Amador, Jose M.

English

Texas A&M University

L-2316
Texas Agricultural Extension Service
Texas Citrus
Diseases Affecting the Fruit
Jose M. Amador*
Diseases that primarily affect citrus fruit are
usually of most concern to handlers and shippers.
Many, however, begin in the orchard and can be
reduced if proper measures are taken. These
measures include avoiding picking fruit while it is
wet from rain or dew and using lined boxes and
trailers to minimize damage to the surface of the
fruit.
Small lesions may be caused by fingernails,
sharp objects and minor bruises. These openings
on the surface of the fruit, although unseen, make
it possible for microorganisms to gain entrance
into the fruit. Sanitation in the field and packing
house also is of the utmost importance. Infection
can be decreased by preventing fruit from coming
in contact with the soil and keeping harvest bags,
field boxes, trailers and trucks clean of debris.
Most post-harvest diseases can be avoided if
management and personnel are aware of the
importance of keeping the fruit free of damage
and contamination.
Many post-harvest diseases occur on citrus.
Only a few of the most common diseases are
discussed in this publication.
Melanose
Of all citrus fruits, grapefruit is affected the
most by melanose. Control of this disease plays an
important role in the Valley, particularly in the
production of gift fruit, because the disease greatly
affects the appearance of the fruit. Small, brown,
raised spots are found on the fruit. Usually,
numerous spots coalesce into a big area, resulting
in the phase of the disease known as Hmudcake
melanose." At other times, Htearstains" are found
on the fruit as the result of spores being washed
·Extension plant pathologist, The Texas A&M University System.
down in water from dew or rain. Infection and
disease development occur only in the orchard
when the fruit is small. Therefore, no spread or
contamination of other fruit occurs during pro-
cessing and storage.
Mudcake or sandpaper symptoms of melanose on
grapefruit.
Tearstaining caused by melanose spores washed
down the fruit by dew or rain.
Texas Agricultural Extension Service. Zerle L. Carpenter, Director. The Texas A&M University System. College Station, Texas
~~--------------
Greasy Spot
Although this disease is primarily a problem on
leaves, the fungus also can infect the fruit. Infection
occurs on cells surrounding pores, causing the fruit
to become spotted or stippled. Areas surrounding
these spots do not color properly because the
cholorphyll present in the cells fails to disappear.
If the spots are numerous, the fruit becomes un-
sightly, resulting in downgrading.
Fruit attacked by greasy spot fungus of guard
cells of stomata; adjacent cells remain green longer
than normal.
Flyspeck
The disease derives its name from the small
black specks formed on the rind in areas im-
mediately surrounding the oil glands. The fungus
that causes this disease prevents infected spots
from attaining the typical yellow color of mature
citrus fruit. The contrast between green and yellow
color lowers fruit grade, even though there is no
effect on fruit or juice quality. Thus, it is of little
consequence to fruit used for processing.
No effective economic program has been
developed for the control of flyspeck. Tests with
fungicide sprays in the summer have increased the
percentage of clean fruit in some cases.
Rind-Oil Spot
Also known as oleocellosis, this disease has
caused heavy losses to growers and shippers of
Marrs and navel oranges picked early in the
season with green rinds. It also may affect other
citrus varieties. The spotting is caused by oil
released from oil glands. The extruded oil kills
rind cells, causing them to turn brown. The spots
may vary from less than 0.5 inch in diameter to
large, irregular areas involving much of the fruit's
surface. The spots remain brown in contrast to the
yellow color of the normal rind after degreening
treatment. Fruits harvested wet are more seriously
damaged by this disorder.
Fruit should be picked when the fruit surface is
dry and should be handled carefully so that oil
glands are not punctured or ruptured. Rind-oil
spot can be prevented or reduced by: (1) picking
fruit in afternoons of clear, sunny days, (2)
deferring picking 2 or 3 days after a rain or an
irrigation, (3) using fiberboard-lined field boxes or
padded trailers and (4) having pickers use cotton
gloves.
Brown Rot
This fruit disease is caused by the same species
of Phytophthora that causes foot rot. The fungus
can attack fruit on the tree during periods of
excessive rains or during irrigation. Infection by
the fungus results in decayed areas that are brown,
firm and leathery. At first, the fungus cannot be
observed on the fruit. Later, a white velvety
growth appears on the surface of the fruit,
