III

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144
482

 

HTHS

A SIUDY OF SOME OF THE EFFECFS OF
CEREAIN ARYLOXY HERBICID‘ES’ ON

STRAWBERRY PLANTS

Thesis for the Degree of DH. D.
MECHIGAN STATE UNIVERSETY
Renald Wayne Camgbefil
1957

 

 

This is to certify that the
thesis entitled
A STUDY OF 80333 OF THE AFFECT?) OF BETA II
ARYLOIY IERTBICIDTCQ Oi? STIL!‘J..'EELL711' PLAIITS

presented by

Ronald Ziayne Caxijoell

has been accepted towards fulfillment
of the requirements for

a n . v .+ 4 y.
i .1 .AJ 0 degree In liOI U+Cultux e

 

QRZW
Arthur E. Kitchell

Major professor

0-169

  
      

  

' LIBRARY

Michigan State
University

 

 

A STUDY OF SOME OF THE EFFECTS OF CERTAIN
ARXLOXX'HERBICIDES ON STRAWBERRY PLANTS

BY

Ronald Wayne Campbell

AN ABSTRACT

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

DOCTOR OF PHILOSOPHY

Department of Horticulture

1957

Approved_% 5‘. W

 

A STUDY OF SOME OF THE EFFECTS OF CERTAIN
ARYLOXY HERBICIDES ON STRAWBERRY PLANTS

by Ronald Wayne Campbell

This study was an attempt to determine the influence of
various formulations of 2,4-dichlor0phenoxyacetic acid (2,4-D)
and the related sodium, 2,4-dichlorophenoxyethyl sulfate
(sesone), on yields and on the physiological and morphological
develOpment of strawberries. Only Blakemore variety plants
were used.

The transpiration rates of plants growing in the green-
house were not affected by treatments each of the amine salt,
at a rate equivalent to 1 pound per acre; the ethyl, butyl,
isopropyl or butoxyethanol esters of 2,4-D, at a rate equiv-
alent to 0.5 pound per acre; and sesone, at a rate equivalent
to 6 pounds per acre. Transpiration rates were significantly
reduced when the ethyl and butoxyethanol esters were applied
to plants at rates equivalent to 1.5 pounds each per acre.
At that rate, both esters induced severe hyponasty of leaves
and closing of some of the stomata, which reduced the loss of
water vapor.

Five esters of 2,4-D (methyl, ethyl, butyl, butoxyh
ethanol, and prepylene glycol butyl other forms) were applied
to strawberry plants growing in the greenhouse to determine
if the length and structure of the alcohol portion of the

molecule affected the activity of the ester. These esters

were formulated to possess the same 2,4-D acid equivalent.
The dry weights of the shoots and roots of the plants treat-
ed at l milligram per plant were not significantly different
from the unsprayed controls. There was no evidence of an
exact relationship between the molecular weight of any ester
and dry weight of the shoots and roots When esters were ap-
plied at this rate. However, spray applications of 4:milli-
grams per plant of the same materials significantly reduced
the dry weights of the shoots and roots. This repressive ef-
fect on growth bore a definite relationship to the molecular
weight of the ester. As the molecular weight increased, the
dwarfing effect decreased.

The pentyl ester of 2,4-D was applied to plants growing
in the field to study the effect of different dates of ap-
plication on the relative growth and develOpment of crowns
and roots, as measured by dry weight. Spray applications of
the pentyl ester reduced the dry weight regardless of the
date of application; however, these sprays did not signifi-
cantly change the proportion of crown to roots.

The ethyl, pentyl, and polyethylene glycol esters of
2,4-D, the amine salt of 2,4-D, and sesone were applied in
the field to spring planted strawberry plants to determine
their effect on runner plant formation and subsequent yield.
Spray applications of each material were made in late spring,
early summer, and late summer. Also three spray treatments
were made with each material applied at the times Just indi-
cated. The results showed a highly positive correlation

(r - 0.959) between runner plant production and yield.when
plots receiving the single spray applications at 4, 8, or 16
weeks after planting were compared. All forms of 2,4-D ap-
plied in early summer most severely reduced the number of
runner plants; this date coincides with most active runner
plant initiation and formation. These results suggest the
use of an amine salt preparation at the rate of 1 pound per
acre to be more feasible than any of the ester formulations
tested at 0.5 pound per acre for spring or summer applica-
tions to control broad-leaved weeds in strawberry plantings.
The 2 and 4 pound rates of sesone were used without seriously

affecting plant stand or yield.

A STUDY OF SOME OF THE EFFECTS OF CERTAIN
ARYLOXY’HERBICIDES ON STRAWBERRY PLANTS

By

Ronald Wayne Campbell

A THESIS

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

for the degree of

DOCTOR OF PHILOSOPHY

Department of Horticulture

1957

ACKNOWLEDGMENTS

The author wishes to express his sincere appreciation
to Dr. A. E. Mitchell for his generous help and guidance
throughout the course of this study.

The author also wishes to express his sincere thanks
to Dr. G. P. Steinbauer of the Department of Botany and
Plant Pathology, Dr. C. L. Hammer and Dr. H. B. Tukey of
the Department of Horticulture, and Dean 0. R. Megee for

serving on the guidance committee.

 

TABLE OF

INTRODUCTION . . . . . .
REVIEW OF LITERATURE . .
MATERIALS AND METHODS. .
Experiment One. . . .
Experiment Two. . . .
Experiment Three. . .
RESULTS. . . . . . . . .
Experiment One. . . .
Experiment Two. . . .
Greenhouse Studies
Field Studies. . .
Experiment Three. . .
DISCUSSION . . . . . . .
SUMMARY AND CONCLUSIONS.
LITERATURE CITED . . . .

CONTENTS

Page

. . . . . . . . . . . 1
. . . . . . . . . . . 4
. . . . . . . . . . . 15
. . . . . . . . . . . 15
. . . . . . . . . . . 19
. . . . . . . . . . . 21

O O O O O O O O O C O 23

. . . . . . . . . . . 23
. . . . . . . . . . . 28
. . . . . . . . . . . . 28
. . . . . . . . . . . 43
. . . . . . . . . . . 54
. . . . . . . . . . . '71
. . . . . . . . . . . 81
. . . . . . . . . . . 86

INTRODUCTION

In the growth.and development of the strawberry plant
two general phases, the vegetative and the reproductive, are
involved. These phases are not clear cut and tend to overlap
and vary greatly due to a variety of factors. The strawberry
as grown commercially is propagated vegetatively by off-sets
or by runner plants and thus the hereditary factors are trans-
mitted directly from the mother to daughter plant. Except
whenmmutations occur, the genetic composition of a variety or
clone remains constant. Regardless of the habitat in which
they are growing whether in a greenhouse or in a field, straw-
berry plants are affected by a complexity of environmental
factors. These factors which influence both reproductive and
vegetative growth, include light, temperature, available soil
water and soil solutes, the physical nature of the soil, and
plant spacing. 'Within the past ten years chemicals applied
to strawberries to control insects, diseases, and those used
to control weeds and to regulate runner plant formation may
be added to this list of factors which influence vegetative
and reproductive growth. Probably one most widely publicized
chemical for weed control has been.2,4—dichlorophenoxyacetic
acid (2,4-D).

A.report by Banner and Tukey (27) in 1944, to the effect
that the selective plant-growth.regulator 2,4-D would kill
some weeds yet certain crap plants would remain unhurt, stimp

elated intensive work on chemical weed control in all phases
of crop production. Since Carlson (5) first reported on the
possibility of using 2,4-D for the control of weeds in straw-
berries, a number of chemical femulations of this material
have preven effective in the control of some common broad-
leaved weeds in this crop. Though there may be a wide range
in the susceptibility of different plant species to 2,4-D
effects, it has been reported (64) that the growth regulating
properties are expressed at much lower concentrations than
are the toxic effects.

It has been shown that with proper timing and the correct
concentration 2,4-D amine salt sprays can be used to control
strawberry runner production (9). Other effects of this chem-
ical upon the strawberry plants have been studied in a general
way as reported by Donisen (17), Carlson ('7), Gilbert (25) and
Vietneyer (61). However, these effects have not been shown to
be related to a specific influence of the chemicals on the
physiological and morphological dsvlepment of the strawberry
plant. is the 2,4—D compounds used for weed control have ex-
hibited growth regulating properties (10), (44) and (64), it
was seemed that certain formulations might have a greater
unfavorable influence on plant growth and yield than others.
Also, since the molecular structure of the various formula-
tions are variable, it can be expected that the various for-
mulations might differ in their influence on the physiological
and developmental processes of the strawberry. Thus a study
was undertaken to detemine the influence of various 2,4-D

formulations and the related compound, sodium 2,4-dichloro-
phenoxyethyl sulfate (sesone), on (1) the transpiration rate
of treated plants, (2) the time and extent of develOpment of

the root system, (3) runner plant fomation and (4) yield.

REVIEW OF LITERATURE

The cultivated strawberry belongs to the family Bosaceae
and the genus Frggari .

It is a low growing, nearly evergreen perennial herb
which is prepagated easily by runners and seed. The vegeta-
tive portions of a strawberry plant include the crown, the
runners and the roots.

The crown is first a short fusiform body which may later,
by apical growth, according to lhite (62), became cylindrical
am eventually fork into two or more divisions. Above ground,
the crown is enclosed with leaves which closely encircle it
for some three-fifths of its circumference.

Darrow (14) describes a runner as a much elongated stem
with greatly lengthened internodes. The first node bears a
solitary leaf which often remains rudimentary. A bud poten-
tially capable of development as a crown or runner is borne in
the axil of each such leaf. White (62) found after the runner
has grown diagetropically for several centimeters, that its
tip becomes negatively geotropic, turning up Just beyond the
second node and undergoing considerable thickening. It then
puts forth adventitious roots and soon becomes established as
a daughter crown.

Varieties of strawberries vary greatly in their ability
to produce runners, according to Carlson (5). He lists the
varieties Blakenore, Dunlap andrRobinson as active runner pro-

ducers while the varieties lidland, Catskill and Fairfax pro-
duee comparatively few runners. Although the strawberry is
considered a short-day plant Darrow (15) found that runners
are initiated during long days by most varieties.

Ialdo (60) found that soil moisture had a definite effect
on the number of runners famed during a growing season. In
studying the effects of irrigation on runner production, he
observed that with.no irrigation there were considerably fewer
plants per acre than when irrigation was used. Loree (58)
observed that the nutrient level also had an effect on runner
production. He found that the influence of applications of
calmercial fertiliser on increased runner production depended
on the condition of the plants at the tine of the application.
Several workers have stressed the necessity of devolOping rune
nor plants early in the season in order to obtain maximum
production.

Strawberry roots of runner plants as described by lann
(41) are of two kinds, the adventitious or primary roots and
the lateral or secondary roots. He reports that the adventi-
tious roots which.give rise to the entire root system of all
except seedling plants develop apparently from the central
cylinder of the crown probably from a group of cells which
lie between.pericycle and medulla. However,‘Ihite (62) while
agreeing that these roots come from.the central cylinder sug-
gests that they arise frcm the pericycle. Van Tiegham and
Douliot (57) decided that the adventitious roots developed
from the central cylinder only at the two sides of a Iedian

leaf trace.

