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THE EFFECTS OF IDOPROPYL N-(S-CHLOROPHENYL) CARBAMATE
ON VARIOUS CROPS AND THE RESIDUAL ACTION OF THE
CHEMICAL WHEN APPLIED T0 VARIOUS SOILS

BY

Lewis Frank §tevens, Jr.

A THESIS

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements

for the degree of
MASTER OF SCIENCE
Department of Horticulture

1951

 

 

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INTRODUCTION . . . . .
REVIEW OF LITERATURE .
METHODS AND MATERIALS.
RESULTS. . . . . . . .
DISCUSSION . . . . . .
SUMMARY. . . . . . . .

BIBLIOGRAPHY . . . . .

TABLE OF

CONTENTS

16

28

75

81

84

ACKNOWLEDGMENTS

The author is indebted to Dr. C. L. Hamner and to
Mr. R. F. Carlson for their advice and inspiration.
Grateful acknowledgment is also due to the Pittsburg Glass
Company for the financial support of this project and for
furnishing the chemical material. Sincere thanks also to
my wife, Mrs. Caroljean Stevens, for her encouragement

and for her assistance in collecting the data.

INTRODUCTION

The chemical iSOpropyl N-phenyl carbamate is rapidly
becoming an important compound for weed control. This
compound, better known simply as IPC, has been shown to
be promising as a selective herbicide for controlling some
grasses among broadleaved crops. The limited solubility
and the rapid decomposition of IPC in the soil have led
to increased interest in one of its derivatives, isOprOpyl
N-(S-chlorophenyl) carbamate. The chlorinated IPC is of
special interest because it remains in a liquid state at
ordinary temperatures; is readily soluble with a wide
variety of organic solvents; has shown indications of
lasting for a longer period of time in the soil than does
IPC; and, most important of all, the introduction of a chlorine
atom to the IPC molecule has caused increased phytotoxicity.

It is the purpose of this study to determine the effects
of S-chloro IPC on such crops as.alfa1fa, clover, oats,
wheat, rye, sorghum, soybeans, and corn; and also to deter-
mine its rate of decomposition in light, heavy, and organic

soils under various environmental conditions.

REVIEW OF LITERATURE

IsOprOpyl N-phenyl carbamate was first shown to be
important as a selective plant growth regulator when Temple-
man and Sexton (33), in a comparison of fifty arylcarbamic
esters and related compounds, found that concentrations
which arrested the growth of cereals did not affect man-
golds, sugar beet, flax, rape, or yellow charlock.

Allard at El (2) found that concentrations of from
1 1/2 to 6 milligrams per four inch pot of soil either
stunted or killed seedlings of cats, wheat, corn, barley,
and non-flooded rice; was less injurious to soybeans,
kidney beans, cowpeas, sunflowers, radishes, turnips, and
sugar beets; and actually showed a possible stimulatory
effect on tomatoes. This tolerance of dicotyledonous plants
to the compound was not entirely consistent since appli-
cations to potatoes caused a reduction in growth, and the
germination of buckwheat was completely prevented. The
evidence was sufficient, however, to warrant recommendation
that the compound be tested for use as a herbicide on weedy
grasses. Allard, De Rose, and Swanson (1) also showed
mixtures of the chlorOphenoxyacetic acids with IPC would
inhibit seedling development of both dicotyledonous and
monocotyledonous species indicating that these mixtures had

promise as general herbicides.

fl

3

It was not until August of 1947 that 3-chloro IPC was
synthesized at Oregon State College, and to this date very
little information on this compound exists in published
form. Freed (16) in his work with the chlorinated derivative
has found it similar to IPC in effectiveness to various
species, but under conditions of high.moisture and high
temperature it may persist in the soil from.two to three
times longer than IPC. De Rose (11) also suggested its
value as an herbicide after comparative studies of carbamp
ates under greenhouse conditions in which he found that
crabgrass seed germinated and deve10ped in all pots except
those which had been treated with this compound.

To present a discussion of the growth regulating
abilities of 3-chloro IPC it becomes necessary to assume
the compound to be much like IPC. Therefore, the review
which.follows will be the results of investigations made,
for the most part, with IPC.

Ennis (14) and Doxey (12) have shown that treatment
of oat, rye, and onion roots with IPC resulted in cells
with polyploid nuclei, due to impaired action of the spindle
fibers. Ennis also describes certain histological changes
which occur due to treatment. In general, be found that
the increase in chromosome number resulted in increased
cell volume of the cortical cells of the primary root,
adventitious root initials, and cells of the apical meri-
stem. This increase in cell volume was not observed in

some stelar cells, although.the chromosome number did

4
increase, presumably due to their lack of capacity to en-
large. He suggested the use of IPC to induce chromosome
changes in cereals and grasses. These facts give insight
to the mode of action which this chemical and its derivatives
have on plant growth. Hewever, Mitchell, Burris, and Riker
(23) have observed that IPC, applied to tomato slices at
a concentration of 0.002 M, reduced respiration below that
of the controls, although it was less effective, in this
respect, than other plant growth regulators having a free
carboxyl group on an aromatic ring. This may indicate that
there is a combination of factors involved in the ability
of IPC to induce growth responses.

Thompson, Swanson, and Norman (36), in an attempt to
compare the growth regulating activities of many different
organic compounds, found that IPC showed 46 percent of the
activity of 2,4-dichlor0phenoxyacetic acid as determined
by the response of germinating corn seedlings, 16 percent
with the "kidney bean single droplet water test", and 90
percent with the "kidney bean single droplet 011 test".

This illustrates the low solubility of IPC in water. A

For maximum.effectiveness IPC should be applied to.
the soil rather than to the plant itself. This fact was
illustrated by Ennis (13), who found that cats and barley,
sprayed with IPC when the soil was not exposed, did not show
the characteristic injury which.was reported by Templeman
and Sexton (33). However, when the soil was exposed, injury

occurred and grain yield was reduced.

5

It was established by Allard, Ennis, and De Rose (2)
that young cereal plants were more susceptible to appli-
cations of IPC than were older plants. It has, therefore,
been considered that the most efficient applications are
those made when plants are in a young stage of development,
or those made before seedling emergence.

The herbicidal preperties of IPC have been demonstrated
by several research workers (4, 5, 22, 34, 39). Carlson (4)
found that IPC was inhibitory to the growth of rhizomes of
quackgrass (Agropyron repens 2,) in greenhouse tests.
Concentrations of 100 parts per million caused rhizomes
to develop but few leaves, and concentrations above 500
parts per mdllion completely stopped the deve10pment of new
shoots. Weeds which he cited as resistant to treatment are
lamb's quarters (Chenopodium £23m Ed, thistle (Cirsium
arvense (L.) Scopol, ragweed (Ambrosia elatior 14.), and
clover (Trifolium repens 19). In a later report, welcott
and Carlson (39) stated that field applications of 30 pounds
of IPC per acre were effective in delaying bud development
of quackgrass rhizomes for 30 to 60 days, but that such
treatments did not kill rhizomes, and inhibition was not
permanent. Lachman (22) delayed the growth of chickweed
in onions for a period of three weeks by the use of 5 pounds
per acre, while Carlson and Moulton (5) obtained satisfac-
tory control of chickweed in strawberries with concentra-
tions as low as 5 pounds per acre. Applications were made

in September, October, and November with successful control

at all times. Templeman and Wright (34) obtained good
control of grasses and Polygonum.species with 2 1/2 and
with 5 pounds of IPC per acre, and mixtures of 5 pounds

of IPC with 1 pound of 2,4-dichlorophenoxyacetic acid or
2-methyl-4-chlorophenoxyacetic acid gave good results on
weed species which were not susceptible to one of the other
of the compounds used in the mixture. The mixtures were
superior to IPC alone when applied to chickweed and Gallium
aparine.

That 3-chloro IPC appears effective on many grass
species not effectively controlled by IPC, has been stated
by Freed (16). Among these are the Panicoideal group,
which.includes water grass (Echinichola cru31galli (L.)
Beauv.). and barnyard millet (Setaria 322,). Both IPC and
3-chloro IPC appear to be equal in action on chickweed and
purslane, while 3-chloro IPC is more effective on species of
Polygonum. Danielson (8) has had successful control of
chickweed in spinach with.2 pounds of 3-chloro IPC per acre.
A comparison of 2,4-dichlor0phennxyacetic acid, IPC, and
3-chloro IPC by De Rose (11), has shown that 2 and 5 milli-
grams of 3-chloro IPC per pound of soil prevented the
development of crabgrass seedlings beyond the height of 5
millimeters after emergence, while no apparent effect was
noted on crabgrass with treatments of IPC below 5 milli-
grams per pound of soil, and 2,4-dichlor0phenoxyacetic
acid was found to be intermediate in its action on crab-

grass. Crabgrass seedlings, in pots treated with.0.5 milli-

7
gram.of 3-chloro IPC per pound of soil, made only slight
recovery.

The importance of the type and degree of injury to
crops due to herbicidal applications can not be over empha-
sized, hence an abundant amount of literature exists which
describes the effect of IPC on various species of economic
importance (5, 15, 21, 25, 29, 31, 34, 35).

Taylor (31) observed that cereals grown in nutrient
solutions, containing as low as 0.25 parts per million of
IPC, responded abnormally. Growth was inhibited and changes
occurred in the root system, one of the most common of which
was a swelling of the root tips. Low concentrations encour-
aged the development of an increased amount of shoots.
Treated plants remained alive, but the leaves became dark
green and highly cutinized or leathery. The compound stime
ulated small tillers on wheat plants and adventitious roots
on older rice plants.

Millet, Indian grass, Amber sorghum, and Bermuda grass
were not affected by applications of 5 pounds of IPC per
acre, in an experiment carried on by Mitchell and Marth (25).
Fesque, Ryegrass, Redtop, Thmothy, orchard grass, Quack-
grass, and Barley failed to emerge after the above treat-
ment, while Bluegrass emerged only slightly. At much.higher
concentrations (30 to 60 pounds per acre) the less sensi-
tive grasses, such as sorghum.and Sudan grass, grew to a
height of l to 3 centimeters but failed to develop further.

These stunted plants failed to produce seed. At concen-

8
trations of 50 to 100 pounds per acre, crabgrass extended
only 1 to 2 centimeters above the level of the soil and
eventually died. Two pound applications of IPC failed to
reduce the growth of spinach, onions and table beets. Sugar
beets were only temporarily checked, and radishes were
affected slightly.

Ennis (15) reports that 13 monocotyledonous species
treated with IPC showed a lack of root and shoot elongation
with an accompanied swelling of these parts. The roots
became stubby and bulbous, and the coleoptile region exhib-
ited a definite dwarfing with the leaves becoming dark
green. No epinasty occurred as it did in similar appli-
cations of 2,4-dichlorophenoxyacetic acid. Fifteen of 39
dicotyledonous plants tested gave some response to IPC.
Nine of these were permanently inhibited: the hypocotyl
became enlarged and failed to elongate; the root system
remained stunted; the cotyledons did not fully expand;
and the stem.apex failed to grow. Applications of IPC to
the tops of oat plants in the "boot" stage stepped the
development of the panicle, while similar treatments in
the seedling stage failed to give this response.

