Tropical Fruits:Diagnostics

TROPICAL FRUITS: Pests and Nutritional Disorders

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Algal Leaf Spot (Cephaleuros virescens)

Algal leaf spot occurs commonly on mango and can be easily recognized by the presence of conspicuous orange, rust-colored, velutinous spots, which vary from 5 to 8 mm in diameter, on both leaf surfaces. The causal agent is a green alga. A wet or humid environment within the tree's canopy is conducive to the spread and establishment of the alga. Algal leaf spot can be managed by increasing tree vigor via proper fertilization and irrigation, by pruning the canopy and removing weeds beneath the trees to increase air circulation and sunlight penetration, and by wider tree spacing.

Alternaria Fruit Spot (Alternaria alternata)

Alternaria fruit spot is a major fruit disease in orchards grown in dry areas. Alternaria fruit spots are depressed, circular to oval lesions that eventually become black as a result of pathogen sporulation. The pathogen infects senescing petioles and produces large numbers of conidia on fruit surfaces. Alternaria fruit spot rarely develops on fruit kept or ripened at room temperatures after harvest. The best form of control is a biweekly application of chlorothalonil or mancozeb.

Alternaria Rot (Alternaria alternata)

Alternaria rot or black spot of mango causes blossom disease and postharvest fruit rot in ripening fruits. Small, black, circular spots develop around the lenticels. The pathogen also attacks mango inflorescences, resulting in a significant decrease in fruit-set. The origin of inoculum for the first fruit infections is infected leaves and twigs. Germinated conidia penetrate fruit lenticels making a wound not necessary for entry. The differences in disease incidence among stored mangos from different growing regions are closely related to the number of hours with relative humidity over 80% that occurred during fruit growth. The best control measures include a regular field spray program, postharvest fungicide treatment, and through enhanced ripening with ethylene.

Anthracnose and Fungal Scald (Colletotrichum musae)

Anthracnose occurs in all banana-producing countries. On yellowing fruit, brown blotches develop that become sunken and covered with orange or salmon-colored spore masses. Symptoms develop on green fruit following peel injury. Conidia of anthracnose occur primarily on dead banana trash and are common components of banana plantation microflora. Growth and sporulation are optimum at 27-30 °C and little growth occurs at temperatures below 15 °C. The disease also infects banana bracts, flowers, petioles, and leaves. Control of anthracnose and fungal scald begins with clean field practices.

Armillaria Root Rot (Armillaria mellea)

Armillaria root rot affects the major roots and crowns of avocado and usually occurs in small, limited areas and does not threaten the destruction of the grove. Infected trees may decline slowly and exhibit yellow leaves and poor growth, or they may undergo a rapid wilt and die with the dead leaves still attached. The pathogen's life cycle includes several morphological forms including basidiomes, basidiospores, mycelia, pseudosclerotia, and rhizomorphs. The fungus lives in the soil as a colonizer of large roots or other wood pieces, and it can not survive without such a food base. Colonization of the woody portion of the root follows, producing a wet rot that can be easily torn apart in the advanced stages of the disease. While the pathogen may be quite innocuous on hosts in undisturbed habitats, it can colonize entire root systems of plants after they have been cut during land clearing. Exposing the crowns and large roots of affected citrus to air has retarded the spread of the fungus in this host.

Avacado Anthracnose (Colletotrichum gloeosporioides)

Anthracnose causes fruit drop and rot and reduces the fruit shelf life during storage and transport. Anthracnose is the most common form of decay affecting mature avocado fruit. Large numbers of conidia of the fungus are produced on dead, infected twigs, leaves, and fruit that have not dropped. Infection takes place at any time from fruit-set to harvest. Since the fungus remains quiescent in the cuticle of unripe fruit, infection can be prevented either with protective treatments or by treating the fruit with postharvest fungicides that penetrate the infection site and good cultural practices. The export of high-quality avocados can be achieved by a combination of field and postharvest applications of fungicides, correct storage conditions, and the use of resistant cultivars.

Avacado Black Streak (ABS)

Avacado black streak appears after a period of environmental or cultural stress, such as insufficient water. Cankers usually appear first on the lower trunk or on the underside of a lower branch, but they appear occasionally on the upper trunk. Scraping the bark surface over the lesion reveals shallow, polymorphic, reddish brown dry areas that occasionally extend into the cambium. Other symptoms include yellowing, early bloom, branch dieback, leaf blotching, zinc deficiency, bunchy growth, wilting of foliage, and rapid death of new growth. Although there is some evidence of spread of the disease in the field, it has not been artificially transmitted. Current management consists of maintaining plant health with good fertilization and watering practices and preventing stress.

Avacado Scab (Sphaceloma perseae)

Scab is a serious problem on avocado in the humid tropics and subtropics. The most distinct scab symptoms occur on fruit. Lesions on leaves are less conspicuous, because they most often occur in the upper part of the tree canopy. Scab is exacerbated by cool, moist weather. The best form of control is to apply copper fungicides or benomyl to the trees.  

Bacterial Black Spot (Xanthomonas campestris pv mangiferaeindicae)

Bacterial black spot is found in most tropical and subtropical countries where mangos are cultivated. Mango leaves, stems, and fruit are all susceptible to infection. Stem lesions appear as blackened cankers that form longitudinal cracks and also exude gum. Fruit lesions develop as water-soaked halos around lenticels or wounds and soon become raised and then blacken and crack open. The pathogen lives year round as an epiphyte on mango, and high concentrations of inoculum reside in leaf and stem lesions. The causal agent survives for only a few days in soil and for a few months on plant debris incorporated into the soil. Resistance to bacterial black spot varies greatly among mango cultivars, and many of those developed in Florida are very susceptible. Sprays of copper compounds during rainy weather also combat the disease.

Bacterial Canker

Similar canker symptoms have been observed on trunks and branches of avocado in all the major avocado-growing areas of South Africa, in several counties of California, and in Australia. In each of the affected countries, cankerous lesions appear first as slightly sunken, darker areas on the bark where there is a dry, watery pocket beneath each sunken area. The watery, dry areas under the surfaces of cankers are typically colonized by a wide variety of bacteria. Bacterial canker presumably is spread through nursery practices, since young cankerous lesions occur on newly planted trees. Completely removing infected trees from groves and screening nursery stock for the presence of the pathogens are probably the most promising methods of control.

