WEEDING LETTUCE AND ENDIVE WITH CIPI IN MUCK SOIL
V. L. Guzman and E. A. Wolf
This is a Mimeographed Reprint from the Pro-
ceedings of the Eighth Annual Meeting of the
Southern Weed Control Conference held in St.
Petersburg, Florida on January 17, 18 and 19,
WEEDIG LETTUCE AND ENDIVE WITH CIPC IN MUCK SOIL*
V. L. Guzman and E, A. Wolf
University of Florida, Everglades Experiment Station
Preliminary experiments conducted at this station in the spring
of 1952 indicated that isopropyl N-(3-chlorophenyl) carbamate (CIPC) was
one of the best pre-emergence herbicides for lettuce and endive (1). Fur-
ther tests with various herbicides and rates indicated that for pre-emer-
gence weeding of lettuce and endive 10 pounds per acre of CIPC was the
optimum rate* Sodium trichloroacetate (TCA) and 3-p-chlorophenrl 1-1-di-
methylurea (CMU) were not as effective, Lettuce appeared to be more tol-
erant to CIPC, TCA and CMU than endive (2).
Two herbicides, one specific for grasses and the other for broad-
leaf weeds, were caubined and applied as pre-emergence treatment to lettuce
and endive. The best stand of lettuce and endive resulted from the combi-
nation of any two of the followings 8 pounds of CIPC, 15 pounds of TCA
and 0,75 pounds of CMU (2), Pelletized CIPC also was tried. Rates of 4 to
10 pounds per acre did not affect either stand or growth of lettuce plants.
The control of weeds, however, was not as effective as with the correspond-
ing rates of the liquid formulation (3). Up to this point, the criteria of
evaluation was tolerance of the crop to the herbicide measured by stand
counts and observations of growth rate. These results indicated, however,
that CIPC was the best herbicide for lettuce and endive when taking into
consideration the over-all performance on both crops and weeds.
The object of this work was to study further the effects of dif-
ferent rates of CIPC on lettuce and endive.
Methods and Procedure
Herbicide rates are given in terms of active ingredients per acre.
They were applied at a pressure of 25 p.s.i. in 30 gallons of water per
covered acre. After seeding,at a depth of 0.5 inch, the ground was rolled
except where otherwise indicated and the herbicide applied. Great Lakes
lettuce and Full Heart Batavia endive varieties were used. Weeds were
counted in one square foot taken at random per plot about 3 weeks after
In the first experiment (October 28, 1953), the seed beds were
handled by using three methods: 1. "Rolled" after seeding the ground
was rolled and the herbicide then applied; 2. "Disced" the herbicide was
*This work was in part made possible by a grant from Columbia Southern
applied, the ground was lightly disced and then seeded, and 3. "Normal" -
the herbicide was applied after seeding without rolling or discing. A split
plot design was used with six replications. Main plots were 60 feet long
by 4 feet wide, and sub-plots 10 feet long by 4 feet wide, with one row each
of lettuce and endive 2 feet apart The rates of CIPC used were 0, 8, 10,
12, 14 and 16 pounds. In the second experiment ( November 13, 1953), ran-
domized blocks were employed with plot 30 feet long by 4 feet wide with one
row of lettuce and one of endive 2 feet apart. The ground was rolled after
seeding and rates of 0, 6, 8, 10, 12 and 16 pounds of CIPC were applied.
Among the treatments of a third replicated experiment (harvest in progress
at time of writing this paper) were post-emergence weeding of lettuce and
endive with pelletized and liquid CIPC at the rates of 10 and 6 pounds re-
spectively. The pellets, clay particles of 16-30 mesh impregnated with 20%
of CIPC, were distributed by hand,
Results and Discussion
First pre-emergence experiment: CIPC showed a significant reduction of weeds
over the untreated check (Table 1). Later observations indicated that the
number of weeds were about the same in the CIPC treated plots but stunting
of the weeds was much more pronounced at the higher rates. Although the
number of weeds was not significantly different due to the three methods
of handling the soil, the "rolled"plots showed smaller weeds and longer
residual effect of the CIPC. Most of the weeds in this treatment remained
small or died later, particularly in the plots receiving the higher rates
of CIPC. The "normal" treatment was second best, and gave control almost
as lasting as the "rolled" treatment.
The check plots were hand weeded three times: "disced" plots were
weeded twice. Most of the "rolled" plots were not weeded except a few sub-
plots treated with the lower rates of CIPC in the weediest part of the field.
"Normal" plots were weeded once; a few of the sub-plots of the 8- and 10-
pound rates were weeded twice. Although weed counts may be a good criteria
of evaluating herbicidal effects, under field conditions, this may not be
the case. Since the counts have to be made at a certain date, it is pos-
sible that some of the low rates appeared as good at that particular time
as the high rates. However, the stunting and the length of residual effect
on weeds that usually accompanies the use of high rates is of major impor-
tance, Careful observations of the herbicide's over-all performance on
crops and weeds is much more important than a given figure on which statis-
tical calculation can be made.
Significant reduction in yields of endive occurred at 12-, 1U-
and 16-pound rates of CIPC (Table 1). The stunting effect of CIPC on en-
dive plants was evident from the time of germination. The check in growth
was severe at rates of 12, lU and 16 pounds and noticeable at rates of 8 and
10 pounds. Recovery from this condition was in direct proportion to the a-
mounts of CIPC used. At rates of 12, 1U and 16 pounds recovery was only par-
tial, while at 8 and 10 pounds it was more rapid and the yields were not
Table 1. Yields in pounds of marketable lettuce and endive, and number
of weeds as affected by various rates of pre-emergence CIPC
treatment (October, 1953).