As a new shoot or runner begins to grow, it was observed
by Ian and Ball (40), that the large adventitious roots de-
velop very rapidly. The crown of the young plant grows rapid-
ly and additional adventitious roots form, usually in small
groups. These roots are white in color with few branches and
may develop a considerable length by the end of the growing
season. During the summer, the older portions of these roots
turn from white to yellowish brown and numerous fibrous lat-
erals appear. lew white adventitious roots are produced un-
til growth stops in the fall.

llann (41) found that the fibrous roots which oonsitute
the bulk of the absorbing system of the plant in the spring
and early summer become functionless as soon as new roots are
developed in late summer. These functionless fibrous roots
rapidly decay, and a new system of absorbing lateral roots is
developed on the vigorous adventitious roots arising from
younger portions of the rhizome, while the original main roots
continue to increase in thickness. He describes the chief
functions of the main adventitious roots as first, to pene-
trate the soil rapidly and to constitute a framework upon
which the absorbing system of fine fibrous roots is built up
to support the plant during the following season, and second-
ly, to develop specialised tissues which function mainly as
storage and anchoring organs in the subsequent life of the
plants.

It has been demonstrated by Tucker (5'?) that there is a
steady increase in the bulk of the root system from the time

of planting in the spring to late in the fall. laximm root
growth occurs in the late summer and early fall. The most
rapid develogment of roots generally follows an earlier in-
crease in the crowns. Normally the increase in the root sys-
tem occurs approximately one month after the increase in the
shoot.

It was found that the periods of new root formation fol-
low periods of starch accumulation and a corresponding high
percentage of dry matter in the plant as a whole. The devel-
oment of roots at both periods is accompanied by a rapid dis-
appearance of accumulated carbohydrates and a decrease in the
percentage of dry matter of both roots and rhizomes.

A number of factors are known to affect the vegetative
growth of the strawberry. The effect of the system of culture
used on root distribution has been studied extensively. It
has been shown by Schrader (51) that most of the strawberry
roots are found in the upper 12 inches of the soil. The great-
est concentration of roots is found in the upper three-inch
zone. Roots are more concentrated in the region of greatest
plant population under the matted row system of culture as
well as in the immediate region of the spaced plant when a
spaced system is used. This pattern follows into the lower
layers of soil as well. Spaced plants develop a greater per-
centage of roots in lower soil layers than do the matted row
plants. The greater root develoment of matted row plants be-
fore fruiting may at least be partially responsible for the
smaller fruit site under the crowded matted row that many

strawberry varioties develop, compared to the larger fruit
size from thinned rows.

Other comparisons of the root develOpment of plants grown
in the matted row system and spaced plants (58), show a sig-
nificant increase in the size of the root systems expressed
in dry weight of the plants grown under the spaced systom.
Similar relations were seen in the length of roots. Further,
it was noted that the dry weight increase of roots in the
matted rows ceased about September 1 while the roots of the
spaced plants showed a continued increase until October 6.

The nutrient level of the soil has been shown by Gardner
(24) to affect the extent of root deve10pment. A.definite re-
sponse to a complete fertilizer treatment regardless of time
of application as compared to no fertiliser treatment was
shown by the increased dry weight of roots grown under the
matted row and the spaced plant system.

The removal of all Blakemore runners thereby fruiting
only the original plants during the second fruiting year, was
found by Crane and Rant (13) to result in.much.greater yields
than were obtained from either a conventional renewal practice
or by permitting the thinned rows to revert to a.matted row
condition. This increase in yield was prhmarily'due to the
fact that the thinned plants were able to accumulate larger
leaf areas, root systems and food reserves as reflected by
the dry weight data presented.

Since roots of plants are dependent on their shoots for

the carbohydrates essential to growth, whatever affects pho-

tosynthesis and the use of carbohydrates in the shoot will
affect also root growth. Reciprocally, any injury to or in-
adequacy of the root system will hinder shoot growth. Kramer
(36) reports that root and shoot growth are rather closely
correlated and, if the development of one is modified, growth
of the other is likewise modified. Reduction in photosyn-
thetic surface resulting from injury to leaves by hail, in-
sects or fungi will be reflected also in reduced growth of
the root system.

A comparison of the root and top develOpment of 18 straw-
berry varieties by Hanson (30) showed considerable variation
between varieties. In general there is a relationship between
top and root develOpment. Varieties with poor root systems
have been reported by Shoemaker (52) to be shallow with little
' branching, to possess a larger percentage of dead roots and
root tips, to have a limited spread, to lack root hairs and
to show a general lack of thriftiness.

The use of chemical sprays on the shoots has been report-
ed by Fults and Payne (23) as affecting the roots of the com-
mon bean. It was found that spraying bean shoots with DDT in-
creased the number of branch roots.

The chemical, sodium 2,4-dichlor0phenoxyethyl sulfate
(sesone), has come rapidly to the fore as a weed-killer in
strawberries (20), (35), (52). Data of its effect on runner
formation have been reported by Carlson (9) and Denisen (1'7).
This material, according to King (35), has little effect on
plants until it comes in contact with the soil where it is

10

changed into a chemically active form by the soil microorgan-
isms; then it can be absorbed by the plant roots. Audus (2)
found evidence that the soil microorganisms acting upon this
cmpound generated only one toxic compound which, due to its
behavior, he thought to be 2 ,4-D acid.

Widespread use has been made of 2 ,4-dichlorophenoxyacetic
acid (2,4—D) to control weeds in strawberry plantings since it
was first reported as a strawberry herbicide in 1947 by Carlson
(s). Humorous workers (5), (6), (25), (4'7), (54), (so) have
shown that while varieties of strawberries differ in tolerance
to the action of 2 ,4-D, these differences in tolerance did not
appear important within the range of the concentrations neces-
sary for satisfactory weed control. Carlson (6) suggested 1/4
to 1/2 pound of 2,4-D acid per acre. Davidson (16) applied
1/2 pound and 1 pound of 2 ,4-D acid in the forms of the sodium
salt and an amine and reported that while the 1 pound rate
produced slight formative effects, later growth and fruiting
appeared normal. Gilbert (25) found that 2 pounds per acre
of 2 ,4-D acid as a preplanting treatment followed by l and
1 1/2 pounds as post planting treatments gave good weed con-
trol without injury to the strawberry plants. Slife and Ball
(54) who applied an amine at rates from 1/2 to 3 pounds of
2,4~D acid per acre on the variety Premier reported that the
higher rates caused greater growth effects but that all treat-
ed plots were normal in appearance after one month. The iso-
propyl ester of 2,4—D at 1 pound acid equivalent per acre pro-
duced epinasty of the petioles and runners according to Denisen

ll

(17).. However, yields were not reduced significantly the fol-
lowing spring.

A beneficial reduction in runner plants was obtained by
Carlson (9) when two applications of 2 ,4-D were made at the
rate of 1 1/2 pounds per acre. He reported that the inhibit-
ing chemicals had proved most effective when applied during
the initiation and early differentiation of the runner. In
first year plantings it was suggested that the first appli-
cation should be made immediately after the flowers have been
removed. A second application was suggested to be made about
one month later. In fruiting beds the first application was
suggested after harvest and after the planting has been re-
juvenated. This application is followed by a second spray
three to four weeks later.

This reduction in runner plants as a result of 2,4-D
sprays was verified by Denisen (1'7). He suggests that a re-
duction of rooted runners of the plants sprayed with 2,4-D
may result from the active material on the soil which may
inhibit root primordia for several days after application.

The effect of .01 percent aqueous solutions of 2,4-D on
the stem anatomy of selected species of plants has been re-
ported by Skoog _e_t 5;. (53). They found the most common re-
sponses to be a swelling of the stems and the presence of
lateral roots in treated species which included Coleus,
Verbena, and sweetpotato. In these plants the tissues re-
sponsible for proliferation and root formation were the cam-

bium, phloem parenchyma, ray cells, and pericycle. It was

reported by Swanson (56) that applications of 2 ,4-D acid
greatly stimulated root fomation in the young kidney bean.
Lee (37) found that 2,4-D applications to corn resulted in an
abnormal developnent of brace or aerial roots including fas-
ciation, to produce a collar like effect around the base of
corn plants. Hansen and Buckhols (29) took note of the re-
duction of primary root length in several inbred lines of
corn treated with 2,4-D. The younger portions of roots of
strawberry plants sprayed with 2 ,4-D amine at 2 pounds per
acre were observed by Carlson (6) to swell to approximately
twice their nomal diameter. He reported the plants as being
severely stunted for about three weeks following the spray ap-
plication but that the plants appeared fully recovered at the
end of the season.

The effect of spray applications of 2 ,4-D acid on the
rate of transpiration of bean seedlings was investigated by.
Brown (4). He found a definite decrease in the rate of water
loss in the sprayed seedlings and reported this to be asso-
ciated with the marked curling of the leaves, the decrease in
the ‘rate of leaf expansion, the decrease in the rate of accu-
mulation of water and solid materials within the leaves, and
an ultimate wilting of the leaves. Carlson (5) reported a
slight browning of the roots-of some strawberry plants which
he attributed to 2,4—D treatments.

Sprays applied during bloom may result in the production
of button berries according to Hibbard and Hemphill (32).
Carlson (6) found that 2,4-D sprays had an inhibitory effect

13

on strawberry flowers and suggested that the material might
be used to eliminate the flowers in first year plantings.

The toxicity of 2,4-D in the soil according to Ahlgren
at 51;. (l) is directly affected by (l) decomposition by
microorganisms, (2) leaching, (3) absorption of the soil col-
loids, and (4) soil reaction. They suggest the first two
factors are directly related to moisture and temperature.

All are influenced by soil texture, structure, and the amount
of organic matter present.

Harvey and Robbins (31) concluded that warm, moist soils
generally hasten the decomposition of the 2,4-D making it non-
toxic to plants as these conditions favor the growth and mul-
tiplication of the microorganisms which are able to decompose
the chemical. They also reported that more 2,4-D is retained
by heavy soils than by a light one.

It was found by Hanks (28) that water leached from soils
treated with 2,4-D contained phytotoxic amounts of 2,4-D.
Weaver (63) determined that in the soil both cation exchang-
ers and anion exchangers absorbed much 2,4-D acid and also
much of its salts. He found that when 2,4-D is absorbed it
is relatively non-toxic. It was observed by Crafts (11) that
the rate of decomposition of the 2 ,4-D molecule is increased
by an increase in soil acidity. Therefore toxicity remains
for a longer time in soils high in lime.

Many experiments indicate the similarities between plant
hormones and 2,4-D compounds. The latter are reported by
Crafts (10) am Lucas and Hammer (39) as being readily absorb-

14

ed by leaves and are apparently taken up and transported most
readily in the nondissociated form. Mitchell and Brown (44)
found that after having been absorbed by leaves, 2,4-D in as-
sociation with sugars is transported away from the leaf, on
which it has been applied, to other parts of the plant.
Numerous references are available on some effects of
2,4-D on the strawberry and other plant Species. No studies
were found relating the effects of the molecular structure of
2,4-D compounds to the physiological and morphological devel-
oment and yield of the strawberry. This information is lack-
ing also for sesone which has been reported by Audus (2) as
being decomposed to 2,4-D acid by the soil microorganisms.

