REVIEW OF COMMON DISEASES IN
AVOCADO, PINEAPPLE & CITRUS
DISEASES IN AVOCADO
• Blast and bacterial fruit spot : Pseudomonas syringae
• Crown gall : Agrobacterium tumefaciens
• Bacterial canker : Pseudomonas syringae
• Anthracnose : Colletotrichum gloeosporioides
Glomerella cingulata [teleomorph]Armillaria
• Shoestring root rot : Armillaria mellea
Rhizomorpha subcorticalis [anamorph]
• Black mildew : Asteridiella perseae
• Branch canker : Botryosphaeria disrupta
• Butt rot : Ganoderma zonatum
• Cercospora spot (blotch) : Pseudocercospora purpurea
• Clitocybe root rot : Armillaria tabescens
• Collar rot :Sclerotinia sclerotiorum
• Dematophora root rot : Dematophora necatrix
Rosellinia necatrix [teleomorph]
• Dieback : Diplodia cacaoicola
• Fruit rot (includes stem end rot & fruit spots) : Botryosphaeria obtusa
• Heart rot : Oxyporus latemarginatus
• Leaf spot : Bipolaris sorokiniana
Cochliobolus sativus [teleomorph]
• Phomopsis spot : Phomopsis spp.
• Physalospora canker : Physalospora perseae
• Root rot : Pythium spp.
• Rosellinia root rot : Rosellinia bunodes
• Phytophthora root rot : Phytophthora cinnamomi
• SunblotchAvocado : sunblotch viroid
• Trunk pitting : Graft transmissible agent
Miscellaneous diseases and disorders
• Algal spot : Cephaleuros virescens Kunze
• Blackstreak : Unknown cause
• Dieback : Copper deficiency
• Edema : Physiological
• Littleleaf rosette :Zinc deficiency
• TipburnExcess :mineral salts
Glomerella cingulata [teleomorph]Armillaria
• Anthracnose symptoms can develop on flowers, fruit, leaves, or twigs
• Infected fruit is the most serious concern, but most fruit damage does
until after harvest
• Unhealthy or dead leaves are the most obvious symptom in groves.
• Spots form on leaves, beginning as yellow, then brown discolorations
that coalesce into large dead areas. Necrosis occurs across or
between leaf veins, on leaf margins, and most often at leaf tips. If
disease is severe, trees drop many leaves prematurely.
• New shoots can develop brown or purplish lesions, and shoots may
• Infected flower heads can turn dark and die without producing fruit, or
young fruit may form and then drop.
• After harvest, lesions become blacker, larger, and increasingly
sunken. Lesions eventually spread over the entire fruit surface and
throughout pulp. When the fruit is cut in half through one of the
lesions, rot extending into the flesh often exhibits a hemispherical
• Good cultural practices in the grove and proper preharvest and
postharvest fruit handling.
• Prune out dead limbs and twigs where fungi sporulate. If many dead
leaves are entwined in the canopy, knock them out of the tree.
• Prune low limbs to at least 2 feet (60 cm) off the ground to reduce
humidity within canopies by improving air circulation.
• Keep fruit dry and cool until sold.
• Postharvest temperature is especially critical to anthracnose
development. Cool fruit to 41°F as soon as possible after harvest.
Delays of longer than 6 hours before cooling and higher pulp (air)
temperatures during these delays will result in increased postharvest
• Chemical Control:
Anthracnose is rarely significant enough in California avocado groves
to warrant fungicide application. Copper compounds thoroughly
sprayed on healthy tissue can prevent infection
Avocado Black Streak
• Black streak appears as an elongated dark discoloration on bark.
• Small cankers can develop in a direction that parallels the direction of limb
or trunk growth but sometimes cankers encircle limbs or the trunk.
• On green shoots and young trees, lesions look like black blotches with
• Cankered bark develops shallow cracks that ooze sap, which dries as a
brownish or white powder on the bark surface.
• Black streak lesions can be very small or encompass the greater part of the
trunk. Cankers often first appear on the lower trunk and the underside of
lower limbs and then later appear higher in the tree. Scraping off bark over
the canker reveals shallow reddish brown to black areas.