Bacterial Heart Rot (Erwinia chrysanthemi)

These diseases are mostly prevalent in South East Asia and affect the "Spanish" varieties more than others. Bacterial Heart Rot. Water-soaked lesions on the white, basal portions of leaves in the central whorl is an early symptom. The causal bacterium is disseminated by wind, wind-blown rain, and insects and ants. The fruit collapse phase usually appears on maturing fruit 2-3 weeks prior to normal ripening. Infection occurs at flowering or through wounds. Infected fruit should be destroyed or removed from the field.

Bacterial Soft Rot (Erwinia spp.)

Both rhizome and pseudostem tissues can be infected with bacterial soft rot. Rhizome rot occurs following the planting of suckers or rhizome pieces that have freshly cut surfaces. In general, the rhizome and pseudostem bacterial rots of banana are sporadic, poorly characterized, and result mainly from cultural practices that can be altered.

Banana

Bananas are treelike, perennial herbs, 2-9 m in height, that arise from large, subterranean rhizomes. Suckers are grouped shoots that arise laterally and in a radial fashion from the base of the rhizome. Primary roots, 5-8 mm in diameter, arise on the rhizome from beneath the base of the oldest surviving leaves. Upon flowering, the true stem and associated growing point rise from within the rhizome and emerge from the top and through the center of the pseudostem. Bananas are propagated vegetatively, either with suckers or with rhizome pieces. Bananas have high water requirements with a minimum of 25 mm per week is needed throughout the year for optimal growth. Bananas are heavy feeders. Exported bananas must be of high quality. Fruits intended for local consumption can be left on the plant until they are fully developed, whereas those that will be exported must be harvested when green and somewhat immature.

Banana Bunchy Top (BBT)

Banana bunchy top is the most important virus-induced disease and one of the five most important diseases that affect banana. The disease is transmitted by the banana aphid, Pentalonia nigronervosa. Bananas are vegetatively propagated. Because the symptoms are quite distinct when the disease is fully developed, primary identification has been based on symptoms in regions where the disease occurs. The best form of control is to use noninfected planting material and destroy all infected plants in the field.

Banana Streak (BSV)

This disease is characterized by yellow striate mosaic, broken lines, and diamond-shaped patterns along the veins. Foliar symptoms of the infection sometimes resemble those caused by the cucumber mosaic virus infection. Banana streak is transmitted in a semi-persistent manner by the citrus mealybug. The only other known host is sugarcane. Banana streak can be controlled effectively by the eradication of infected plants and the use of virus-free planting material.

Botryodiplodia Finger Rot (Botryodiplodia theobromae)

This finger rot is common in boxed bananas shipped from Central and South America to European markets when transit times exceed 14 days. Symptoms usually begin at the flower end of the finger or at a wound site. The disease is a common inhabitant of decaying banana trash and can be controlled by minimizing fruit injury, treating fruit with systemic fungicides, rapidly reducing fruit temperatures following harvest, and excluding overmature fruit from shipment.

Bract Mosaic

Bract mosaic is a newly recognized disease that occurs only in the Philippines and India. Symptoms may develop at any stage of plant development. Although the cause of bract disease is not known, a potyvirus is suspected because of the presence of flexuous rod-shaped particles in affected tissue and the transmission of the disease by aphids in a non-persistent manner. The best form of control is to use clean stock for new plantings and eliminate infected plants from the field.

Brown spot and Diamond Spot (Cercospora hayi)

Brown spot occurs on peduncles, fruit crowns, and fingers. Diamond spot first appears on the peel of green fruit as slightly raised, yellow spots that are 3-5 mm in diameter and is caused by a complex of fungi. Dead banana and weed foliage are the principal sources of inoculum for brown spot and diamond spot. The Fusarium species in the complex are prevalent on decaying and dead leaf trash where they sporulate under moist conditions. The same procedures used to control pitting disease will control brown spot and diamond spot.

Bud Rot and Nut Fall (Phytophthora spp.)

Bud rot is probably found wherever coconuts are grown. The heart leaf becomes yellow, wilts, collapses, and is removed easily from the tree. Affected nuts develop spotted dry areas, evident on the inside and outside of the nut, which are brown to black with yellow borders. Secondary infections by other microorganisms occur in the bud and nut. Bud rot and nut fall are probably spread primarily via rain-splashed zoospores. Species of Phytophthora require moist conditions to infect their hosts. The best form of control is through the use of fungicides.

Bumpy Fruit

The bumpy fruit disorder is associated with boron deficiency. Boron deficiency appears to be related to shallow, rocky soils and dry conditions. Applications of 0.25% borax to foliage and of 1-3 kg of elemental boron per hectare to the soil have increased petiole boron levels and prevented deficiency symptoms on subsequently formed fruit.

Bumpy Fruit Bumpy fruit causes a fruit deformation and bleeding of latex beginning at an early age and appear to become more severe as fruit get older. The bumpy appearance is the result of localized, deficient areas that stop growing. Adjacent unaffected tissue continues to enlarge, imparting a misshapen, bumpy appearance to the fruit.

Bunchy Top

The first symptom of bunchy top is a faint spotting of the upper leaves. Single insects of leafhoppers can transmit the bunchy top agent, which can also be transmitted by grafting. The best form of control is the use of resistant cultivars.

Burrowing Nematode Root Rot (Radopholus sireills)

The burrowing nematode occurs throughout the tropics and subtropics. The most obvious indication of nematode damage in bananas is the uprooting of plants. The burrowing nematodes enter primary roots, which are fleshy and of varying thicknesses, and feed exclusively on the cells in the cortex, progressively destroying the tissue. All stages of the disease are vermiform and motile and may be found in roots, rhizomes, and soil. Pathogenic variation occurs among populations from different regions and from other hosts. In areas not previously cultivated with bananas, the disease should be excluded by the use of noninfected planting material. There are a number of techniques for controlling nematodes in infested rhizomes including paring the diseased tissue, treating the rhizomes with hot water (15-25 minutes at 55 °C), dipping them in a nematicide suspension, or coating them with a nematicide contained in a clay-based slurry.