Lechman (21) reports that beans, spinach, beets, and
onions survived treatments of IPC from.2.5 to 10 pounds
per acre, although grasses were effectively controlled.

Five pounds of IPC per acre did not cause injury to
kale, mangolds, lettuce, onions, beans, peas, lucerne, sugar

beets, or swedes in the experiments of Templeman and Wright (34).

These treatments were applied at least 2 weeks before
sowing, however.

Carlson (5) has shown that strawberry plants treated
with applications as high as 25 pounds of IPC per acre had
yields equal to those of plants in hand weeded rows. The
roots of the treated plants appeared more vigorous than the
‘check plants except when the 25 pound rate was used. This
treatment caused a darkening of the roots and the.formation
of new roots at the crown.

The phenomenon of increased growth.due to very low
concentrations of IPC has been observed by several investi-
gators on certain species, with various growth regulators.
However, Thompson (35) used several growth.regu1ators,
including IPC, at very low concentrations to determine if
these treatments would increase the yield of alfalfa. No
increase in yield was obtained where the crOp was not in,
competition with plants which would be killed by treatments.

The information available on 3-chloro IPC indicates
that it is selective to the same crops as IPC, but more
toxic at high concentrations. De Rose (11) found that
rates of 0.5 and 1 milligram.per pound of soil had no
effect on germinating,peas, soybeans, and cotton, but stunted
growth of these plants occurred at a 2 milligram rate, and
inhibited germination occurred at a 5 milligram.rate. These
higher concentrations also severely stunted strawberry
transplants. When cotton was treated in pots which also

contained crabgrass seedlings the cr0p appeared normal at

10
the 5 milligram rate. All other plants were stunted by
high concentrations of 3-chloro IPC when grown in pots
which included crabgrass. Danielson (8) has observed that
spinach plant stands were reduced from 12 to 14 percent
after 2 pounds of 3-chloro IPC had been applied. He did
not consider this to be particularly harmful since the
plants usually need thinning anyway. Freed (16) relates
that both IPC and 3-chloro IPC are being used to control
annual grasses in perennial grass crops grown for seed,
and in most of the legumes. The clovers of the red clover
group are an exception -- they appear to be susceptible to
both compounds. The use of these compounds on beets, straw-
berries, and certain ornamentals, as azalea, has shown
IPC to be the least toxic of the two.

One very interesting point, which deserves mention, is
the action of IPC in preventing the sprouting of potato
tubers in storage. Rhodes_gt'gl'(29) compared IPC with
alpha-naphthylacetate and found it much superior in reducing
sprouting.

The factors contributing to the degree of residual
action of plant growth regulators when applied to the soil
have been investigated to a limited extent. By far the
largest amount of work has been done with 2,4-dichlorophen-
oxyacetic acid, and it has been assumed that these factors
described for 2,4-D contribute to the persistence of most
herbicides.

That different compounds vary in ability to last in

11
the soil, has been well established (9, 10). De Rose and
Newman (10) compared 2,4-dichlor0phenoxyacetic acid with
2,4,5-trichlor0phenoxyacetic acid and 2emethyl-4-chloro-
acetic acid, and found that 2,4,5-trichlorophenoxyacetic
acid persisted for a longer period than did the other comp
pounds, independent of concentration, temperature, or soil
moisture. De Rose (9) also has shown that applications of
50 pounds of IPC per acre completely lost its inhibitory
effect within 60 days while 50 pounds of 2,4-dichlorophen-
oxyacetic acid lasted nearly 80 days.

The influence of the soil on the breakdown of herbi-
cides can be broken down into five main categories: soil
moisture; soil temperature; soil reaction; organic matter
content; and microbial action.

De Rose (9) leached soils treated with IPC and 2,4-
dichlorophenoxyacetic acid and found these compounds present
in the leachate. Crafts (6) found that 2,4-dichlorophen-
oxyacetic acid does not move freely by percolation, and
that excessive amounts of water are required to leach this
compound downward, with leaching being more pronounced in
sandy loam.than in clay loam. Hanks (18), working with 2,4-
dichlorOphenoxyacetic acid and its calcium salt, observed
that leachates of treated peat soils were non-toxic at the
end of 2 weeks, and all other soils used except one, which
was naturally alkaline, had leachates which were non-toxic
after 6 weeks. Brown and Mitchell (3) have indicated that

2,4-dichlor0phenoxyacetic acid was inactivated most rapidly

12

at a moisture content of 30 percent. Mitchell and Marth
(24) found 2,4-dichlor0phenoxyacetic acid to last as many
as 18 months in air dried soil, while it is without toxic
effects in about 28 days in warm moist soil. Hernandez and
warren (19) have made similar observations.

De Hose and Newman (10) state that persistance varies
inversely with the soil temperature. Crafts (6) and Brown
and Mitchell (3) also give support to this statement.
Hernandez and warren (19) stored soils treated with 2,4-
dichlorophenoxyacetic acid at various temperatures and found
that persistance was greatest at the minimum temperature
of 40 degrees.

Kries (20) has shown inactivation to be less rapid
in soils of high alkalinity, and Hanks (18) has indicated
that limed soils do not effect persistance but that these
soils which are naturally alkaline remain toxic for a longer
period. Crafts (6), in observation of several California
soils, has concluded that 2,4-dichlorophenoxyacetic acid
is broken down more slowly in naturally alkaline and neutral
soils than in acid soils. A very interesting point in this
connection is that Weaver (3?) has found that 2,4-dichloro-
phenoxyacetic acid is more strongly adsorbed by cation
exchangers of the hydrogen form, while IPC is adsorbed
equally by those of the hydrogen, calcium, and sodium.form.

The addition of leaf mold to soils treated with 2,4-
dichlorophenoxyacetic acid strikingly reduced the degree of
persistance of toxicity in the experiments of Erica (20).

. 13

Brown and Mitchell (3) found that the addition of small
amounts of manure increased the rapidity with which this
compound disappeared, but that applications of 2,000 to
8,006 pounds of manure per acre retarded inactivation.
Hernandez and warren (19) have shown that 2,4-dichlorophen-
oxyacetic acid was leached more rapidly from.soils low in
organic matter than from.soils high in organic matter.

Brown and Mitchell (3); De Rose and Newman (10);
Hernandez and warren (19); and Newman 2£.E$.(27)' have
shown that herbicides last longer in soils which.have been
autoclaved in contrast to non-autoclaved soils. Compounds
included in these various experiments include IPC, 2,4-
dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic
acid, and 2-methyl-4-chlorophenoxyacetic acid. This has
led to the belief that much of the disappearance of toxicity
after application is due to the action of microorganisms.

The action of plant growth regulators on the soil
population has not gone without investigation. Newman (26)
found that as the acidity of the soil increased 2,4-dichloro-
phenoxyacetic acid, 2qmethy1-4-chlorophenoxyacetic acid,
and 2,4,5-trichlor0phenoxyacetic acid, at 125 and 500 parts
per million, showed increasing inhibitory effects on the
soil population. Hewever, IPC, ethyl-2,4-dichlorophenoxy-
acetic acid, and ethyl-Z-methyl-4-chlor0phenoxyacetic acid
were equally inhibitory to organisms at all pH levels. The
author proposed that growth regulators are inhibitory to
soil life only in undissociated form. He also found that

 

 

 

 

14
2,4-dichlorophenoxyacetic acid, 2¢methyl-4-chlorophenoxy-
acetic acid, 2,4,5-trichlorophenoxyacetic acid, and IPC
inhibited nitrification of ammonium sulfate at high con-
centrations. Tests for carbon dioxide evolution showed
that the above compounds were also inhibitory in this
respect, with IPC being the least inhibitory. Smith 33 a}:
(30) found 2,4-dichlor0phenoxyacetic acid did not reduce
the total count of microorganisms, but that nitrate and
nitrite forming organisms were injured by 100 parts per
million. The nitrite organisms were more sensitive than
the former.

Newman and Thomas (28) applied 2,4-dichlorophenoxy-
acetic acid to soil which.had been pretreated with the same
compound and found the residual action.much.1ess after a
second application, but when soils were pretreated with
compounds related to 2,4-dichlorophenoxyacetic acid the
persistance was not reduced. This suggests that the organ-
isms responsible for the decomposition of 2,4-dichloro-
phenoxyacetic acid are quite specific.

The specific residual properties of IPC are of interest.
Wolcott and Carlson (30) reported that IPC was inactivated
under field conditions, within 30 to 60 days, depending on
the concentration. weaver (38) found IPC lasted only 12
days in a three-to-one mixture of silt loam and coarse sand,
with a moisture content of 18.2 percent, and a pH of 8.1.
He used concentrations as high as 220 parts per million

based on the dry weight of the soil. Mitchell and Marth (25),

(1

[I

a.

 

15

however, have shown that 2 pounds per acre lasted almost
2 months. Taylor (32) applied IPC at rates of from.l to 4
pounds per acre on neutral and alkaline soils in the field
and found that IPC lasted only 5 weeks. Newman 23.2$.(27)
have made an extensive study of the persistance of IPC in
the soil. In their experiments oat seedlings emerged 0,
40, 50, 80, and 100 percent of controls after 8 days with
treated soils incubated at 10, 15, 20, 25, and 50 degrees
Centigrade. After 20 days there was only a slight stunting
of seedlings at the 10 degree level, and after 56 days there
was no visible toxic effects at any temperature level. After
19 days IPC had disappeared at all moisture levels except
100 percent water holding capacity and flooded soil. Silt
loam, with a pH of 6.7, treated with 9, 44, 220, and 1,102
pounds per acre showed a loss of toxicity in 15, 19, 56,
and 39 days. In still another experiment the compound
was broken down in three weeks despite the concentration.

De Rose (11) has compared the residual action of IPC
with.5-chloro IPC, and his results were quite significant.
While IPC at the rate of 2 milligrams per pound of soil
inhibited barley seeds for less than 24 days, the S-chloro
compound lasted from.48 to 56 days. His results indicated
strongly the ability of S-chloro IPC to last for a longer
period than IPC.

I.

I,
f!

I.

I“

 

METHODS AND MATERIALS

The chemical used in the following experiments has
the name isopropyl N-(S-chlorophenyl) carbamate. The
emperical formula of this compound is 06H401NH00203H7,

and it was used exclusively in the following formulation:

ISOpropyl N-(S-chlorophenyl) carbamate . 40.6%
Xylene e o e e e e e e e e o o e o o o c 58.2%
Isopropyl alCOhOle o e e e e o o e o e o 5.1%
Atlas G1255o o o e e 3 o e e e o o o e c 18.1%

The concentrations used were based on the actual
weight of 3-chloro IPC per unit weight of soil. In each
case the chemical was suspended in enough water to insure
adequate coverage of the soil or leaf surface, as the case
demanded.

In the eXperiments to determine the residual action,
the terms light, heavy, and organic soil will be used. These
soils are mixtures described in Table l. The reaction of ‘
these soils ranged from pH 6.0 to pH 6.5 where the reaction
was not adjusted.