MATERIALS AND METHODS
Experiment One

The transpiration studies were conducted with the Blake-
more variety. The, plants were dug in the fall after they had
become dormant and were stored at 33° F. for a minimum of
eight weeks or until they were planted in the greenhouse.

In February 1954, six weeks prior to the start of the
experiment, the plants were removed from storage and planted
in five-inch unglazed clay pots. The roots were pruned uni-
forme and all plants were pruned to four leaves per plant.

The soil mixture used consisted of three parts of loam, one
of sand, and one of peat. At the beginning of the experiment
the average moisture content of the soil was 55 percent of
its moisture holding capacity. The plants were well estab-
lished by the time the experiment began. The unglased pots
in which the plants were grown were lowered into one-gallon
tin cans onto blocks that held the top of the clay pets to a
level one-fourth inch above the tOp of the cans. The space
between the surface of the potting soil and the top of the
pots was partially filled with coarse sand.

The potted plants were sealed in the cans with waterproof
oil cloth covers. Two holes, each one-half inch in diameter,
were cut in the covers. One hole in the center of the cover
allowed for fitting the covers around the crown of the plants
and the second hole was used for addition of water to the pot.

16

The covers were placed around the plants by slitting the covers
from one side to the center hole and later sealing with water-
proof tape. Figure 1 shows typical plants sealed in this manner.

Water added to the pots during the course of the experi-
ment spread through the sand layer and uniformly into the soil
below. The space inside the cans around the pot provided for
aeration. At the close of each experiment, the plants were
found to have their roots well distributed throughout the soil
mass.

The plants were weighed daily and water was added every
third day to restore them to their original weight. A solution
balance with an accuracy of i one gram was used for these
measurements .

A continuous record of the bench level temperatures was
recorded by a themograph throughout the experiment.

Twelve days after the spray applications were made, the
leaves from all plants were removed, blueprinted and the image
areas measured with a planimeter. In calculating transpiration
rates, the water loss was based on the area of leaf surface at
the close of the experiment. This procedure was used based on
the assumption made by Miller (41) that any change in leaf
area throughout the experiment is proportional for all plants
and any increase in weight is very insignificant, when com-
pared to the large loss in weight due to transpiration.

The greenhouse study on transpiration was divided into
two parts. Forty-eight plants were used in the first study.
The daily weight losses were recorded for a ten-day period

17

aAIO4.

 

Figure 1. Typical plants sealed in the manner used in the
transpiration studies.

18

prior to treatment with the chemical. On the basis of the
water losses during this period, the plants were divided into
three levels: low, medium, and high. Two plants were then
selected from each ”level” group so that each treatment group
consisted of six plants. Each plant received 10 milliliters
of solution. Except for the sesone which was poured onto the
soil in each pot, the 2,4-D materials were applied as sprays
using a half-pint atomizer. Each plant received 10 milli-
liters of solution. The oil cloth covers were removed during
the spraying treatment and the discharge was directed so that
all of the drip fell into the pots.

Materials included in this study were the ethyl, butyl,
isopropyl, and butoxyethanol esters of 2,4-D at 0.7 millin-
grams per plant; the amine 'salt of 2,4-D at 1.4 milligrams
per plant; and sesone at 4.2 milligrams per plant.1 All rates
of the chemical materials presented in this paper are based on
the active ingredient in each compound.

In a second test, strawberry plants were divided also as
described in the first study into three levels of transpire-
tion based on the rate of water loss established during a
preliminary period and six plants were used per treatment.
The treatments were made up of the ethyl and butoxyethanol
esters of 2,4-D used at the rates of 0.7, 1.4, and 2.1 milli-

grams per plant, making six groups of treated plants.

 

1 Ten milligrams per square foot is equal to 1 pound per
acre. Thus if a plant container with 0.20 square foot sur-
face receives 2 milligrams, the rate per acre is equal to 1
pound.

19

Supplemental light was applied as needed to produce a
twelve-hour photo-period, which has been shown by Darrow (15)
to be optimum for general growth of strawberry plants.

Experiment Twa

Greenhouse Studies

in experiment was conducted in the greenhouse to study
the effect of various 2,4-D ester fomulations on the time an
extent of root development of strawberry plants.

Blakemore plants which had been dug the last of October
1952 and stored at 33° F. were planted the following March in
one-gallon cans in the greenhouse and provided with coalitions
favorable for growth. After they were established, and prior
to treatment, all but six leaves were removed from each plant
in order that the plants would be as unifom as possible
initially.

Five 2,4-13 esters of varying molecular weight were used
to detenine if the length and structure of the alcohol por-
tion of the molecule would affect the activity of the ester.
These esters were formulated to possess the same 2,4—1) acid
equivalent and included the methyl , ethyl, butyl, butoxy-
ethanol, and the propylene glycol butyl ether fem. Twenty
plants were used for each chemical treatment with each plant
receiving 10 milliliters of solution. Each ester was applied
at concentrations of l and 4 milligrams per plant thus making
a total of ten groups of treated plants. These materials
were sprayed over the plants with a hand atomizer, with the

20

excess being allowed to drop on the soil surface around the
plant. A second application was made at these rates 18 days
after the first application.

The plants were allowed to grow for 60 days following
the first treatment after which they were removed from the
cans and washed carefully. The roots were cut from the crown
and, together with the above-ground portion of the plant,
were dried in an oven at 85° 0. Thus, the dry weights of the
shoots and roots were obtained.

Field Studies

In this experiment the pentyl ester of 2 ,4-D was applied
at different times during the growing season to determine the
effect of the spray on root growth and develOpment. Dry
weights of the crowns were obtained as a measure of possible
effects of sprays on growth of the above-ground portion of
the plant.

Approximately twelve hundred Blakemore plants were set
April 2, 1955 at intervals of 24 inches between plants and 48
inches between rows. The plants were divided into replicates
of 75 plants each. Four treatment blocks each consisting of
four replicates were selected at random. Three different
times of application of the pentyl ester of 2,4-D were com-
pared. Three blocks were sprayed with 0.5 pound acid equiv-
alent on May ll, two blocks on July 6, and one on September 1.
No runner plants were allowed to root. Plants were lifted in
batches” of 20 at intervals of four weeks beginning on May 11
and continuing through October 4. Control plants were also

21

lifted at each of the six sampling dates. In lifting the
plants, a cylinder of soil 18 to 24 inches in diameter and
about 15 inches deep was removed. The plants were then soak-
ed in a tub of water and the soil was carefully washed from
the roots. The leaves were all removed so that only the
petiole bases remained attached to the crown. The roots were
cut from the crowns and both crowns and roots were placed imp
mediately into a drying oven at 85° 0. Dry weights of the

crowns and roots were recorded.
Experiment Three

The influence of various forms of 2,4-D and of sesone
on the inhibition of runner plants has been reported by Carl-
son (9) and Denisen (17) but little information is available
on the relationship between runner plant set and yield as
affected by these materials. This study was designed to
determine the effect of several 2,4-D formulations and of
sesone on runner plant production in a first year planting
and on subsequent yields the following spring.

On April 15, 1952 Blakemore strawberry plants were set
18 inches apart in the rows spaced at four foot intervals.
The planting included the control plants and a total of 29
treatment blocks, each consisting of four replicates of 20
plants per replicate. Each herbicide was applied as a single
spray on Hay'l3, four weeks after planting; on June 10, eight
weeks after planting; and on August 5, 16 weeks after plant-
ing. An added treatment was included for each.herbicide con-

22

sisting of three spray applications made at 4, 8, and 16
weeks after planting.

The chemicals included the ethyl ester, the pentyl ester,
the polyethylene glycol ester, and the amine salt formulation
of 2,4-D. This made a total of 16 different treatments of
2,4-D which were compared. The ester formulations were ap-
plied at the rate of 1/2 pound acid equivalent ani the amine
salt at 1 pound acid equivalent per acre. In the sesone
study, plots received three applications of spray and other
plots single spray applications at the times indicated for
the 2,4-D chemicals at rates of 2, 4, and 6 pounds per acre,
making a total of 12 sesone treatments. All the chemicals
were applied by knapsack sprayer at a volume of 40 gallons
per acre.

At the end of the growing season, a count was made of
the total number of runner plants produced in each replicated
plot. During the harvest season of 1955, yield records were
taken from all the plots.

RESULTS
Experiment 1

In the first phase of the transpiration studies, Blake-
more runner plants, pruned to four leaves and transplanted in-
to five-inch pots, were divided into high, medium, and low
level groups based on their rates of transpiration determined
in a preliminary study.

Chemicals used included the ethyl, butyl, isopropyl, and
butoxyethanol esters of 2,4—D applied at 0.7 milligrams per
plant, the amine salt of 2,4-D at 1.4 milligrams per plant and
sesone at 4.2 milligrams per plant. The plants were weighed
daily and water added every third day to restore them to their
original weight. The rate of transpiration was expressed as
grams per square centimeter of leaf area. An analysis of
variance of the data indicated that there were no significant
differences in transpiration rates between the plants treated
with the various chemicals or between the sprayed plants and
the unsprayed control plants. The average rate of transpir-
ation per unit of leaf area decreased after spraying in all
cases except on those plants to which sesone was applied.
However, none of the changes were great enough to be statis-
tically significant. When plants of various levels of trans-
piration were considered, significant differences were found
between plants of some levels (Table 1).

It was found that in the high level group these plants

Table 1. The effect of various forms of 2,4-D and sesone
on the daily transpiration rates of Blakemore

strawberry plants. The plants were divided into

24

three levels on the basis of the rate of transpi-
ration during a ten day period prior to spraying

 

Actual chemical :Mean rate of transp ration

 

applied per plant: rams centimeters da
Treatment (milligrams) : High Medium Low

Sesone 4.2 2.15 1.80 1.08
Butoxyethanol

ester 2,4-D 0.7 1.51 1.57 1.02
Butyl ester

2,4-D 0.7 1.44 1.49 1.21
Ethyl ester

2,4.D 0e7 2e04 1052 1.19
Isopropyl ester

2,4-D 0.7 1.82 1.48 1.29
Amine salt

2,4-D 1.4 1.48 1.45 1.27
Control 0.0 1.78 1.51 1.51

 

LeSeDo 5% - 0e69

sprayed with sesone had a transpiration loss significantly
greater than the plants sprayed with the butyl ester fen of
2,4-D. However, none of the water losses of any of the treat-
ed plants were significantly different from the controls.

There were no significant differences between treatments
or between treatments and controls in either the medium or low
level groups of plants.

When the plants of the various levels were compared, it
was found that the low level plants transpired significantly
less than the high level plants receiving the chemical treat-
ments sesone and the ethyl ester form of 2,4-D. There were
no other significant differences between plants of the dif-
ferent levels treated with any of the spray materials.

The results of the second phase of the study pertaining
to the influence of certain chemicals on the transpiration
rate of strawberries using the ethyl ester and butoxyethanol
ester of 2,4-D at the rates of 0.7, 1.4, and 2.1 milligrams
per plant on Blakemore plants are given in Table 2. Here
also the transpiration rates of the plants had been deteminv-
ed during a ten-day preliminary period and each treatment con-
tained plants with similar transpiration rates.