Butt and Black Rot (Ceratosystis paradoxa)

Because the pathogen is a wound parasite, the soft, black rot starts at the point at which seed material detaches from the mother plant. Black rot of the fruit is characterized by a soft, watery rot and white leaf spots are initially small, brownish, and wet. Infection of the pineapple fruit occurs through wounds. Storing seed material on the mother plants during dry weather provides excellent control. Black rot is commercially controlled in fresh fruit by minimizing the bruising of fruit during harvest and handling, by refrigeration, and with the use of chemicals.  

Cadang and Tinangaja (CCCVD)

Tinangaja leaf symptoms resemble those of cadang-cadang, but symptoms on nuts differ. The mode of spread of the disease is unknown. It can be detected in pollen, husks, and embryos of coconut. The discovery of viroidlike sequences related to the disease in coconuts in many areas indicates that movement of germ plasm between countries should be regulated. There are no control measures available.

Carpellody

Carpellody or "cat-face" fruit result when stamens develop abnormally into carpel-like fleshy structures.

Cercospora Black Spot (Cercospora papayae)

Cercospora black spot occurs wherever papayas are grown. Fruit spots start as tiny black dots that eventually enlarge to about 3 mm in diameter. Leaf spots are irregularly shaped, grayish white, and 1-5 mm in diameter. Primary inoculum comes from papaya leaves in nearby orchards. The best form of control is to apply protective fungicide sprays at 14- to 28-day intervals.

Cigar End Rot (Trachysphaera fructigena and Verticillium theobromae)

Cigar-end rot is an economically important disease in central and western Africa. Two fungi are associated with cigar-end rot in central and western Africa. One or both of these pathogens may be present in infected tissues. Conidiophores of T. fructigena are simple or bear a terminal vesicle with pedicellate conidia. Solitary or small groups of conidiophores of V. theobromae are produced on infected tissues. The frequency of cigar-end rot increases during periods of high humidity and rainfall. In fruit infected only with V. theobromae, premature ripening does not occur, and rotting does not continue after harvest. Control of cigar-end rot begins in the field with the frequent removal of dead flowers followed by bagging bunches with perforated polyethylene sleeves.

Cladosporium Speckle (Cladosporium musae)

Cladosporium speckle affects the older leaves of banana plants growing in humid environments. In Central America, a diffuse, grayish brown blotching is evident on the upper surface of older leaves. Conidia of the disease are carried by air currents and germinate in moisture to infect leaf tissue. There are no control measures available.

Cordana Leaf Spot (Cordana musae)

This is a common disease of banana. Pale brown, oval patches, ranging from one to several centimeters in diameter, form on the leaf lamina, particularly toward the leaf margins and in association with leaf tears. The disease sporulates abundantly on the undersides of lesions. Under moist conditions, conidia germinate and form appressoria within 8 hr of their deposition on the leaf surface. The best form of control is to apply protective fungicides.

Crown Mold and Rot

These diseases are present in all banana-growing areas of the world and are particularly troublesome in exported fruit with transit times exceeding 14 days. Crown rot begins as a softening and blackening of tissues at the cut crown surfaces. A water-soaked, dark band of creased and bruised tissue becomes evident on pedicels subjected to excessive flexing during handling and transit. Crown rot is caused by a complex of fungi found colonizing on banana leaves, flowers, bracts, and transitional leaves. Crown rot incidence and severity vary depending on the organisms that gain entry and on climatic conditions. The best form of control is good sanitation practices and applying a postharvest fungicide treatment.  

Decline (Botryosphaeria ribis)

Mango decline is a general decline of mango trees that occurs in calcareous soils in southern Florida and probably in Israel. Symptoms include interveinal yellowing and marginal and tip drying of leaves, leaf drop, a gradual dieback of young twigs that progresses to larger branches, and a reduction in the growth of secondary roots. Several fungi have been isolated from discolored vascular tissue, but only this fungus consistently induced tip dieback when used to inoculate young, potted trees. Trees that are most susceptible are deficient in iron and manganese and possibly in other microelements.

Dry Rot (Mycosphaerella spp.)

Dry rot is a common disease wherever papayas are grown commercially. Fruit surface lesions are slightly sunken, circular, black, and up to 4 cm in diameter. Stem-end rot resembles the surface lesions on fruit. Infections on flowers and young fruit are initially brown, becoming dark and sunken. The fungus colonizes senescing leaves and petioles and produces abundant fruiting structures on dead leaves and petioles that serve as the primary inoculum in the field. The best form of control is to apply fungicidal sprays and use a hot water treatment at 48 °C for 20 minutes to reduce stem-end rot.  

Freckle (Guignardia musae)

Freckle is a common leaf and fruit spotting disease of banana in the southern Asian and Pacific regions. Two types of leaf spotting occur primarily on the upper surfaces and sometimes on the lower surfaces of older leaves. Spots also form on fruit. Ascocarps are globose and have a distinct neck. During wet weather, ascospores are discharged from ascocarps, and conidia are exuded from pycnidia as white, gelatinous tendrils. Conidia are disseminated in water, and most are carried a short distance before they germinate. Pycnidia develop in lesions of all sizes, some of which contain fewer than five dead cells. Secondary infections may occur on the leaves and leave a streaklike manner. Freckle symptoms are tolerated on fruit in local markets in Southeast Asia, Australasia, and the South Pacific.

Freckles

Freckles are a disorder of the fruit epidermis that are common on most commercial papaya cultivars. Freckles usually occur on the exposed surface of fruit facing away from the stem.

