Everglades Experiment Station
Belle Glade, Florida
Mimeographed Report No. 18
WEEDING CELERY SEEDBEDS WITH SOLVENT NAPHTHAS
by James C. Hoffman
WEEDING CELERY SEEDBEDS WITH SOLVENT NAPHTHAS
James C. Hoffman
Associate Horticulturist, Everglades Experiment Station
Belle Glade, Florida
Hand-weeding celery seedbeds has been a very costly operation in the
Everglades. It is evident that profits from this crop will be substantially in-
creased if hand-labor can be reduced in the future.
Solvent naphthas have been used to kill weeds selectively in carrots and
related plants (3,4). This paper is a continued study of weeding celery seedbeds
with solvent naphthas (2).
The expense of weeding with solvent naphthas will vary but it is gener-
ally much cheaper than by hand. Growers in the area have indicated that the cost
of celery seedbed weeding is extremely variable, it being necessary frequently to
expend as much as 900 man hours to handle 1 acre of seedbeds. This same amount
of weeding is possible by the application of 35 gallons of a suitable naphtha.
If one cares to consider the extreme, or a very weedy seedbed, the ratio of number
of dollars expended might be as much as 1:30 in favor of the chemical method. This
ratio is proposed after consideration of the number of hours required for hand-
weeding and rate per hour, as compared with the price of the solvent and expense
of application. The ratio would not be as wide under sparser weed growth*
Materials and Methods
The solvent naphthas used in the tests here reported were obtained from
the following sources:
Sovasol No. 5 from Socony-Vacuum Oil Company
Stanisol from Standard Oil Company of Indiana
Stoddard Solvent from Gulf Oil Company
It is very important that the physical characteristics of these herbi-
cides be known, as many variations may occur. A number of the physical properties
of the above materials are listed in Table 1. Grigsby (1) has suggested that all
naphtha-like products having a closed flash point of 100-1100 F., regardless of
trade name, are of value as selective weed control materials for carrots and
The plots were 4 x 20 feet in size for the first two experiments de-
scribed in Tables 2 and 3, and 4 x 10 feet as described in Table U. Each treat-
ment was replicated 5 times in a randomized design and plants were taken from 5
randomisamples, each with 1 square foot of area. The variety of celery used in
both fall and winter tests was Special No. 763 and Supreme Golden in the summer
The solvent naphthas were applied at full strength. All treatments
were made by the use of a knapsack sprayer. The rate of application was varied
from 25 to 75 gallons per acre of seedbeds in some preliminary tests during the
spring of 1947. Thirty seedbeds 4 x 210 feet are considered 1 acre. This leaves
a space of 3 feet between each bed for watering and tapering the bed banks.
The rate of application can be calculated to determine the linear speed
of the spray equipment. This calculation is possible if the diameter of the ori-
fice, pressure, number of nozzles and area covered are known. As for example, a
nozzle with an orifice diameter of 0.035 inches will deliver 12 gallons per hour
at 60 pounds pressure. If one nozzle is considered and the spacing is 18 inches,
it must move at an average speed of 1.9 miles per hour to apply 35 gallons per
It was found in this first test, not reported in detail here, that a low
rate of application is desirable and that weed control was just as effective with
applications of 35 gallons per acre as with 75 gallons. If the plants are not
damping-off and the roots are well developed, no injurious effects have been ob-
served on seedbed plots sprayed at the rate of 35 gallons per acre. However, this
is not true when larger amounts are applied, or when the plants have a diseased
In the tests here reported all plots were sprayed at an approximate rate
of 35 gallons per acre of seedbeds. The celery seed germinated in approximately 8
days after being sown on the soil surface. Time of treatment with the various
solvents after seeding is given in Tables 2, 3 and 4. The plots listed as un-
sprayed were hand-weeded in the same manner as is generally practiced by commercial
growers of the area.
Discussion of Results
Injurious effects were never observed on any of the celery plants in the
tests here reported. Hand-weeding was not necessary on any of the plots sprayed,
as all weeds were killed in the early stages of development on these seedbeds in-
cluding: Commelina nudiflora L.--creeping day flower or wandering jew; Eleusine
indica (L.) Gaertn.--goosegrass; Erechtites hieracifolia (L.) Raf.--American burn-
weed; Gnaphalium spathulatum Lam.-cudweed; and Portulaca oleracea L.--purslane.
It is not the claim, however, that these chemicals will kill all weeds in any given
Plants harvested were classed as desirable for setting and were pulled
at this stage of development. Plants from all treatments of the 19L7 fall crop
were transplanted and good quality celery developed with no significant differences
between the treatments or unsprayed plants. In no case has an oily flavor been
detected in the mature celery. However, this flavor has been detected in the small
Differences between any of the data recorded in Tables 2, 3 and I are not
considered significant, since the treatment variance is not significantly larger
than the error variance. These results indicate that celery seedbeds sprayed with
solvent naphthas, as here described, produce plants equally as good in quality as
those obtained from unsprayed, hand-weeded beds.
