of electrons or hydrogen atoms, otherwise this whole
process of the conversion of energy ceases. Under normal conditions
oxidized Y obtains hydrogen from water, leaving oxygen gas as the
product. However, in the presence of substituted ureas, such as monuron,
this step is inhibited, and as a consequence there is an interference of
the photosynthetic cycle. Both researchers seem to agree that the point
of inhibition is at the stage where oxidation of water takes place. Very
recent studies by Ashton, et. al. (3) on changes in the fine structure of
chloroplasts in relation to herbicides affecting photosynthesis would tend
to support Van Overbeek's assumption that it is the chlorophyll molecule
itself that is damaged.

Though there is a drastic upset of the oxidation-reduction equilibrium,
it must be pointed out that these herbicides would not just affect the
chlorophyll molecule. They must have other consequences. Crafts (1 l)
cites many examples such as: the loss of turgor, chlorosis, progressive
dieback of leaves and retardation of mitosis in meristems in barley. In
soybeans and tomatoes: chlorosis, collapse of young leaves, and disorgani-
zation of palisade tissue is common. Good also points out that there must
be additional effects aside from inhibition of photosynthesis and ultimate
starvation of the plant.

As stated previously, the triazine herbicides, an example of which is
simazine, interfere with photosynthesis just as do the substituted ureas.
Klingman (18) states that scientists do not fully understand just how simazine
causes death of the plant, but it has been shown that simazine interferes
with the cleaving of water into hydrogen and oxygen, an essential part of the
Hill reaction. This is, of course, the same point where the substitute ureas
have their effect, and therefore a complete reiteration of the inhibitory

mechanism is unnecessary.

 

ll

Naturally the ultimate cessation of photosynthesis due to this in-
hibition must eventually result in starvation of the plant. Though this is
not a primary cause of death, it may have something to do with the
chlorotic injury. If the chlorophyll molecule is injured, it will not be
able to utilize the nutrients needed for food and chlorophyll synthesis.
Certainly this would antagonize the chlorotic situation even more. Nu-
trient balances have been found to be upset by the use of herbicides.
Analysis of peach leaves that were treated with simazine showed magnesium
levels to be much higher than control plant leaves. Other element levels,
such as boron, were also drastically upset. Additional mineral effects
have been noted; for example, an interaction between phosphorus and
diuron has been shown to occur (11). When phosphorus is applied to the
soil of cotton and ryegrass cultures, it will counteract the effects of diuron
in the one -quarter to two part per million range, and bring the green weight
production of treated cultures up to that of controls.

Though the past information gives some insight into the cause of
chlorotic injury, it does not explain the reason for symptoms such as
veinal and interveinal chlorosis caused by herbicides which presumably
have the same killing mechanism. One explanation for this difference has
been proposed by Good (14), who states that if the inhibitor (herbicide) is
more soluble in some cellular substances than in water, it may accumulate
in the first cells it comes to without spreading throughout the plant. Thus,
a herbicide that is more soluble in fatty substances of the cell would accumu-
late immediately around the veins, causing a typical veinal chlorosis. A
herbicide held less tightly in the cells would be washed out of these regions
by the passage of the transpiration stream, and would accumulate in the
interveinal area and along the edges. The injury symptom of this herbicide

would appear as interveinal chlorosis.

12

Undoubtedly, no one factor is responsible for chlorosis, but rather
several interacting factors, such as the mode of action and solubility
of a herbicide. The problem will not be solved until these, and other

questions related to them are accurately answered.

MATERIALS AND METHODS

Field Experiments - General

 

Two experimental plots, located at the Michigan State University
Horticulture Farm, were planted on a Hillsdale fine sandy loam during
October of 1963. Both plots were clean cultivated before planting with
rooted cuttings of the following ground covers: Euonymus fortunei vegeLa

(wintercreeper), Pachysandra terminalis (Pachysandra or Japanese Spurge),

 

Vinca minor (Myrtle), and Hedra helix baltica (Baltic Ivy).