Fruitlet Core Rot

Fruitlet core rot, black spot, fruitlet brown rot, and eye rot are disorders in which the central part of an individual fruitlet is discolored brown to black. In fruitlet core rot, septa between locules become dark to medium brown with gray, water-soaked centers. The degree to which these symptoms develop appears to depend on the time of infection, the pathogen or mixture of pathogens that is present, the cultivar, and the environmental conditions. Various species of bacteria have been isolated from tissue affected by fruitlet core rot. P. funiculosum is soilborne, and its conidia require exogenous nutrients (e.g., sucrose and glucose) and a pH of 3.5 to germinate. F. subglutinans is a soilborne fungus that can colonize the heart of the growing pineapple plant. Very high populations of the red mite have been associated with epidemics of F. subglutinans-induced fruitlet core rot in Hawaii.

Fusariosis (Fusarium subglutinans)

Fusariosis is known only in South America and is primarily a fruit disease, but it can also affect the pineapple plant. Infection probably occurs through open flowers, although major levels of disease also occur after developing inflorescences are inoculated. Fusariosis is most effectively controlled by planting disease-free seed material and by controlling insects, particularly the pineapple fruit caterpillar. The best form of control is to use resistant cultivars where available.

Fusarium Fruit Rot (Fusarium solani)

Fusarium solani is a weak pathogen that requires some kind of predisposing factor that stresses or injures the fruit before the fungus becomes established. Lesions are small (up to 15 mm in diameter) and depressed. Fusarium solani is also known to cause a rot of young papaya fruit (3-5 cm long), especially during wet weather. The best form of control is to apply preventive fungicide sprays in the field and hot water dips for harvested fruit.

Fusarium Wilt (Fusarium oxysporum)

Fusarium wilt is a widespread and destructive disease. Fusarium wilt does not discolor fruit internally, and young plants, less than 1.5 m tall and less than 4 months old, do not develop symptoms. The pathogen is capable of survival in previously colonized host tissue, in soil as chlamydospores, or as a parasite of weed hosts. The disease spreads in infected rhizomes or suckers. The best form of control is to use resistant cultivars and pathogen-free rhizomes and suckers.  

Ganoderma Butt Rot (Ganoderma spp.)

Initial symptoms closely resemble those caused by drought. G. boninense Pat. produces a very irregular basidiocarp that is flat to subungulate, dimidiate to stipitate, and may measure 150 mm in diameter and 50 mm in thickness. G. tornatum (Pers.) Bresad. produces a sessile, dimidiate basidiocarp that is 45 cm at its widest diameter and may be 10 cm thick at its base. A cut through the basidiocarp shows the cutis to be hard, thick, and olivaceous. G. zonatum Murrill forms a kidney-shaped, sessile, dimidiate basidiocarp. Natural spread of Ganoderma spp. that affect palms is believed to involve airborne basidiospores, root contact with infested soil, and root graft transmission of the pathogen. In plantation situations and landscapes, the incidence of butt rot is highest in older palm populations (greater than 10 years). Butt rot can be controlled by preventing the entry and establishment of these pathogens, clean sanitation efforts, and the use of fungicides.

Gray Leaf Blight (Pestalotiopsis palmarum)

Symptoms begin as small (approximately 2 mm in diameter) yellow to brown spots on leaflets and rachises. On potato-dextrose agar, colonies of the disease are initially white and fluffy. The pathogen does not exhibit much host specificity, and several species of palm, as well as some non-palm hosts, are affected. Infection events have apparently not been studied in coconut palm. Control measures are usually needed only in nurseries through the use of fungicides.

Gray Leaf Spot (Pestalotiopsis mangiferae)

Gray leaf spot, although common on mangos in the tropics, is usually a minor problem. The disease is characterized by the presence of whitish gray, irregular, discrete leaf spots, varying from a few millimeters to a few centimeters in diameter. Fungicides that used to manage other foliar diseases will help control gray leaf spot.

Guignardia Spot (Guignardia spp.)

Guignardia spot is caused by an unidentified Guignardia species. Control requires close monitoring and accurate control of postharvest quarantine heat treatments.  

Infectious Heart Rot

Infectious yellow, mosaic, and heart rot are all diseases caused by various strains of cucumber mosaic virus under different environmental conditions. Symptoms depend on the strain of the disease that is involved, on ambient temperatures, and probably on the genotype of the host. The disease is transmitted in a non-persistent manner by aphid species. Over 200 crop species in 40 families, including many weeds and members of the Cucurbitaceae and Solanaceae, are recorded hosts of the disease. Disease usually occurs in new plantings where vectors have been disturbed and new weeds are established. Most species and cultivars of Musa are susceptible to infectious heart rot. This disease is of minor importance and there are no control measures available.

Internal Breakdown of Fruit ==

Internal breakdown is characterized by a breakdown of the flesh that often begins early in fruit development. The cause of internal breakdown is not clear but increased nitrogen fertilization has resulted in an increased occurrence of the disorder. Calcium is important for maintaining cell membrane stability and conferring rigidity to cell walls. Although other cultivars can be affected, internal breakdown of mango fruit occurs mainly in Indian cultivars or those with an Indian pedigree. The occurrence of internal breakdown can vary seasonally and by location, and a large percentage of fruit in any area can be made unmarketable by the disorder.

Internal Browning

Internal browning, also termed endogenous browning or black heart, is a physiological disorder of pineapple fruit. The initial symptom is a small, grayish, translucent zone at the base of the fruitlet adjacent to the fruit core. Internal browning is induced by above-normal polyphenol oxidase activity. This can be caused by extreme temperature differences between the day and night or by refrigerating fruit and then exposing them to higher ambient temperatures. Development of the internal browning symptom can be reduced by coating the fruit with waxes that reduce gas exchange.

Internal Yellowing (Enterobacter cloacae)

In ripening papaya fruit, internal yellowing causes a yellow discoloration of the flesh and the affected area is soft and has diffuse, spreading margins and an offensive, rotting odor. Fruit ripeness is a factor in the development of internal yellowing. The disease cycle and epidemiology of the disease can only be speculated. Although it has been recovered from hot water treatment tanks, it is believed that these tanks are not a major source of infection in processed papaya fruit. Control of internal yellowing is currently limited to postharvest hot water quarantine treatments, which effectively reduce disease incidence in papaya fruit.  

