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Blossom Drop, Reduced Fruit Set, and Post-Pollination
Disorders in Tomato1
Monica Ozores-Hampton, Fnu Kiran, and Gene McAvoy2
1. This document is HS1195, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and
Agricultural Sciences, University of Florida. Original publication date July 2012. Visit the EDIS website at http://edis.ifas.u.edu.
2. Monica Ozores-Hampton, assistant professor, and Fnu Kiran, biological scientist, Horticultural Sciences Department, UF/IFAS Southwest Florida
Research and Education Center, Immokalee, FL 34142; and Gene McAvoy, county Extension director and regional vegetable extension agent, UF/IFAS
Hendry County Extension Service, LaBelle, FL 33975.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to
individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national
origin, political opinions or aliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A&M University Cooperative
Extension Program, and Boards of County Commissioners Cooperating. Thomas A. Obreza, Interim Dean
Blossom drop and reduced fruit set in tomato can seriously
impact yields. Growers in Florida routinely experience such
problems and inquire about the cause and possible preven-
tative measures to reduce ower loss and improve yields.
e problem can be frustrating and dicult to manage in
Tomato owers are complete owers in that they have both
male (stamens) and female (pistil) parts within the same
ower (Figure 1). e yellow stamens wrap around the
greenish pistil in the center of the ower (Mills 1988). e
stamen has two parts: lament and anther, and the pistil has
three parts: ovary, style, and stigma (Figure 2). e style is
the long stalk that reaches up to the bumpy, sticky stigma,
which extends beyond the surrounding stamens. Tomatoes
are self-pollinated at the rate of 98% or more. Pollination
occurs primarily between 10 a.m. and 4 p.m. (Levy, Rabi-
nowitch, and Kedar 1978). Tomatoes need biotic or abiotic
agents to assist in pollination.
Figure 1. Reproductive features of tomato ower. Left: female pistil.
Center: open tomato ower. Right: male stamens.
Credits: Monica Ozores-Hampton Figure 2. Tomato ower structure
Credits: Carlos Ozores
In open-eld production, pollination is accomplished by
wind. Tomato owers hang down (Figure 3), and anthers
are located above the stigma. e pollen is released and
falls downward onto the stigma. Insect pollinators are not
important for pollination of tomatoes grown in open-eld
production (Levy, Rabinowitch, and Kedar 1978; Ozores-
Hampton and McAvoy 2010).
In greenhouse production, where plants are protected from
the wind, growers used to mechanically shake individual
ower trusses or entire plants to stimulate the release of
pollen. However, the predominant means of accomplishing
pollination now is through the use of bumble bees. e
bumble bee sonicates for pollination, meaning it vibrates its
wing muscles without ight. is causes the whole ower to
vibrate, and a cloud of pollen is released onto the bee’s body
and onto the stigma at the same time.
Blossom drop is dened as the loss of owers (Figure 4).
Several factors, usually related to some type of stress, can
cause tomato plants to drop their blooms. e stress may be
either nutritional, environmental, or a combination of the
two. However, anything that interferes with the pollination
and fertilization processes may result in ower loss (Levy,
Rabinowitch, and Kedar 1978; Mills 1988; Ozores-Hampton
and McAvoy 2010). Without pollination, which stimulates
fruit set, the owers die and drop. is condition can
aect tomatoes, peppers, snap beans, and other fruiting
vegetables. In tomatoes, blossom drop is usually preceded
by the yellowing of the pedicle. Tomato owers must be
pollinated within approximately 50 hours or they will abort
and drop o. is is about the time it takes for the pollen
to germinate and travel up the style to fertilize the ovary at
temperatures above 55°F.
Potential Causes of Blossom Drop
e primary causes of blossom drop in tomatoes are
environmental (e.g., temperature and relative humidity
[RH]) or cultural (e.g., lack or excess of nitrogen [N] fertil-
ity). Secondary causes can include lack of water, reduced
or extended light exposure, excessive wind, insect damage,
foliar disease, excessive pruning, or heavy fruit set.
Primary causes of blossom drop
Temperature: Tomato plants drop their owers under
extreme temperature regimes, such as high daytime tem-
peratures (above 85°F), high nighttime temperatures (above
70°F), or low nighttime temperatures (below 55°F) (Table
1). Optimal growing conditions for tomatoes are daytime
temperatures between 70°F and 85°F. While tomato
plants can tolerate more extreme temperatures for short
periods, several days or nights with temperatures outside
the optimal range will cause the plant to abort owers and
fruit and focus on survival (Mills 1988). Temperatures
over 104°F for only 4 hours can cause the owers to abort.