The transpiration rates of the plants treated with 0.7
and 1.4 milligrams of each of the ethyl and butoxyethanol
esters were not significantly different from those of the con-
trols. The plants treated with each 2,4-D ester at 2.1 milli-
grams per plant showed a significant reduction in transpira-
tion rate when compared with the controls and with the other

26

Table 2. The effects of various concentrations of the ethyl
and butoxyethanol esters of 2 ,4-D on the daily trans-
piration rates of Blakemore strawberry plants.

 

 

: :
: Actual chemical : Average rate of
:applied per plant: transpiration
Treatment : (milligrams) z(grams/centimeterszflday)
: :
Ethyl ester
2 ’4-D 00.7 2067
Butoxyethanol
ester 2,4-D 0.7 2.33
Ethyl ester
2,4-D 1.4 2.42
Butoxyethanol
ester 2,4-D 1.4 2.51
Ethyl ester
2,4-D 2.1 1.89
Butoxyethanol
ester 2,4-D 2.1 1.87
Control 0.0 2.44

 

L.3.D.5%. . . . . . . . .o.44

2?

treatments. In all instances the transpiration rate was high!
er for the plants receiving the ethyl ester 2,4dD spray than
for those sprayed with.the butoxyethanol ester form although
these differences were not significant.

All 2,4-D treatments caused marked formative response
similar to that described by Zimmerman and Hitchcock (66).
The degree of response induced was in direct relationship to
the concentration of 2,4-D applied. The plants sprayed with
the lowest concentration, 0.7 milligrams of the ester forms,
showed only slight curvature of the younger leaves and peti-
oles. This effect had nearly disappeared at the end of ten
days. The plants sprayed with.1.4 milligrams of the ester
forms were intermediate in the amount of hyponasty induced.
The young leaves were quite severely curved upward toward
the midribs while most of the petioles exhibited some twist-
ing. The plants sprayed with 2.1 milligrams of the ester
forms exhibited extreme formative effects. The petioles were
twisted quite severely and there was considerable hyponasty
exhibited by the leaves. This condition persisted until the
end of the experiment and it made blueprinting of the leaves
difficult.

A microscopic examination showed a number of stomata
closed in those areas where the formative effects were pro-
nounced. This would explain in part the decrease in trans-
piration noted when 2.1.milligrams of the esters were applied
to the plants.

28

Experiment 2

Greenhouse Studies

A study was made to determine the effect of various 2,4AD
ester formulations on the time and extent of root development
of Blakemore runner plants growing in the greenhouse after
having been transplanted from the field into gallon cans.

Five esters of 2,4-D, the methyl, ethyl, butyl, butoxy-
ethanol, and the propylene glycol butyl ether esters, were
each applied. Concentrations each of l and 4 milligrams of
eachumaterial were used with 10 milliliters of solution being
sprayed over the plant. All plants received a second appli-
cation at these rates 18 days after the first.

The spray applications of all of the ester fonns produced
considerable formative effects on the leaves and petioles of
treated plants. All the leaves of the plants receiving the
first spray applications March 6 at the l.milligram concene
tration showed hyponastic effects. The younger leaves curled
considerably more than the older ones; all of the petioles
showed some twisting. These formative effects had completely
disappeared when the second spray applications were made on
March 24, 18 days later. Following the second applications,
hyponasty of the leaves and twisting of the petioles as dean
cribed above were noted. The younger leaves of the plants
sprayed with the ethyl and butyl ester forms showed some curl-
ing at the end of 18 days indicating the dwarfing effect to be
greater than after the first spray application. With.the ex-

29

ception of persistence, it was impossible to visually detect
any pronounced difference in induced formative effects on the
plants treated with the l milligram concentrations of the
various 2,4-D esters.

All ester sprays applied at the rate of l.milligram per
plant, excepting the propylene glycol butyl ether ester, de-
creased the dry weight of the roots and shoots when compared
with.the controls (Table 3). However, none of these differ-
ences were statistically significant. Further, there were no
significant differences between treatments. The average dry
weight of the shoots and the roots of the plants receiving
the butyl ester spray were respectively 2.59 and 1.40 grams,
with a shoot-root ratio of 1.85. This compared with an
average dry weight of 2.74 grams for the shoots and 1.52
grams for the roots of the plants sprayed with the propylene
glycol butyl ether ester form, and a shoot~root ratio of 1.80.
The plants sprayed with the butyl ester formulation were the
smallest and those sprayed with the propylene glycol butyl
ether ester the largest of all the treated plants. The sheet-
root ratio of the plants sprayed with the latter material was
the lowest of all the spray treatments applied at the l milli-
gram concentration. This ratio indicated a preportionately
larger root system in those plants sprayed with the propylene
glycol butyl ether ester of 2,4-D than was found in the other
sprayed treatments. This was in addition to the absolute difb
ference in size as mentioned above.

Malformation of the leaves and petioles of the plants re-

50

 

 

 

 

 

 

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31

ceiving 4 milligrams of the various ester forms was very pro-
nounced. As a result of the first spray application on
larch 6, hyponasty occurred in all leaves. Many of the
younger leaves were severely curled with the leaf margins
folded toward the midrib. The petioles were badly twisted;
in some cases the leaves were completely inverted for a few
days. A definite dwarfing effect was noted on all sprayed
plants. A differential browning of the margins of some of
the leaves was noted. The tips of the leaves were most
commonly injured with the browning s olden extending more than
three-eights of an inch from the apex of the leaf. For the
most part the necrosis was confined to the serrations of the
leaflets. This type of injury is shown in Figures 2 to 6.
Considerable leaf curvature was still in evidence 18 days
after the first an aying although now leaves were being pro-
duced and most of the petioles had straightened. In every
case, the second spray application made on larch 24 at the
rate of 4 milligrams per plant produced effects very similar
to those caused by the first application. On some plants
young leaves which had just emerged from the crown were killed.
In general the injury to both the leaves and petioles was more
severe thus reflecting the 1m reased concentration. The
dwarfing effect was pronounced.

The 4 milligram applications produced rather severe in-
jury to the roots (Figures 7 and 8). The youngest roots were
more susceptible to injury than were the older ones. Also,

injury was observed to be greatest in the youngest or tip

32

 

rim. 2e

The effect of two applications of

4 milligrams each of the butyl ester
of 2 , 44), made eighteen days apart, on
the petioles and leaves of Blakemore
strawberry plants. The two upper
plants were untreated.

 

F18”. 3 e

The effect of two applications of

4 milligram each of the ethyl ester
or 2, 4-D, made eighteen days apart, on
the petioles and leaves of Blakemore
strawberry plants . The two upper
plants were untreated.

33

 

Figure 4 e

The effect of two applications of
4 nilligrans each of the propylene
glycol butyl ether ester of 2, 4-D,
made eighteen days apart , on the
petioles and leaves of Blake-ore
strawberry plants. The two upper
plants were untreated.

 

Fig”. 5e

The effect of two applications of

4 milligrams each of the butoxyethanol
ester of 2, 4-D, made eighteen days
apart, on the petioles and leaves of
Blakenore strawberry plants. The two
upper plants were untreated.

55

 

Figure 6. The effect of two applications of
4 milligrams each of the methyl ester
of 2, 4-D, snde eighteen days apart, on
the petioles and leaves of Blakenore
strawberry plants. The two upper
plants were untreated.

36

3'7

 

Figure 7 .

The primary roots on the right are from
Blakenore strawberry plants that received
ho applications of 4 milligrams each of
the butyl ester of 2, 41-1). The sprays
were applied eighteen days apart. The
roots on the left are from untreated
plants.

Figure 8.

 

The roots on the right are from Blakemore
strawberry plants that received two spray
applications of 4 milligrams each of the
ethyl ester of 2, 4-D. The spray treat-
ments were nude eighteen days apart. The
roots on the left are from untreated
plants.

38

39

portion of the individual root. Secondary roots were killed
back more severely than the primaries. Little growth was
noted until three weeks after the second spray application.
The plants sprayed with either the methyl or ethyl ester for-
mulations appeared to be more severely injured than the plants
sprayed with the other ester forms. This is reflected by dry
weights of the treated shoots as seen in Table 3.

All of the esters applied at the rate of 4 milligrams per
plant significantly decreased the dry weight of the roots
and the shoots when compared with the controls.

The average dry weights of the roots and shoots of the
plants treated at the higher or 4 milligram rate with the
methyl ester form were 1.09 and 1.63 grams respectively. This
was significantly less than the average dry weights of the
roots and shoots of the plants sprayed with three of the ester
formulations. The average dry weights of the roots and shoots,
for the plants treated with the various 2,4-D forms were as
follows: butyl 1.24 and 1.90 grams, butoxyethanol 1.32 and
2.08 gram and propylene glycol butyl ether 1.34 and 2.24
grams. The weights of the roots are listed first. The average
dry weights of the roots of the plants sprayed with the ethyl
ester was 1.14 grams which was significantly less than that
of the plants sprayed with either the butoxyethanol or
propylene glycol butyl ether forms. It was found that the
average dry weight of the shoots of the plants sprayed with
the ethyl ester was 1.68 grams. Thus, these shoots were

significantly smaller than those sprayed with either the butyl,

40

the butoxyethanol or the propylene glycol butyl ether esters.
The butyl ester spray treatment decreased the average dry
weight of the roots of sprayed plants when compared to those
plants treated with either the butoxyethanol or the propylene
glycol butyl ether esters, although this reduction was not
significant. However, it was found that the shoots of the
butyl ester treated plants were significantly smaller, being
0.18 and 0.34 grams lighter than those of the plants sprayed
with the butoxyethanol and be propylene glycol butyl ether
forms.

The average dry weights of the roots and shoots were less
in all the treatments when the plants received 4 milligrams
of active ingredients as compared to l milligram, indicating
a positive relationship between concentration and growth
inhibition.

The differences in average dry weights of the roots and
shoots between the plants treated with 1 milligram and 4
milligrams of the three esters of lowest molecular weight,
the methyl, the ethyl and the butyl forms were highly signifi-
cant. For the plants receiving 1 milligram of the methyl
ester the average dry weight of the roots and shoots were
1.45 and 2.70 grams respectively or 0.38 and 1.07 grams more
than for the plants treated with the same material at 4
milligrams concentration. When the average dry weights of
the plants sprayed with the ethyl form at l and 4 milligrams
were compared, the roots of the plants receiving the lower

concentration were on the average 0.25 grams lighter and the

41

shoots 0.97 grams lighter than those plants sprayed at the
4 milligram concentration. An average dry weight of 1.40
grams and 1.24 grams each was obtained for the roots of the
plants receiving 1 milligram and 4 milligrams in that order
of the butyl ester formulation. The average dry weight of
the shoots were 1.90 and 1.24 grams for the plants sprayed
with l and 4 milligrams respectively of the same ester.