The terms pro-planting, pre-emergence, and post-emergence
when used to describe the time of application, demand defin-
ition. Pre-planting treatments were applied to the soil before
the CrOp was planted; pro-emergence treatments were applied
to the soil after planting but before the crop seedlings

emerged from the soil; and post-emergence treatments were

17

applied after emergence of the crOp seedlings.
For the convenience of the reader the description of

the work done will be divided into four parts: (1) Labor-
atory technique used in determining the residual action of
3-chloro IPC in various soils; (2).Greenhouse experiments
to determine the residual action of S-chloro IPC in various
soils; (5) A field experiment to compare the residual action
of S-chloro IPC with IPC; and (4) Field experiments to

determine the toxicity of 5-chloro IPC to various crops.

TABLE 1

A DESCRIPTION OF HOW SOIL MIXTURES WERE PREPARED
IN EXPERIMENTS INVOLVING THE RESIDUAL ACTION
OF 5-CHLORO IPC

 

 

Soil mixture Kind and amount of soil in mixture

Light soil 1/2 sand
1/2 garden soil

 

Heavy soil 1/4 clay
1/4 sand
1/2 garden soil

Organic soil 1/4 peat
1/4 sand
1/2 muck

 

Laboratory Experiment Involving A Technique Used In
Determining The Residual Action of 5-Chloro IPC
In Various Soils
Five gram.samples of light, heavy, and organic soil

mixtures, which had been air dried, were shaken with 25

18
milliliters of water containing 0, 1,000, 5,000, 10,000,
50,000, 100,000, and 200,000 parts per million of S-chlorc
IPC based on 5 grams of soil. The shaking process lasted
for 2 minutes to ensure contact of the chemical with the
soil particles. The mixture of soil, chemical, and water
was then filtered through a filter paper, and the leachate
collected in a beaker. A 5 milliliter sample of the leach-
ate from.each treatment was added to a Petri dish containing
15 cucumber seeds (Marketer variety) placed on a filter
paper. The Petri dishes were covered and the cucumber seeds
were allowed to germinate for 4 days at room.temperature,
after which the root length of each seedling was measured
and recorded.

Similarly, a 5 milliliter sample of 25 milliliters of
water containing 0, 1,000, 5,000, 10,000, 50,000, 100,000,
and 200,000 parts per million of S-chloro IPC, which had
not been.mixed with the soil, was applied to 15 cucumber
seeds in a Petri dish. These seeds were allowed to germinate
along with the seeds treated with the soil leachates, to
determine the sensitivity of cucumber seeds to the concen-
trations of 5-chloro IPC used.

Subsequent leachings of these soil samples were made
at weekly intervals for 7 weeks. Leaching was accomplished
with 25 milliliters of water, and, as before, a 5 milli-
liter sample of the leachate was applied to 15 cucumber
seeds, which were allowed to germinate for 4 days. The color
of the leachates and the length of the seedling roots were

Observed.

If a - {I 3m_1_

 

 

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-
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19

Greenhouse Experiments To Determine Residual Action
0f 5-Chloro IPC In Various Soils

Experiment I. Portions of light, heavy, and organic

 

soils were divided into thirds and the acid reaction of
each third adjusted to pH 5, pH 7, and pH 8.5 respectively.
The adjustment to an acid reaction was made with.dilute
sulfuric acid; the adjustment to a neutral reaction was
made with calcium carbonate; and the high.a1kaline con-
dition was accomplished by adding calcium carbonate until
no further change in reaction occurred, and then raising it
to pH 8.5 by the addition of sodium carbonate.

Samples of each soil and each reaction were placed in
number 10 tin cans in such a way that there were 5 cans
containing light soil with a pH 5, 5 cans containing light
soil with a pH 7, and 5 cans containing light soil with a
pH 8.5. A similar number of cans containing heavy and
organic soils were prepared.

On April 17, 1951, 25 oat seeds were planted in the
cans at a depth of about 1/2 inch, water was added to field
capacity, and the soils were treated with 2 and 24 pounds
per acre of 5-chloro IPC by pouring it over the surface of
the soil. Each.treatment included one can of each.kind of
soil and each reaction. Untreated controls of each.kind
of soil and of each.reaction were also used as shown in
Table 2.

The cat seeds were allowed to germinate and continue
growth.for approximately 10 days. The tOps of the cat seed-
lings were cut off at the surface of the soil and the fresh

2O

 

 

 

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21
weights were recorded. Planting was repeated after weights
were taken, and this continued approximately every 10 days
until the treated soils produced seedlings of a weight
equal to or above the weight of those grown in the control
cans.

The cans were not allowed to drain and care was taken
to keep the soil moisture at about field capacity. At
each.planting the soil in the tOp 5 inches was mixed to
insure contact of the seed with the soil.

Experiment_II. Three groups of fifteen number 10
tin cans were filled with light, heavy, and organic soils
respectively. Before filling these cans, holes were punched
in the bottom to allow drainage and a filter paper was laid
inside to prevent the loss of soil particles. After filling,
the cans were placed on two 2“ x 4" boards in such a manner
that beakers could be placed beneath the cans to catch the
leachate.

Twenty-five oat seeds were planted in each.can at a
depth of about 1/2 inch. Each.group of 15 cans was further
divided into groups of five. One can of the 5 was saved
as a control while the other 4 cans were treated with 2,

S>6, 12 and 24 pounds of 5-chloro IPC per acre based on the
“(fl/weight of the soil. The soil was then brought to field
capacity and finally leached with.l, 1 1/2, and 2 surface
inches of water. The treatment was applied on April 28, 1951.
The fresh weight of the tops of the seedlings was taken

after about 10 days and the cans were replanted at the end

22
of 2 weeks. The soils were leached every week after the
initial leaching with the same amount of water. Replanting
was continued until the growth of seedlings in the treated
soils was equal to or greater than the seedlings grown as
controls.

After each leaching a 5 milliliter sample of the leach,
ate from.each can was added to a Petri dish containing
10 cucumber seeds. The seeds were allowed to germinate at
room temperature for 4 days at which time the lengths of
the roots were measured and recorded.

After the toxic effects of the 5-chloro IPC had dis-
appeared from.the surface of the soil treated with the
highest concentration (24 pounds per acre), as determined
by the growth of the cat seedlings, the soil in the cans
was divided into thirds to separate the upper 2 inches,
the middle 2 inches, and the lower 2 inches. These individ-
ual soil layers were put into four inch.pots and planted
with cat seeds. After 10 days the fresh weight of the tops
of the seedlings was recorded. Each.kind of soil was treated
individually in this respect, since the compound did not
disappear as rapidly from the organic soil as it did from the
light and heavy soil.

Table 5 illustrates the experimental set up for this
leaching experiment.

Experiment III. One hundred and sixty-two four inch

 

pots were divided into equal groups of three to be stored
at temperatures of 55, 55, and 75 degrees Fahrenheit. Each

23

 

 

 

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n mqmda

24
group of 5 was again divided into thirds to be filled with
light, heavy, and organic soils. Each kind of soil was
treated with 2 and 24 pounds of 5-chloro IPC per acre based
on the weight of the soil, and a number of pots were kept
for controls. Addition of the compound to the soil occurred
June 22, 1951.

The pots were then placed in sand filled flats so that
it would not be necessary to water them from the top and
thus keep leaching to a minimum. The respectiVe groups
were then stored: one in a cold storage room with a temper-
ature of 55 degrees Fahrenheit; one in cold storage at 55
degrees Fahrenheit; and the other in the greenhouse, where
temperatures averaged about 75 degrees Fahrenheit. The
soil in the pots was kept moist at all times. Every 2 weeks
for a period of 12 weeks a series of pots, of each treat-
ment and kind of soil, and from each storage temperature,
were removed. Twenty oat seeds were planted to a.depth
of 1/2 inch in each pot. These seeds were allowed to
germinate and develop for a period of 2 weeks. The fresh
weights of the tops of the seedlings were recorded.

A Field Experiment To Compare The Residual Action
0f 5-Chloro IPC With IPC

A field plot 24 feet by 8 feet was further divided
into lesser plots of 4 feet by 4 feet. On July 5, 1951,
three of these plots were sprayed with IPC in concentrations
of 2, 6, and 12 pounds per acre, and another 5 plots were

sprayed with 5-chloro IPC in the same concentrations. Plots

25
were spaced such that there were at least two controls on
either side of a treatment, as shown in Table 4. The chem-
icals were added to one quart of water and applied with a
compressed air sprayer. Isopropyl N-phenyl carbamate was
applied as a 50 percent wettable powder.

Oat seeds were scattered over the plots by hand and
each plot was raked to insure contact of the soil with the
seeds. Two weeks after planting 10 seedlings were weighed
and these fresh weights recorded.. Replanting was continued
in the same manner every 2 weeks until the weight of the
seedlings grown on the treated plots was equal to or greater
than those grown on the control plots.

This experiment was carried out on Hillsdale sandy
loam soil graded into Grandy sandy loam. The reaction
ranged from pH 6 to pH 6.5. This also describes the soil
used in the next experiment on crOp toxicity.

Field EXperiments To Determine The Toxicity
0f 5-Chloro IPC To Various Creps

A field plot, 75 feet by 500 feet, was divided into
270 smaller plots each 2 feet by 20 feet. The rows ran
lengthwise with 15 plots to the row and 2 rows were allowed
for each of 9 crops. A space 2 feet wide was allowed
between each row of plots.

An equal number of plots were allowed for each of 5
treatments: (1) pre-planting; (2) pre-emergence; and (5)
post-emergence. Each.division of treatments included a

control and l, o, 6, and 12 pounds of 5-chloro IPC per acre

26

 

 

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Hoapnoo Hoapnoo Hoapooo
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¢ mnmda 7‘

27
based on soil weight. All plots were assigned a treatment in
a random fashion and each treatment was repeated twice.

On May 20, 1951 the pre-planting treatment was applied.
The chemical was added to 5 gallons of water and applied with
a compressed air sprayer to all plots designated to receive
the particular concentration. Between May 21, 1951 and
May 24, 1951 the crops were planted. The seeds were sowed
by hand and the rows were raked by hand after sowing. The
corn was planted in hills 1 1/2 feet apart and the soil was
not raked after planting. The following crops were planted:
alfalfa, red clover, ladino clover, rye, oats, wheat, soy-
beans, sorghum, and corn.

On May 26, 1951 the pre-emergence treatment was applied,
and 1 month after the germination of all crops (June 29, 1951)
the post-emergence treatment was applied. On June 15, 1951
the percentage of germination of seedlings developing from
the pre-planting and pro-emergence treatments was recorded.
These data were obtained by counting the number of crop
plants found in 4 samples of 1 square foot each, from.ell
treated plots. On June 22, 1951 the percentage of weeds
killed in the pre-planting and pre-emergence treatments
was recorded. The data were taken by counting the number
of weeds per square foot in the manner mentioned above.
Between July 15, 1951 and July 31, 1951 plants were dug
from each control plot and from.each treated plot and the

fresh.weights of the roots and shoots were recorded.

RESULTS

Results Of The Laboratory Experiment To Determine
The Residual Action 0f 5-Chloro IPC In Various Soils

Concentrations of 5-chloro IPC shmilar to those applied
to the soils were also added to 25 milliliters of water so
that a 5 milliliter sample could be used to test the sensi-
tivity of the cucumber seeds when the concentration was at
its maximum. Table 5 shows that the cucumber seed test was
sensitive in the range of concentrations used.