If nighttime temperatures fall below 55°F or rise above
70°F, or if daytime temperatures rise above 85°F, the pollen
becomes tacky and nonviable, preventing pollination
from occurring and causing the blossom to dry and drop
(Chester 2004; Levy, Rabinowitch, and Kedar 1978; Mills
1988; Ozores-Hampton and McAvoy 2010).
Low temperature: Low temperatures interfere with the
growth of pollen tubes, preventing normal fertilization. e
pollen may even become sterile, which causes blossoms to
drop.Tomato fruit do not set until nighttime temperatures
are above 55°F for at least two consecutive nights (Chester
2004; Ozores-Hampton and McAvoy 2010).
High temperature: Sustained high temperatures, especially
at night, rapidly deplete the food reserves that are produced
in the tomato during the day. e result is sticky pollen,
Figure 3. Open tomato blossoms hanging downward direct the pollen
from the anthers to the stigma.
Credits: Monica Ozores-Hampton
Figure 4. Blossom drop on tomatoes, January 2010, Immokalee, FL
Credits: Monica Ozores-Hampton
altered viability, and poor or no pollination. Ultimately,
the blossom dries and falls o. Female ower parts can
also undergo morphological changes, such as drying of the
stigma (Mills 1988; Ozores-Hampton and McAvoy 2010).
Relative humidity: e ideal RH for tomato growth and
development ranges between 40% and 70%. Relative
humidity plays a major role in pollen transfer. If RH is
lower than the optimal range, it interferes with pollen
release because the pollen is dry and unable to stick to the
stigma. If RH is higher than the optimal range, the pollen
will not shed properly (Mills 1988; Ozores-Hampton and
Nitrogen: High or low application rates of N fertilizer can
cause blossom drop. High rates of N encourage the plant
to produce excessive vegetation at the expense of fruit
set. Low N produces spindly vines with low food reserves
that cannot support a tomato crop (Chester 2004; Levy,
Rabinowitch, and Kedar 1978; Mills 1988; Ozores-Hampton
and McAvoy 2010).
Secondary potential causes of blossom
Low or high soil moisture: Tomatoes have deep roots that
can penetrate up to 5 feet. Low soil moisture stresses and
weakens the plants. e root zone should be kept uniformly
moist throughout the growing season to develop a large
root system and reduce plant stress (Chester 2004; Ozores-
Hampton and McAvoy 2010).
Heavy fruit set: When a tomato plant has produced a large
number of blossoms, the resulting fruits compete for the
limited food supplied by the plant. e plant will automati-
cally abort some owers. Once the initial crop is harvested,
the problem should subside as the plant’s nutritional status
comes back into balance (Levy, Rabinowitch, and Kedar
1978; Mills 1988; Ozores-Hampton and McAvoy 2010).
Wind/pruning: Excessive wind can desiccate owers and/
or physically knock them o, reducing fruit set. Excessive
pruning can reduce the amount of energy the plant pro-
duces and thus can reduce ower production and fruit set.
Light: Lack of sucient light or extended exposure to light
can reduce fruit set.
Insect damage or disease: Growers should use adequate
cultural practices to control insects and diseases. Fungal
diseases—such as botrytis, heavy bacterial spot, or bacterial
speck pressure—have a negative eect on fruit set.
Hormones and Tomato Fruit Set
Hormones are natural organic compounds produced by the
plant, which regulate responses, such as bud development,
root growth, and fruit setting. Hormones can also be
produced articially and applied to regulate plant growth.
Hormone treatments can be eective during periods of
low nighttime temperatures, but the resulting fruit may
be seedless, of poor quality, and suer from puness and
blossom-end scar (Minges and Mann 1949). However,
favorable results were obtained when hormones were ap-
plied with hand sprayers directly on the owers rather than
to the whole plant (Chen and Henson 2001). Whole-plant
application can result in plant injury. Hormone treatments
do not increase total marketable yields of tomatoes but
can shi a portion of the yield to earlier in the season (by
increasing fruit size). Normally, one application at owering
and another application 15 days later produce improved
ower and fruit set (Chen and Henson 2001). ere are
many hormones and nutritional products commercially
available that may increase tomato blossom and fruit set,
but generally these products do not produce consistent
results. Currently, the UF/SWFREC Vegetable Program is
testing commercially available products that may have an
eect on tomato and pepper ower and fruit set in growth
chambers under high and low temperatures and RH.