accompanied by a strong fermenting odor. Because
the fungus is commonly found in the soil, fruit low
on trees often is infected by rain-splashed soil.
Winds can spread the actively growing fungus to
fruit in the upper tree. The fruit must be wet for
some time before infection by the brown rot
fungus occurs.
The best control for brown rot is sanitation
during transit and in the packinghouse. Dis-
infecting the boxes is important; treatment with
disinfectant solutions and refrigeration are effective
for prevention.
Stem End Decay
This disease is caused by the fungus Diplodia
natalensis and often is detected at the packing-
house or in transit. Decay occurs around the stem
end and advances in streaks down the side of the
fruit. There is no fungal growth on the surface of
the fruit.
Decay is reduced by dipping the fruit in fungicide
solutions before placement in degreening rooms.
----------------~
Promptness in handling and shipping, as well as
refrigeration during transit, help reduce losses
caused by stem end decay.
Brown discoloration from stem end decay.
Green and Blue Molds
Green mold, the most important of these two
post-harvest diseases, is caused by the fungus
Penicillium digitatum. A rapid breakdown occurs
in fruit punctured or bruised during harvesting
and packing operations. The fungus enters the
fruit through wounds. Therefore, the disease can
occur on fruit on the tree, in the packinghouse, in
transit, in storage and in the marketplace. A white
mold is first seen growing on the peel. The mold
later turns green because of the large number of
green spores produced. Decayed fruit becomes soft
and shrinks.
Green mold (left) and blue mold (right) cause soft
decay of fruit, accompanied by heavy sporulation
of casual organisms.
As its name implies, blue mold, caused by the
fungus Penicillium italicum, differs from green
mold by the bluer color of the powdery mass of
spores that develops over the surface of the fruit.
Conditions favoring the two diseases are similar.
Both fungi grow best at a temperature of 75° F
and their development is slowed by lower temper-
atures. Cooling citrus fruit during storage and
shipping is an effective way to decrease damage.
Losses from green and blue molds also can be
reduced by taking precautions at harvest and in
transit not to injure the fruit and by treating the
fruit in the packing shed with a fungicide solution.
Grapefruit Chilling Injury
Most citrus fruit can be injured when exposed to
low temperatures for extended periods of time
even though these temperatures remain well over
the freezing point. Grapefruit is more susceptible
than oranges to damage caused by chilling
temperatures. The symptoms are varied, consisting
usually of irregular, superficial discoloration of the
surface of the fruit and rind pitting. The size of
the sunken lesions tends to be smaller and lesions
are more numerous as the temperature nears
32°F.
Chilling injury to citrus fruit can be avoided by
carefully selecting temperatures for citrus storage
or transport. However, because rot and decay
increase as the temperature increases, a proper
balance must be maintained. Fruit must be picked
at proper maturity and handled carefully both in
the field and in the packinghouse to avoid chilling
injury.
Chilling injury of citrus fruit.
@\---------------------
Chemical Damage
Many chemicals are used in the production of
citrus in South, Texas. Herbicides, fungicides,
insecticides and acaricides are needed to guarantee
maximum production of marketable fruit. Although
the proper application of these products will not
result in damage to tree or fruit, sometimes
mixing several products or applying these under
certain atmospheric conditions will result in
spotting, pitting or other damage to leaves and
fruit. Because of the intensive agriculture practiced
in the Valley, orchards often are located next to
fields where other crops are grown. As a result,
products that can be harmful to citrus, such as a
cotton defoliant, sometimes are applied in close
proximity. Care is needed in applying these
products in the proper concentrations and avoiding
weather conditions that could result in damage.
Chemical damage to fruit may resemble symptoms
of parasitic diseases.
Acknowledgement
Appreciation is expressed to Pete Timmer and Mike Davis, former plant pathologists,
Texas A&I University Citrus Center, Weslaco, Texas, for photographs in this publication.
Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socioeconomic
level, race, color, sex, religion, handicap or national origin.
Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as
amended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Zerle L. Carpenter, Director, Texas
Agricultural Extension Service, The Texas A&M University System.
1.5M-8-88, New HORT 2-2; PP


Texas Citrus Diseases Affecting the Fruit.