Figure I indicates that 5-chloro IPC was leached from
light, heavy, and organic soils by 25 milliliters of water,
but that the amount leached from each soil was not related
to the concentration, with the lowest concentration an
exception. There is also shown some tendency for each
leaching to remove less of the chemical from.the soil,
probably because there was progressively less of the chem-
ical to be removed as the leaching proceeded from.week to
week.

No comparison can be made of the property of the
individual soil mixtures to lose the chemical by leaching,
since the leachate from the control sample of the organic
soil stimulated the roots of the cucumber seedlings to grow
to almost 5 times the length of roots of seedlings grown in

29

TABLE 5

INHIBITION OF THE PRIMARY ROOT OF GERMINATING CUCUMBER
SEEDS TO VARIOUS CONCENTRATIONS OF S-CHLORO IPC WHICH
WERE ADDED TO TWENTY-FIVE MILLILITERS OF WATER TO BE

COMPARED WITH TOXIC EFFECTS OF SIMILAR
CONCENTRATIONS ADDED TO SOIL

-
*7

Concentration of Amount of inhibition of cucumber
5-chloro IPC in roots expressed as a percentage
parts per million of the growth of normal roots

 

1,000
5,000
10,000
50,000
100,000

NUIbCDQQO

200,000

30

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Figure I. Graphs showing the loss of 5-chloro

IPC from 5 gram samples of 5 soils with 25
milliliters of water, as measured by the

 

 

 

51
leachates of light and heavy soil. This was probably due
to the extra nutritional value of the organic soil.

At the outset of this leaching experiment the leach-
ates obtained from the soils treated with the highest con-
centrations were cloudy. This cloudy appearance was inten-
sified as the concentration was increased. After the eighth
week, however, the leachates from the organic soils, even
at the highest concentration, were clear although the chem-
ical contained in these leachates remained toxic to germin-
ating cucumber seeds. This clearing of leachates, from
week to week as the eXperiment continued, was not observed
with the light and heavy soils.

The response of the cucumber seedlings to these con-
centrations of 5-chloro IPC was of interest. The most
severe injury was expressed by an extreme swelling at the
cotyledonary plate with the root failing to develop. Milder
injury was expressed by the development of a swollen, club—
like primary root from.which.no secondary roots developed.
Seemingly less toxic concentrations caused growth that was
more nearly normal but injury was shown by the shorter
length of the primary root as compared to the roots produced
by seedlings in the control cultures.

’ It was also observed that the soils treated with
‘//50,000, 100,000, and 200,000 parts per million leached more

slowly than those soils treated with the lower concentrations.

The soils with the higher concentrations also failed to dry

. out from week to week, while the soils treated with the lower

7 71- i__n.—--.-—-—-

 

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52
concentrations became dry within 24 hours after leaching.

If the experiment could have been extended until all
toxic effects were removed, the data would have been more
complete, however due to an unforeseen accident the experi-
ment was discontinued after eight weeks.

Results Of Greenhouse Experiments To Determine The
Residual Action 0f 5-Chloro IPC 0n Various Soils
Experiment I. Figure II is a graphical representation

of experiments involving the effect of soil reaction on the
persistance of 5-chloro IPC in light, heavy, and organic soil.

It can be clearly seen that the acid soils, when
treated with 2 pounds per acre, lost their toxic effect on
oat seedlings before these soils of pH 8.5. The heavy,
organic, and light soils at pH 5 were completely free of
inhibitory action due to 5-chloro IPC in 9, 18, and 57 days,
while the alkaline heavy, organic, and light soils did not
produce normal oat seedlings for 18, 57, and 47 days
respectively. The loss of the chemical from.neutral soils
was somewhat more variable, with the light soil being non-
toxic in 29 days, and the heavy and organic soils in 47 days.

The opposite relationship occurred when these soils of
different reaction were treated with 24 pounds per acre.

The alkaline soil was not toxic after 72 days in the case of
the heavy soil, and 95 days in the case of the light and

organic soils (Figures III and IV). In the acid, heavy soil
the chemical remained active up to 108 days, and in the acid,

light and organic soils the toxic effect was still present

ngs: (a) pH 5 -
acre, (d) pH 7 -
/8.0I'60

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, (0) p37 - 2 lbs.

cre, (f) pH 8

the inhibition of oat seedli
/acre
/a

pH 5 - 24 lbs.
cre, (e) pH 8.5 - 2 lbs.

Graphs showing the loss of 5-chloro IPC from.5 soils adjusted
, (b)

to 5 pH levels, as measured by
/acre
24 1bs./a

Figure II.
2 lbs.

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Figure III. Growth of oat seedlings in heavy soil adjusted
to pH 8.5, 47 days after treatment with 5-chloro IPC:
(1) control, (2) 2 lbs./acre, and (5) 24 lbs./acre.

‘ ____.—"/

 

Figure IV. Growth of oat seedlings in soils adjusted to pH 8.5,
47 days after treatment of (1) heavy control soil, (2) heavy
soil. (5) light soil, and (4) organic soil at the rate of

55
159 days after treatment. .Again, the neutral soil varied
from this relationship with the light and heavy soils be-
coming non-toxic in 84 days whereas the organic soil remained
toxic more than 159 days.

During this experiment the highly alkaline soil formed
a dark crust at the surface, and did not dry out as rapidly
as did the neutral and acid soils. This was assumed to be
a black alkali condition due to an abundance of sodium
carbonate. Black alkali soils are known to result in a
deflocculation of the soil colloids with.the soil becoming
puddled. The development of anaerobic conditions in the
soil usually ensues.

In this experiment, and in all of the following experi-
ments in which oats were used as a test crop, the seedlings
showed a characteristic response to 5-chloro IPC. At very
high concentrations seeds failed to germinate at all. At
progressively lower concentrations: a swollen coleoptile
appeared, but no roots grew; the roots grew but remained
short and swollen at the tips, while the leaf blade deve10ped
to a height of 1/2 to 1 inch with the tissue becoming
brittle and dark bluish-green in color (often these seed-
lings would die 2 or 5 days after germination); the growth
was nearly normal, but the leaf blade showed signs of
epinasty. Usually when a soil became completely free of
toxic effects the cats grew at a much greater rate than the
controls, with later plantings developing at thesame rate
as controls. This indicates that very light applications of

36
S-chloro IPC may be stimulating to the growth of cats.

Experiment II. The amount of surface water applied
to light, heavy, and organic soils did not appear to in-
fluence the length of time required for the toxic effects
of S-chloro IPC to disappear, as is shown in Figure V.
However, the type of soil to which the chemical was applied
did influence the loss of toxicity (Figure VI). The light
and heavy soils usually were completely free of toxic effects
on the test crop in 50, 60, 76, and 104 days for rates of
2, 6, 12, and 24 pounds per acre respectively, while the
toxic effect was lost from the organic soil in approximately
44, 76, 90, and 148 days depending on the rate of appli-
cation.

The use of the cucumber seedling test to determine the
relative amounts of 5-chloro IPC in the leachate from the
light, heavy, and organic soils, proved to be unsatisfactory.
No significant results were obtained, either because the
chemical did not leach the full depth of the soil (6 inches),
or because the cucumber seedlings did not respond at low
concentrations of the compound.

One hundred and four days after treatment, the cans of
light and heavy soils were dumped and soil from each can
divided into 5 layers so that the toxicity remaining below
the surface soil could be determined. The degree to which
these three soil layers inhibited the growth of germinating
oat seeds is illustrated in Figure VII. Apparently there

are toxic effects remaining below the surface even after the

,c

 

37

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Figure Va. Graphs showing the loss of s-chloro IPC
from.light soil after weekly leachi s with various
amounts of surface water, as measure by the in-

hibition of oat seedlings.

58

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Figure Vb. Graphs showing the loss of S-chloro IPC

from heavy soil after weekly leachings with.various
amounts of surface water, as measured by the in-
hibition of oat seedlings.

59

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Figure Vc. Graphs showing the loss of 3-chloro IPC
from organic soil after weekly leachings with various
amounts of surface water, as measured by the in-
hibition of oat seedlings.

4O

 

Figure VI. The growth of oat seedlings in light, heavy,
and organic soils 102 days after treatment with 24 lbs./

acre of S-chloro IPC and weekly leaching with one inch
of surface water.

' 3

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Figure IX. The growth of oat seedlings in heavy soil 4 weeks

after treatment with 2 lbs ./acre of S-chloro IPC and storage
at 75, 55, and 35° F.

41

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42
chemical has disappeared from the surface soil. Similar
data for the organic soil are also shown in Figure VII. In
this case, the soil was divided into layers 148 days after
treatment. Only in the.soil leached with 1 inch of surface
water was there a trace of the chemical. In nearly all
cases where therewas a trace of 5-chloro IPC present, the
amount in the lower 2-inch layer was less than that in the
other layers.

Experiment III. Temperatures below 75 degrees Fahren-

 

heit delayed the breakdown of 5-chloro IPC very markedly.
Figure VIII shows the effects of temperatures of 55, 55,
and 75 degrees Fahrenheit on loss of 5-chloro IPC applied.
to light, heavy, and organic soils. In light soil the toxic
effects from.the application of 2 pounds per acre, were lost
in 4 weeks at a temperature of 75 degrees, while at temper-
atures of 55 and 55 degrees the soil was still toxic after
12 weeks when the experiment was terminated. When the
light soil was treated with 24 pounds per acre and stored
at 75 degrees the cat seeds germinated and the soil lost
most of its toxicity after 12 weeks. This was not the case
when the soil treated at the 24 pound rate was stored at
the lower temperatures, since the cat seeds did not germin-
ate over the 12 week period.

Similarly, heavy soil treated with 3-chloro IPC and
stored at 75 degrees became non-toxic after 2 weeks, in
the case of the 2 pound rate, and 10 weeks, in the case of

the 24 pound rate.- At the lower temperatures the 2 and 24

43

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44
pound rate remained toxic for over 12 weeks. The effect
of temperatures on the toxicity of heavy soils after 4
weeks is illustrated in Figure IX. (See page 40).

At a temperature of 75 degrees S-chloro IPC persisted
in the organic soil 2 weeks at the 2 pound rate and more
than 12 weeks at the 24 pound rate. It is interesting to
note that, at the lower temperatures, the toxic effects of
2 pounds per acre dissipated in 6 weeks in the organic soil
qand that the loss of 24 pounds of 5-chloro IPC closely
correspond at all storage temperatures. This suggests
that temperature is not as important a factor in delaying
the breakdown in organic soil as are other variables.

Results Of The Field Experiment To Compare
The Residual Action Of 5-Chloro IPC With IPC

This experiment was designed to compare the residual
properties of 5-chloro IPC with those of IPC under field
conditions. Figure X shows the degree of inhibition of
germinating oat seedlings when seeds were planted at 2-
week intervals in plots treated with 2, 6, and 12 pounds
per acre of each of the previously mentioned compounds.