CIPC lbs/A Lettuce Endive Weeds
0 14.0 16.5 19 9
8 13.5 15.9 8* S
10 12.6 14.9 8* 4*
12 12.2 13.7* 7* 3*
14 11.4 12.3* 7* h*
16 13.9 12.0* 5* 3*
LSD .05 NS 2.1 6 4
* Significantly different from the Check
Lettuce plants were slightly checked in growth by rates of 12
pounds or more of CIPC. Recovery from this condition took place in about
15 days. Lettuce yields were not affected by any of the rates tested.
Methods of handling the soil in relation to the herbicidal treat-
ment did not affect yields of either lettuce or endive.
Second pre-emergence experiment: Table 2 presents the number of weeds and
stand of lettuce and endive as well as number and weight of marketable
lettuce and endive heads. The use of 10 pounds or more of CIPC resulted
in highly significant reduction of weeds. In this particular test, weed
counts correlated with observations of weed control in the field. Rates
of 10 pounds or more produced severe stunting of weeds, many of which died
later. In order to keep the plots free of weeds it was necessary to hand
weed the check plots three times. The plots which received 6 to 8 pounds
of CIPC were weeded twice, and the plots receiving 10 to 16 pounds of CIPC,
once (mostly pulling a few large weeds). The stand of lettuce was unaf-
fected, but the stand of endive was reduced significantly by the 16-pound
treatment. Temporary reduction in growth rate of lettuce was noted at the
16-pound rate. Endive was stunted slightly at rates of 10 and 12 pounds
and more severely at 16-pound rates. Recovery in growth rate was attained
except for some plants growing in the 16-pound rate treatment which never
reached marketable size. Yields and marketable stand of lettuce were un-
affected by the rates used. A highly significant reduction in yield and
stand of endive at harvest time resulted from the use of 16 pounds of CIPC.
Lettuce was more tolerant to high concentrations of CIPC than endive.
Table 2. Effect of various rates of CIPC applied as a pre-emergence treat-
ment on weeds, stand and yields of lettuce and endive (November,
CIPC Weeds Stand before thinning Yields Lbs* Marketable Heads
Lbs/A Lettuce Endive Lettuce Endive Lettuce Endive
Ck. O 138 91 165 43.8 43.3 24 29
6 117 95 141 47.1 45.5 24 29
8 145 99 172 44.5 43.7 23 30
10 80** 94 154 48.6 40.3 25 28
12 61** 97 149 45.7 44.1 26 30
16 33** 83 111* 35.7 27.9 22 18
LSD 0 35 NS 34 NS 9.2 NS 4
.01 47 -- N 12.4 6
* Significantly different from check.
*N Highly Significantly different from check
Comparing the over-all results of both experiments, better control
of weeds was obtained in the first test. There were no appreciable differ-
ences in temperature at the time of applying the chemicals and afterwards
(medium temperature for the first 3 weeks after treatment was 68.90 F for
the first experiment and 68.40 F for the second). Rainfall for October was
7.7 and for November 0.95 inches. Experiment one was planted on October 28
and was located adjacent to a field of rice which for the most part was kept
flooded. Although soil moisture determinations were not made, higher soil
moisture was evident in the field of the first experiment. It is possible
that the high soil moisture at the time of CIPC application and thereafter
was at least in part responsible for the excellent control of weeds attained.
Yields of lettuce were unaffected, but endive yields were reduced
significantly at the 12-, 14-, and 16-pound rates in the first experiment
and only at the 16-pound rate in the second. The same factor which inter-
acted with the herbicide to produce better control of weeds in the first
experiment also appeared to have affected the endive yields.
Post-emergence experiment:- Liquid CIPC at the 6-pound rate applied a few
days before thinning caused severe damage to endive and to a lesser degree
to lettuce. The first 10-pound application of pelletized CIPC did not pro-
duce any visible injury to lettuce, endive, or weeds. It was necessary to
hand weed the plots and make a second application of freshly prepared pel-
lets. The control of weeds after the second application was good to ex-
cellent, but some reduction in growth rate of the endive and very light re-
duction in growth rate of lettuce occurred. The lettuce and endive plants,
whether damaged by liquid or pelletized CIPC, have recovered to a large
Good to excellent control of weeds was accomplished with pre-
emergence application of CIPC on lettuce and endive growing in muck soil.
The duration of weed control appeared to depend on the rates of CIPC,
method of handling the soil in relation to herbicidal treatment, and the
moisture in the upper layer of soil. CIPC rates of 10 pounds or more, ap-
plied after rolling the ground when the upper layer of soil was relatively
high in moisture content at medium temperature of 680 F, gave a commercial
control of weeds until harvest. With endive, some injury occurred with
rates of 12 pounds or more of CIPC. A rate of 8 to 10 pounds of CIPC seems
safe for endive. Lettuce tolerated higher rates than endive, but 10 pounds
of CIPC per acre seems sufficient. Ten pounds of pelletized CIPC and 6
pounds of the liquid formulation, applied before thinning, appears promis i.,
ing for post-emergence weeding of lettuce and endive. The liquid form pro-
duced more damage to endive than to lettuce.
1. V. L. Guzman and E. A. Wolf, Weed control investigations. University
of Florida, Agricultural Experiment Station Annual Report. 226. 1952.
2. __, Weed control investigations in vegetable
crops. University of Florida, Agricultural Experiment Station Annual
Report. 251. 1953.
3. Weed control investigations in vegetable
crops. University of Florida Agricultural Experiment Station Annual
Report, 1954 (in print).