The plants receiving 4 milligrams each of the-higher
molecular weight esters, the butoxyethanol or the propylene
glycol butyl ether forms, produced shoots with an average
weight of 2.08 and 2.24 grams. This was a highly significant
reduction of .41 and .50 grams respectively of the shoots of
butoxyethanol and the propylene glycol butyl ether sprayed
plants as compared to the plants treated with these esters
at the rate of 1 milligram. The average weight of the roots
of the plants treated with the butoxyethanol ester at 4 milli-
grams was 1.32 grams or .09 grams less than those plants
receiving 1 milligram of this material; this difference was
not significant. However, the average dry weight of the roots
of the plants receiving 4 milligrams of the propylene glycol
butyl ether ester was 1.34 grams as compared to 1.52 grams
for the plants treated with 1 milligram. This difference was
significant.

These data as presented indicate a positive relationship
between the concentration used and the effects of the 5 esters
of 2, 44) upon growth of the plants as reflected by the dry
weights of the roots and shoots. With the exception of the

42

roots of the plants sprayed with the butoxyethanol form, the
differences in average dry weights of the roots and shoots
between.fihe plants treated.nith l milligram and 4 milligrams
of each of these esters were highly significant. a more
definite relationship between the molecular weight of the
ester and phytotoxicity was obvious in those plants receiving
the 4 milligram.applications than in those sprayed with.l
milligram. As the molecular weight of the ester increased
the average dry weight of the roots and shoots increased in
every instance. This relationship was not as absolute in
these plants sprayed with the different esters at a concen-
tration of l milligram;

A comparison of the shoot-root ratios showed that the
4 milligram.application of all the esters reduced the average
dry weights of the shoots proportionately more than they
affected the roots (Table 3). Further, it was noted that,
with the exception of the methyl and ethyl esters, the shoot-
root ratio increased Iith.the increase in molecular weight
of fihe chemical. {Apparently with the rise in molecular
.weight, the total dwarfing effect became less as indicated
by the increase in.tota1 dry weight and the growth of the
shoots was inhibited less in proportion to the roots. The
1 milligram application appeared to affect the plants less
than the heavier concentrations of 4 milligrams of'the
various esters of 2,4-D, as the shoot-root ratios were far
less variable. The ratios of most of the treated groups were

similar to that of the controls. The effect of some of the

43

2, 440 esters on the shoot and root development can be seen
in Figures 9 and 10.
Field Studigg

The pentyl ester of 2, 440 was applied at the rate of
0.5 pound per acre to a first year planting of Blakemore
plants at different times during the growing season in order
to see how the material affected the growth of the roots and
crowns.

The experiment was planned so that the influence of
different numbers of spray could be determined. Comparisons
were made of the effect between single, double and three-
spray applications. The effects of the spray applications at
different dates on the growth of crowns and roots as expressed
by total dry weights is shown in Figure 11 and in Table 4.
For convenience of reference the plants sprayed May 11 were
designated as Group I, those sprayed May 11 and July 6 as
Group II, the plants receiving 3 sprays, one each on May 11,
July 6 and September 1 are referred to as Group III and the
controls as Group IV.

Some twisting of the petioles occurred following each
2, 4-D application. Many of the sprayed leaves showed some
formative effects, with the younger leaves showing consider-
able hyponasty. Numerous leaves were rather severely injured
as a result of the lay and July spray applications due prob-
ably to the abnormally high temperatures experienced. Gon-
siderable necrosis was observed at the edges of many leaves

and several young leaves were completely killed following these

Figure 9.

 

44

The lent on the left was treated with two
appl cations each of 4 milligrams of the
ethyl ester of 2,4-D eighteen days apart.
The plant on the right was not sprayed.
These plants are of the Blakemore variety.

Figure 10 e

 

The plant on the left received two appli-
cations each of 4 milligrams of the
propylene glycol butyl ether ester of
2,44), eighteen days apart. The plant on
the right was not sprayed. These plants
are of the Blakemore variety.

45

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The effect of sprays, of the pentyl ester of
Kay 11, July 6 and September 1.

2,4-D at 0.6 pound per acre, on the growth
of crowns and roots of Blake-ore strawberry

plants.

Figure 11.

47

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48

applications. Damage to the leaves after the September appli-
cation was much less than noted after the first two sprays.
Although each spray application produced a dwarfing effect in
every instance, the plants recovered and the deformative
effects disappeared within about two weeks after spraying.

By June 8, the mean dry weights of the crowns and roots
for the Group IV plants, the controls, were 0.59 grams and
0.86 grams in that order. These weights were significantly
greater than those for the other 3 groups of plants each of
which received a spray on May 11. On this date for Group I

 

the mean weight for the crowns was 0.57 gram and for the roots
0.82 gram, for Group II 0.56 gram and 0.81 gram, and for Group
III 0.56 gram and 0.80 gram. Although these 3 groups of
plants were smaller than the controls, as indicated by the
mean weights of the crowns and roots, no significant differ-
ences in size were apparent between the 3 groups of plants
which had each received a spray application on May 11.

The samples taken July 6 indicated that there was a
significant increase in size of both crowns and roots in all
plant groups as compared with those plants weighed June 8.

The mean weight of the crowns of Group IV plants was 0.91
gram which was significantly greater than the 0.84 gram
recorded for Group II, the 0.82 gram for Group I and the
0.81 gram for Group III plants. The mean weight of crowns
for the Group III plants was significantly less than the mean
weight of the crowns of the Group II plants. This difference

may have been due to sampling error since the number of sprays

49

and kind of spray received by both.groups were identical at
the time the weights were determdned. In.August the average
dry weights of the crowns and roots of the control plants
were found to be 1.23 and 1.91 grams each.

The average dry weights of the Group I plants sprayed
only on.May 11 were considerably less than those of the con-
trols; but, these plants were much larger, as indicated by
mean dry weight, than the Group II and Group III plants each
of which received sprays on May 11 and July 6. The mean
weights of the crowns and roots of the Group I plants were
1.13 and 1.77 grams respectively. For the Group II plants
these figures were 0.82 and 1.39 grams. The mean weight of
crowns for the plants in Group III was 0.84 gram.and for the
roots 1.43 grams.

The mean weights of the crowns and roots of the Group IV,
the control, on September 1 were still significantly greater
than those of the Group I plants although the differences
which were 0.04 gram for the crowns and 0.06 gram for the
roots had lessened considerably. The mean weight of the crowns
for the Group III plants was 0.40 gram.less than the controls
and for the Group II plants 0.43 gram.less. The mean weight
of the roots of the Group III plants was 0.64 gram.less and
of the Group II 0.69 gram.less than the mean weight of the
roots of the control plants.

0n the final sampling date, October 4, the difference in
the average dry weights of crown and roots between the Group

IV plants or controls and the Group I plants which received a

50

single spray on May 11 was not great. The mean weight for
the crowns and roots of Group I were 2.33 and 3.38 grams
respectively while the mean weights for the Group I plants
were 2.27 grams for the crowns and 3.32 grams for the roots.
This difference in weight was barely significant. Both groups
of plants, however, were considerably larger than the remain-
ing two groups of plants. A significant difference was now
apparent between the average dry weights of the Group II
plants sprayed on May 11 and July 6, and the Group III plants
which received sprays May 11 , July 6, and September 1. The
latter plants were considerably smaller with a mean weight
of 1.57 grams for the crowns and 2.30 grams for the roots as
contrasted with comparable weights of 1.99 and 2.92 grams for
the crowns and roots of the Group II plants.

The crown-root ratio showed a uniformly steady increase
in all treatmmts for the first three sampling dates (Table 5).
On July 6, the third sampling date, the crown-root ratios had
increased significantly in all treatments including the con-
trols. The ratios on this date were 0.79 for the plants each
of Groups I and II and 0.78 for Groups III and IV. This
suggests that the most rapid development of roots generally
follows an earlier increase in weight of the crowns. The
increase in the root system followed the increase in the crowns
about a month. No effects of spray treatment on the crown-
root ratios were evident at this time. On August 3, the fourth
sampling date, an abrupt drop in the crown-root ratio was noted

in all groups. There was a decrease of 0.15 in the crown-root

51

 

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52

ratio of the Group I plants, a decrease of 0.20 for Group II
plants, a loss of 0.19 for the Group III plants and a value
of 0.14 less for the Group IV plants than was obtained on
July 6. These decreases in the crown-root ratio were signif-
icant only for the plants of Group II and III but barely
missed significance in the other two groups. By September 1
the crown-root ratios were: for the plants of Group I 0.60,
for Group II 0.59, for Group III 0.59, and for Group IV 0.60.
A reduction of 0.04 was noted in the crown-root ratio for the
plants each of Groups I and IV when compared to these same
values of the same groups August 3. The crown-root ratios
for the plants of Groups II and III remained the same as those
obtained the previous month. The ratios of all the groups
were now significantly less than at the beginning of the
experiment on May 11. 4

During the period July 6 to September 1, the proportion
of root to crown increased markedly in all groups regardless
of treatment. The greatest development of adventitious or
primary roots was observed during this interval, while much
of the root growth during the prior months had been the origin
and development of the secondary or ”feeder" roots. Although
the differences were not significant, the plants of Groups II
and III both of which received a second pentyl ester spray on
July 6 showed lower crown-root ratios on August 3 than the
plants of the other two groups not receiving the spray on this
date. This would indicate the tendency of the sprays applied
July 6 to check the growth of the leaves and crowns

53

proportionately greater than the growth.of the roots. The
roots increased in.dry weight considerably, apparently at the
expense of the above ground portions of the plant. The toxic
effects of the sprays evidently affected the roots relatively
less than the crowns, possibly for the most part indirectly,
by reducing the growth.of the leaves and crowns.

As indicated previously, there was only little or no
decrease in.crown-root ratios of the various groups of plants
from.August 3 to September 1. This would indicate that root
formation.had slowed somewhat during this period.

When the samples were taken October 4, the crown-root
ratios of all the plant groups had again increased suggesting
that proportionately the crowns had increased in dry weight
at a more rapid rate than the roots. At this time the crown-
root ratio of the three groups of plants receiving the pentyl
sprays at different dates were identical at 0.68 and were
only slightly less than the ratio of 0.70 for the controls.
At no time in this experiment were significant differences
in.crown-root ratio found between any of the treatment groups,
including the controls at the same sampling date. This would
indicate that the sprays under the conditions of this experi-
ment did not greatly effect the relative growth of the crowns

and roots.

Experiment 3

The materials, ethyl, pentyl, and polyethylene glycol
esters of 2,4-D at i pound, the amine salt of 2,4-D at 1
pound, and sesone at 2, 4, and 6 pounds per acre were applied
to a spring planting of Blakemore strawberries. Spray applica-
tions of each.materia1 were made four weeks after planting,
eight weeks after planting, and 16 weeks after planting.
Three-spray applications of the chemicals at the rates listed
above were made also, with each.material being applied at
each of the three dates. This experiment was designed to
compare the effect of various 2,4-D formulations and of sesone
applied at several concentrations on the yield as affected by
the number of runner plants produced.

A definite relationship between dates of spray treatment
and the number of runner plants produced was noted (Table 6).
These data show significant differences in runner plant set
and also in yield between plants treated each at 4, 8, and 16
weeks after planting. The average number of runner plants in
the control plots was 311 and these plants produced an average
of 16 quarts.

All of the 2,4—D ester sprays caused a significant reduc-
tion.in plant stand and in yield as a result of the spray
application made May 13, four weeks after planting then
compared with the controls.