The 2 pound rate of IPC was toxic for only 4 weeks,
while the 6 and 12 pound rate was toxic for 6 weeks. Plots
treated with 2 pounds of 5-chloro IPC, on the other hand,
did not produce normal seedlings until 8 weeks after treat-
ment, and the higher concentrations were still toxic after
12 weeks. Figure XI shows the comparative growth of oat
seedlings in plots treated with 2 and 6 pounds per acre

after 6 weeks.

45

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t
V V
E a E
3‘ 4 a c 4.7 n7 i 4 A r A ’4’ . A a i‘ 4 a 7.
8 W1 A! /u III/A5 [may

Figure X. A graph showing the inhibition of
oat seedlings which.were planted at 2-week
intervals in field plots treated with
(a) 2 lbs./acre, (b) 6 lbs./acre, and
(c) 12 1bs./acre of 5-chloro IPC and IPC.

-'.‘-'-

o'A .. -
_-‘-e I , P1..-

4"!- ,

r. -
- \. ‘
. t

Figure XI. The growth of oat seedlings, in plots (from left
to right) treated with 2 and 6 pounds per acre of 5-chloro
IPC and IPC as compared to seedlings from controls, 6 weeks
after treatment.

-

Figume XX. The effects of pre-planting treatments of S-chloro

IPC at the rate of 12 pounds per acre on corn are shown at
the riiht- Seedlinss from control plots are shown on the

     

47

The weather data for the 12-week period after treat-
ment is presented in Table 6. It is of particular interest
to note that the average temperature during this period
was 10 degrees lower than the temperatures used in the
greenhouse experiments, which.may account in part for the
very slow loss of the 2 pound rate of 5-chloro IPC in the
field. It is also evident that the temperatures were some-
what higher while IPC was still active. A comparison of
these compounds at higher temperatures might have given
different results.

The cat seedlings responded, in terms of observable
injury, very similarly to both treatments. These responses
have been previously described.

This experiment was stopped at the end of 12 weeks
because of a killing frost which occurred on September 28,

1951.

Results Of The Field EXperiments To Determine The
Toxicity Of S-Chloro IPC To Various Crops

The survival of the seedlings of 9 crops grown in
field plots treated with pre-planting, and pre-emergence
applications of 5-chloro IPC is shown in Table 7. The
survival of weed seedlings in the same plots is presented
in Table 8. The data, summarizing the effect of pre-plant-
ing, pro-emergence and post-emergence applications of S-chloro
IPC on the fresh weight of roots and shoots, the total fresh
weight, the percentage of the total weight of the control,

and the shoot-root ratio of the various crops tested, are

48

TABLE 6

WEATHER DATA OF THE SUMMER OF 1951 FROM THE LANSING
AIRPORT SHOWING THE TOTAL RAINFALL AND AVERAGE
TEMrERATURE DURING THE 12 WEEK PERIOD IN WHICH

FIELD EXPERIMENTS TO DETERMINE THE RESIDUAL
ACTION OF b-CHLORO IPC WERE CARRIED ON

 

f

 

 

 

Tim f Total inches of precipitation from the time
e o of application to 12 weeks after application
application
July August September .Total
July 5 1.06 2.84 1.80 5.70

 

 

‘ J

Average temperature from time of application
to 12 weeks after application

July August September Total
average

Time of
application

JUly 5 6905 66.4 6U03 65.4

 

49
TABLE 7

PERCENTAGE OF CROP SEEDLINGS SURVIVING TREATMENTS OF
3-CHLORO IPC APPLIED (1) BEFORE PLANTING AND
(2) AFTER PLANTING BUT BEFORE EMERGENCE OF THE CROP

W
Pounds per acre

 

 

Application . l 5 6 12
Corn*
Pro-planting 84 74 6o 16
Pre-emergence 100 100 100 65
Soybeans**
Pro-planting 100 90 74 90
Pre-emergence 95 95 79 84
Wheat**
Pre-planting 8 O O O
Pro-emergence 49 48 56 56
Oats**
Pro-planting 46 4 2 O
Pre-emergence 66 41 54 14
Rye**
Pro-planting 16 O O O
Pro-emergence 6O 56 42 5O
Sorghum**
Pro-planting 85 ll 15 10
Pro-emergence 100 55 4O 51
Alfalfa**
Pro-planting 64 49 45 4
Pre-emergence 81 87 5O 8
Red Clover**
Pre-planting 78 21 8 5
Pro-emergence 75 17 46 5

Ladino Clover**
Pre-planting 65 21 14 2
Pro-emergence 88 87 79 5

iiTercentage of:hills survivin per plot
**Percentage of seedlings surv v ng per square foot

 

TABLE 8

50

PERCENTAGE OF WEEDS PER SQUARE FOOT SURVIVING TREATMENTS
OF S-CHLORO IPC APPLIED (1) BEFORE PLANTING AND
(2) AFTER PLANTING BUT BEFORE EMERGENCE OF THE CROP

 

Pounds per acre

 

 

Application 1 3 5 12
Corn
Pre-planting 79 57 54 25
Pre-emergence 57 59 59 ll
Soybeans
Pre-planting 64 56 6O 14
Pre-emergence 75 57 29 7
Wheat
Pre-planting 100 55 56 41
Pro-emergence 91 64 25 ' 9
Oats
Pro-planting 115 ' so 55 so
Pro-emergence 70 75 45 5
Rye
Pre-planting 180 140 100 70
Ere-emergence 90 6O 80 20
Sorghum
Pro-planting 7O 6O 5O 5O
Pro-emergence 90 55 4O 5O
Alfalfa
Pro-planting 80 55 5O 7
Pro-emergence 77 50 5O 7
Red Clover
Pro-planting 78 55 59 8
Pro-emergence 81 42 78 ll
Ladino Clover
Pro-planting 75 58 46 8
Pro-emergence l4 5

119

45

 

51
shown in Tables 9 through 17 and in Figure XII. The
information concerning the injury to each crop is presented
in the following order: alfalfa, red clover, Ladino clover,
soybeans, rye, oats, wheat, sorghum, and corn.

Alfalfa. The pre-planting treatments appear to be very
toxic even at the lowest rate, while the pro-emergence
treatment resulted in a 10 to 20 percent reduction of crop
plant emergence in the l to 5 pound rates. The pre-emer-
gence application reduced weeds from 20 to 50 percent in
the plots treated with 1 and 5 pounds. Pre-planting treat-
ments above 1 pound and pro-emergence treatments above 5
pounds caused a severe stunting of many plants. Some seed-
lings grew to a height of 1/2 inch and remained in that
condition throughout the summer. The main axis and leaves
failed to elongate, resulting in the formation of tiny
rosettes. A few of these seedlings died in 4 to 5 weeks.

Post-emergence applications resulted in a very notice-
able chlurotic condition on the terminal leaves. Although
this condition became more noticeable at the higher concen-
trations, it was present in plots treated with as little as
1 pound. These leaves eventually dried as can be seen in
Figure XIII. Because of the location of the growing point
and its lack of protection, post-emergence applications
terminated growth.

There was a tendency for shoot-root ratio to increase
with the dosage in the pre-planting and pro-emergence treat-

ments. This increase in shoot growth was due to the lack of

52

TABLE 9

EFFECTS OF TREATMENTS OF 5-CHLORO IPC ON THE FRESH WEIGHT
OF ALFALFA PLANTS. APPLICATIONS WERE MADE
(1) BEFORE PLANTING, (2) AFTER PLANTING BUT BEFORE
EMERGENCE, AND (5) AFTER EMERGENCE AND DEVELOPMENT
OF THE CROP. DATA BASED ON THE WEIGHT IN GRAMS
OF 24 PLANTS TAKEN FROM EACH PLOT.

 

 

. Jeight Weight Total Percent Shoot-

Treatment of of weight of root
‘ shoots roots control ratio
Control 14.8 5.4 18.2 100 4.4

1. Pre-planting
1 1bs./acre 19.0 4.8 25.8 151 4.0

5 1bs./acre 15.5 5.5 19.0 104 4.4
6 1bs./acre 15.5 5.5 18.6 102 4.6
12 1bs./acre 20.5 5.0 25.5 129 6.8
2. Pre-emer ence
1 lbs.§acre 15.5 5.5 16.8 92 4.1
5 lbs./acre 14.0 5.5 17.5 ~ 95 4.2
6 leQ/acre 16.5 508 20.1 110 4.3
12 lbs./acre 26.0 5.8 29.8 164 6.8
5. Post-emergence
1 lbs./acre 15.8 5.5 17.1 94 4.2
3 le./acr8 12.5 2.8 15.1 83 4.4
6 lbs./acre 9.8 2.8 12.6 69 5.5
12 1bs./acre' 9.8 2.5 12.1 67 4.5

 

55

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Figure XII. Graphs showing the effects of 5-chloro IPC on

the fresh weights of 9 crops grown in plots treated at
various times with 1, 5, 6, and 12 pounds per acre.

Figure XIII. The reduced foliage of alfalfa plants caused
by post-emergence applications of 12 lbs./acre of 5-chloro

IPC is shown at the right, and control plants are shown
at the left.

Figure XVII. The spiraling of the leaves of stunted rye
plants caused by pro-emergence applications of 6 lbs./
acre of 5-chloro IPC is shown at the right, and control

 

55
competition with weeds. Figure XIV shows the increase in
branching which occurred on many plants as the rate of
treatment increased. These data also point to the severe
reduction in weight of crops treated with a post-emergence
application of 5-chloro IPC. This can be explained by the
reduction in photosynthetic activity due to the loss of foliage.

Red Clover. Pre-planting and pre-emergence applications

 

were very toxic to germinating seedlings. Weed growth was
also reduced effectively. Surviving crop plants were
stunted similarly to alfalfa seedlings, but this stunting
was observed at even the lowest rates used. At harvest
time plots treated with the higher rates contained many
plants which.were sending out stolons. Again, as in the
case of alfalfa, this was probably due to the lack of com-
petition with weeds, although the data do not show the_
tremendous increase in weight of treated plants as do the
data for alfalfa.

Post-emergence treatments showedvery nearly the same
effects on red clever as on alfalfa. In alfalfa the leaves
became chlorotic after treatment and then died, while the
leaves of red clover became necrotic almost immediately
after treatment. However, because the growing point was
protected, some plants appeared to return to normal growth
with new leaves arising to function in place of the old

ones. It is possible that these plants would survive.

56

 

Figure XVI. The reduced foliage of soybeans caused by
post-emergence applications of 12 lbs./acre is shown
on the right, and a control plant is shown on the left.

..,a
V - . “v ”a".
- ...? “‘;- "%‘*H- .. _
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‘-L.‘--" 12'. -._.'_‘_-x-_A .5: L‘r." ' '-A:.' 4‘53Kg‘6 ‘ _‘-

 

Figure XIV. The effects of 5, 6, and 12 1bs./acre of
5-chloro IPC applied as pre-plantin treatments on

n1fn1fn as nnmnared tn cnntrnl nlan.g shown nn .hn loft-

57

TABLE 10

EFFECTS OF TREATMENTS OF 5-CHLORO IPC ON THE FRESH WEIGHT
OF RED CLOVER PLANTS. APPLICATIONS WERE MADE
(1) BEFORE PLANTING, (2) AFTER PLANTING BUT BEFORE
ENERGENCE, AND (5) AFTER EMERGENCE AND DEVELOPMENT
OF THE CROP. DATA BASED ON THE WEIGHT IN GRAMS
OF 24 PLANTS TAKEN FROM EACH PLOT.