 

 

Pre-emergence Studies

 

The objective of the first experim ent conducted in the field was to
evaluate established and recently introduced pre-emergence herbicides in
new ground cover plantings.

A completely randomized design was used having nine treatments, in-
cluding the cont rol. All treatments were replicated three times, each re-
plication consisting of four plants of each of the above mentioned species.

The treatments made shortly after planting were as follows: 2-chloro-4, 6-bis
(ethylamino)~s-triazine, (simazine), at 2 lb/A; 2, 6-dichlorobenzonitrile,
(dichlobenil), at 3 lb/A; dichlobenil at 6 lb/A; simazine plus 1, l-dimethyl-4,4-
dipyridylium cation, (paraquat), at 2 plus 1/8 Ib/A respectively; N,N-dimethyl-Z,
2-diphenylacetamide, (diphenamid), at 8 lb/A; 3-(3,4-dichlorophenyl)-l, l-dim-
ethylurea, (diuron), at 2 lb/A; 2, 6-dinitro-N,N-di-n-propyl-a,a,a-trifluoro-p-
toluidine, (trifluralin), at 6 lb/A; 2,4-bis(isopropylamino)-6-methylmercapto-s-

triazine, (prometryne), at 2 lb/A, and a nontreated control.

Postemergence Studies

The second field experiment was conducted to study the use of herbicides

for postemergence weed control in established ground cover plantings.

l3

14

The experimental plot was allowed to become infested with weeds so
that there would be a good source of seed the following spring. The in-
tention here was to simulate an established ground cover planting, having
actively growing weeds, and then to treat these plots in an attempt to re-
move the weeds without harming the ground covers. In addition to having
much thinner ground cover growth, the weed populations under these con-
ditions were heavier and more varied than in a normal established planting.
However, it was felt advisable to study the herbicides' effects on simulated
plantings before laying out plots in established plantings. A completely
randomized design of the same type used on the fall treated plots was used,
with the exception that ten treatments were applied, including the control.

The treatments applied on June 26,. 1964 were as follows: untreated control;

hoe weeded check; N-cyclooctyl-N,N-dimethylurea plus N-phenyl-N-methyl-N-
methoxyurea, (H-150), at 2 lb/A; 3-(3,4-dichlorophenyl)-l-methoxy-l-methylurea,
(linuron), at 2 lb/A; linuron at 4 lb/A; simazine at 2 and 4 lb/A; 80% 3,4-dich-
lorobenzyl-N-methylcarbamate 20% 2,3-isomer, (UC 22463), at 2 lb/A; dich-
lobenil at 4 lb/A, and 2, 2-dichloropropionic acid, (dalapon), at 5 lb/A.

Treatments for both the fall and spring tests were applied with a small
plot sprayer, as designed by Ries and Terry (24).

Both plots were irrigated, and fertilized with 500 lb/A of 12-12-12 ferti-
lizer. The pre-emergence plots were rated on May 21, June 17, and July 20,
1964. The postemergence studies were rated on July 15 and August 4, 1964.
The ratings for weed control were on a 1 to 9 scale, where 1 was no control,

6 commercially acceptable control and 9 excellent control (little or no weeds).
Injury ratings were made on the basis of a 1 to 5 scale, 1 being no visible

injury, 3 severe chlorosis or burning, and 5 being death.

15

The data were statistically evaluated using analysis of variance.
Where a significant F value occurred, Duncan's Multiple Range Test

was used to compare mean difference.

MATERIALS AND METHODS

Greenhouse Experiments

 

Experiment I
The first of a series of experiments was started December 15,

1963, in the Horticulture Greenhouse at Michigan State University. These
experiments were designed to determine at which levels herbicides could
be used to induce chlorotic injury rather than severe burning, and to study
possible causes of herbicide induced veinal and interveinal chlorosis.