• This discoloring forms mottled areas of dead and live tissue or merges into
one large necrotic area. It rarely extends into the wood and can be removed
easily by inserting a knife blade under the canker and prying upwards.
Because trees can die with very few lesions, the lesions appear to be a
symptom of the disease and not the cause of tree death.
• Maintaining plant health with good fertilizer and irrigation
practices, and preventing stress.
• Adequate irrigation with high quality water is believed to
be especially important.
Avocado Root Rot (Phytophthora
• Foliar symptoms of avocado root rot include small, pale green or
• Leaves often wilt and have brown, necrotic tips.
• There may be little leaf litter under infected trees.
• Small branches die back in the tree top, exposing other branches
and fruit to sunburn because of the lack of shading foliage.
• Fruit production declines, but diseased trees frequently set a heavy
crop of small fruit.
• Small, fibrous feeder roots are scarce at advanced stages of this
disease. Where present, small roots are black, brittle, and dead from
• Cultural Controls
Use cultural practices that promote growth of the tree while discouraging
growth of the pathogen.
• Provide favorable soil conditions
• Plant on well-drained soil, or improve drainage by planting on a soil berm,
deep-ripping impervious subsoils, or installing subsurface drains.
• ] Use certified disease-free nursery stock.
Request certified, disease-free plants, especially when planting new areas,
because disease is especially damaging to young trees.
• Plant resistant rootstocks. Certain rootstock cultivars are more tolerant of
root rot, including Dusa, Latas, and others.
• Prevent soil or water movement from infested areas.
• Soil solarization
• Establish a barrier. Establish the barrier around healthy sections of the
grove, at least two tree rows beyond where tests indicate the fungus is
• Irrigate carefully:Appropriate irrigation is the single most critical practice
for improving tree health and managing root rot.
• Use high-quality irrigation water:Irrigation water with high overall salinity
or an excess of boron, chloride, or sodium promotes infection of roots by
• Apply gypsum and mulch.:Create soil conditions that suppress
development of Phytophthora root rot
• Provide appropriate nutrition: Moderate amounts of nitrogen promote
good growth that helps avocado better tolerate root rot. Avoid excess
amounts of fertilizer, especially avoid large amounts of animal manures or
other products high in ammonia or salts. Avocado roots are sensitive to
ammonia and salts.
• Rotate crops.
• Chemical control: Certain phosphonate fungicides (phosphorous acid and
phosphonate compounds) can markedly improve trees' ability to tolerate,
resist, or recover from infection by Phytophthora cinnamomi. Good control
requires using fungicides in combination with other recommended practices,
such as careful irrigation practices and applying wood chip mulch.
( Xanthomonas campestris )
• Bacterial cankers appear as slightly sunken, dark areas on the bark
and vary in size from about 1 to 4 inches in diameter.
• Bark around cankers may crack. Fluid often oozes and dries,
leaving a white powder around or over the lesion.
• Usually cankers appear and spread upward in a line on one side of
the trunk or branch.
• Cutting under the bark surface reveals a decayed, reddish brown
necrotic pocket, which may contain liquid. Dark streaks in the wood
radiate out both above and below from the lesions.
• Severely affected trees may have pale, sparse foliage and low yields
on one branch or on the entire tree, but this is rare.
• Normally the disease is a minor problem. Usually no control is
necessary on established trees.
• If the disease is severe and yield is affected, remove the tree.
• Keep trees healthy and provide good cultural care.
• Provide appropriate amounts and frequency of irrigation and good
uniformity of water distribution among trees.
• Use certified, disease-free nursery stock if available. Regularly
inspect young trees and remove and dispose of young trees if they
• Nurseries should use stringent sanitation, regularly screen stock for
disease, and dispose of affected trees so they are not planted
Armillary Root Rot (Oak Root
( Armillaria mellea)
• Infected trees usually die prematurely, and young trees often die
quickly after infection.
