Everglades Experiment Station
Belle Glade, Florida
Mimeographed Report No0 5
HORMONE PLANT GROWTH REGULATORS INCREASE TOMATO YIELDS
by James C. Hoffman
Hormone Plant Growth Regulators Increase Tomato Yields
James C. Hoffman
During the last decade hormone plant growth regulators have been used in
many ways to increase yields and quality of fruits and vegetables. Many reports
have been published concerning the application of several organic acids to the
flowers of greenhouse-grown tomatoes. The most promising of these so-called hor-
mones for increasing tomato yields have been indolebutyric acid, beta-naphthoxy-
acetic acid and para-chlorophenoxyacetic acid. There is a positive correlation
between increased yields, light intensity, nitrogen supply and temperature. Green-
house tomatoes in the north are grown during the winter months when the light in-
tensity is usually low and often the temperatures fall below 500 F. in the green-
house during the hours of darkness These factors reduce pollination and fertili-
zation and final yields of tomatoes. Generally, the carbohydrate/nitrogen
relationship of such plants is not balanced; resulting in vigorous growth with
reduced fruit-set and yields. Support is here given that these hormones stimulate
fruit-set when applied at the proper time but not during a normal tomato growing
environment. This supports many conclusions that hormones have not increased
yields when applied to field-grown tomatoes during mid-summer,
Since tomatoes are grown in Florida during the winter months when the
environmental conditions are often unfavorable for maximum fruit-set and develop-
ment, it is logical that some stimulation from certain hormones may increase
fruit-set and final yields.
Preliminary experiments were established November 24, 1947, at the
Everglades Experiment Station. The flowers of each cluster, at the time of an-
thesis or full bloom, were sprayed with 1 application of hormones, at the rate
of 2 quarts of the formulations per acre. A total of 2 applications were applied
to cover those flowers producing fruit for the first harvest. A hand-operated
Cornalius hydraulic-aerosol sprayer was used to spray the flowers.
Later flowers formed at a time when the average low temperature was
above 580 F. During this period plants growing under all treatments set fruit
at approximately the same rate.
The temperature prevailing during the two weeks of fruit-set for the
first harvest averaged 69.h F. for the period from 6:00 A. M. to 6:00 P. M., and
61.20 F. for the period from 6t00 P. M. to 6:00 A. M. or a general average tempera-
ture of 65.30 F. The average low was 57.00 F. Information has been established
at the California Institute of Technology that tomato fruit-set is greatly reduced
when the temperatures fall below 580 F.
The treatments in this test include two commercial formulations, namely:
Dowspray 202 and NO-SEED. These formulations may be diluted with water and there
is no difficulty in forming a stable spray, whereas indolebutyric acid does not
dissolve in water and often crystallizes out after being dissolved in ethyl alcohol
and added to water. Beta-naphthoxyacetic acid must first be dissolved in the
minimum amount of ethyl alcohol and then added to a final volume of water for
dilution to the desirable concentration.
There is a definite trend of increased yields by the application of
hormones when these two varieties of tomatoes are grown under low tempera ures on
organic soils. Grothen's Globe treated with Dowspray 202 and Rutgers treated with
NO-SEED produced yields significantly higher than the same varieties grown on the
The majority of fruit produced by the hormone-treated plants were seed-
less or pathenocarpic, and were considered equal in quality to the tc natoes with
seed. If one is prejudice against eating tomato seed, the parthenocarpic fruit
would then be classed superior to the seeded checks.
A similar test has been completed on the sandy soils of the East Coast
near Boynton. No increased yields were obtained by the hormone applications.
These sand land plots were very low in nitrogen as compared to organic soils. The
temperature averaged 30 F. higher on the sand than on the organic soils at the
Experiment Station. Possibly, these differences in amount of nitrogen and in-
creased temperature account for the lack of response when tomatoes grown on sandy
soils are sprayed with hormones.
These tests should be considered very preliminary as much additional
work needs to be done before definite recommendations can be made. Rate of ap-
plication and concentrations may even need to be varied when applied to different
varieties and under different environmental conditions.
Table 1. Effect of Hormone Plant Growth Regulators upon the First Harvest of
Tomatoes, Everglades Experiment Station, Belle Glade, Florida, 1947.
GROTHEN'S GLOBE Dowspray 202 BNOA NO-SEED Check L.S.D.(5%) L.S.D.(1%)
(1) (2) (3) (4) (5) (6)
Number Fruit Per Plant 6.22 5.10 5.98 5.00 0.97 1.37
Average Fruit Wt. (Grams) 119 120 123 116 -
Yield (Pounds Per Acre) 7607 5976 7188 5645 1702 2386
Number Fruit Per Plant 3.98 3.70 4.12 3.40 0.70 0.99
Average Fruit Wt.(Grams) 132 137 137 129 -
Yield (Pounds Per Acre) 5072 4895 5490 4256 1085 1521
(1) Dowspray 202 is a formulation by the Dow Chemical Company,
Midland, Michigan, of indolebutyric and beta-naphthoxyacetic
acids. Four fluid ounces of the 202 was diluted to a final
volume of 1 gallon in soft water. The final spray contained
2,000 PPM of gamma 3-indolebutyric acid and 50 PPM of beta-
(2) Applied at the rate of 50 PPM of beta-naphthoxyacetic acid
in soft water.
(3) NO-SEED is a formulation by the Science Products Company,
1230 E. 63rd Street, Chicago 37, Illinois. Eight fluid ounces
of the NO-SEED was diluted to a final volume of 1 gallon in soft
(4) No hormone plant growth regulators ware applied.
(5) Difference necessary for significance between any 2 treatments
at odds of 19:1.
(6) Difference necessary for significance between any 2 treatments
at odds of 99:1.