The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
Gulf Coast Station Mimeo Report 57-2 (Rev. 56-4) Y A
t DEC 171956p-
CONTROL OF BLOSSOM-END ROT OF TOMATOES EC 17 1956
0. M. Geraldson
The physiological disorder of tomatoes known as blossom-end rot is of
general occurrence wherever tomatoes are grown. In Florida, where approximately
50,000 acres of tomatoes are grown annually, estimated average losses amount to
3-5 percent of a crop that is valued from $500 to $2500 per acre. A loss of
fruit as high as 50 to 75 percent has been observed in some fields. Certain
fields or areas tend to produce varying amounts of blossom-end rot every season
while other fields may be affected one season, but not the next. There is also
considerable variation in the susceptibility of different varieties.
Blossom-end rot first becomes nppnrent as a water-soaked area under the
fruit wall on the blossom end of the fruit. The lesion usually develops rapidly,
eventually resulting in a blackened, dry, sunken, leathery spot. The dead tissue
is frequently attacked by saprophytic organisms (which feed on dead and dying tis-
sue). Another form of the disorder occurs as an internal browning or blackening
and may be present without the characteristic end rot being visible.
Recent research at the Gulf Coast Experiment Station hns indicated that
a deficiency of calcium is a fundamental cause of blossom-end rot. All of the
factors, frequently associated with the prevalence and severity of blossom-end
rot of tomatoes, can be grouped into two major categories according to the mechan-
ism by which they adversely affect calcium uptake. These are as follows:
1. Excessive soluble magnesium, potassium, sodium or ammonium salts or
a deficiency of soluble calcium salts (low calcium ratio) cause a decreased calci-
um uptake and an increased prevalence and severity of blossom-end rot. Comparing
equal amounts of the competitive salts indicates that ammonium decreases calcium
uptake to the greatest degree; sodium the least.
2. Excess total salts also can cause a calcium deficiency and has fre-
quently been associated with blossom-end rot even when the measurable calcium
ratio is considered high or adequate.
Needless to say, excess salts plus a low calcium ratio are most favor-
able for severe outbreaks of blossom-end rot.
Unfavorable moisture relationships have been associated more often
with blossom-end rot and blackheart than any other factor. The role of moisture
is considered as secondary in that it facilitates the operation of the primary
factors. Salts, during dry weather or as a result of fertilizer top dressings,
accumulate in the surface soil and rainfall moves these salts downward into the
'effective' root zone, decreasing the calcium ratio and often also increasing
total salt concentration in that zone. Insufficient soil moisture (decreasing
the soil moisture concentrates the salts already present) as well as addition
and accumulation of fertilizers can cause excessive concentrations of salts. Ex-
cessive soil moisture favors the accumulation of ammonium salts inhich on an equiv-
alent basis (compared with the other cations) causes the most severe calcium de-
Excess soluble salt and excess of certain nutrients such as nitrogen
and potash have frequently been associated with the prevalence and severity of
blackheart and blossom-end rot. Additions of lime or superphosphate have some-
times been associated with a reduction of the incidence. These factors would bo
considered primary in that they directly affect the calcium rating or total splt
Rapid growth, another associated factor, would be considered as accen-
tuating because it tends to increase the calcium requirement per unit of time.
A consistent supply of calcium from the soil solution is especially
important because for all practical purposes, calcium within the plant is not
trenslocated from older plant tissue to younger. Therefore, the soil solution
supply must be constant as well as adequate at all times. Any combination of
factors that causes the plant requirement for calcium to exceed the supply,
whether it is of a temporary nature or a deficiency of longer duration, can be
a3soeinted with the disorder.
1. Primary objective maintain to the best degree possible a favorable
calcium ratio by supplying more soluble calcium salts and avoiding excesses, as
much as possible, of soluble potassium, magnesium or ammonium salts as well as
excess total soluble salts.
Most virgin sandy soils in Florida contain insufficient amounts of poten-
tially soluble calcium. Calcium from the common liming materials is usually only
slowly soluble. When liming materials containing magnesium are utilized, less
calcium as well as greater amounts of a competitive salt are being supplied pr"
,nit of liming material. However, the more soluble magnesium, potassium or ?-1-
mcnium salts, supplied mainly from fertilizers and decomposing organic material,
are potentially main sources of competitive soluble salts. Amounts of nitrate
or ammonium nitrogen can vary with the amount and rate of breakdown of organic
matter as well as with amounts added in fertilizers. A high ammonium level i.
favored by low soil pH's and excessive soil moisture. (It is not recommended
that the nitrate sources of nitrogen replace the ammonium, because excess nitrate
can inczsase the calcium requirement). Superphosphate, gypsum, calcium nitrat.,
and calcium chloride are good sources of potential soil solution calcium. S.:ils
cropped for a number of years and receiving periodic additions of liming material
and superphosphate gradually accumulate a good supply of potentially soluble cal-
cium. The subsoil calcium, whether native or due to movement from that added to
the top soil, is also important when considering the calcium supplying capacity
of a soil.
2. Supplementary Objective periodically utilizing 4 pounds of calcium
chloride/100 gal./acre as a foliar spray during the time when the plant requile-
r.ent is expected to exceed the supply.
Timing is the key to successful use of calcium sprays for control of
blossom-end rot and is governed to a great extent by considerations discussed
above. Calcium sprays should be applied within 24-48 hours after rains (es-
pecially if surface salts had accumulated and have been leached into the 'effec-
tive root zone. When excess salts are causing blossom-end rot, sprays are the
only successful means of supplying the calcium soil amendments in such cases
are generally not recommended. Sprays should also be used during period of mo"t
rapid growth. Calcium sprays should always be considered as supplementary to that
supplied from the soil solution and used accordingly.
If trouble is anticipated in the immediate future or if blossom-end rot
is developing, a calcium chloride spray (4#/100 gal. has been mixed and applied
with most fungicides and insecticides with no observed or known ill effects) can
be used as frequently as twice a week until the unfavorable balance no longer ea:-
ists. A regular spray program cannot be recommended because prolonged perioic.s
application may cause a leaf burn (found to be serious only during hot weather and
at concentrations in excess of 4#/100 gal.) Also such a procedure, if on a weekly
basis, may not necessarily be successful in controlling blossom-end rot because
proper timing often requires more frequent application.
The interrelated effects of the several contributing factors will be -'-
centuated to the degree the primary objective (favorable calcium ratio) of the con-
trol method has been neglected and thus make the supplementary objective (calc.:!-
sprays) that much more difficult.
Points of Emphasis in Control of Blossom-end Rot of Tomatoes
1. Florida tomato soils often contain insufficient amounts of soluble cal-
cinm end application of such a material as gypsum is frequently recommended as a
moans of obtaining a more favorable calcium ratio.
2. Overall foliage sprays supply calcium to the leaves which probably sl.oows
more of the limited soil solution calcium to reach the fruit and thus prevent de-
velopment of blossom-end rot. Although sprays are successfully used for control,
it is not as efficient as if the calcium could be supplied directly into the fruit.
3. Depending on the causal factors, various combinations of the primary end
supplementary objectives of the control method are recommended to try and insure a
constant and adequate supply of calcium at all times.