Florida Citrus Fruit
Florida Agricultural Research and Educati n Center
Lake Alfred, Florida 33850
Florida Cooperative Extension Ser ce OCT 2 3 1987
Institute of Food and Agricultural Sci nces
University of Florida, Gainesvill
-Uriniversity of Fda
A. A. McCornack, W. F. Wardowski, and G. E. Brown'
Decay of Florida citrus can be greatly reduced with good
)ve management and handling practices during harvesting
d packing. The most common postharvest fungus diseases of
)rida citrus are stem-end rot (Diplodia natalensis or Phomopsis
ri) and green mold (Penicillium digitatum). Sour rot (Geo-
chum candidum) and anthracnose (Colletotrichum gloeospori-
les) can at times cause commercially important losses of
indarin-type citrus fruit.
After being picked, citrus fruit is subject to stem-end rind
eakdown, a peel injury caused by dehydration which predisposes
lit to decay. Rapid handling, holding fruit at high relative
midity, particularly during degreening, and applying a pro-
:tive wax coating are the best means of reducing stem-end
id breakdown. High relative humidity in storage rooms and
ring transit also helps to maintain fruit turgidity and fresh-
ss. When fruit is held in wooden containers such as pallet
xes or in wirebound containers, the relative humidity should
90 to 98%. For storage of fruit packed in fiberboard cartons,
native humidity should be lower (85-90%) to prevent carton
Tolerances-Florida state regulations specify that citrus fruit
ipped by a registered packinghouse must be treated with an
proved fungicide. As evidence of postharvest fungicidal treat-
ant, fruit must have a minimum residue set by the Florida
apartment of Citrus, Official Rules, Chapter 20-33. Five post-
,rvest citrus fungicides approved under Federal regulations
.d their maximum tolerances in the U.S.A.3 are:
Thiabendazole (TBZ) .................---------------. 10 ppm
Benomyl (Benlate) -........-........-- ...--------------------- 10 ppm
Sodium o-phenylphenate (SOPP) .....---....---------.-------- 10 ppm
Sec-butylamine (2-aminobutane) --.............-- ----...-- 30 ppm
Biphenyl (diphenyl) .......-- ......-- ------------------110 ppm
Florida Department of Citrus; Cooperative Extension Service,
IFAS; and Florida Department of Citrus, respectively.
All postharvest use rates are stated in terms of active ingredi-
Consult authors for export tolerances.
CUUIIui at, iu.lJ, bte.
SOPP (sodium o-phenylphenate) is more effective for control-
ling decay of oranges than of grapefruit or mandarin-type fruits.
SOPP reduces stem-end rot and green mold and provides some
control of sour rot and benzimidazole-resistant molds.
Concentration and Formulation-A 2% aqueous solution of
SOPP applied at pH 11.5 to 12.0 is the most effective treatment.
One formulation contains 2% SOPP, 0.2% sodium hydroxide for
pH control, and 1% examine. Water emulsion waxes with 1%
SOPP are also available. Soap and foam formulations for washing
fruit usually have little fungicidal value. (Residues are ex-
pressed in terms of o-phenylphenol).
Methods of Application-SOPP can be used to replace the
detergent during washing or can be applied to washed fruit.
During washing, SOPP may be applied as an aqueous recovery
flood or foam. Washer brushes should be rinsed at the end of
each day's run to remove SOPP residues. Washed fruit may be
treated with an aqueous recovery flood, foam, or water-based
wax containing SOPP. Fresh water should be used to rinse non-
waxed SOPP formulations from fruit after 2 to 3 minutes treat-
ment time. Concentrations of SOPP solutions, applied with hexa-
mine, should be maintained near 2.50 with a Brix hydrometer
standardized at 200C. The pH of aqueous solutions lacking hexa-
mine must be maintained at 11.5 to 12.0 to prevent peel injury.
Water-based waxes containing SOPP are nearly as effective
as aqueous treatments. Adequate wax should be applied to ob-
tain thorough coverage. Do not exceed the maximum legal resi-
due tolerance by applying waxes containing SOPP to fruit
treated with aqueous applications of this fungicide.
2-Aminobutane (sec-butylamine) controls green mold but is
less effective against stem-end rot, particularly that caused by
Diplodia natalensis. Sour rot and anthracnose are not controlled
by 2-aminobutane, but this fungicide has some value for com-
bating benzimidazole-resistant strains of green mold.
Concentration and Formulation-2-Aminobutane is usually
formulated as the phosphate salt and can be applied as a 1 to
2% aqueous solution.