The plants sprayed with the pentyl ester form and those
sprayed with the polyethylene glycol ester produced signifi-
cantly greater numbers of runner plants and significantly

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56

higher yields than those plants sprayed with the ethyl ester
of 2,4-D. The plots receiving the polyethylene glycol form
produced an average of 205 runner plants and 15.15 quarts of
berries as compared to the pentyl sprayed plots with an
average of 195 plants and a berry yield of 14.82 quarts. The
ethyl spray application resulted in an average plant stand

of 179 runner plants and a yield of 14.57 quarts of berries.
This is in agreement with the results of the greenhouse study
in Experiment 2, where the low molecular weight ester forms
were found to be more phytotoxic than‘the esters of higher
molecular weight. The 2 ,4-D amine spray applied at this date
significantly reduced the plant stand without causing a
decrease in yield when compared to the unsprayed control
plots. Apparently the decrease in the number of plants was
beneficial in that the competition between the roots of runner
plants was lessened. The number of berries was reduced but
the size of the berries was increased in these plots.

Plants sprayed with sesone four weeks after planting did
not differ materially from the control plants in the number
of rooted runner plants produced regardless of the application
rate used. The average yield of 16.57 quarts from the plants
sprayed with sesone at the rate of 2 pounds per acre was
significantly higher than the controls, isoreas, the pro-
duction of the plants sprayed at the rate of 4 and 6 pounds
was not greatly different from the control.

Iith the exception of the sesone spray at the rate of
2 pounds per acre, all sprays applied June 10, eight weeks

57

after planting, resulted in.a decrease in plant stand when
compared with the plants sprayed May 13, four weeks after
planting, and with the controls. An explanation of the general
reduction of runner plants is that this treatment data coin-
cided with the period of most active runner production.

Carlson (9) found that two applications of 2,4-D per acre
inhibited 46 percent of the strawberry runners from.forming
on sprayed plants. The first spray was applied immediately
after harvest. It was during this time that the greatest
activity in runner initiation and formation was noted.

All of the plants receiving the 2,44D ester sprays on
June 10 showed a significant reduction in runner plants pro-
duced and in yield when compared to those plants treated
May 13 with.the same materials. The plants treated with.the
ethyl and pentyl esters of 2,4-D produced a significantly
smaller number of runner plants than those plants sprayed
with the polyethylene glycol ester, indicating the greater
phytotoxicity of the low molecular weight esters. This was
reflected also in the significantly lower yields obtained
from.the plants treated with either the ethyl or pentyl esters.

While the plants sprayed with.the amine salt showed a
decrease in plant stand and yield as compared with.the plants
sprayed May 13 with this material, the yield was not signif-
icantly different from.the controls despite a nearly 22 per-
cent reduction in runner plants. This is further indication
of the relationship between plant stand and yield.

The spray applications of sesone at 2 pounds per acre

58

did not significantly alter the average number of runner
plants produced when compared with the plants sprayed with
this material at the same rate four weeks earlier on May 13.
However, the plants treated with 4 pounds, produced an
average of 293 runner plants which were significantly fewer
than for the controls or for the plants sprayed with 4 pounds
of sesone on May 13. Neither of the spray applications of
sesone made at the 2 or 4 pounds per acre rate, 8 weeks after
planting, reduced the yields the following spring when
compared to the controls. The plots receiving an application
of sesone at 6 pounds per acre showed an average reduction of
38 runner plants and of 1.70 quarts when compared with the
plants treated four weeks earlier.

In these plots receiving the 2,4-D ester spray applica-
tions August 5, 16 weeks after planting, both the yield and
plant stand were significantly higher than found for those
plots treated with the same materials May 13 and June 10.

The average plant stand for the control plots was 311 plants
which was significantly greater than for the plots receiving
sprays. Also, a significant difference in the number of
plants produced was observed between the plots sprayed with
the different esters. The average number of runner plants
for the plots treated with the ethyl form was 217, for the
plots receiving the pentyl sprays 232 plants, and for the
polyethylene glycol sprayed plots 249 plants. When compared
with the controls, the yields. were found to be reduced sig-
nificantly only by application of the ethyl ester of 2 ,4-D.

59

These data continue to show the phytoxicity of the esters
to be related to the molecular weight. The plants sprayed
with the ethyl ester were significantly lower in runner plant
production and yield than the plants sprayed with the poly-
ethylene glycol ester. Plants sprayed with the pentyl ester
had an average runner plant production of 232 plants and a
yield of 15.72 quarts. These values were significantly less
than the averages of 249 plants and 16.17 quarts obtained
for the plants sprayed with the higher molecular weight
material, the polyethylene glycol ester. It should be noted
that the ester sprays, applied on August 5, although all in-
hibited runner plant production significantly, did not reduce
the plant stand to the extent as did the materials applied
May 13 and June 10. This increase in plant stand could be
attributed to the fact that by August 5 the period of most
active runner initiation was passed and thus the 2,4-D
sprays were less effective on inhibiting runner plant pro-
duction. The fact that the August 5 spray applications did
not excessively inhibit runner plant production is shown by
the average yields of the plants sprayed with the pentyl
ester and those sprayed with the polyethylene glycol ester
which were 15.72 quarts and 16.17 quarts. These yields‘were
not significantly different from.the average yield of the
controls which.was 16.00 quarts. The beneficial effects of
greater plant spacing are reflected by these yields.

An average of 308~runner plants was established in the
plots receiving the amine salt sprays on August 5, which was

 

 

60

significantly greater than.the 254 plants and 243 plants
produced in the plots sprayed respectively May 13 and June
10 with.the same material. In fact, there was no significant
difference in the plant stand of the plots receiving the
amine preparation 16 weeks after planting and the control,
further indications that the period of most active runner
initiation was past. Neither was the yield significantly
different than that of the control, suggesting that the spray
application of this material at this time affected neither
the runner plant production nor yield.

The only significant differences observed in the plots
receiving sesone were in.the plots to which the 6 pound appli-
cation was made. Both the yield and average plant stand of
287 plants and the average yield of 15.65 quarts were signif-
icantly higher than those of the plots receiving this material
at the same rate eight weeks earlier. On June 10 the average
plant stand was 266 plants and the yield was 14.25 quarts.
Only significant differences in plant stand existed between
the controls and the plots receiving sprays at the rate of
6 pounds of sesone on August 5. While the number of runner
plants produced was barely significantly lower than the con-
trols, there were no significant differences between yields.

‘When combination.treatments consisting of sprays at
each.of the 3 dates were made with each.material, all of the
2,44D ester sprays drastically reduced the number of runner
plants produced. The average number of runner plants pro-
duced in the plots sprayed with.one of the three esters were
for ethyl sprayed plots 46 plants, for those treated with the

61

pentyl ester 55 plants, and for those receiving polyethylene
glycol sprays 69 plants. The yields of these plots were also
Inch.below that of all the others treated as well as the
control plots. The average yield per 20-foot plots were 4.99
quarts for the plots treated with the ethyl ester, 5.17
quarts fer the plots receiving sprays of the pentyl ester,
and 6.47 quarts for the plots treated with the polyethylene
glycol ester. There were significant differences apparent
between the effects of the three esters on plant stand and
yield. Plants treated with the polyethylene glycol ester
sprays produced a significantly higher number of runner plants
and yield than those plants receiving three-spray applications
of the ethyl and pentyl esters.

The three-spray applications of the 2,44D amine sprays
significantly reduced the average plant stand from 311 runner
plants to 249 when compared with the controls (Table 6).
However a like comparison indicated that the yields of the
sprayed plots were not significantly lowered. There were no
significant differences in plant stand between plots receiv-
ing the three-spray amine application and those sprayed with
the amine fornmlation.once each on May 13 and June 10. There
were, however, significantly fewer plants produced than in
these plots receiving the amine spray on August 5. It was
interesting to note that none of the plots receiving the
2,44D amine sprays differed significantly in yield from.each
other or from.the controls. The plots producing the greatest
number of runner plants had the lowest yield of all plots

62

treated with the amine sprays although as previously stated,
these differences were not significant. It appears that the
extra runner plants produced in these plants rather than

increasing yields actually tended to decrease them slightly.

All of the three-spray treatments of sesone reduced
significantly the number of runner plants formed when these
plots were compared to the controls and the other plots
receiving the sesone sprays (Table 6). These values were 288
plants for the plots receiving the three-spray applications
at the rate of 2 pounds, 255 plants for those plots treated
at the rate of 4 pounds, and 199 plants for the plots receiv-
ing the three-spray applications of sesone at the rate of
6 pounds per acre. Only those plots receiving 6 pounds of
sesone were significantly lower in yield than the controls.
Both the plots receiving the 2-pound and 4-pound rates of
sesone, produced significantly less berries than the plots
receiving the same concentration on May 13. The berries from
the plots receiving three sprays of sesone at the 4-pound
rate were larger than the berries from the control plots
again emphasizing the chemical inhibition of runner plants
which favorably affected plant spacing.

A comparison of averages for all treatments shows a
close relationship between plant stand and yield (Table 7).
The correlation of the number of runner plants with the yield
was highly significant (r '-' 0.985) (Figure 12). Plants spray-
ed with the amine salt of 2 ,4-D produced fewer runner plants
but had a higher average yield than those sprayed with

 

 

 

Table 7. A comparison of the effects of sesone and various
formulations of 2,4-D used for weed control upon
the runner plant production.and.subsequent yields
of the Blakemore strawberry.

: Rate : Mean : Mean
2 Per Acre : Plant : Yield
Chemical : (pounds) : Stand : (quarts)
Ethyl ester
2,440 .5 141.6 11.73
Pentyl ester
2,4AD .5 149.9 11.94
Polyethylene
glycol ester
2,4-D .5 167.9 12.72
Amine salt
2,4-D 1.0 261.5 15.76

Sesone 2.0 304.5 16.13

Sesone 4.0 290.5 15.89

Sesone 6.0 264 e0 14e81

Check 0 e0 311.0 16 e00

L.S.D. between treatment avers e

5 7.44 0.07
1% 10.01 0.10

I M QUAIZTé

YIELD

 

 

 

"L

L

l

023 ISO I75 200 225 230 273 330 325

NUMBER OF- IZUMMEIZ. PLANTé

Figure 12. Regression of number of runner plants on
the yield in quarts of Blakemore strawberry
plants. These are averages for 20 foot

p10t.e
(Y= 0.02650): + 8.11) (r = .935)

65

6 pounds of sesone. Although the amine salt formulation
sprays contained twice as much 2,4-D acid equivalent than
did the ester formulation sprays, a comparison of'the
average plant stand showed that plots treated with.the vari-
ous ester formulations had a highly significantly reduction
in plant stand when compared with plots treated with the
amine formulation. The plants in the ester sprayed plots
were considerably less productive than those plants in the
plots treated.with.the amine formulation.

When only the single spray applications made 4, 8, or
16 weeks after planting were compared, an even closer rela-
tionship between plant stand and yield was observed (Table 8).
The correlation of the number of runner plants with the yield
was highly significant (r 8 0.959) (Figure 13). The average
plant stand of those plots sprayed with 6 pounds of sesone
was greater than those sprayed with the amine salt of 2,44D.
The yield was lower. Berries produced on all the plots
sprayed only once with 2,44D were larger than those sprayed
with sesone and those produced on the control plants, thus
reflecting the effect of tie inhibition of excessive runner
plants by the 2,4-D treatments.