Injured leaves were analyzed since it was felt that nutrient imbalances
played a role in the development of chlorotic symptoms. All analyses were
made at the plant analysis laboratory in the Department of Horticulture,
Michigan State University, East Lansing. Samples were analyzed spectro-
graphically for phosphorus, calcium, magnesium, sodium, manganese, iron,
copper, boron, zinc, molybdenum and aluminum. Nitrogen determinations
were made by the standard Kjeldahl method and potassium was determined
by use of the flame photometer.

Rooted cuttings of Pachysandra treminalis (Japanese Spurge) and Hedra

 

helix baltica (Baltic Ivy) were planted in a 1-1-1 mixture (soil, sand and peat)

 

in four inch pots. Two cuttings of Japanese Spurge were planted in each pot.
Those pots containing Ivy had only one cutting each of this species. The
plants were then treated with four herbicides: simazine, prometryne, diuron,
and simazine plus l-n-butyl-3-(3,4-dichlorophenyl)-l-methylurea, (neburon).
All four treatments were applied at three rates, four-tenths, four, and forty
parts per million (ppm). 100mls of the solution were applied each time an
application was made. Soybean seedlings were grown in each pot as indicator
plants. Observations and notations were made on the type of injury that

resulted.

l6

l7

Experiment H
A second experiment was started on March 21, 1964, to study
the cause of herbicide chlorosis, and, if possible, gain some insight into
the reasons for veinal and interveinal symptoms.

Rooted Pachysandra cuttings were potted in a fashion similar to those
in the first experiment. Two cuttings were planted in each four inch pot,
containing a 1-1-1 mixture of soil, sand and peat. The herbicides used
were: simazine, prometryne, diuron and neburon. Neburon was substituted
for the simazine -neburon combination used in the first greenhouse experiment.
This was because no injury occurred to Pachysandra with the use of this
combination.

A completely randomized design was used, with each of the four treatments
being replicated six times. Each replication consisted of one pot containing
two plants. 100 ml of solution were applied each time the treatments were
made. All chemical solutions were mixed using commercial grade wettable

powder 8 .

Experiment III
A third greenhouse experiment, similar to the second test, but using

soybeans, was started on April 15, 1964, in an endeavor to get more rapid
results. Six seeds were sown in each four inch pot containing the same soil
mixture used in the past. After a few weeks of growth, three plants were
removed leaving the better plants for experimentation. The four treatments,
used at the rates of .25, l and 4 ppm were as follows: simazine, prometryne,
diuron and neburon.

A completely randomized design was used with each of the four treatments
being replicated six times at each concentration. Once again, as in previous

experiments 100 milliliters of solution were applied each time a treatment

18

was made.
In both the second and third greenhouse experiments injured leaves

were removed from the plant and nutrient analysis was conducted.

RESULTS

Field Experiments

 

Pre -emergence Studies -- The results of the first rating showed that
control with all eight herbicides was excellent (Table l). The second
rating trade on June 17 showed that all treatments except trifluralin
gave better control than the checks. However, only diuron at two pounds
per acre, simazine, at two pounds per acre, and the simazine-paraquat
combination, at two pounds plus one-eighth pound per acre respectively,
gave cont rol that was commercially acceptable. At the time of the final
rating only simazine resulted in better control than the check plots, and
this was not commercially acceptable.

All the Ivy plants were winterkilled, and as a result no injury ratings
could be made relating to these plants. The myrtle in one replication of
the diuron treatment, applied at two pounds per acre, was killed but no
injury occurred to this species in any of the other replications of this
treatment, so death was assumed to be due to some other factor.

Postemergence Studies -- The results from the second field experiment

concerned with weed control in established ground cover plantings were not

I as rewarding as the first. Of the eight herbicides used, only one gave good
postemergence control (Table 2). This was linuron at the rate of two and
four pounds per acre. Unfortunately, the injury to the gr01md covers was
severe, and would make the control commercially unacceptable. The hoe
weeded check gave good weed control for only three weeks. Some interesting
trends appeared that may be worthy of further experimentation; Simazine at
two and four pounds per acre and dalapon at five pounds per acre gave notice-

able control of grasses. There was some minor injury to the ground covers.