• Mature trees may die quickly or slowly, or may recover at least
temporarily if conditions become good for tree growth and poor for
• Wilted, downward-hanging foliage is often the first obvious symptom
of Armillaria root rot. Other symptoms include foliage yellowing, leaf
drop, and dieback of upper limbs. During the rainy fall and winter,
groups of short-lived mushrooms often grow around the base of
• The most reliable sign of Armillaria root rot is fungal growth in
cambial tissue. If trees exhibit aboveground symptoms of infection,
cut off bark at the base of the tree and crown to diagnose the
presence of Armillaria mycelium.
• Provide a good growing environment and proper cultural practices
and use good sanitation to manage Armillaria root rot.
• Providing good drainage and avoiding excess irrigation are
• Shade any exposed root crowns from sunburn.
• Once trees die, remove them and any immediately adjacent trees
that may also be infected. Remove the stumps and as many root
pieces from the soil as possible. Thoroughly clean all soil from
equipment and leave soil on-site before removing equipment.
( Avocado Sunblotch)Viroid ASBVD
• Narrow yellow, red, or necrotic streaks that often are associated with
shallow lengthwise indentations along the twig.
• Fruit may show white or yellow blotches or streaks that mayor may
not be depressed.
• Fruit that remains green at maturity usually have white or yellowish
areas, while fruit that turns black usually have whitish areas that turn
red as the fruit mature.
• Leaves may have white or yellowish variegated areas, and they
often are deformed.
• Leaf symptoms are uncommon in the field. Rectangular cracking
and checking of the bark on the trunk and larger branches ("alligator
• Trees affected by the disease are often stunted and have sprawling
• Use of trees registered as disease-free, which involves
careful selection of disease-free scions and seed
• Trees with symptoms should be removed from the
orchard and remaining stumps should be killed. Indexing
of suspect orchards can be done to identify positive
trees. Pruning tools and harvesting clippers should be
sterilized between trees.
• It is important that pruning tools be disinfected before
moving from one tree to another.
(Sphaceloma perseae )
• On the fruit, spots are first oval, slightly raised, and brown to
purplish-brown. As the fruit mature, spots coalesce and the centres
of these spots become sunken . A large portion of the fruit may
• The lesions on the leaves are less well-known and less readily
observed, because they most often occur in the upper part of the
• Scab starts on leaves as discrete, small spots less than 1/8 inch (3.5
mm) in diameter. The spots are especially common on veins on the
underside of leaves. As leaf spots develop, they very often take on a
star-like pattern with the centre eventually dropping out to give a
• Symptoms on petioles and twigs include oval to elongate spots that
may, on hurried inspection, be confused with scale insects.
• Scab infection is favored by cool, moist conditions. This fungus is a
pathogen of young tissue.
• The fruit of all varieties become resistant once they reach about half
• Chemical sprays play an important role in the adequate control of
• There is considerable variability among varieties in their
susceptibility to scab. Lula, Hall, and most avocado seedlings are
• The varieties Booth 3, 5, 7, 8; Monroe; Choquette; and Trapp are
moderately susceptible. Waldin, Pollock, Booth 1, and Collins are
only slightly susceptible.
• Individual spots on leaves are very small and brown to purple in
• The angular appearance of the leaf spots is highly diagnostic Many
of these leaf spots are surrounded by yellow haloes.
• During the rainy season, grayish spore masses may be seen on the
surface of the spots with a hand lens. Individual leaf spots may
coalesce to form irregular areas of brown tissue.
• On the fruit, damage begins as small, irregular, brown spots that
enlarge and coalesce. Fissures often appear in these spots and are
very commonly entry points for the anthracnose fungus.
• Wind and rain play an important role in dissemination of C. purpurea
spores. Insects may also spread the pathogen. The most favorable
time of year for fruit infection appears to be during the rainy season
from May through September.
• The disease can be controlled to a great degree by
timely fungicide applications. However, control is more
difficult and requires more fungicide use for late-maturing
varieties, such as Lula and Choquette.
ALGAL LEAF SPOT
• Produces leaf spots on avocado, barely visible at first, but attaining
1/4 inch (6.2 mm) in diameter within a few months.