Lasiodiplodia Fruit and Stem End Rot (Lasiodiplodia theobromae)

The overall symptoms of fruit and stem-end rot can be distinguished from dry rot by the wider, more extensive, translucent lesion margin. Sporulating lesions are black and have a rough surface formed where the pycnidia in the stromata meet. Stem-end rots caused by this fungus have been most troublesome on fruit that are vapor heated for fruit fly quarantine purposes.

Lesion Nematode Damage

The disease causes uprooting, root lesions, and rhizome discoloration. The disease is characterized as migratory endoparasites, and both juvenile and adult stages are capable of invading roots. Eggs are laid in the root and rhizome tissue, and the life cycle may be entirely endoparasitic.

Lesion Nematode (Pratylenchus brachyurus)

Dark epidermal and conical root lesions occur in the area of nematode feeding. Eggs are usually deposited in the cortex of the root. Preplant population densities can be reduced by very clean fallow, by fumigation, by crop rotation with legumes, and by adding soil amendments such as cassava residues or extracts of the Neem plant.

Lethal Yellowing

A yellowing of foliage begins with the lowest (oldest) fronds and eventually extends to involve the entire crown. Symptoms on dwarf types include premature nut drop and drying of the inflorescences followed by a pronounced browning of older fronds, rather than the yellowing that is observed on the tall types. Following an initial disease outbreak, further spread of lethal yellowing is characterized by a "jump-spread" pattern, indicating airborne spread involving a flying vector. The best form of control is to use resistant cultivars.  

Mango Anthracnose (Colletotrichum gloeosporioides)

Anthracnose is found in all mango-production areas of the world and is most important where high rainfall and humidity occur. The initial symptoms on leaves are small, dark brown spots that may group together to form irregular lesions that are greater than 1 cm in diameter. On inflorescences, symptoms begin as small, dark spots. Green fruit may develop small brown spots that usually do not enlarge until after harvest. Fruit lesions are initially superficial, going more than 5 mm into the flesh only after they cover much of the fruit surface. Conidia (7-20 X 2.5-5 µm) are hyaline, unicellular, and either cylindrical with obtuse ends or ellipsoidal with a rounded apex and a narrow, truncate base. The fungus produces conidia on dead twigs and leaves and on other host tissues. Resistant cultivars should be used where they are available. A disease forecasting system based on temperature and leaf wetness readings has been developed to identify strategic periods for field applications of fungicides. Although a good field program will assist postharvest anthracnose control, additional measures are usually needed for its control after harvest, especially if fruit are held in storage or are shipped.

Mango Scab (Elsinoe mangiferae)

Young leaf, twig, flower, and fruit tissues are especially susceptible. Lesions on young fruit are gray to grayish brown with dark, irregular margins. Conidiophores of the disease are erect, sinuous, and wider at the base. Young, succulent tissues of the host are usually infected. Fungicidal sprays are usually an adequate form of control.

Marbling Disease (Acetobacter peroxydans)

Marbling disease occurs in all pineapple-production areas. Higher incidences seem to appear when the flowers are open at high temperatures accompanied by rainfall. The most common symptom is a yellowish to reddish brown to very dark, dull brown discoloration of fruit tissue. Infection occurs through open flowers and cracks in the fruit. There are no measures of control available.

Mealybug Wilt (Dysmicoccus spp.)

Mealybug wilt can be a very destructive pineapple disease and is associated with feeding by mealybugs. Plants of the Cayenne varieties are more susceptible to the wilt. The first symptom is a reddening of the leaves. At least two species of mealybugs are associated with mealybug wilt in most of the major pineapple-production areas of the world. Mealybugs themselves do not cause the disease directly but seem to introduce the infection into the plant. Ants are necessary for colonies of mealybugs to develop. The ants protect mealybugs from parasites and predators and remove the "honey-dew" from the insects which they in turn use as a food. Ants also move the mealybugs from one place to another. This is the reason why often there are no mealybugs left on plants with the symptoms. They have been moved to other more healthy plants. Mealybug wilt is managed when ants are controlled with an appropriate chemicals. Baits are usually most effective. Good weed control is also important as the mealybugs can live on other plants as well as pineapples.

Moko Disease (Pseudomonas solanacearum)

Moko affects many commonly grown dessert bananas, plantains, and cooking bananas. The disease is transmitted by insects through the cushions on the peduncle and occurs when abundant inflorescences are present. Wilt symptoms have not been observed on most plants in the field. In plantations where Moko disease is already established, it is essential to have routine plant inspection and eradication programs as well as thorough disinfestation of pruning knives. Bluggoe and similar cooking bananas are most likely to suffer epidemic waves of Moko.  

Nematodes

Nematode-induced decline of mango has been reported in regions with warm temperatures and sandy, moist, well-drained soils. Feeding and penetration by nematodes within the roots of mango may produce a variety of tree-decline symptoms. Numerous nematode species have been associated with roots of declining mango. Populations fluctuate on the basis of soil moisture content and soil temperature. In addition, the age of mango trees appears to be highly correlated with nematode populations. The best forms of control include good cultural control methods, proper preplant chemical applications, and planting in noninfested sites.  

Papaya Anthracnose (Colletotrichum gloeosporioides)

Anthracnose of papaya is an important postharvest disease in most tropical and subtropical regions. Symptoms include the development of round, water-soaked, sunken spots on the bodies of the ripening fruit or irregular to circular spots that are 1-10 mm in diameter, sharply defined, occasionally slightly depressed, and red dish brown. The petioles of papayas support abundant development of the disease. Primary inoculum is disseminated by wind or rain. The environmental conditions that favor the pathogen are high temperatures (optimal is 28 °C) and high humidity. Protective fungicide sprays applied at 14 to 28 day intervals, depending on rainfall, are recommended. A hot water dip at 48 °C for 20 minutes reduces anthracnose.