19

20

Table l. - Effect of fall application of herbicides on pre-emergence

weed control in ground cover plantings.

 

 

 

 

Treatments Fat: Weed Control Ratings—7

5/21/64 6/17/64 7/20/64
simazine 2 9. 0 c 8. 0 c 4. 7 b
simazine 81 parath 2 8: 1/8 8.3 c 8.3 c 3.0 a b
diuron 2 8.7 c 8.3 c 2.7 a b
diphenamid 8 8. 0 c 5. 0 b 1. 0 a
prometryne 2 8.7 c 4. 7 b l. 0 a
dichlobenil 3 7. 7 c 4. 0 b l. 0 a
dichlobenil 6 8.0 c 4.3 b 1.0 a
trifluralin 6 3.7 b 2.7 a b 1.0 a
none --- 1.0a 1.0a 1.0 a
*/

- All ratings are the average for three replications, rating scale

1 = no control; 6 = commercially acceptable control;
9 = excellent control.

Values, in columns, followed by the same letter are not significantly
different.

Values not followed by the same letter are significantly different at the
1% level.

21

Table 2. - Effect of spring application of herbicides on postemergence

weed control in ground cover plantings.

 

Ratings
7/15/64 8/4/64
Treatments Rate lb/A Weed control Injury Weed control Injury

 

 

 

 

 

none ---- 1.0 1.0 1.0 1.0
hoe check ---- 9.0 1.0 5.3 1.0
H-150 2 1.3 1.0 1.0 1.0
linuron 2 7.0 4.0 2.0 4.0
linuron 4 7. 3 4. 0 6. 0 4. 0
simazine 2 2.3 2.7 2.0 2.3
simazine 4 2.7 1.0 2.7 2.0
UC22463 2 1.3 1.7 1.3 2.3
dichlobenil 4 1. 3 l. 0 l. 0 l. 0
dalapon 5 2.7 2.3 2.0 2.7
1/

- All ratings are the average for three replications; rating scale for

weed control: 1 = no control, 6 = commercially acceptable control,
9 = excellent control; injury rating scale: 1 = no injury, 3 = severe
chlorosis and burning, 5 = death.

DISCUSSION

Field Experiments

 

Pre -emergence Studies -- Certain factors should be mentioned when
considering the time period over which commercially acceptable control
was achieved. Abnormally large sources of certain weed seed, such as
grasses, could have come from adjacent treatments which gave poor control
as early as May. In addition, certain ecological factors should be considered.
that may have had an effect on the results. Both the simazine and the simazine-
paraquat combination had a replication in the western corner of the plot which
was consistantly lower in its control rating. A probable cause of this was the
existance of a low spot in that particular location into which much water from
adj acent areas drained. This probably caused excessive leaching out of the
herbicide. Stroube and Bondarenko (27) reported that five months after treat-
ment with two pounds per acre of simazine, during which approximately ten
inches of rain fell, the equivalent of 1/4 pound per acre remained in the top
six inches of the soil. Burnside et. al. (7) also reported the leaching of
simazine into the lower layers. At the same time weed seed was carried into
this low region in wash water. Evidence of this can be found by examining
the weed populations that were present. A recording of the weed populations
found in each replication was made on July 7, 1964. In each case the replica-
tions for these two treatments in this particular location contained a larger
number and variety of weeds than those in other sections of the plot.

An examination of the plots in September indicated that simazine was

still showing discernible weed control, even though not commercially

acceptable .

Postemergence Studies -- The methods by which the more popular ground

covers spread could account for the difficulty in controlling weeds in established

22

23

plantings without injuring wanted plants. Pachysandra spreads by means

of rhizomes which give rise to new shoots. Myrtle and Ivy, on the other
hand, spread by roots forming at the nodes of trailing Stems. In each case
the major root mass is located at, or very near, the soil surface. This is
the area where many herbicides are most active.

On the basis of the herbicides tested, postemergence control of extensive

masses of weeds in established ground cover plantings using herbicides is
not yet possible, and will be an important area for research in the present

and future.