Methods of Application-2-Aminobutane is applied to un-
washed fruit as an aqueous flood or nonrecovery spray or to
washed fruit after degreening and before waxing. Fruit should
not be rinsed after treatment with 2-aminobutane.
it is not effective against sour rot. Sporulation of green mold
oppressed and some control of benzimidazole-resistant molds
mcentration and Formulation-Diphenyl is a vapor-phase
ficide that must be applied where the vapor can be main-
ed. Diphenyl is impregnated into porous paper at the rate of
grams per each 11 in. by 17 in. pad. Individual fruit wraps
aining diphenyl are available for gift fruit. The distinctive
Sof this fungicide is objectionable to some people, but it soon
pates from the fruit when the pads are removed. The fungi-
I effect usually persists for nearly a week after the pads are
rated from the fruit. Diphenyl pads must be stored in air-
t containers as they soon lose their effectiveness in an open
ethods of Application-Diphenyl is commonly applied by
ing 2 pads in each 4/5 bushel carton of fruit. One pad is
lly placed over the bottom layer of fruit and the second
er the top layer. Diphenyl pads are especially recommended
n perforated plastic bags of fruit are packed in master car-
. Pads are placed in the master carton, not in the bags.
ie best application method for oranges, grapefruit, and
ins is in a closed carton or tight compartment filled with con-
ers of fruit packed with diphenyl pads. When diphenyl pads
used with mandarin-type fruits such as 'Dancy' tangerines,
'cotts', and tangelos, wirebound boxes or well ventilated
ons should be used to prevent excessive diphenyl residues.
iphenyl pads are well suited as a fungicide for small volume
fruit operations because fungicide application equipment is
required. Use in large commercial packinghouses is less
rable because of the labor cost associated with placing pads
Grading before Fungicidal Treatment
applying Fungicides to Graded Fruit-Fungicides should only
applied to fruit that is to be packed. Grade after washing and
ire fungicidal treatment, except when SOPP is used for
thing. An average packout of 60% means that fungicidal costs
be reduced by not treating 40% of the fruit.
ecay can be controlled by refrigeration, especially when fruit
been treated with a postharvest fungicide. Varietal differ-
!s must be considered when selecting temperatures for cool-
the reason for use. When a bagmaster carton is so labeled, the bags
of fruit packed in the carton do not require individual fungicide
Typical labels could read:
"Thiabendazole used as a fungicide."
"Sodium o-phenylphenate and biphenyl applied as fungi-
Labels must declare all fungicides used and must not include
fungicides that are not used. For labeling purposes, use the
first name of the fungicides as listed in the previous paragraph.
TBZ and Benlate
TBZ (thiabendazole) and Benlate benomyll) are the most
effective postharvest citrus fungicides. These materials, classi-
fied as benzimidazoles, are similar in fungicidal activity and are
generally applied by the same methods. Stem-end rot and green
mold are effectively controlled when either of these fungicides
is applied correctly. They provide some control of anthracnose,
but none of sour rot, black rot, and benzimidazole-resistant
strains of mold.
Concentration and Formulation-TBZ should be applied at a
concentration of 1,000 ppm (0.1%) either in a water-based wax
or as a water suspension. Similar applications may be made with
Benlate, using a concentration of 600 ppm (0.06%). Benlate can
also be applied in solvent-type waxes. Water-based wax Benlate
formulations must be freshly prepared because this fungicide
is unstable at the high pH level of such waxes. TBZ and Benlate
are only slightly soluble in water; therefore, suspensions must
be constantly agitated to insure uniform treatment.
Preharvest applications of Benlate 50W at 1 to 2 pounds/acre
will aid in reducing decay, particularly when postharvest fungi-
cide applications are delayed by degreening.
Methods of Application-Apply TBZ and Benlate as nonre-
covery sprays on unwashed fruit before degreening or on washed
fruit that has been "damp dried" with absorber (do-nut) rolls.
A recovery flood is not recommended because there is no rapid
method to determine the suspension strength of either TBZ or
Benlate. After a nonrecovery water application of TBZ or Ben-
late to washed fruit, excess moisture may require removal with
absorber rolls if dryer capacity is not adequate. Fruit should not
be brushed or rolled after waxes are applied, except for a half
turn midway through the drying operation.
ing, storing, or transporting, because of differential suscepti-
bility to chilling injury. Early grapefruit should be shipped at
600F, and the temperature may be reduced to 550F, then 500F
as the fruit becomes more mature. Late season grapefruit picked
from trees with new spring growth may again become highly
susceptible to chilling injury and should be shipped at 600F.
Transit temperatures for fruit that has been held in storage
should not exceed storage temperatures. The following table lists
recommended temperatures suitable for transportation to mar-
ket and for storage.
Variety Transita Storageb
Grapefruit 50-60 50-60
Lemons, limes 50 50
Mandarin-type fruits 50 40
Oranges 50 32-34
a. Temperatures for short-term storage and domestic transit.
b. Optimum temperatures for maximum storage life.
The postharvest fungicides mentioned in this publication have
been approved by the Food and Drug Administration and the
Environmental Protection Agency ONLY if residues do not ex-
ceed the specified tolerances. If postharvest fungicides are
handled, applied, or disposed of improperly, they may be in-
jurious to humans, domestic animals, desirable plants, pollinating
insects, fish, or other wildlife, and may contaminate water sup-
plies. Handle all pesticides with care. Follow instructions and
heed all precautions on the container label.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Cooperative Extension Service, IFAS, University of Florida
and United States Department of Agriculture, Cooperating
Joe N. Busby, Dean
Single copies free to residents of Florida. Bulk rates available upon request.
Please submit details on request to Chairman, Editorial Department,
Institute of Food and Agricultural Sciences, University of Florida,
Gainesville, Florida 32611.
This publication was printed at an annual cost of $330.87 or
61/2 per copy to provide information on how to reduce decay,
increase profits, and increase customer satisfaction for Florida