 

 

Weight Weight Total Percent Shoot-

 

Treatment of of weight of root
shoots roots control ratio
contI’Ol 25.9 304 27.3 100 7.0
l. Pro-planting
1 lbs./acre 20.0 5.5 25.5 85 6.1
3 le./acre 25.0 2.0 27.0 99 12.5
6 lbs./acre 20.0 2.8 22.8 84 7.1
12 lbs./acre 21.1 2.8 25.9 88 7.5
2. Pre-emer once
1 1b3.§acre 20.1 2.9 23.0 84 6.9
3 le./acre 24.8 3.6 28.4 104 609
6 lbs./acre 24.9 5.5 28.2 105 7.6
12 1bs./acre 25.8 5.9 29.7 109 6.6
5. Post-emergence
1 lbs./acre 19.5 5.5 25.8 87 5.9
5 lbs./acre 22.6 2.9 25.5 95 7.8
6 1bs./acre 17.9 5.6 21.5 79 5.0
12 1bs./acre 15.2 2.4 17.6 . 65 6.5

 

58

Ladino Clover. The data presented show plants in all

 

treated plots to be stimulated over controls. This is
assumed to be due to the fact that seeds were sown too
thickly causing the crop plants in the controls to compete
with each other resulting in reduced growth, while the
thinning of plants resulting from treatments increased growth.
There is, however, the same trend in the weight at harvest
as was observed for alfalfa. Post-emergence applications
caused a necrosis of the leaves shortly after the chemical
was sprayed over the plants, but the growing point was not
injured and the crop may have eventually resumed normal
growth. The higher rates, applied as pre-planting and pre-
emergence sprays, caused many plants to send out stolons,
probably because of the lack of competition.

Pro-emergence applications at the rate of 5 pounds
per acre were fairly successful. In this case, only 10
percent of the seedlings were killed while weed growth was
reduced almost 60 percent. Because of the thickness of
the planting, this thinning of 10 percent appeared to be
more satisfactory than if no thinning had occurred.

Soybeans. The reduction of seedlings, due to treat-

 

ments of 5-chloro IPC, was fairly low. Crop plants growing
in plots treated with pre-planting and pro-emergence
applications in the 6 to 12 pound range responded in various
ways. Some of the seedlings grew to a height of 2 inches
and remained in this dwarfed condition for 5 to 6 weeks,

and then died. These dwarfed plants failed to grow satis-

59

TABLE 11

EFFECTS OF TREATMENTS OF 5-CHLORO IPC ON THE FRESH'WEIGHT
OF LADINO CLOVER PLANTS. APPLICATIONS WERE MADE
(1) BEFORE PLANTING, (2) AFTER PLANTING BUT BEFORE
EMERGENCE, AND (5) AFTER EMERGENCE AND DEVELOPMENT
OF THE CROP. DATA BASED ON THE WEIGHT IN GRAMS
OF 24 PLANTS TAKEN FROM EACH PLOT.

 

 

‘Weight weight Total Percent Shoot-

 

Treatment of of weight of root
shoots roots control ratio

Control 6.5 ' 0.9 7.4 100 7.2

l. Pro-planting

1 lbs./acre 12.0 1.7 15.7 185 7.1

3 1bS./acre 12.9 1.5 14.4 195 8.6

6 lbs./acre 8.5 0.8 9.3 126 10.6
12.1bs./acre 15.6. 1.2 14.8 200 11.5

2. Pro-emergence

l 1bs./acre 9.9 1.2 11.1 150 8.5
5 1bs./acre 8.5 0.8 9.5 126 10.6
6 lbs. cre 21.9 5.0 24.9 557 7.5
12 lbs./acre 20.1 1.7 21.8 295 11.8
5. Post-emergence
1 lbs./acre 10.4 1.1 11.5 155 9.5
5 1bs./acre 8.1 0.8 8.9 120 10.1
6 1bs./acre 7.6 1.0 8.6 116 7.6
12 le./fi0re 7.2 0.8 8.0 108 9.0

 

60

TABLE 12

EFFECTS OF TREATMENTS OF 5-CHLORO IPC ON THE FRESH WEIGHT
OF SOYBEAN PLANTS. APPLICATIONS WERE MADE
(1) BEFORE PLANTING, (2) AFTER PLANTING BUT BEFORE
EMERGENCE, AND (5) AFTER EMERGENCE AND DEVELOPMENT
OF THE CROP. DATA BASED ON THE WEIGHT IN GRAMS
OF 24 PLANTS TAKEN FROM EACH PLOT.

W
weight ‘Weight Total Percent‘ Shoot-

 

Treatment of of weight of root
shoots roots control ratio
Control 250 42 292 100 6.0
l. Pre-planting
1 lbs./acre 501 45 544 118 7.0
5 lbs./8cre 252 47 299 102 5.4
6 1bs./8cre 558 62 400 157 5.5
12 lbs./acre 414 51 465 159 8.1
2. Pre-emer ence
1 lb8.§acre 266 56 502 105 7.4
5 1bs./acre 589 52 441 151 7.5
6 1bs./acre 414 58 472 162 7.1
12 lbs./8cre 597 54 451 155 7.4
5. Post-emergence
1 lbs./acre 200 55 255 80 6.1
5 lbs./acre 212 58 250 86 ,5.6
6 lbs./8cre 148 29 177 61 5.1

12 1bs./ecre 152 56 168 58 5.7

 

61
factory roots so death was probably due to the lack of water
absorption. Other cr0p plants grew to normal size, and many
produced large numbers of branches. Most of the plants,
growing in plots treated at the higher rates, developed a
swelling of the tissues at the crown of the plant, and in
some cases the plants would bend at this point and the stem
would lay on the ground until growth proceeded upward from
a node higher up on the shoot. This is illustrated in
Figure XV.

The post-emergence applications injured the foliage
of soybeans more than any other crop tested. This was
probably due to the ease with which the leaves retained the
individual droplets of the spray. The serious reduction in
growth due to post-emergence treatments is illustrated by
the data and shown in Figure XVI. The growth curves for
the various pre-planting and pre-emergence rates are
similar to those discussed for previous crops. Again,
shoot-root ratios indicate that the increase in weight due
to these treatments is due to greater photosynthetic activ-
ity caused by the lack of competing weeds.

'fizg. Pre-planting treatments were severely toxic to
rye. Only 16 percent of the crop plants survived the
1 pound rate applied before planting. These surviving
plants, however, sent up extremely large numbers of shoots
from the crown. This tillering was also observed in plots
' treated with pre-emergence sprays, but to a-lesser extent.

These shoots were very dark green in color as compared to

  

    

.
I
Z

. ~ '1 \
'fl’ 1.‘ '
r . , .‘ '
I? i\~ .\“

l . ‘ . \
~ \

Figure XIX. The increased number of shoots at the base of
sorghum plants caused by pre—planting treatments of
5-chloro IPC at the rate of 12 lbs./acre is shown at the
right, and a control plant is shown at the left.

‘ t‘~ 'k
\

 

Figure XV. The swelling and breaking of the tissues at the

base of soybean plants, and also the increased branching
caused by pre-planting applications of 5-chloro IPC is

TABLE 15

EFFECTS OF TREATMENTS OF 5-CHLORO IPC ON THE FRESH WEIGHT
OF RYE PLANTS. APPLICATIONS WERE MADE
(1) BEFORE PLANTING, (2) AFTER PLANTING BUT BEFORE
EMERGENCE, AND (3) AFTER EMERGENCE AND DEVELOPMENT
OF THE CROP. DATA BASED ON THE WEIGHT IN GRAMS
OF 24 PLANTS TAKEN FROM EACH PLOT.

 

 

Weight weight Total Percent Shoot-

 

Treatment of of weight of root
shoots roots control ratio
Control 55 12 45 100 2.8
l. Pre-planting
1 lbs./acre 117 28 145 522 4.2
5 lbs./acre 0 0 0 0 0
6 lbs./acre O O 0 0 O
12 lbs./acre 0 0 0 0 0
2. Pre-emer ence
1 1b8.§a0m 55 12 47 104.. 2.9
5 lbs./acre 61 15 74 164 4.6
6 lbs./acre 65 9 74 164 7.9
12 1bs./acre 85 10 95 207 8.5
5. Post-emer ence
1 lbs./Ecre 26 15 59 87 2.0
5 lbs./acre 52 15 45 100 2.5
6 lbs./acre 26 9 55 77 2.9

12 lbs./acre 55 18 55 118 1.9

 

64

the control plants, and the growth of the plant was low
and spreading. Most of the crop plants surviving the pre-
planting and pre-emergence treatments had leaves which were
tightly curled in a spiral type of growth, but this con-
dition did not persist beyond the first few weeks of growth.
Figure XVII illustrates this type of injury. (See page 54).

The growth curve for the pre-emergence treatment shows
that, similar to crops previously discussed, lack of com-
petitions has increased growth. Post-emergence treatments
did not consistently reduce the weight of the crop, but the
shoot-root ratio shows that the shoot growth was reduced
in proportion to that of the roots. When the chemical was
applied to the mature plant the leaves wilted and in a few
cases died. However, the crop recovered fairly rapidly.

The rye plants grown under control conditions made
such early growth that it crowded out most of the weeds, so
that the reduction of weeds was greater in the control
plots than in many of the treated plots. Because of a
severe infestation of rust, the validity of these tests on
rye may have been reduced.

2233, The data presented for oats are very similar
to that of rye, except that growth was reduced by the 12
pound rate applied after planting, and the weight of the
crop was reduced by post-emergence applications.

As was the case with rye, the applications of 5-chloro
IPC before and after planting caused many plants to tiller

more abundantly than the plants grown in the control plots.

65

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66
Many of the seedlings responded as did the oats planted
in treated soil in the greenhouse. The primary leaf was
bluish-green, cupped at the end, and very brittle. Seed-
lings injured in this way grew about 1 inch above the soil,
and soon died. At the higher concentrations surviving
plants developed a swelling at the nodes, with a corres-
ponding change in the direction of the growth of the shoot.
It was due to this response, pictured in Figure XVIII, that
the plants grown in treated soil lodged so severely. The
leaves of surviving plants retained the same dark color
and brittle tissue as described for seedlings. Post-
emergence applications delayed the emergence of flower
spikes from 1 to 2 weeks.

@2253. .All pre-planting treatments were eventually
lethal to wheat. The response to pre-emergence treatments
was similar to that of the grains previously mentioned.
Post-emergence applications reduced the weight of the crOp
at harvest but did not decrease the shoot-root ratio, which
contradicts the previous statement that the chemical, when
applied to the mature plant, reduces shoot growth over that
of root growth.

Treatments applied to the soil caused many seedlings
to remain dwarfed. Those plants which greW'more normally
tillered extensively; Treatments applied to the leaves
caused wilting and, in some cases, death of the leaf tissue.

The entire crop of wheat was infested with rust, as
was the rye, so that the results of this experiment may not

be the results that would be obtained from a non-infested crop.