RESULTS

Greenhouse Experiments

 

Experiment I
Seven treatments were applied over a period of thirty-nine days

before any symptoms appeared. (First and second treatment separated by
thirteen days). Injury occurred first on the indicator plants at the highest
(40 ppm) concentration, with death occurring rapidly. Two to seven days
later, most of the Ivy plants at this concentration became necrotic in
patches, localized mainly along the leaf margins. Some yellowing of the
leaf margins and eventually the entire leaf occurred, but this rapidly changed
to brown necrotic areas without any definite veinal or interveinal chlorosis
developing. The injury started in the leaves nearest the base of the plant,
with abscission occurring before the leaves in the tip region were completely
dead. The same symptoms developed for all four herbicides, and death of
all the Ivy plants at this highest concentration for all four treatments occurred
approximately three and one-half months after the first application.

Injury symptoms did not show as rapidly with Pachysandra. They were
first apparent about ninety days after the treatments were initiated in the
case of prometryne and diuron, and about one-hundred days in the case of
simazine. No injury was noted on the simazine-neburon combination. Once
again, injury was confined to those plants receiving the highest concentration
(40 ppm). The injury symptoms started as yellowing and then changed to small
brownish necrotic patches which enlarged covering the entire leaf. Some mild
veinal chlorosis was noted on the diuron treated plants. Death of all the plants
receiving prometryne and diuron occurred approximately ninety days after the
first treatment. In the case of simazine, only four out of eight plants were
killed, and no death occurred among those plants treated with simazine plus
neburon in combination at the highest concentration.

24

25

Since the injury found on Ivy was not usually of a distinct chlorotic
nature, it was decided to discontinue the use of this plant and concentrate
on Pachysandra which had produced the desired symptoms.

One other problem was the long period of time needed before the
symptoms fully developed. Having noted that the soybean indicator plants
achieved fully developed symptoms rapidly, it was decided that a third
experiment would be conducted using soybeans as the plant material rather

than ground covers.

Experiment 11 and III

Injury symptoms appeared on both Pachysandra and soybean plants
that were treated with prometryne. ‘ The characteristic injury was a definite
venial chlorosis. Pachysandra also showed a veinal chlorosis with diuron,
yellowing being most prominant at the basal portion of the petiole. Some
minor yellowing occurred on diuron treated soybeans, but could not be
distinguished as veinal or interveinal. Simazine caused an interveinal
chlorosis on soybeans, but no injury occurred on Pachysandra plants treated
with this same chemical at a concentration of 40 ppm. Neither the soybeans

nor the Pachysandra showed any injury from neburon treatments.

Analysis of the leaf material collected showed differences between
controls and treated plants in the element levels of sodium, calcium, iron
and zinc. Not enough leaf material could be collected to replicate the treat-
ments, consequently these results cannot be considered as trends in the

nutrient levels of various herbicide treated plants.

DISCUSSION

Greenhouse Experiments

 

Unfortunately, not enough leaf material could be collected to fully
study nutrient imbalances in treated leaves as had originally been planned.
Some points should be noted. As stated in the literature review, Good (14)
feels that veinal and interveinal injury may be accounted for due to differences
in the solubility of the herbicides in some cellular substances, in contrast
to solubility in water. He states that the phenylureas appear to be less
tightly held in the cells. Presumably, the transpiration stream in passing
through the main vein region of the leaf washes out the herbicide, which then
accumulates at the leaf margins and in the interveinal areas, causing an
interveinal chlorosis. The phenylurea used by Good , leading to this hypo-
thesis, was monuron, having a solubility in water of 230 ppm. One of the
phenylureas used in this study was diuron, which, as stated in the foregoing
results, caused a veinal chlorosis. This was also reported by other workers
using diuron (26). It is interesting to note that the solubility in water of
diuron is only 42 ppm. Relating the work done by Good with the results ob-
tained from experiments conducted in this study, it appears that the water
solubility of a herbicide within a certain group (phenylureas, triazines,
acylanilides, etc. ,) plays a role in the form of chlorotic injury it induces.
It is logical to hypothesize that if two materials are both in the root zone,
the one of higher solubility will be more readily absorbed by the plant,
all other factors being equal. As a consequence a greater ammmt of the
more soluble herbicide would be present in the plant and, provided it isn't
held tightly by the cell, could be washed into the intercostal areas by the