Papaya Diseases By Viruses

Papaya droopy necrosis virus has been reported only in Florida. The initial symptoms of papaya droopy necrosis are drooping and recurvature of the leaves in the upper portions of the crown and the leaves may also be marginally dry. Initial symptoms of papaya apical drying are yellowing of the affected plant followed by the rapid wilting and deterioration of younger leaves.

==Papaya Ringspot (PRV)

Papaya ringspot is one of the most destructive diseases of papaya and occurs in nearly every region where papaya is grown except Africa. Symptoms induced by different isolates of the virus may vary in intensity, but dark green, often slightly sunken rings are diagnostic. Other key symptoms are an intense yellow mosaic on leaf lamina and numerous "oily" streaks on the stem. Papaya trees of all ages are susceptible and generally will show symptoms 2-3 weeks after inoculation. The disease is rapidly spread by several aphid species in a non-persistent manner. Efforts to control papaya ringspot have included roguing, breeding for tolerance, cultural practices, and cross protection.

Phytophthora Cankers (Phytophthora spp.)

At least three species of Phytophthora cause crown and collar cankers on avocado trees: P. cinnamomi, P. citricola, and P. heveae. The Phytophthora cankers originate at or below ground level and may extend as high as 3 m on the trunk. Foliar symptoms in trees with advanced cases of trunk canker are similar to those caused by Phytophthora root rot. The development of these canker diseases is stimulated in poorly drained, wet soils. Measures to prevent and control canker diseases are similar to those described under Phytophthora root rot.

Phytophthora Fruit and Root Rot (Phytophthora palmivora)

Heavy fruit losses caused by the disease frequently occur during rainy periods. Infected young fruit on trees usually show water-soaked lesions that exude milky latex. The top portion of the fruit-bearing part of the stem is very susceptible to infection during rainy periods. In poorly drained areas, the fungus initially attacks lateral roots of papaya which are especially susceptible during the first 3 months after seedling emergence. Although sporangia and zoospores may survive in soil for short periods, chlamydospores are the main survival structures for the disease in nature. Root rot of papaya seedlings seldom occurs during first plantings because of the absence of the pathogen. Rain and wind are the two major factors in spreading the disease. The pathogen produces abundant sporangia on the surface of infected fruit, causing disease outbreaks in the orchard and in orchards nearby. Phytophthora root rot of papaya seedlings is most serious during rainy periods. Temperature also influences disease severity because of its effect on growth and sporulation of the pathogen. Phytophthora fruit rot of papaya can be controlled with preventive fungicides, such as mancozeb or basic copper sulfate, applied to the fruit column and good cultural practices.

Phytophthora Heart and Root Rot (Phytophthora spp.)

Phytophthora heart rot and root rot of pineapple are limited to soils with high pH values and wet environmental conditions. Young plants, especially crown plantings are very vulnerable. Rainfall (or heavy irrigation) causes splashes which carry the fungus into the heart of the plant. Young leaves of infected plants fail to elongate and become yellow. A specific odor comes from the rotting area. The primary inocula of the Phytophthora species are chlamydospores either free in soil or in infested plant debris where they can survive for many years. Raised beds and good surface drainage reduce disease levels dramatically as well as lowering the pH of the soil to 4.5 or lower. Very effective control is now available by dipping the planting material in fungicides prior to planting.

Phytophthora Root Rot (Phytophthora cinnamomi)

The most important and most widely distributed avocado disease is Phytophthora root rot. On avocado, the fungus primarily causes a rot of the small feeder roots, which become blackened and brittle and eventually die. It results in a gradual decline, dieback, and in many cases, the eventual death of the tree. The disease forms several different spore stages that are involved in disease development or survival which include sporangia, chlamydospores, and oospores. It is one of the species of Phytophthora that can be easily isolated and that can be recovered from infected tissue and soil by several methods. Excess soil moisture can encourage the development of the disease. The pathogen can be disseminated in several ways, including soil movement on nursery stock and by equipment, by water which can carry zoospores and other propagules and infected root pieces, and very occasionally by seeds taken from infected fruit. Infection by is optimum at soil temperatures of 21-30 °C. Reducing soil pH controls some diseases caused by the fungus such as rhododendron wilt and pineapple crown rot. Soil moisture is the primary environmental factor influencing development. With soilborne pathogens which do not have widespread, indigenous distributions, prevention of disease by limiting the introduction of the pathogen is very important. Another important aspect of prevention is to plant trees in soils that have good drainage. The phosphonates and its active breakdown product phosphorous acid and potassium phosphite (where approved for use), have been effective when applied by foliar application, trunk paint, injection, or soil application.

Pink Disease (Erythricium salmonicolor)

Pink disease can be recognized by the appearance of silky white threads at the forks of branches or twigs and orange pustules are also produced on infected bark. The anamorph and teleomorph of the fungus are formed during wet conditions. The disease has a wide host range that includes rubber, cocoa, guava, coffee, rambutan, citrus, mangosteen, jackfruit, chempedak, langsat, carambola, black pepper, and bushy legumes. The successful control of pink disease depends on early and accurate identification of the disease symptoms followed by prompt application of a fungicide. Alternatively, infected branches can be removed, and exposed surfaces can be treated with a wound dressing.

Pink Disease (Erwinia herbicola)

The incidence of pink disease is usually low. Fruit turn brown to black when they are cooked during the canning process. The bacteria are carried to the pineapple flowers by nectar-feeding insects. Controlling the vectors with insecticides is the primary means of managing pink disease.

Pitting Disease (Pyricularia grisea)

Round, sunken lesions, 4-6 mm in diameter, appear on fruit nearing maturity and after harvest. Lesions also occur on pedicels and on fruit crowns and can increase finger drop, a serious quality defect. The conidia are attached singly at the broader end on mostly unbranched conidiophores. Pitting disease is seasonal and is most prevalent during months with high rainfall. The principal source of inoculum for pitting disease is hanging banana leaf trash, including the transition leaves and bracts. Lesions can develop within 3 weeks on fruit approaching harvest. Frequent removal of inoculum reservoirs is essential for pitting disease control.