Texas A&amp;M Repository

L-2316Texas Agricultural Extension ServiceTexas CitrusDiseases Affecting the FruitJose M. Amador*Diseases that primarily affect citrus fruit areusually of most concern to handlers and shippers.Many, however, begin in the orchard and can bereduced if proper measures are taken. Thesemeasures include avoiding picking fruit while it iswet from rain or dew and using lined boxes andtrailers to minimize damage to the surface of thefruit.Small lesions may be caused by fingernails,sharp objects and minor bruises. These openingson the surface of the fruit, although unseen, makeit possible for microorganisms to gain entranceinto the fruit. Sanitation in the field and packinghouse also is of the utmost importance. Infectioncan be decreased by preventing fruit from comingin contact with the soil and keeping harvest bags,field boxes, trailers and trucks clean of debris.Most post-harvest diseases can be avoided ifmanagement and personnel are aware of theimportance of keeping the fruit free of damageand contamination.Many post-harvest diseases occur on citrus.Only a few of the most common diseases arediscussed in this publication.MelanoseOf all citrus fruits, grapefruit is affected themost by melanose. Control of this disease plays animportant role in the Valley, particularly in theproduction of gift fruit, because the disease greatlyaffects the appearance of the fruit. Small, brown,raised spots are found on the fruit. Usually,numerous spots coalesce into a big area, resultingin the phase of the disease known as Hmudcakemelanose." At other times, Htearstains" are foundon the fruit as the result of spores being washed·Extension plant pathologist, The Texas A&M University System.down in water from dew or rain. Infection anddisease development occur only in the orchardwhen the fruit is small. Therefore, no spread orcontamination of other fruit occurs during pro-cessing and storage.Mudcake or sandpaper symptoms of melanose ongrapefruit.Tearstaining caused by melanose spores washeddown the fruit by dew or rain.Texas Agricultural Extension Service. Zerle L. Carpenter, Director. The Texas A&M University System. College Station, Texas~~--------------Greasy SpotAlthough this disease is primarily a problem onleaves, the fungus also can infect the fruit. Infectionoccurs on cells surrounding pores, causing the fruitto become spotted or stippled. Areas surroundingthese spots do not color properly because thecholorphyll present in the cells fails to disappear.If the spots are numerous, the fruit becomes un-sightly, resulting in downgrading.Fruit attacked by greasy spot fungus of guardcells of stomata; adjacent cells remain green longerthan normal.FlyspeckThe disease derives its name from the smallblack specks formed on the rind in areas im-mediately surrounding the oil glands. The fungusthat causes this disease prevents infected spotsfrom attaining the typical yellow color of maturecitrus fruit. The contrast between green and yellowcolor lowers fruit grade, even though there is noeffect on fruit or juice quality. Thus, it is of littleconsequence to fruit used for processing.No effective economic program has beendeveloped for the control of flyspeck. Tests withfungicide sprays in the summer have increased thepercentage of clean fruit in some cases.Rind-Oil SpotAlso known as oleocellosis, this disease hascaused heavy losses to growers and shippers ofMarrs and navel oranges picked early in theseason with green rinds. It also may affect othercitrus varieties. The spotting is caused by oilreleased from oil glands. The extruded oil killsrind cells, causing them to turn brown. The spotsmay vary from less than 0.5 inch in diameter tolarge, irregular areas involving much of the fruit'ssurface. The spots remain brown in contrast to theyellow color of the normal rind after degreeningtreatment. Fruits harvested wet are more seriouslydamaged by this disorder.Fruit should be picked when the fruit surface isdry and should be handled carefully so that oilglands are not punctured or ruptured. Rind-oilspot can be prevented or reduced by: (1) pickingfruit in afternoons of clear, sunny days, (2)deferring picking 2 or 3 days after a rain or anirrigation, (3) using fiberboard-lined field boxes orpadded trailers and (4) having pickers use cottongloves.Brown RotThis fruit disease is caused by the same speciesof Phytophthora that causes foot rot. The funguscan attack fruit on the tree during periods ofexcessive rains or during irrigation. Infection bythe fungus results in decayed areas that are brown,firm and leathery. At first, the fungus cannot beobserved on the fruit. Later, a white velvetygrowth appears on the surface of the fruit,accompanied by a strong fermenting odor. Becausethe fungus is commonly found in the soil, fruit lowon trees often is infected by rain-splashed soil.Winds can spread the actively growing fungus tofruit in the upper tree. The fruit must be wet forsome time before infection by the brown rotfungus occurs.The best control for brown rot is sanitationduring transit and in the packinghouse. Dis-infecting the boxes is important; treatment withdisinfectant solutions and refrigeration are effectivefor prevention.Stem End DecayThis disease is caused by the fungus Diplodianatalensis and often is detected at the packing-house or in transit. Decay occurs around the stemend and advances in streaks down the side of thefruit. There is no fungal growth on the surface ofthe fruit.Decay is reduced by dipping the fruit in fungicidesolutions before placement in degreening rooms.