‘When comparing all of’the ester spray treatments with
respect to time of application, it was found that all of the
spray treatments applied 16 weeks after planting or on August
5 had the least effect on runner plant stand and yield
(Table 6). Further, the plots sprayed 8 weeks after planting

on June 10 showed the greatest reduction in runner plant

The effect of three applications of various 2,44D

 

 

 

Ttbl. 8e
formulations and.of different concentrations of
sesone on stand of runner plants and subsequent
yield of Blakemore strawberries. The treatments
of 2,4-D and sesonewere made 4, 8 and 16 weeks
after planting.
: Rate 3 Mean : Mean
3 Per Acre 3 Plant 3 Yield
Chemical 3 (pounds) 3 Stand 3 (quarts)
Ethyl ester
2,44D .5 172.6 13.98
Pentyl ester
2,4-D .5 181.0 14.19
Polyethylene
glycol ester
2,4-D .5 200.6 14.81
Amine salt
2,4éD 1.0 268.3 15.80
Sesone 2.0 310.0 16.16
Sesone 4.0 302.3 15.98
Sesone 6.0 285.6 15.28
Check 0.0 311.0 16.00
L.S.D. between treatment average
5 7.44 0.07
1% 10.01 0.10

IM QUARTb

YIELD

 

67

 

 

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I5"

:4-

:3-

m

'iso r15 .3. 255 2;. 215— 300 as?
NUMBER. OF RUNNER. pLANTb

Figure 13. Regression of number of runner plants on the

yield in quarts, of Blakcmore strawberry
plants. These values are averages of 20-foot
DIOtSe

(Y: 0.01383X + 11.77) (r = .959)

68

production and yield in all instances of any of the plots
receiving only one spray. The plots sprayed 4 weeks after
planting on May 13 were intermediate in their response to
the ester sprays which is indicated by runner plant produc-
tion and yield.

The differences between time of application were highly
significant. It has been suggested earlier that the inhibi-
tion of strawberry runner plants was greatest if certain
herbicides were applied when the initiation and development
of runner plants was most rapid. This period of greatest
runner plant activity would begin about the middle of May,
reaching its peak about the third week in June and then
gradually decreasing during the rest of the growing season.
Therefore, time of application could be the explanation of
the relative effect of the sprays applied May 13, June 10,
and August 5 on runner plant production.

It was noted that the yield of the plants sprayed on
August 5 with the ethyl form of 2,4-D was barely significantly
lower than for the control plants, while the plots receiving
the pentyl or polyethylene glycol esters did not vary signif-
icantly in yield. The plots receiving the last two materials
showed the beneficial effects of greater plant spacing by the
greater size of the berries as compared with the control.
Where the runner plant inhibition was excessive, as was true
for all plots receiving the three-spray applications of each
ester, a drastic decrease in yields resulted (Table 6}.

The plants sprayed on different dates with the amine form

69

reflected the seasonal responses in.runner plant production
similarly to these plants receiving tie ester sprays. The
differences in.runner plant production, however, were barely
significant. Runner plant inhibition was greatest as a result
of the June 10 spray, less severe in the plots sprayed May
13, and least in the plots sprayed August 5. The yields
were not significantly different between plots treated on
different dates, treated with different chemical formulations,
and the controls. As stated previously, the yields from the
plants receiving the three-spray treatment of the amine salt
were not significantly lower than those of the controls.
There were no significant differences in runner plant
production between the plots receiving sesone at the 2 pound
per acre rate on different dates. The plant stand*was
barely significantly reduced in the plots receiving 4 pounds
of sesone on June 10 when compared with plots receiving the
same material on the other two dates. This reduction in
plant stand was not reflected in yield. The plants sprayed
Jane 10 with 6 pounds of sesone produced a significantly
lower number of runner plants and berries than the other
plots receiving the same treatment in May or in August. The
plots receiving three applications of 6 pounds of sesone at
4, 8, and 16 weeks after planting were greatly affected as
evidenced by the average number of runner plants produced and
the subsequent yields which.were 199 plants and 13.42 quarts.
Although sesone applied as single sprays at the rate of 6
pounds per acre reduced the plant stand significantly when

70

applied 8 weeks and 16 weeks after planting, the yields were
reduced only by the treatment 8*weeks after planting, as
previously reported. The accumulative effect of the three-
spray treatment was apparently sufficient to reduce both

runner plant stand and yield.

DISCUSSION

In the greenhouse transpiration studies, it was found
that none of the chemicals, all members of the 2,4-D family,
when applied at the rates normally used for weed control in
strawberries, affected the transpiration rates of strawberry
plants (Tables 1 and 2).

However, when the ethyl and butoxyethanol esters of
2,44D were applied to the plants at the rate equivalent to
1.5 pounds per acre or three times the amount normally
employed to control weeds in strawberry plantings, the tran-
spiration rates were significantly lowered (Table 2). Simi-
lar results were obtained by Brown (4) working with bean
plants. He found that 2,4-D sprays on bean leaves brought
about a decrease in the transpiration rate during the three
days immediately following treatment. Mitchell (45) reported
a reduction of water loss from.detached tops of kidney bean
seedlings that had been treated while intact with chlorine-
substituted phenoxy compounds.

The leaves of the strawberry plants sprayed with.the
high concentration equivalent to 1.5 pounds per acre of the
ethyl and butoxyethanol esters of 2,44D exhibited pronounced
formative effects, curling severely after treatment. During
this period, the affected leaves were quite crisp and
brittle. A.possible explanation for this condition is that
the 2,440 caused some of the stomates to close thus result-

ing in a definite increase in the turgor pressure of the

’72

cells. Microscopic examination of strips of epidermis taken
from treated leaves showed some stomatal closure. It has
been reported by Ferri and Raclid (19) that the stomata of
several species of plants closed at least partially follow-
ing soil treatments with 2,4-D. Treatment of the leaves

or the soil with 2,4-D was followed by partial stomatal
closure according to Bradbury and Ennis (3). They suggested,
on the basis of evidence obtained, that stomatal closure in
treated leaves was a direct effect of the growth-regulator
on the leaves rather than an indirect effect on the water-
absorbing mechanism 'of the roots.

It is realized that greenhouse conditions are consid-
erably different from those encountered in the field. The
lack of control of environmental conditions would make this
type of study difficult in the field. However, there is no
reason to believe that the results obtained in the greenhouse
were materially different from what could be expected in the
field.

When the effect of various 2,4-D ester formulations on
the vegetative growth of strawberry plants was compared, a
direct relationship between toxicity and length of the carbon
chain of the alcohol was noted. The short chain esters were
more phytotoxic than the esters of higher molecular weight.
Evidence of this was the greater formative effects, in-
creased hyponasty and petiolar curvature, as well as the
decreased dry weight of the roots and shoots of the plants
sprayed with the short chain esters (Table 3). It has been

75

suggested by Robbins, Craft and Raynor (49) that, then a
long chain alcohol is used to formulate a 2,4-D ester, the
high molecular weight of the alcohol might dilute the toxic
group thus causing the compound to be less toxic than one
formed from.a short chain alcohol.

The increased phytotoxicity of the short chain esters
may in part be due to the absorption of the volatile vapors
through the stomata. It has been established that in general
the greater the molecular weight of the ester, the lower the
volatility. Marth and Mitchell (42) have reported the methyl
ester of 2,4-D as being the most volatile of a number of
ester formulations tested. They found also that the ethyl,
butyl and isopropyl esters were more volatile than the esters
of higher molecular weight. Mullison (46) exposed tomato,
bean and cotton plants to esters of low molecular weight and
observed that a number of them were sufficiently volatile to
cause decided plant responses. He reported that as the hump
ber of carbon atoms in the aliphatic portion of the 2,4-D
ester is increased the volatility decreases. He further
observed that an alkanolamine salt and the sodium salt of
2,44D were non-volatile, as determined by the responses of
the exposed plants.

It was noted in.these experiments that all of the esters
used reduced the dry weight of the roots and shoots of the
strawberry plants and that this reduction was greatest in
those plants sprayed with the esters of low molecular
weight. Further, on a percentage basis, the plants treated

74

with the short chain esters showed a greater reduction in
the dry weight of the shoots as compared to the roots of

the plants than those plants sprayed with the high.molecular
weight solutions (Table 3). It is possible that this dif-
ferential effect on the dry weight of the shoots might have
been due to either a physical or chemical difference in the
ester. It has been reported by Frear (21) that esters of
an aliphatic nature can penetrate the cuticle of plants
readily but once inside the leaves, they do not enter the
aqueous phase in any appreciable amount. He suggests such
forms of 2,4-D to be effective in killing the leaves of
plants, but that they are not translocated as well as the
salts or esters formed from.higher alcohols which are soluble
in both water and lipoids.

When the pentyl ester of 2,4~D was applied to a first
year planting of Blakemorc plants at 3 different dates
during the growing season, it was observed that each spray
while decreasing the total dry'weight of the plants did not
equally affect thecrown-root ratio (Tables 4 and 5). A
rather uniform.increase in crown-root ratios for the first
3 months indicated that the above ground portions of the
plants were increasing faster than the roots. The spray
applied in May did not alter this relationship. In August
however, a definite drop in crown-root ratios was observed
in all plots including the unsprayed controls. This suggests
a continued growth of the root system.following a decline in
crown growth, and is in agreement.with findings reported by

75

Mann (41) and Mann and Ball (40).

Ihile all plants showed a definite drop in crown-root
ratio in August, those plants receiving a pentyl ester spray
application 4 weeks earlier in July had a lower crown-root
ratio than the unsprayed plants, although this difference
was not significant. This lower crown-root ratio observed
in the sprayed plants in midsummer suggests that at this
stage spray applications of the pentyl while decreasing the
size of the crown and roots had a relatively greater effect
on decreasing the size of the crown. This would seem to
indicate that, while the action of the ester may have been
systemic, the toxic effect was not uniform throughout the
sprayed plants. Since each pentyl ester spray application
appeared to inhibit leaf growth and development for 10 to 14
days, it is conceivable that some translocation of carbo-
hydrates to the roots continued during this period. This may
have accounted for the greater increase in dry weight of the
roots. It was during this midsummer period that the most
rapid development of the primary roots was observed. Prior
to this time most of the root growth consisted of the
initiation and development of the secondary roots. The
pentyl ester applications evidently were more toxic to
secondary roots than to the primary roots as injury and
death to the former were observed frequently when there was
no noticeable injury to the primary roots. Since the
crowns were much larger in July and August than in May,

translocation of the 2,4-D to the roots may have been slower.

76

'By early October the crown-root ratio of all plots in-
cluding those receiving a spray in September had risen signif-
icantlya There were no significant differences between the
crown-root ratio of sprayed and unsprayed plants. Root
formation had slowed somewhat and on a percentage basis the
crowns were increasing in dry weight at a more rapid rate
thus accounting for the higher ratios.

These findings emphasize a fact reported by others (9)
(18) (32) (6) that the age of the plant and the stage of
development of the tissues have a strong bearing on the effect
of 2,4-D applications on strawberry plants. It has‘becn
shown (9) (18) that this material will inhibit runner produc-
tion when applied prior to initiation of the runner buds.
Spray applications during or following blossoming have
inhibited flower and fruit production ( 9) (32) .