 

67

 

 

Figure XVIII. The swelling at the nodes and the lodging of
oats caused by pre-emergence applications of S-ohloro IPC
at the rate of 6 lbs./acre is shown at the left, and a
control plant is shown at the right.

‘ Q. ’
"l.

 

x“.

Figure XXI. The development of brace roots at the second

node of corn plants caused by pre-planting applications of
S-chloro IPC at the rate of 12 1bs./acre is shown at the

TABLE 15

EFFECTS OF TREATMENTS OF 3-CHLORO IPC ON THE FRESH'WEIGHT
OF WHEAT PLANTS. APPLICATIONS WERE MADE
(1) BEFORE PLANTING, (2) AFTER PLANTING BUT BEFORE
EMERGENCE, AND (3) AFTER EMERGENCE AND DEVELOPMENT
OF THE CROP. DATA BASED ON THE WEIGHT IN GRAMS
OF 24 PLANTS TAKEN FROM EACH PLOT.

 

 

Weight Weight Total Percent Shoot-

 

Treatment of of weight of root
shoots roots control ratio
Control 45 9 54 100 5.0

l. Pro-planting

1 1bs./acre O O O O O
3 1bs./acre 0 o o o o
.6 lbs./acre o o o o o
12 lbs./acre o o o o o
2. Pre-emer ence
l lbs.§acre 38 6 44 81 6.3
3 lbs./acre 64 lO 74 137 6.4
6 lbs./acre 79 8 87 161 9.9
12 lbs./acre 113 9 122 226 12.6
3. Post-emer ence
1 1bs./§cre 38 8 46 85 4.8
3 lbs./acre 47 7 54 100 6.7
6 lbs./acre 36 6 42 78 6.0
12 lbs./acre 31 5 36 67 6.2

 

62

Sorghum. The data show the tremendous growth which
can occur when competition is reduced. Here again, however,
the shoot-root ratios do not support the idea that the
increase in weight, shown by plants grown in treated soil,
is entirely due to the lack of competition, or that the
reduction of photosynthetic leaf area, caused by the appli-
cation to the plant itself, is responsible for the decrease
in weight.

Pro-planting and pro-emergence treatments were for the
most part toxic to germinating seeds. Many surviving seed-
lings remained dwarfed and eventually died, while others
grew to a much larger size than the control plants. At
the very high rates, several shoots would arise from the
crown and grow vigorously as illustrated in Figure XIX.
Treated plants, in the early stages of growth, exhibited a
marked purpling of the leaf margins.

Post-emergence applications caused a severe necrosis
of the upper leaves. However, the crop was very quick to
form.new leaves, and resume normal growth.

12333. Corn, like sorghum, made tremendous growth
when weed competition was eliminated.

Pro-emergence treatments in the l to 6 pound range
were highly successful. The crop showed no apparent injury
and the weeds were controlled. Pre-planting treatments
reduced the germination, and the 12 pound rate was eventually
lethal to all plants. Many seedlings in these plots displayed
a swollen, distorted coleoptile, and similar effects on the

79

TABLE 16

EFFECTS OF TREATMENTS OF S-CHLORO IPC ON THE FRESH'WEIGHT
OF SORGHUM PLANTS. APPLICATIONS WERE MADE
(1) BEFORE PLANTING, (2) AFTER PLANTING BUT BEFORE
EMERGENCE, AND (3) AFTER EMERGENCE AND DEVELOPMENT
OF THE CROP. DATA BASED ON THE WEIGHT IN GRAMS
0F 24 PLANTS TAKEN FROM EACH PLOT.

 

 

Weight Weight Total Percent Shoot-

 

Treatment - of of weight of root
shoots roots control ratio
Control 258 33 291 100 7.8
1. Pre-planting ‘
1 lbs./acre 229 34 263 90 6.7
3 1bs./acre 945 171 1116 383 5.5
6 lbs./acre 1182 210 1392 478 5.6
12 lbs./acre 1347 209 1556 535 6.4
2. Pre-emer ence
l lbs.§acre 189 39 228 78 4.9
3 lbs./acre 324 42 366 126 7.7
6 1bs./acre 618 90 708 243 6.9
12 1bs./acre 566 67 603 218 8.4
3. Post-emer ence
l los./§cre 210 25 235 81 8.4
3 lbs.[acre 175 21 196 67 8.3
6 los./acre 116 17 133 46 6.8

12 1bs./acre 108 13 121 42 8.3

 

I"

71

TABLE 17

EFFECTS OF TREATMENTS OF 3-CHLORO IPC ON THE FRESH‘WEIGHT
OF CORN PLANTS. APPLICATIONS WERE MADE
(1) BEFORE PLANTING, (2) AFTER PLANTING B 1 BEFORE
EMERGENCE, AND (3) AFTER EMERGENSE AND DEVELOPMENT
OF THE CROP. DATA BASED ON THE WEIGHT IN GRAMS
OF 24 PLANTS TAKEN FROM EACH PLOT.

   

.. O—----¢.—-.-

Percent

 

ws- —.-—~—.,w--..~__.~._-l_'

Shoot-

 

Weight weight Total
Treatment of of weight of root
shoots roots control ratio
Control 811 95 906 100 8.5
1. Pro-planting 7
1 1bs./acre 1368 158 1526 168 8.7
3 1bs./acre 1498 360 1858 205 4.2
6 1bs./acre 2828 589 3417 377 4.8
12 lbs./acre 0 0 0 0 0
2. Pre-emer ence
1 1bs.§acre 1316 182 1498 165 7.2
3 1bs./acre 1685 234 1919 212 7.2
6 lbs./acre 1736 275 2011 222 6.3
12 1bs./acre 1931 350 2281 252 5.5
3. Post-emer ence .
1 lbs./§cre 1273 154 1427 158 8.3
3 1bs./acre 1367 107 1474 163 12.7
6 lbs./acre 793 78 871 96 10.2
12 lbs./acre 689 59 748 83 11.7

 

78
young roots. The dwarfing of these seedlings is pictured
in Figure XX. Those crop plants which survived the pre-
planting treatments often showed signs of injury similar
to those found in sorghum, in that the margins of the leaves
became purple. Plants grown in plots treated with a 6
pound pre-planting treatment or a 12 pound pro-emergence
treatment developed many brace roots at the second node,
as shown in Figure XXI. The root systems of plants in the
same plots were weak and many of the plants were blown
over in a severe wind storm on July 27, 1951.

The flower structures appeared from 1 to 1 1/2 weeks
earlier on crop plants in plots treated with pro-planting
and pre-emergence applications. Also the color of the
leaves of plants grown in those plots was dark green in
contrast to the pale green leaves of plants grown on the
control plots. These responses were at least in part due
to the reduced competition with weeds.

Post-emergence applications caused a chlorotic band
across the new leaves which developed shortly after the
crop was sprayed. This was probably because the chemical
ran down the leaves and accumulated at the growing point,
and injured the meristematic leaf tissues. The tissue in
this yellow band eventually died and the leaf broke in half.
The plant recovered very quickly, however, and the crop grew
normally.

General remangg. The weather data for the pre-planting,

pro-emergence, and post-emergence treatments are presented

73
in Table 18. Small amounts of rainfall occurred after the
pre-planting and pre-emergence treatments, but it is probable
that moistening of the soil only served to distribute the
3-chloro IPC more evenly. No rain fell for 5 days after
the post-emergence applications.

Weeds were killed only by pre-planting and pro-emer-
gence applications. Although no attempt was made to deter-
mine the differential control of grasses and broadleaved
weeds, the greatest reduction was of crab grass (Digitaria
sanguinalis (L.) Scop.), which seriously infested the
control plots. Nut grass (Cyperus esculentus L.) and
witch.grass (Panicum.capillare L.) were also reduced markedly
due to applications of 3-chloro IPC. Among the broadleaved
weeds that appeared to be reduced were purslane (Portulaca
oleracea L.) and rough cinquefoil (Potentilla_norvegica L.).
Those weeds surviving the treatments were lamb's quarters
(ChenOpodium.3123m.L.) and rough pigweed (Amaranthus £22327
flexus L.). weeds which grew in the plots treated with
the highest rates, were dwarfed and flowering was delayed.

Post-emergence applications did not kill the weeds
that had germinated, but the growth of all of the weeds
mentioned above, with the exception of rough pigweed, was
noticeably delayed. The delay was in direct proportion to

the concentration of the chemical applied.

TABLE 18

74

WEATHER DATA OF THE SUMMER OF 1951 FROM THE LANSING AIRPORT
SHOWING THE TOTAL RAINFALL AND AVERAGE TEMPERATURE
DURING THE PERIOD OF FIELD EXPERIMENTS INVOLVING
THE TOXICITY OF 5-CHLORO IPC ON VARIOUS CROPS

 

 

Type and time
of application

Total inches of precipitation from time
of application until harvest

 

 

May June July Total
Pre-planting
May 20 1.59 3.26 0.97 5062
Pre-emergence
May 26 1.02 3026 0.97 5025
Post-emergence '
1111116 29 "" 0.00 0097 0.97

 

 

 

Type and time
of application

Average temperature from time of
application until harvest

 

 

May June July Total*
Pre-planting
May 20 62.0 65.8 70.5 66.0
Pre-emergence
May 26 60.7 65.8 70.3 65.3
Post-emergence
June 29 -" 66.5 70.3 68.4

 

*AVerage

DISCUSSION

The data presented indicate that 3-chloro IPC is leached
from the soil, but at concentrations up to 24 pounds per
acre, the degree of leaching is not materially affected by
an increase in the amount of surface water added to the
soil. The practicality of the cucumber seedling test with
low concentrations of 3-chloro IPC is doubtful. The use of
this test to determine the depth of leaching or the con-
centration in the surface soil might well be adapted to
testing other growth regulators.

.The length of time that 3-chloro IPC persists in the
soil is definitely influenced by the type of soil to which
it is applied. Contrary to previous investigations with
certain other herbicides, this compound remains toxic longer
in soils high in organic matter than in soils low in organic
material. Since traces of the chemical were found in the.
lower layers of light and heavy soils, while none appeared
in the lower layers of the organic soil it seems probable
that the organic soil holds the molecules of 3-chloro IPC
at the surface in greater concentrations than do the other
soils tested.

Previous work with other growth regulators has shown
that the acid soils are the first to lose toxicity, with

76
the alkaline soils tending to be toxic the longest. This
was the case when low concentrations of 3-chloro IPC were
used. However, at the 24 pound rate the alkaline soil
lost the toxic effects of the chemical very rapidly in
relation to the neutral and acid soils. The black alkaline
condition mentioned previously may have been the reason
for this rapid loss in toxicity. If anaerobic conditions
were established in these alkaline soils then it may be
reasonable to assume that breakdown of 3-chloro IPC is more
rapid under anaerobic conditions. The reason for the
breakdown of the chemical in acid soils being delayed at
the high concentration may be that the soil organisms were
continually being inhibited by such an extreme pH level.