----------------~Promptness in handling and shipping, as well asrefrigeration during transit, help reduce lossescaused by stem end decay.Brown discoloration from stem end decay.Green and Blue MoldsGreen mold, the most important of these twopost-harvest diseases, is caused by the fungusPenicillium digitatum. A rapid breakdown occursin fruit punctured or bruised during harvestingand packing operations. The fungus enters thefruit through wounds. Therefore, the disease canoccur on fruit on the tree, in the packinghouse, intransit, in storage and in the marketplace. A whitemold is first seen growing on the peel. The moldlater turns green because of the large number ofgreen spores produced. Decayed fruit becomes softand shrinks.Green mold (left) and blue mold (right) cause softdecay of fruit, accompanied by heavy sporulationof casual organisms.As its name implies, blue mold, caused by thefungus Penicillium italicum, differs from greenmold by the bluer color of the powdery mass ofspores that develops over the surface of the fruit.Conditions favoring the two diseases are similar.Both fungi grow best at a temperature of 75° Fand their development is slowed by lower temper-atures. Cooling citrus fruit during storage andshipping is an effective way to decrease damage.Losses from green and blue molds also can bereduced by taking precautions at harvest and intransit not to injure the fruit and by treating thefruit in the packing shed with a fungicide solution.Grapefruit Chilling InjuryMost citrus fruit can be injured when exposed tolow temperatures for extended periods of timeeven though these temperatures remain well overthe freezing point. Grapefruit is more susceptiblethan oranges to damage caused by chillingtemperatures. The symptoms are varied, consistingusually of irregular, superficial discoloration of thesurface of the fruit and rind pitting. The size ofthe sunken lesions tends to be smaller and lesionsare more numerous as the temperature nears32°F.Chilling injury to citrus fruit can be avoided bycarefully selecting temperatures for citrus storageor transport. However, because rot and decayincrease as the temperature increases, a properbalance must be maintained. Fruit must be pickedat proper maturity and handled carefully both inthe field and in the packinghouse to avoid chillinginjury.Chilling injury of citrus fruit.@\---------------------Chemical DamageMany chemicals are used in the production ofcitrus in South, Texas. Herbicides, fungicides,insecticides and acaricides are needed to guaranteemaximum production of marketable fruit. Althoughthe proper application of these products will notresult in damage to tree or fruit, sometimesmixing several products or applying these undercertain atmospheric conditions will result inspotting, pitting or other damage to leaves andfruit. Because of the intensive agriculture practicedin the Valley, orchards often are located next tofields where other crops are grown. As a result,products that can be harmful to citrus, such as acotton defoliant, sometimes are applied in closeproximity. Care is needed in applying theseproducts in the proper concentrations and avoidingweather conditions that could result in damage.Chemical damage to fruit may resemble symptomsof parasitic diseases.AcknowledgementAppreciation is expressed to Pete Timmer and Mike Davis, former plant pathologists,Texas A&I University Citrus Center, Weslaco, Texas, for photographs in this publication.Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socioeconomiclevel, race, color, sex, religion, handicap or national origin.Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, asamended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Zerle L. Carpenter, Director, TexasAgricultural Extension Service, The Texas A&M University System.1.5M-8-88, New HORT 2-2; PP

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Texas Citrus Diseases Affecting the Fruit.

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Texas Citrus Diseases Affecting the Fruit.

Abstract

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Full text

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Texas A&M University

Texas A&amp;M Repository

Texas A&M Repository