transpiration stream. Plausible as this seems with the phenylureas, it

26

27

raises question with the triazines. Here simazine having a solubility in
water of only five ppm, causes interveinal chlorosis, whereas, prometryne
with a solubility in water of 48 ppm causes veinal chlorosis. It should be
noted, however, that these two compounds differ in that simazine possesses
a chloro group on the benzene ring, whereas, prometryne has a thio group
instead. This could make some difference in the ability of the plant to

14 labled simazine has

absorb the simazine ion. Once inside the plant, C
been shown to move readily in the transpiration stream (13). In a test
simulating conditions in the apoplast, paper was used with water as the

only solvent. Movement was not correlated either directly or indirectly
with water solubility (13). Thus, it seems that once in the plant, regard-
less of the water solubility and provided the material is not held by the

cell, movement in water won't be affected. How readily it may be absorbed

by the plant may have an effect on the total amount moved, and as a result

on the injury incurred.

SUMMARY

The use of herbicides in ground cover plantings, and triazine and
phenylurea induced chlorosis were studied.

Field tests were conducted to evaluate fall applied pre -emergence
herbicides in new ground cover plantings, and spring applied postemergence
herbicides in established ground cover plantings. Simazine at two pounds
per acre, diuron at two pounds per acre, and simazine plus paraquat at
two plus one-eighth pound per acre respectively gave the best results when
applied as a pre-emergence treatment.

None of the postemergence herbicides used gave acceptable weed control
without causing severe injury to the ground cover plants.

Investigation of triazine and urea caused chlorosis under greenhouse
conditions showed that there was no true correlation between solubility and
chlorosis caused, but indicated that the availability of a herbicide to the
plant, as influenced by it's water solubility, can have an effect on the

expression of veinal versusinterveinal chlorosis.

28

10.

LITERATURE CITED

Anonymus. "The Holy Bible, " Revised Standard Version, Book of
Genesis 1, Verses 1, ll, 12.

. "Amizine and other Amitrol-Simazine combinations for

weed control in Woody Plants. " Amchem Tech. Serv. Data Sheet.

H-80. 1960.

Ashton, Floyd M. , Ernest M. Gifford, Jr. and Thana Bisalputra.
"Structural Changes in Phaseolus vulgaris induced by Atrazine,
II Effect on fine Structure of Chloroplasts. " Bot. Gazette. 127 (5)
pp 336-343. 1963.

Audus, L.J. "The Physiology and Biochemistry of Herbicides. "
Academic Press. pp 387-399. 1964.

Birdsell, Duncan G. , Donald P. Watson and Buford H. Grigsby.
"Toxicity and Efficiency of Selected Herbicides on Representative
Ornamental Plants. " Weeds. 6:34-41. 1958.

Blackman, G.E. "Plant Growth Substances as Selective Weed Killers.
A Comparison of certain plant-grth substances and other
selective herbicides." Nature (London) 155:497. 1945.

Burnside, O.C., E.L. Schmidt and R. Behrens. "Dissipation of
Simazine from the Soil. " Weeds. 9:477-484. 1961.

Carlson, R. F. "CMU as a Herbicide in Vineyards. " Quart. Bull. ,
Mich. Agr. Exp. Sta. 38:409-412. 1956.

Carlson, R. F. and F. B. Widmoyer. "A progress report of the Effect
of N-l-Naphtyl phtalamic (Alanap) and 2, 4-dichlorophenoxyethyl
sulfate (Sesone) on 11 Species of Ground Cover Plants. " Mich.
Agr. Exp. Sta. Quart. Bull. 34, (4), 599-604. 1957.