Table 1.--Average Comparative Physical Characteristics of
3 Solvent Naphthas.1
No. 5 Stanisol Solvent
Gravity, o API .. . 8.6 49.6 48.5
Specific gravity 60/600 F. 0.786 0.781 0.786
Flash point (closed)o F. .105 108 104
Flash point (open)o F. .115 112 -
Initial boiling point o F. .310 316 312
Final boiling point o F. ,385 394 394
Aromatics, percent .. . 15.8 10-11 ---
1 Data supplied by oil company concerned.
Table 2.-Number and Weight of Special No. 763 Celery Plants Harvested 79 Days After Seeding from 5 Randomized
Blocks, 1947. 1
Days after seeding -
No, 5 Stanisol No. 5
6 o 17-
Total number plants 51 53 46 45 48 52 46 49 46
Green weight (grams) 649 664 621 638 634 666 720 684 733
1 Average of 5 random samples 1 square foot each taken from 4 x 20 foot blocks.
Table 3.-Number and Weight of Special No. 763 Celery Plants Harvested 88 Days
After Seeding from 5 Randomized Blocks, 1948. 2
Sovasol Sovasol Stanisol Stoddard Unsprayed
Treatments No. 5 No. 5 Solvent (Hand-weeded)
Days after seeding 9 9 and 61 9ard61 9 and 61
Total number plants 91 80 81 83 78
Green Weight (grams) 342 328 373 317 312
Dry weight (grams) 29.4 28.1 31.1 28.8 29.3
Percent dry weight 8.60 8.57 8.34 9.09 9.39
2 Average of 5 random samples 1 square foot each taken from 4 x 20 foot blocks.
Table iU.-Number and Weight of Supreme Golden Celery Plants Harvested 62 Days After Seeding
From 5 Randomized Blocks, 1948. 3
Stanisol Stoddard Stoddard Stoddard Stoddard Unsprayed
Treatments4 850 F. Solvent Solvent Solvent Solvent (Hand-weeded)
850 F. 780 F. 860 F. 950 F.
Days after seeding 8 8 10 10 16
Total number plants 100 91 88 10 89 81
Green weight (grams) 338 366 361 387 378 372
Dry weight (grams) 15.5 15.6 14.6 15.2 14.8 15.5
Percent dry weight 4.59 4.26 4.04 3.93 3.92 4.17
3 Average of 5 random samples 1 square foot each taken from 4 x 10 foot blocks.
4 Temperature at time Solvent Naphtha was applied.
Until more research is done, only solvent naphthas with characteristics
such as are listed in Table 1 should be used for weeding celery seedbeds in
southern Florida. Complete coverage of weeds is necessary and should be accom-
plished with the least amount of solvent naphtha possible. Thirty-five gallons
should be adequate when applied as a pre-emergence treatment or when the seedlings
have developed to the stage of 2 to 6 leaves. After this stage of plant develop-
ment, if the beds are free of weeds, it is unlikely that additional weeding will
be a serious problem.
Weeding with solvent naphthas is not recommended if an acre of seedbeds
can be hand-weeded with 50 man hours, considering the present price of materials
The use of a nozzle with an orifice diameter of approximately 0.035
inches, that will deliver a flat, fan-shaped spray is more desirable than the
conventional cone-type. However, the cone-type nozzle has been used with success.
It is suggested that applications of solvent naphthas be made only when
the foliage is free from droplets of rain or dew.
The spraying should be done when the weeds are very small. Generally,
only 1 application is necessary if properly timed.
Solvent naphthas are combustible and consequently open flames or smoking
should not be allowed near the chemicals.
Continuous contact with the skin should be avoided, as slight irritations
These materials are solvents and have been noted to act very slowly on
rubber hose; however, they are not harmful to synthetic rubber hose. This neces-
sitates frequent replacement of such hose, according to the amount of its use and
its care in storage.
Until more information is available, the application of these solvent
naphthas should be confined to seedbed weeding, as there Pre indications that
celery plants treated in more mature stages of growth develop an incipient terminal
bud injury. This incipient terminal bud injury often develops celery with small,
undesirable hearts. Undesirable flavors also have been noted at harvest time.
1. Grigsby, B. H. Oil sprays for the control of weeds in carrots end related crops.
Mich. Agr. Exp. Sta. Quarterly Bull. Vol. 28, No. 3. Feb. 1946.
2. Hoffman, James C. Weeding celery seedbeds with solvent naphthas. Fla. Agr.
Exp. Sta. Press Bull. 651. April 1948.
3. Minshall, Wm. H. and V. A. Helson. The herbicidal action of oils. Dominion
Dept. of Agr. Ottawa, Canada. Div. of Bot. and Plant Path. Contribution No.
959.. Sept. 1968.
4. Sweet, R. D., R. Kunkel, and G. J. Raleigh. Oil sprays for the control of
weeds in carrots and other vegetables. Proc. Amer. Soc. Hort. Sci. h45:40-hh4.