Powdery Mildew:

Scattered patches of superficial, cottony mycelia, and powdery spore layers group together to cover affected plant parts with a whitish bloom. Powdery mildew causes the most serious losses when flowering and growth flushes occur during dry, cool conditions. Mango cultivars differ in their susceptibility to powdery mildew. Sulfur sprays provide reasonable control but can scorch flowers and young fruit in warm, sunny conditions.

Powdery Mildew (Oidium caricae)

This common disease generally causes little damage or yield loss on bearing trees, where lesions are usually found on senescent leaves. Diffuse mats of white mycelium commonly develop on the lower leaf surfaces, especially in areas adjacent to the leaf veins, and occasionally on the upper surfaces of leaves. Although leaves of all ages are considered susceptible, infection is largely confined to older leaves as they approach senescence. Papayas are the only known host of the disease. The best form of control is applications of wettable sulfur, sulfur dust, or lime sulfur if needed.

Pseudocercospora Spot (Pseudocercospora purpurea)

Pseudocercospora spot or blotch is one of the most common diseases of avocado in Florida and in other production areas where warm, humid, and rainy conditions persist. Symptoms occur on leaves, stems, and fruit. On fruit, lesions begin as small flecks, which later become slightly sunken, irregular, and brown to brownish black. Most initial inoculum probably comes from infected leaves. Very small fruit (less than 4 cm in diameter) and those at or near maturity are nearly immune. Timely applications of fungicide are important, and benomyl or certain copper fungicides can be used.

Purple Stain Rot (Erwinia herbicola)

Purple stain of papaya is an internal fruit disease without external symptoms. Purple stain appears to be most common during the winter months of January and February.  

Red Ring Disease (Bursaphelenchus cocophilus)

Symptoms vary widely with environmental conditions and with the species, age, and cultivar of the palms that are affected. Feeding by R. palmarum larvae causes severe damage to the crown of diseased coconut palms. Red ring nematodes can be cultured by inoculation in coconut palms older than 1 1/2 years, in husks of nearly mature coconut fruits, and in excised leaf stalks (leaves 6 to 13 on a nut-bearing coconut) that have been trimmed of the pinnae and whose cut ends have been coated with paraffin. The rate of disease development is affected by the species and age of the host palm and by other factors. Experimental inoculations of nuts on inflorescences or of nonwounded stems of coconut do not lead to red ring disease. Phytosanitation is currently the best method of red ring management.

Reniform Nematode (Rotylenchulus reniformis)

The reniform nematode occurs on many plants from the tropics to temperate regions. Primary roots are dry and lack significant secondary root formation. Shoot growth suppression is inversely related to initial population density of the nematode. The immature females feed semi-endoparasitically with the anterior one third of their bodies inside the root. Allowing the soil to lie fallow for several months followed by preplant fumigation to reduce populations to very low levels is the most common control practice in infested plantations.

Reniform Nematodes (Rotylenchulus reniformis)

The reniform nematode is the most important nematode pest of papaya. Aboveground symptoms on plants infected by the reniform nematode are similar to those associated with lack of proper nutrients, chronic moisture stress, or poor soil aeration. Juveniles, which hatch from eggs, are less than 500 µm long. Both nematode-infested sites and infected seedlings should be avoided when growing papayas.

Rhizopus Soft Rot (Rhizopus stolonifer)

Rhizopus soft rot, also known as watery soft rot, is a common postharvest disease of papayas. Rhizopus soft rot of papaya is characterized by a soft and watery rot that quickly causes the collapse of the entire fruit but leaves the cuticle intact. The disease is caused by two fungi both of which are commonly found in soil, compost, and other decaying plant matter. The incidence of Rhizopus soft rot increases during rainy weather, higher humidity, and an increase in the number of fruit lesions caused by other fungi. The most important control measure is sanitation in and around the packing plant. Heat treatment used for quarantine purposes is effective in killing mycelium but does not kill all spores. Preventive field fungicide sprays control Rhizopus soft rot by reducing field inoculum levels.

Root Knot Nematodes (Meloidogyne javanica)

Root-knot nematode species are important pineapple pests in several countries. Root growth is suppressed because of infection at the root tip. The life cycle begins as a one-celled egg, which passes through embryogenesis and results in a first-stage juvenile within the egg. Gall formation is initiated by the feeding process of the second-stage juvenile in the meristematic region of the root tip. Root-knot nematodes are normally managed with preplant fumigation.

Root Knot Nematodes (Meloidogyne spp.)

Root-knot nematodes may cause severe galling of roots, stunting of plants, and death of seedlings in sandy soils. Aboveground symptoms on heavily infected plants are similar to those described for the reniform nematode. The dissemination and size of the second-stage juvenile of the root-knot nematode are similar to that of the reniform nematode. A single female deposits an average of 350 eggs in the eggmass. Preplant fumigation is effective against root-knot nematodes.

Rosellinia_RootRot (Rosellinia necatrix)

Aerial symptoms of Rosellinia root rot are yellowing of foliage and absence of new shoot growth. Belowground symptoms are characterized by rotting of small roots by the white mycelium, which spreads to larger roots. Infected trees often persist for 2-3 years, showing yellowing of the foliage and absence of growth above heavily rotted roots. The fungus that causes the disease produces densely aggregated, spherical, black, short, pedicellate perithecia, 1-2 mm in diameter, embedded in a mat of brown, septate hyphae. The disease can survive for considerable periods on old, rotted roots left in the ground. The fungus spreads by many means along and within roots of infected plants to roots of neighboring trees, in root fragments and infested soil, and in water. Optimal conditions for growth of Rosellinia root rot include high soil moisture (close to field capacity) and temperatures of 20-25 °C. Control measures consist mainly of preventing the fungus from spreading in soil and removing possible infection sources.  

Sigatoka Leaf Diseases (Mycosphaerella spp.)