In this study, spray applications of the pentyl ester
reduced the dry weight of crowns and roots regardless of
the date of application. Although some minor variations
were observed, the pentyl ester sprays did not significantly
thange the proportion.of’crown to root, as shown by the crown-
root ratios.

When various 2,4-D formulations and the compound sesone
were compared to determine their effects on the:number of
runner plants produced and on yield of Blakemorc plants,
several relationships were observed.

Distinct differences were found regarding the influence
of some of the materials on plant stand and yield (Tables 6,

77

7 and 8). The ester formulations used were of low, medium
and high molecular weight and all were found to reduce
plant stand and yield more than the amine salt containing
twice as much 2,4-D acid equivalent. This difference in
toxicity was verified by Robbins, Crafts and Raynor (49) who
reported the toxicity of all the esters of 2,4-D on an acid
equivalent basis as being nearly twice that of the acids and
salts of the same material.

It is probable that the observed difference in phyto-
toxicity is due in part to differential absorption of the
various materials by the sprayed portions of the plants.
Ahlgren et a1 (1) thought the polarity of the herbicidal
molecule to be closely related to the absorption phenomena.
They reported the salts of 2,4-D to be polar while the ester
forms were found to be nonpolar. Since the waxy cuticle of
plant leaves and stems are nonpolar, the nonpolar herbicides
tend to be absorbed more rapidly than the polar herbicides.
The lipoid nature of the cuticle is widely recognized and
Crafts (12) has pointed out that any material applied to
a leaf surface may (a) remain on the outer surface, (b) pene-
trate into the cuticle and remain there in solution in the
lipoids, or (c) penetrate into the cuticle and then dissociate
and enter the aqueous phase of the epidermal cells and
eventually reach the vascular system.

As previously stated, it has been found that the salts
of 2,4-D penetrate the cuticle of the leaf with difficulty,
but the portion that does penetrate into the leaves is

0'

78

readily taken up by the aqueous phase of the cells. It has
been mentioned also that esters of an aliphatic nature can
penetrate the cuticle readily but once inside the leaves
they do not enter the aqueous phase in any appreciable
quantities, because of their nonpolar nature. This may
partially explain the greater phytotoxicity of the short-
chain esters.

It has been found by Robinson and Willard (50) that
ester formulations of 2,4-D are safer to use as pre-emer-
gence sprays than the amine salt formulations. They advance
as reasons for this finding that the esters are not leached
as readily as the amine salts but remain "fixed” in much
greater concentrations in the first inch of the soil.

The dhemical sesone has proven effective in killing
germinating seeds of both grasses and broad-leaved weeds.
This'morkzsuggests that the material may be applied to
strawberry plantings at the 2- and 4-pound rates without
seriously affecting plant stand and yield. Indications are
.that at 6 pounds per acre enough of the material may be
absorbed by the roots to adversely affect plant production
and yield when sprays are applied in early summer or when
applications are made in the spring, early summer and late
summer at this rate. Environmental factors dcubtlessly
influence the effectiveness of this chemical. In these
studies the soil moisture was maintained at a.near Optimum
level. Observations made on plantings where the soil

moisture content was low at the time of application and for

 

 

 

 

79

sometime afterward indicate that the toxicity of sesone to
strawberry'plants was of a low order (54). Further, the
effectiveness of the material as a germinative toxicant
against weed seeds was greatly decreased. Freed (22)
reports that in the soil sesone is activated to 2, 4-dichlcro-
phenoxyethanol, but whether it is activated to 2,4-D acid
has not been definitely established. However, he suggests
that chromatography of the soil constituents after treatment
with sesone has given evidence that the ultimate active
product may be 2,4-D acid. If this is true, the differen-
tial selectivity then would be dependent on the relative
tolerance of the strawberry to the low concentrations of
this chemical.

An intimate relationship was found between the time of
application of the 2,4-D ester formulations, the sesone at
6 pounds and plant stand. All of the ester treatments and
the 6 pound per acre application of sesone applied in early
summer, June 10, resulted in a definite reduction in the
number of runner plants produced. This date of application
coincided with the period of most active runner formation
which probably was responsible for the greater effects of
these chemicals than when they were applied early in the
spring or later in the summer. This agrees with reports
by Denisen (1'7), Carlson (9), Hibbard and Hemphill (:52).

A.number of the spray chemical treatments, although
reducing the plant stand significantly, did not uniformly
reduce yield (Table 6). This failure of the yield to

 

reflect the plant stand could be due to a runner plant
inhibition by some of the materials which.resulted in less
root competition.within the rows and an increase in size of
plants and berries.

When.2,4éD is to be utilized as a herbicide to control
established broad-leaved weeds in strawberry plantings, it
appears that the use of an amine salt preparation at the
rate of 1 pound per acre would be more feasible for spring
or summer applications than any of the ester formulations
tested at 0.5 pound per acre. On the other hand, it is
indicated by this study that high molecular weight non-
volatile esters can be applied in late summer or early fall
with no resultant reduction in yield. The ester formulations
are more effective against broad-leaved weeds than the amine
salts. A beneficial runner plant inhibition may be obtained
from.the use of the 2,4-D sprays.

 

 

 

SUMMARY AND CONCLUSIONS

1. Sesone and the amine salt, the ethyl, butyl,
isopropyl and butoxyethanol esters of 2,4-D were tested
on Blakemere strawberry plants growing in the greenhouse
to determine their effect on the transpiration rate. Sesone
was applied to the soil directly around the plants at a
rate equivalent to 6 pounds per acre while the other mate-
rials were applied directly on the plants as sprays. The
esters were used at rates equivalent to 0.5 and 1.5 pound
per acre while the amine salt was used at a rate equivalent
to 1 pound per acre.

(a) The transpiration.rate of the strawberry plants
was not affected by the use of sesone applied at a rate
equivalent to 6 pounds per acre, the amine salt of 2,449 at
a rate equivalent to 1 pound per acre, or to any of the
ester formulations applied at a.rate equivalent to 0.5 pound
per acre.

(b) ‘When the ethyl and butoxyethanol esters were
applied at a rate equivalent to 1.5 pounds per acre, there
was a significant reduction in the transpiration rates of
the treated plants. The use of these esters at this high
concentration induced severe hyponasty of the leaves. This
condition resulted in the closing of the stomata which.in
turn reduced the loss of water vapor.

2. Five esters of varying molecular weight including

Fx

5

82

the methyl, ethyl, butyl, butoxy ethanol and the propylene
glycol butyl ether esters of 2,44D were applied to Blakemore
strawberry plants growing in the greenhouse at two different
rates.

(a) The dry weights of the shoots and roots of the
plants treated at the rate of l mdlligram per plant were not
significantly different from the unsprayed controls. There
were significant differences in the drwaeights of the plants
sprayed with the different esters but no exact relationship
between the molecular weight of the ester and dry weight of
the shoots and roots were detected.

(b) Spray applications of 4 milligrams per plant
of the same materials resulted in significant reduction of
the dry weights of the shoots and roots of all sprayed
plants. Furthermore, this repressive effect on growth bore
a definite relationship to the molecularweight of the ester,
as the molecular weight increased the dwarfing effect
decreased.

5. The pentyl ester of 2,4-D was used on plants grow-
ing in.the field to study the effect of different dates on
application of a representative ester formulation of 2,44D
upon the relative growth and development of strawberry
crowns and roots. Late spring and late summer spray treat-
ments while decreasing the total dry weight of the sprayed
plants did not greatly affect the crown-root ratio. The
most rapid period of root growth was observed in mid-summer

following an earlier increase in crown.growth. Although

 

 

 

 

 

 

 

 

 

the differences were not significant the sprays applied in
midsummer retarded root growth proportionately less than
crown.growth, indicating that the dwarfing effect was not
as great in the roots. Apparently due to the larger size
of crowns and leaves, less 2,4-D was translocated to the
roots than earlier in the season when the plants were
smaller. It is likely that after the spray was applied
some translocation of carbohydrates continued from.the
leaves and crowns to the roots. Rapid development of the
primary roots was observed during this period. The pentyl
ester 2,4qD sprays were found to retard the growth.and
development of the secondary roots to a greater extent than
the primary roots. The secondary roots were injured severe-
ly or killed when there was no noticeable injury to the
primary roots. '

4. Several related herbicides including the ethyl,
pentyl and polyethylene glycol esters of 2,4-D, the amine
salt of 2,4-D and sesone were applied under field conditions
to spring planted Blakemorc strawberry plants. Spray appli-
cations of each material were made in late spring, early
summer and late summer. Three-spray treatments were made,
with each material being applied at the times indicated
previously. These materials were usedto determine their
effect on runner plant formation and subsequent yield.

(a) «All of the 2,4-D ester sprays applied at the
rate of 0.5 pound per acre reduced significantly runner
plant formation regardless of the time of application. The
yields were reduced significantly also except for the plants

(I

sprayed with the pentyl ester or the polyethylene glycol
ester form.in later summer.

(b) The amine salt of 2,4-D used at twice the
actual acid rate used for the ester formulations resulted
in a reduction of runner plants when a single spray appli-
cation was made in late spring and in early summer and
when a three-spray treatment was used. There was no signif-
icant reduction in yield in any of the amine sprayed treat-
ments. These data indicate that the 2,4-D amine salt can
be utilised at the rate of one pound per acre to control
broad leaved weeds in strawberry plantings. These sprays
also tend to reduce the number of runner plants produced,
thus preventing overcrowding in the row. The size of the
individual berries is considerably increased as a result.

(c) The stand of plants was significantly re-
duced in the plots receiving the three-spray treatments of
sesone at the rate each of 2 and 4 pounds. The yields were
not reduced in any of the plots to which sesone was applied
at these rates. Single applications of sesone at the 6
pounds rate in the early and late summer caused a reduction
in plant production as did the three-spray treatments made
each at the same rate. Yields were reduced except for the
late spring and late summer treated plants in all plots
sprayed with sesone at the rate of 6 pounds per acre. The
results of this study indicate that applications of sesone
at the rate of 2 to 4 pounds per acre may be made on

strawberry plantings 2 or 3 times during the growing season

85

without seriously affecting plant stand and yield.

(d) A comparison of the averages of all treat-
ments showed a highly positive correlation (r I 0.959)
between runner plant production and yield when plots
receiving the single spray applications made at 4, 8 or 16
weeks after planting were compared.

. (e) With respect to time of application, all of
the forms of 2,4-D applied on June 10, eight weeks after
planting, most severely reduced the number of runner plants.
This date of application coincided with the period of most
active runner plant initiation and formation, confirming
the effectiveness of 2,4-D as a runner plant inhibitor.

(f) Although several spray treatments including
all of the amine salt applications and the pentyl and poly-
ethylene glycol ester applications made on August 5 signifi-
cantly reduced the plant stand, the yields were not signifi-
cantly lowered. This suggests that the inhibition of runner
plants resulted in greater plant spacing, thus reducing the
root competition for water and soil nutrients. The‘berries
of the treated plants were larger than those of the control
plants.

a!

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

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