'4qfttension Veg. Crops I
Mimeo Report 64-5 HUME LIBRARY
TOMATO FRUIT SET JUL 1 1 1972
James M. Stephens
Assistant Vegetable Crops Specialist
University of Florida I.F.A.S. Univ. of Florida
Have you had a tomato fruit set problem In your garden? If so, you
will probably be interested in the following Information explaining what
Is known about why it happens.
Failure of fruit set on tomatoes Is one of the most, if not the most,
widespread problem encountered by Florida vegetable gardeners each-spring.
In most cases, gardeners report large, healthy, vigorously growing plants
with an abundance of yellow flowers--yellow flowers which mysteriously
either drop off or wither up to a brown crinkle Instead of producing fruit.
No one completely understands all the reasons for poor fruit set in
tomatoes; furthermore, some cases seem altogether unexplainable. However,
a great deal of study of the problem has been going on for several years.
As a result, several findings have been made which help explain what is
happening. The following are some of the findings which tend to explain
1, ..High Nighttime Temperatures
It has been well demonstrated in the past that.fruit set in tomatoes
is very sensitive to certain critical temperatures. None of our varieties
most desirable for planting in Florida will set fruit when nighttime
temperatures reach a consistent streak of above 70 F.
With our present-recommended varieties, tomatoes should be set in the
field early enough to avoid unfavorable temperatures at blossom-time. In
South Florida tomatoes should be planted by the last of February. In
Central Florida they should be planted in the month of March. North
Florida gardeners should be able to plant tomatoes in the field as late
as the middle of April with a good chance for abundant fruit set.
There are certain types of-tomatoes,'such as the small-fruited cherry
and, especially the new Summer Cherry, that will set fruit under much warmer
conditions. And, too, larger fruited varieties have been developed which
reportedly are heat tolerant. Hot-set was developed to withstand summer
temperatures, but in trials here In Florida, It has not been any better
than our own varieties. Generally, varieties which set fruit under low
temperature conditions also set fruit at high temperatures. Several such
varieties have come out of Canada with abilities to set fruit when as
cool as 45 F. These same varieties in Texas set fruits abundantly in
hot weather. While these varieties are not being recommended in Florida
because of other poor qualifications, home gardeners might like to
experiment with some such as Cold Set, Early Alberta, Early Lethbridge,
Earlinorth, and Swift. Other.varieties which have been reported to set
fruit In hot weather include Alpha 88 FR, Bounty, Firesteel, and Pinkdeal.
2. Low Nighttime Temperatures
Likewise, during extended periods where the temperature during the
night fails to rise above 55-58 F., tomato varieties recommended for
Florida will not'set'abundant fruit. The optimum night temperature for.
Rutgers appears to be around 62* F. As was mentioned above, certain
varieties not recommended for Florida have set fruit when as cool as
3. Excessive Nitrogen
Tomato plants tend to initiate flower buds under normal conditions
as soon as they have reached a certain size or age. This is the time
of a change over from a vegetative form of growth to a reproductive one.
Generally, nitrogen applied in excessive amounts prior to flowering
will cause the plant to continue vigorous vegetative growth rather than
setting fruit. This especially becomes the case for tomat, plants growing
over septic drains, In rich organic soils, or in heavily manured beds.
Tomato production is usually best when only enough nitrogen is
available during the first couple of months after planting',to permit
development of a large sturdy vine, but not enough to cause a soft type
of growth. Once the plant has a heavy fruit load and tomatoes begin to
ripen, the nitrogen requirement is very high. If the nitrogen supply
Is not adequate at this stage of development, the plants will turn yellow
and defoliate, leaving the fruits exposed and vulnerable to sunscald. The
regulation of the nitrogen supply is an individual field and seasonal pro-
blem and must be adjusted as the season progresses.
4. Excessive Shad6
Tomato fruitfulness is reduced when plants are excessively shaded.
Under this condition, the reduction Is probably due to the performance of
poor plants. Thus, the plants would likely not be vigorous, dark green
Under low soil moisture conditions, when water-stress in the tomato
plant is most likely to occur, flowers often fail to produce a mature
fruit. This condition may result from some hindrance to the fertilization
of the flower, or to the disruption of growth of the little fruit following
Various species of Fnsects, both sucking and chewing, can and do feed
on the ovules, flowers, and partially developed seeds and fruits. Blossom
or young fruit drop may result. This damage in Florida might be due to
insects such as the thrips, pin worms, grasshoppers, aphids, or spider