In other words, the factors causing the early disappearance
of the compound in acid soil were eventually overcome by
the inhibiting effect of the acid medium on soil organisms.
Speculation as to what factors may cause the rapid
breakdown in acid soils, when the chemical is present in
Va low concentration, is of value. It may be that the mole-
cule of 3-chloro IPC must dissociate before it is taken
up by the plant, and that the undissociated form is not
toxic to plant growth. Therefore, as the hydrogen ion
concentration in the soil is increased the amount of dis-
sociated form.wou1d decrease with a corresponding decrease
in toxic action. other factors influencing the loss of the
chemical, diSpersion in the soil by leaching, and micro-

biological decomposition, would occur,'but these factors

L 53"...

- r———-
0‘-

 

77
would be working on a lower concentration of the active
form. Conversely, as the hydrogen ion concentration is
reduced to the point of alkalinity, equilibrium.of the
undissociated form with the dissociated form would be pushed R“\\\
in the opposite direction, causing a very high concentration
of the active form.

One might postulate from this, that the use of a test
crop to determine the concentration in the soil does not
indicate the t0ta1 concentration‘but rather that of the
active form only. A radical change in soil pH under normal
conditions may then liberate or tie up the active form and
effect the toxic action. For example, acid salts applied
as fertilizer might reduce the toxic action of 3-chloro
IPC in the 8011. I

The effect of low temperatures on the residual action
of 3-chloro IPC is similar to that found on the residual
action of other herbicideS'which have been investigated.
Retarded activity by the soil microorganisms which.act to
decompose 3-chloro IPC is probably the best explanation
that can be given for the slower loss of toxic effects at
lower temperatures. From these results it appears that
caution must be used in treating the soil in the fall with
the expectation of growing a sensitive crop on that same
soil in the spring.

The temperature at which treated pots were kept in the
greenhouse was probably higher than the outside summer

temperatures in Michigan. This is illustrated by the fact

78'
that, while the 2 pound rate lasted from 2 to 4 weeks in
the greenhouse, a similar dosage lasted up to 8 weeks in
the field, where the temperature was 10 degrees lower.

There was a definite trend, in the greenhouse eXperi-
ments, for the heavy soil to lose its toxicity earlier than
the other two soils tested (Figure VI). As the rate of.
applicatibn became greater, the difference in the properties
of the various soils to retain toxic effects, was accen-
tuated. Perhaps, if experiments involving residual prop-
erties were carried out using greater rates, more distinct
differences between soils would be observed.

That 3-chloro IPC lasts longer in the soil than IPC
at similar concentrations, has been shown. Another point
of interest, however, is that 3-chloro IPC disappears from
h the soil in the order of its concentration, while IPC
appears to disappear independently of the rate applied to
the soil.

Where the soil treatments of 3-chloro IPC became toxic
to the various crops tested, a stunting of growth was
always observed. This dwarfing effect appeared to be pre-
ceded by a distortion of the new tissue arising from the
embryo, as exemplified by the swollen coleoptile, and root
tips of the grains. This type of injury is similar to that
described by other investigators as occurring due to the
action of IPC. This stunting probably occurs because the

root tissues fail to take up sufficient amounts of water

 

 

 

79
and nutrients. Purple margins on the leaves of corn and
sorghum seedlings and the dark green, brittle leaves of
the oat seedlings indicated a lack of phosphorus.

The curvature or spiral effect observed in the young
leaves of the oat and rye plants may be caused by photo-
tropic responses due to hormonal effects of 3-chloro IPC.

The abundance of shoots arising from the crown of
certain crop plants grown in plots treated with 3-chloro
IPC, demands emphasis. The distortion of tissues at the
cotyledonary plate, so evident on soybeans, may have caused
this increase in shoot growth on plants that had the capacity
to deve10p shoots from that point. However, the increased
growth caused by the elimination of weeds can not be over-
looked as an explanation for the increase in shoot production.

It is obvious that pro-planting treatments were far
more lethal to the cr0ps tested than were the pre-emergence
treatments. This was undoubtedly due to a greater penetration
of the chemical into the soil before planting, and to the
greater distribution throughout the soil occurring as the
soil is disturbed in the planting process. The ability of
corn to survive pre-emergence treatments of such high rates
may be due, at least in part, to the depth at which the
seed was planted.

The development of a large number of brace roots at ~
the second node of many corn plants, accompanied by an
abundant development of fibrous roots, is a response similar

to that observed by Hamner, Tukey, and Carlson (17) on sweet

80
corn treated with 2,4-dichlor0phenoxyacetic acid. This
type of response again appeared to be due to the distortion
of tissues at the crown of the plant. In rare cases the
corn plants broke off at the crown.

Post-emergence treatments produced effects much like
those of a contact herbicide, which leads to the conclusion
that the injury was due to the xylene included in the
formulation rather than the 3-chloro IPC. Currier (7)
has shown xylene to be strongly toxic to several plant
species. He has described this injury as a darkening of
the leaves shortly after treatment, with loss of turgor
resulting in a drooping of the stems and leaves. He also
states that, in bright sunlight chlorophyll was destroyed,
often causing a bleaching of the tissue. Broadleaved plants
were injured more than the grasses by post-emergence treat-
ments, which indicates that the area of the leaf surface
was involved.

In general, the use of 3-chloro IPC on wheat, oats,
and rye for the control of weeds could not be recommended
from the results of these experiments. Applications in the
1 to 3 pound range on sorghum, Ladino clover, and alfalfa
deserve further investigation. Soybeans and corn responded
very well to several of the treatments with good control of
grass weeds. The data show red clover to be the most
sensitive of the legumes to applications of 3-chloro IPC
and therefore the use of the chemical on this crop is not

advisable.

l.

2.

SUMMARY

High concentrations of 3-chloro IPC were leached from

5 gram samples of light, heavy, and organic soils. For
the most part the amount of the chemical leached from
the soil was independent of the concentration.

Light, heavy, and organic soils treated with 2, 6, 12,
and 24 pounds per acre of 3-chloro IPC were leached
with 1, 1 1/2, and 2 inches of surface water each week.
The amount of water used in leaching did not effect the
loss of toxicity from the soil. The chemical persisted
30, 60, 76, and 104 days in the light and heavy soil,
and 44, 76, 90, and 148 days in the organic soil.

3. A 2 pound rate of 3-chloro IPC became non-toxic in

heavy, light, and organic soils adjusted to pH 3 in

9, l8, and 37 days. The same soils adjusted to pH 8.5
were non-toxic in 18, 37, and 47 days. The 2 pound rate
lasted in neutral light 8011 29 days and in heavy and
organic soils 47 days. Twenty-four pounds per acre
lasted 72 days in the heavy alkaline soil and 95 days

in the light and organic alkaline soils. The heavy
acid soil was non-toxic in 108 days and the light acid
and organic acid soils were still toxic after 159 days.
The neutral light and heavy soils were free of toxic

 

 

4.

5.

6.

'82
effects in 84 days, while the chemical remained active
after 159 days in the neutral organic soil.
Temperatures of 35 and 55 degrees Fahrenheit delayed
the breakdown of 3-chloro IPC in light, heavy, and
organic soils. Two and 24 pound rates were toxic in
the light and heavy soils for more than 12 weeks at
these temperatures. The organic soil when treated
with 2 pounds per acre lost its residual action in 6
weeks, while the 24 pound rate was t0xic for more than
12 weeks. At a temperature of 75 degrees toxicity per-
sisted 2 to 4 weeks in the light, heavy, and organic
soil treated with 2 pounds per acre. While heavy soil
which had received an application of 24 pounds per acre
lost its toxicity in 10 weeks, the light and organic
soils treated with the same rate were still toxic after
12 weeks.

In a field comparison of IPC with 3-chloro IPC it was
found that IPC at the rates of 2, 6, and 12 pounds per
acre lasted only 6 weeks despite the dosage used. The
3-chloro IPC lasted 8 weeks at the 2 pound rate, and more
than 12 weeks at the 6 and 12 pound rates. '
Pre-planting, pro-emergence, and.post-emergence appli-
cations were made on corn, sorghum, wheat, oats, rye,
soybeans, Ladino clover, red clover, and alfalfa at

rates of l, 3, 6, and 12 pounds per acre. Post-emer-
gence applications reduced the weight of most crop plants

and delayed the growth of most weeds. Pre-planting

 

 

 

applications to all crops were more toxic than pre-
emergence applications. The best weed control, with
the least injury, occurred in corn and soybeans. Oats,
wheat, and rye were very sensitive to applications of
3-chloro IPC. Treatments applied to the soil gave

excellent control of grass weeds.

l.

2.

3.

4.

5.

6.

7.

8.
9.

10.

ll.

12.

BIBLIOGRAPHY

Allard, R. W., R. H. De Rose, and C. P. Swanson. (Some
effects of plant growth regulators on seed germination
and seedling development. Bot. Gaz. 107:575-583, 1946.

Allard, R. W., W. B. Ennes, R. H. De Rose, and R. J.
Weaver. The action of isopropylphenylcarbamate upon
plants. Bot. Gaz. 107:589-596, 1946.!

Brown, J. W. and J. W. Mitchell. Inactivation of 2,4—
dichlorophenoxyacetic acid in soil as effected by soil
moisture, temperature, the addition of manure, and
autoclaving. BOto Gaz. 1093314-325, 1948.

Carlson, R. F. Destruction of quackgrass rhizomes by
application of isopropylphenylcarbamate. Mich. Agr.
Exp. Sta. Quart. Bull. 29:474-480, 1947.

Carlson, R. F. and J. E. Moulton. Chickweed control
in strawberries. Proc. Am. Soc. Hort. Sci. 54:200-204,
1949.

Crafts, A. S. Toxicity of 2,4-D in California soils.
Hilgardia. 19:141-158, 1949.

Currier, H. B. Herbicidal properties of benzene and
certain methyl derivatives. Hilgardia. 20:383-406, 1951.

Danielson, L. L. Written communication.

De Rose, H. R. Persistence of some plant growth regu-
lators in the soil. Bot. Gaz. 107:583-589, 1946.

De Rose, Robert H. and Arthur S. Newman. The compar-
ison of certain plant growth regulators when applied
to the soil. Soil Sci. Soc. Am. Proc. 12:222-226, 1947.

De Rose, Robert H. Crab rass inhibition with O-iso-
propyl N-(3-chlor0phenyl% carbamate. Agr. Jour. 43:
139-142, 1951.

Doxey, D. The effect of isopropyl phenyl carbamate on
mitosis in rye (Secale cereals) and onion (Allium cepa).
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Ennis, W. B. Some effects of O-isopropyl N-phenyl
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Ennis, W. B. Some cytological effects of O-isopr0py1
N-phenyl carbamate upon Avena. Am. Jour. Bot. 35:15-
21, 1948.

Ennis, W. 8. Responses of crop plants to O-isopropyl
N—phenyl carbamate. Bot. Gaz. 109:473-493, 1948.

Freed, Virgil H. Written communication.

Hamner, C. L., H. B. Tukey, and R. F. Carlson. Appli-
cation of 2,4-dichlor0phenoxyacetic acid to soil as a
pro-emergence spray to prevent lodging and to control
weeds in sweet corn. Mich. Agr. Exp. Sta. Quart. Bull.
30:194-200, 1948.

Hanks, Robert W. Removal of 2,4-dichlorophenoxyacetic
acid and its calcium salt from six different soils by
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