There are two Sigatoka diseases. Both diseases can cause extensive defoliation, but black Sigatoka is usually far more damaging than is yellow Sigatoka. The first symptom of yellow Sigatoka is small (less than 1 mm long) yellowish green flecks that usually appear on the third or fourth leaf from the top of the plant. When disease severity is high, spots may group together, and the leaf dies rapidly, leaving the spots outlined in brown or black against the dark brown background of the dead leaf. The first symptom of black Sigatoka is small yellow flecks that appear on the undersurface of the third or fourth fully expanded leaf. When disease severity is very high, large areas of the leaf may become blackened and water-soaked. Conidia of the fungus form soon after the collapse of tissues in lesion centers. The disease cycle is similar for both diseases. Infection occurs on the youngest leaves of the plant during and immediately after unfurling. The first symptom, yellow flecks, appears about 15-20 days after infection. The best forms of control include using resistant cultivars and applying fungicides and mineral oil combinations.

Sooty Mold

Sooty mold develops of fingers, pedicels, and crowns and are blackish brown blotches. It occurs in cool, rainy weather and can be controlled by applying insecticides.

Speckle (Swamp Spot) and Black Tip (Deightoniella torulosa)

Speckle creates a reddish to black blemish on the finger tips and inner-whorl fingers. It generally is only a problem during a wet season and can be controlled by reducing the exposure to moisture. Black tip shows a black lesions at the flower end of one or more fingers. This area may also appear to be a pale yellow or gray, when older lesions rupture.

Spiral Nematode (Helicotylenchus multicinctus)

The spiral nematode occurs in most regions where bananas are grown. The disease causes lesions on root surfaces and destruction of small feeder roots and is the only endoparasitic species in this large genus. Nematode-free sites and planting materials are required for control.

Squirter Disease

The disease enters cut surfaces at the finger stem ends and rotting becomes evident as the fruit begins to ripen. Dark bands form at the pedicels, and pulp rot progresses toward the finger tips. Eventually, the pulp is reduced to a liquid that is released when pressure is applied to the finger.

Stem Bleeding Disease (Chalara paradoxa)

Stem bleeding disease is known from almost all coconut-producing areas in the world. Infected roots exhibit a decay of pith tissues that generally contributes to a slow decline of the tree. On palms other than coconut palm, the pathogen causes additional disease syndromes with the trunk and roots being the primary infection sites. The pathogen anamorph persists in soil as microconidia and chlamydospores, the latter being more important for longterm survival. Root, bud, and leaf infections have been effectively treated with the fungicide benomyl. Often, stem bleeding or heart rot is correlated with wounding.

Stem Canker and Fruit Rot (Botryosphaeria dothidea)

Dothiorella stem canker causes occasional losses of older avocado trees, particularly in regions with dry summers where trees are water stressed or in regions where trees have been frost damaged. Cankers occur on twigs, branches, or trunks. Stem canker fruit rot is distinct from stem-end rot in that portions of the fruit other than the stem end are affected. Conidia of stem canker form on dead leaves and decayed fruit, whereas ascospores of fruit rot form on dead twigs. Fruit may be indirectly infected by spores or hyphal fragments through wounds or lenticels. The best form of control is to remove any diseased tree parts and correct any environmental or nutritional stresses that favor symptom development.

Stem End Rot

Stem-end rot is a postharvest disease that causes occasional severe losses in avocado fruit, particularly when anthracnose is well controlled and storage conditions are suboptimal. Symptoms develop at the stem ends as the fruit ripen, appearing within 4-7 days at 25 °C. The disease often causes stem-end rot, appears in avocado stems and is produced in tree litter and on dead leaves, twigs, and branches in the canopy and are spread by water and air movement. The spectrum of pathogens that cause stem-end rot depends on environmental conditions. Enclosing fruit in paper bags between fruit-set and harvest will reduce postharvest stem-end rot by excluding airborne inocula and possibly by enhancing fruit vitality. Fruit should not be harvested during rain.

Stem-end rot is a postharvest disease that becomes more prominent as orchards become older and when preharvest fungicide programs have reduced the incidence and severity of anthracnose. Losses can increase when fruit are stored for prolonged periods at low temperatures or when fruit ripen at high temperatures greater than 28 °C. Depending on the fungus involved, variable symptoms develop at the stem end as fruit ripen. The disease causes slow-spreading, tan lesions at the stem end. Several fungi cause stem-end rot. Fungi that cause stem-end rot of mango occur as endophytes in mature stem tissue. The spectrum of pathogens that cause stem-end rot is influenced by temperature, moisture stress, and the nutrition level of the host. Stem-end rot symptoms appear 3-7 days after harvest at 25 °C but can be delayed for an additional 7-12 days at 13 °C. The pathogen can also infect fruit through the stem end at harvest, especially when the fruit are inverted in the soil to facilitate sap removal. Stem-end rot fungi are also associated with twig and branch dieback. When permitted, postharvest immersion of fruit in hot water combined with benomyl for 5 minutes at 52 °C effectively controls stem-end rot. In the future, irrigation, nutrition management, and strategic pruning to promote growth flushes may reduce fruit infection and, hence, the need to control stem-end rot after harvest.

Stemphylium Fruit Spot (Stemphylium lycopersici)

The early symptom of Stemphylium fruit spot is the development of small, round, dark brown lesions. The fungus is also capable of causing a stem-end decay. Regular field sprays with protective fungicides help keep the inoculum level low in the field.

Sunblotch

Symptoms on twigs include a yellow, red, or dry streaking that often is associated with a shallow indentation along the length of the twig. Transmission of the viroid most often occurs when infected budwood or rootstock seedlings are used for grafting. Other than by root-to-root grafts, sunblotch has not been observed to spread in the field. The primary control measure for this disease involves careful selection of disease-free scions and seed sources. Infected trees and stumps in orchards must be removed and burned.  

Verticilium Wilt

The leaves wilt suddenly on one or several branches or on the entire tree. Often, affected trees will send out new, vigorous shoots within a few months after the initial collapse of the tree.  

Wet Fruit Rot (Phomopsis spp.)

Wet fruit rot in its early stages resembles Rhizopus watery soft rot. The infected area is slightly depressed, soft, and translucent. The disease sporulates abundantly on dried petioles that remain attached to the tree. Control of wet fruit rot must begin in the field. The prevention of mechanical wounds during and after harvest is important.