• The slightly raised roughly circular spots are green, yellowish-green,
or rust colored, with rather smooth or fringed margins.
• The alga eventually produces rust-colored, microscopic "spores" on
the raised surfaces of spots . For this reason, the disease is
sometimes called red alga spot.
• Young spots are visible on the upper leaf surface. Later, as they
enlarge and become gray to white, they discolor the opposite, lower
side of the leaf dark green, olive-green, or brown. A yellowish halo
may surround these old spots.
• Wind and rain carry the "spores" from diseased to healthy leaves.
Copper fungicides used for other avocado diseases have provided
control in the past.
• Wind and rain carry the "spores" from diseased to
• Copper fungicides can be used for control this.
• Powdery mildew, caused by the fungus Oidium, is a sporadic
disease affecting only avocado foliage.
• On young leaves the powdery mildew spots are dark green and
covered with a dry powdery layer of the causal fungus.
• On mature leaves, these spots turn purplish brown with a whitish
fungal growth. These spots eventually lose their undersurface fungal
coating, and leave distinctive net-like, brown blotches on the
• Yellowish areas may later appear on the upper leaf surface,
opposite the net-like lesions.
• Powdery mildew can occur in all seasons, but can be
particularly bad during cool, dry times of the year.
• If the trees are being sprayed for the other diseases
mentioned above, the disease severity is not thought to
be above a damage threshold for the crop.
DISEASES OF PINEAPPLE
Diseases of Pineapple
(Ananas comosus (L.) Merr.)
• Bacterial heart rot
• Anthracnose - Colletotrichum ananas
• Butt rot - Chalara paradoxa
• Leaf spot - Curvularia eragrostidis
• Phytophthora heart rot - Phytophthora
• Root rot - Pythium spp.
• Seedling blight - Pythium spp.
• White leaf spot - Chalara paradoxa
• Lesion - Pratylenchus brachyurus
• Reniform - Rotylenchulus reniformis
• Root-knot - Meloidogyne javanica
• Spiral - Helicotylenchus spp.
VIRUS AND VIRUSLIKE
• Mealy bug wilt
• Yellow spot
Tomato spotted wilt virus
FRUIT DISEASES (BACTERIAL)
• Acetic souring
Acetic acid bacteria
• Bacterial fruitlet brown rot
Erwinia ananas pv. ananas
• Fruit collapse
• Marbled fruit
Erwinia carotovora subsp
FRUIT DISEASES (FUNGAL)
• Aspergillus rot - Aspergillus flavus
• Botryodiplodia rot - Lasiodiplodia
• Black rot (water blister) - Chalara
• Fusariosis - Fusarium subglutinans
• Glassy spoilage - Yeast species
• Interfruitlet corking - Penicillium
• Leathery pocket - P. funiculosum
• Nigrospora fruit rot - Nigrospora sphaerica
• Phytophthora - Phytophthora nicotianae
• Rhizopus rot - Rhizopus oryzae
• Yeasty fermentation - Yeast species
BUTT ROT - Thielaviopsis
• Freshly cut or injured tissue is infected
• Soft black rot with dark colored mycelium
and arthrospores develops
• Freshly cut pineapple should not be planted
unless treated with a fungicide or dried out.
• To prevent the spread of the pathogen,
avoid wounds to tissue and remove infected
White leaf spot - Ceratocystis paradoxa/
The first symptoms of white leaf spot is
the appearance of small, light brown to
yellow spots on the middle or upper part
of the leaves.
• Under moist conditions the spots
increase in size, the infected tissues dry
out and show a grayish to white color
• Common pineapple disease, it causes only
slight damage to the pineapple crop. Due to
that no control measure would be justified.