How to Control Tomato Blossom
1. Grow varieties suited to the climate, such as varieties with
greater heat-setting ability
2. Use recommended N rates
3. Water deeply during dry weather
4. Control insects and diseases
Under high temperatures and low RH conditions: Under
controlled production situations (greenhouses), direct a
gentle spray of water at the blossoms twice during a hot
day to improve ower set when daytime temperatures
range between 90°F and 100°F and below 75°F at night.
e evaporating moisture lowers the temperature, raises
the humidity, and jars the pollen loose, thereby improving
ower set. If daytime temperatures exceed 100°F and
nighttime temperatures exceed 75°F, this technique is not
Under high temperatures and high RH conditions:
Watering the foliage is not recommended, especially when
fungal diseases are present.
Catface: is condition involves malformation and scarring
of fruits, particularly at blossom ends. Aected fruits are
puckered with swollen protuberances and can have cavities
extending deep into the esh (Zitter and Reiners 2004).
Causes: Possible causes include extreme heat, cold weather
with nighttime temperatures 58°F or below at owering,
drought, high N levels, or herbicide injury spray. Tomato
varieties with very large fruits are more susceptible (Olson
Control: Avoid setting transplants too early in the season,
grow catface-resistant varieties, and avoid herbicide injury.
Zippering: is condition is characterized by the presence
of brown tissue (resembling a zipper), usually running
from the stem end to the blossom end and caused by
abnormalities during early ower development (Cox, Tilth,
and Coolong 2011; Zitter and Reiners 2004).
Causes: is condition is the result of an anther remaining
attached to newly forming fruit. It is also associated with
incomplete shedding of ower petals when the fruit is
forming. It may sometimes be attributed to high humidity.
In cooler weather, parts of the ower may adhere to the
developing fruit and result in zippering (Olson 2009).
Control: Select varieties that are not prone to zippering.
Puness: is condition is characterized by fruit that ap-
pear bloated, at sided, or angular, leading to oddly shaped
fruit. e locular gel (the liquid that surrounds the seeds)
fails to ll the fruit’s inner cavity, resulting in a fruit with
attened sides that lacks rmness (Cox, Tilth, and Coolong
2011; Olson 2009).
Causes: is condition can be caused by incomplete
fertilization or seed development due to cool temperatures
or, under greenhouse production, by the lack of vibration
or shaking, which assists in releasing the blossoms’ pollen.
Other factors, such as low light or rainy conditions, high N
or low potassium, may also contribute to puness.
Control: Ensure adequate growing conditions and plant
In South Florida, tomatoes are planted continuously
between August and February. Tomato growing seasons are
typically dened as fall, winter, and spring, with planting
dates between 15 Aug. and 15 Oct., 16 Oct. and 15 Dec.,
and 16 Dec. and 15 Feb., respectively (Ozores-Hampton
et al. 2006). Based on planting season, the length of the
growing season averages 18, 20, and 16 weeks for fall,
winter, and spring, respectively. Historical temperatures
(average +/- standard deviation in °F) from a weather
station located in Immokalee, FL, are 79.6 +/- 1.5, 69.0 +/-
4.4, and 67.4 +/- 6.2 for fall, winter, and spring, respectively.
Hence, restrictions in marketable tomato yields in the fall
planting season are primarily due to temperatures above
85°F during the day and 70°F during the night together
with high rainfall and RH (Figure 5a). During the winter,
temperatures below 55°F during the night oen lower
marketable tomato yields (Figure 5b). In the spring season,
Figure 5. Overview of fall, winter, and spring minimum and maximum
temperatures and tomato marketable yields in Immokalee, FL
Credits: Monica Ozores-Hampton
high marketable tomato yields are due to ideal temperatures
during the day and night (70°F and 85°F) (Figure 5c).
In Southwest Florida, tomato variety recommendations are
normally based on disease resistance packages, especially
with regard to resistance to soil pathogens prevalent in
the area. Perhaps breeding for heat or cold tolerance or
high RH (i.e., hot and wet in the fall and cold and dry in
the winter) is not the primary selection factor a breeder
or grower considers, but the breeding is still towards
yield under Florida conditions. Table 2 shows two variety
recommendation programs for Southwest Florida (with
and without Fusarium crown rot) (Ozores-Hampton et al.
In conclusion, temperature and RH are usually out of the
grower’s control. Sometimes the only thing a grower can do
is wait for favorable weather conditions. If weather condi-
tions are optimal and other growers are not having ower
and fruit set problems, the grower should consider cultural
causes of tomato blossom drop and poor fruit set. Selecting
a suitable tomato variety, providing adequate N fertilizer,
watering suciently, and controlling insects and diseases
will potentially ensure high tomato yields. In Florida during
the early fall growing season, growers can get around the
heat issue by selecting heat-tolerant varieties.