Christoph, Roy J. and Emma L. Fisk. "Response Plants to the Herbicide
3-(p-chlorophenyl)-l, l-dimethylurea. " Botanical Gaz. 116(1):1-14.
1954.

29

30

11. Crafts, A.S. "The Chemistry and Mode of Action of Herbicides. "
Interscience Publishers. 1961.

12. Doll, C.C. "Chemical Weed Control Studies in Young Vineyards. "
Proc. 14th N. Centr. Weed Cont. Conf. 48-49. 1957.

13. Foy, C.L. and P. Castelfranco. "Distribution and Metabolic Fate of
Cl4 Labeled 2-chloro-4, 6-bis-(ethylamino)-s-triazine, (Simazine
and Four Related Alkylamino triazines in Relation to Phytotoxicity. "
Proc. of the Plant Physiol. Meetings, Vol. 35, Supplement. p 28.
Aug. 1960.

14. Good, Norman E. "Inhibitors of Photosynthesis as Herbicides. "
World Review of Pest Control, Part 1. 19-28. Spring 1962.

15. Hamner, C.L. and H. B. Tukey. "Herbicidal Action of 2,4-dichlorophen-
oxyacetic and 2, 4, S-trichlorophenoxyacetic acid on Bindweed. "
Science. 100:154-155. Aug. 18, 1944.

16. Hamner, C.L. and H. B. Tukey. "Selective Herbicidal Action of Midsummer
and Fall Applications of 2, 4-dichlorophenoxyacetic acid. " Bot. Gaz.
106:232 -245. Apr. 1944.

17. Hemphill, D.D. "Chemical Weed Control in Vineyards." Proc. 13th N.
Centr. Weed. Cont. Conf. 64-65. 1956.

18. Klingman, Glenn C. and Lyman J. Noordhoff. "Weed Control as a Science. "
John Wiley 81 Sons, Inc. 1961.

19. Meyer, Bernard S. , Donald B. Anderson and Richard H. Bo‘hning. "Intro-
duction to Plant Physiology. " D. Van Nostrand Com. , Inc. pp 292.
1960.

20' Pridham, A.M. S. , Granular Herbicides for Weeds in Ground Cover
Plantings. Proc. N.E.W.C.C. 12:108-110. 1958.

21. . "Crop, Weed and Soil Aspects of Simazine, Atrazine and other
Herbicides in Greenhouse and Field Tests. " Proc. 14th N.E.W.C.C.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31

. "Granular Mylone - A Preplanting Measure for Control of

Perennial Weeds of Nursery and Ornamental Plantings. " Proc.

13th N.E.W.C.C. pp 384-385. 1959.

Ries, S. K. , B. H. Grigsby and H. Davidson. "Evaluation of Herbicides
for several species of Ornamentals. " Weeds. 7:409-417. 1959.

and C. W. Terry. "The design and evaluation of a small-

plot sprayer." Weeds 1:160-174. Jan. 1952.

Runge, George F. "Nursery Weed Control. " Proc. 14th N.E.W.C. C.
165-166. 1960.

Saidak, W. J. and W. M. Rutherford. The Tolerance of Young Apple
Trees to Amitrole, Diuron and Simazine. Canadian Jour. Sci.
43:113-118. April 1963.

Stroube, Edward W, and Donald D. Bondarenko. Persistance and
distribution of Simazine applied in the field. Proc. 17th N.C.W.C. C.
40-41. 1960.

Van Overbeek, J. "Physiological Responses of Plants to Herbicides. "
Weeds. 10 (3):l70-173. 1962.

Wallace, T. "The Diagnosis of Mineral Deficiencies in Plants by
Visual Symptoms. " His Majesty's Stationary Office. pp 31-32.
1944.

Zimmerman, P.W. and A. E. Hitchcock. Substituted Phenoxy and Benzoic
Acid Growth Substances and the Relation of Structure to Physiological
Activity. Contr. Boyee Thompson Inst. 13: 313-322. 1942.

 

 

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