Phytophthora heart rot-
• Symptoms of rotting appeared at the base
of the leaves, in the centre of the leaf
whorl (heart) of young non-flowering plants
• The leaves had turned brownish red and
could be easily pulled off. The base of the
infected leaves had dark brown to black
Leaves from plant with heart rot
• High rainfall and low temperatures favor the
• Dipping the propagating material in a
fungicide solution followed by one spray
application three to four weeks after
planting, and another spray application one
week after forcing
• Soil drainage has to be improved, and
Root rot- Pythium species
• Enhanced by high rainfall, low temperature, poor
drainage and alkaline reaction of the
• Infects the pineapple plant through the root tip and
the infection can occur at any stage of the plant
Change in color of the leaves from the normal
green to yellow, then brown.
The leaves curl and dry progressively from the tip
towards the base
Root Rot Symptoms
• cultural practices
Plants should be set on raised beds
soils should be
drain well and quickly
• Planting in infected soils should be carried out
in seasons unfavorable to P. cinnamomi
(to establish a good root system before
occurrence of conditions favorable to
• treat the propagating material before
planting, and/or to fumigate the soil to
reduce the initial inoculum.
• The soil pH plays an important role on
root rot development since the incidence
of the disease is reduced in lower pH soils.
Mealybug or pineapple wilt
caused by a complex of two viruses (PMWaV-1 and
PMWaV-2) with the mealybug (an insect) as their
Warm weather favours the build-up of mealybugs
• Older plants are less susceptible than younger plants
• plants become yellowish-red to bright red at the leaf
tips, this colouration spreading down the leaf
• inner heartleaves remain normal
• Severely infected plants become stunted and produce
small, undergrade and immature fruits.
• The first effect of the disease usually
appears in the roots, which stop growing,
collapse and then rot
• Results in leaves symptoms similar to the
effect of drought. The root system
collapses and rots before the first leaf
Red Leaf Symptom
• Use planting material from wilt-free areas.
• Plant resistant varieties if available. Some
varieties of pineapple are more resistant to
the virus than others,
• The variety Cayenne (and 'Masmerah') being
highly susceptible. 'Singapore Spanish'
shows some resistance
• Heating pineapple crowns in a large water
bath at 50°C for 30 minutes permitted 100%
plant survival and rendered 100% of the
plants free of pineapple wilt-associated-virus
• Control of the mealybugs using albolineum
oil (white oil) is one way to get rid of the
red leaf symptoms
Pink Disease- Acetobacter aceti
• Difficult to observe in the field since
outward symptoms are not apparent
• Development of a brown color in the flesh
when heating the infected fruits in canning
Pink disease symptoms on pineapple fruit slices originating from a
canned product. Healthy fruit (top), and diseased fruit (bottom).
• Harvesting the fruit before completely ripe
• Promoting fruit production in season
unfavorable to the disease development
• Dusting the fruits with Dissulfoton during
the open flower stage
Fruitlet core rot -Fusarium moniliforme
• light to dark brown soft rot of the fruitlet
• The disease extends from the base of the
style, nectary ducts or placenta towards
• Infected tissue becomes corky, thus
originating a dry rot
• Cross-section of fruit with fruitlet core rot
• In areas where pineapple is grown for canning,
leathery pocket is at times a serious disease since
it reduces slice recovery, thus resulting in losses
to the industry
• applying Endosulfan, 0.05% a.i., in 2500 l of
water/ha at 4 week intervals from 5 weeks before
forcing to 11 weeks post forcing
• Bacterial spot -Xanthomonas campestris
• Blast -Pseudomonas syringae
• Citrus canker -Xanthomonas axonopodis
Powdery mildew -Oidium tingitaninum
Anthracnose = wither-tip
Damping-off - Pythium sp.
Alternaria brown spot -Alternaria alternata
• Viral diseases
• Citrus mosaic-Satsuma dwarf-related virus
• Tristeza -Citrus Tristeza Virus(CTV)
• Citrus nematode-Tylenchulus
Citrus blast Lemon fruit showing
affecting twig of lesions caused by
citrus blast bacterium.
Powdery Mildew on
Orange Citrus Tree
Advanced symptoms Ringspots on fruit of 'Satsuma'
caused by the Citrus mandarin affected by Citrus
Tristeza virus in sweet mosaic virus.
• The citrus nematode,
causal agent of 'slow
decline' of citrus, is a
worm which feeds
within the roots of