Chen, J. T., and P. Henson. 2001. “Summer tomato produc-
tion using fruit setting hormones.” AVRDC February
2001C # 01-511.
Chester, T. 2004. “Tomato harvest versus planting date.” Ac-
cessed July 12, 2011. http://tchester.org/analysis/tomatoes/.
Cox, B., O. Tilth, and T. Coolong. 2011. “Management
of non-pathogenic fruit disorders of tomato in organic
production systems.” University of Kentucky Extension.
Accessed June 29. http://www.extension.org/article/18629.
Levy, A., H. D. Rabinowitch, and N. Kedar. 1978. “Morpho-
logical and physiological characters aecting ower drop
and fruit set of tomatoes at high temperatures.” Euphytica
Mills, L. 1988. Common tomato disorders under desert
conditions. FS-88-60. Reno: University of Nevada Coopera-
tive Extension. http://www.unce.unr.edu/publications/les/
Minges, P. A., and L. K. Mann. 1949. “Improving tomato
fruit set.” California Agriculture July: 8–12.
Olson, S. M. 2009. Physiological, nutritional, and other
disorders of tomato fruit. HS954. Gainesville: University of
Florida Institute of Food and Agricultural Sciences. http://
Ozores-Hampton, M., and G. McAvoy. 2010. “What causes
blossom drop in tomatoes?” e Tomato Magazine 14(4):
Ozores-Hampton, M.,G. McAvoy, S. Olson, K. Cushman,
and N. Roe. 2011. Tomato varieties for Florida — Florida
“red rounds,” plum, cherries, and grapes. HS1189. Gaines-
ville: University of Florida Institute of Food and Agricul-
tural Sciences. http://edis.ifas.u.edu/hs1189.
Ozores-Hampton, M. P., E. Simonne, E. McAvoy, P. Stansly,
S. Shukla, P. Roberts, F. Roka, T. Obreza, K. Cushman, P.
Gilreath, and D. Parmenter. 2006. “Nitrogen BMP eorts
with tomato production in Florida: Update for 2005-2006
season.” Proc. Fla. State Hort. Soc. 119: 284–288.
Zitter, T. A., and S. Reiners. 2004. “Common tomato fruit
disorders.” Vegetable MD Online. Cornell University.
Accessed June 29, 2011. http://vegetablemdonline.ppath.
Table 1. Summary of optimal temperatures for tomato-owering production and fruit set
Temperature (°F) Duration Eect
Above 85°F Several days Flower drop and fruit abort
F 4 hours Flower drop
Above 70°F Several days Flower drop
Below 55°F Several days Flower drop
Table 2. Tomato variety recommendations based on disease incidence, ower production, and fruit set in Immokalee, FL
Month Week 1 Week 2 Week 3 Week 4
No Fusarium crown rot
August ‘Phoenix’/FL 91 ‘Phoenix’/FL 91 ‘Phoenix’/FL 91 ‘Phoenix’/FL 91
September FL 91/FL 47 FL 91/FL 47 FL 47 FL 47
October FL 47 FL 47 FL 47 FL 47
November FL 47 FL 47 FL 47 FL 47
December FL 47/’Tygress’/SVR 200 FL 47/’Tygress’/SVR 200 ‘Tygress’/SVR 200 ‘Tygress’/SVR 200
January FL 47/’Tygress’/SVR 200 FL 47/’Tygress’/SVR 200 FL 47/’Tygress’/ SVR 200 FL 47/’ Tygress’/SVR 200
Fusarium crown rot
August ‘Phoenix’ ‘Phoenix’ ‘Phoenix’ ‘Phoenix’
September ‘Sunkeeper’/’Crown Jewel’ ‘Sunkeeper’/’Crown Jewel’ ‘Sunkeeper’/’Crown Jewel’ ‘Sunkeeper’/’Soraya’
October ‘Soraya’/BHN 585 ‘Soraya’/BHN 585 ‘Soraya’/BHN 585 ‘Soraya’/BHN 585
November ‘Soraya’/BHN 585 ‘Soraya’/BHN 585 ‘Soraya’/BHN 585 ‘Soraya’/BHN 585
December ‘Sebring’/BHN 585 ‘Sebring’/BHN 585 ‘Sebring’/BHN 585 ‘Sebring’/BHN 585
January ‘Sebring’/BHN 585 ‘Sebring’/BHN 585 ‘Sebring’/BHN 585 ‘Sebring’/BHN 585
Note: While this list includes a number of varieties currently popular with Florida growers, it is by no means a comprehensive list of all potential
varieties that may be adapted to the state under the above conditions.