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Bananas have few troublesome pests or diseases outside the tropics. Root rot from cold wet soil is by far the biggest killer of banana plants in our latitudes. Gophers topple them, and snails and earwigs will crawl up to where they can get continuous water, but these pests do not bother the plant.
Pests and Diseases: Banana and plantain are susceptible to a wide range of pests and diseases. Some pests and diseases are highly aggressive or very contagious and easily spread, and once established they are persistent and practically impossible to eradicate. In general, the severity and occurrence of pest outbreaks and plant damage depend upon several mitigating factors:
Environmental conditions: Wet, rainy environments favor fungal and bacterial diseases. Relatively dry weather or climate favors many types of insect outbreaks (e.g., mites) and banana virus diseases; however, some pests, such as scab moths, cause damage during normal weather patterns in the Asia Pacific regions. Disease and pest outbreaks are more common where banana plants are grown together in large numbers (monocultures). The severity of the pest and diseases infections depends upon the environment.
Specific banana variety: Although most banana varieties are susceptible to certain severe diseases, some varieties are far more sensitive than others. For example, Fusarium wilt was responsible for destroying many commercial plantations of the once popular and widely grown variety ‘Gros Michel’, also known as ‘Bluefields’. With regard to banana bunchy top virus—which has now spread throughout Southeast Asia and much of the Pacific—the most susceptible varieties are in the Cavendish subgroup (‘Chinese’, ‘Williams’, ‘Grand Naine’, ‘Valery’). Members of the Pome subgroup are more tolerant of bunchy top, i.e., ‘Brazilian’ types (Hawaiian “Apple”), French Polynesian ‘Rio’ or ‘Pime’, and ‘Australian Improved Lady Finger’. Some varieties or types of bananas are well suited for local conditions and are tolerant of existing pest and disease populations. These are primarily the “new varieties” such as FHIA-01, FHIA-02, FHIA-03, ‘Giant Kalapua’, which are not quite as well received as the older types but are relatively disease resistant. Researchers worldwide are continually working to develop disease-resistant varieties.
Specific disease or pest: Several significant pests and pathogens of general agricultural concern are parasites of Musa spp. (e.g., sap-feeding insects and root-knot nematodes). These pests have wide host ranges and may initiate or cause significant damage to some crops (e.g., vegetables). Because Musa spp. Attract ants, some sap-feeding insects (e.g., aphids) may be a concern for certain vegetable intercropping designs with Musa spp.
Insect pests of banana in the Pacific Insect pests of banana can cause significant damage to fruits (e.g., thrips, moths/caterpillars, scales), leaves (e.g., mites, moths/caterpillars), corms, and pseudostems (e.g., weevils), and can transmit important plant pathogens (e.g., aphids transmit banana bunchy top virus). Damage due to insects can greatly reduce the marketability of banana fruits.
Listed and described below are some of the most common and important insect pests of bananas in the Pacific region.
APHIDS:
Aphis gossypii (melon aphid), Pentalonia nigronervosa (banana aphid)
The banana aphid is a serious pest of banana due to its ability to transmit banana bunchy top virus (BBTV). Aphid excretion of “honeydew” provides a nutritional substrate for sooty mold fungi, which affects fruit quality and physically block photosynthesis. Banana aphid populations are often tended by ant species.
BEETLES:
Adoretus sinicus (Chinese rose beetle)
The Chinese rose beetle, Adoretus sinicus, and other rose beetles are common pests on all major banana-producing islands in Hawai‘i and the Pacific. The larvae primarily dwell in the soil and leaf litter surrounding the plant crop, and the adults do the damage to banana. The adult beetle is nocturnal and feeds primarily on leaf and interveinal tissue. Chinese rose beetle damage is most easily detected on younger plants.
Cosmopolites sordidus (banana weevil): The banana root borer can be very damaging to commercial and home growers. The larvae bore into corms, suckers, and roots; extensive root destruction is possible; diminished plant growth and yield results; premature toppling of plants and plant death (of young plants) can occur. A night-feeder, the borer can be trapped by baiting the field with slices of banana pseudostem.
Management:Peel the rhizomes free of lesions and immerse in hot water at 54°C for 10 minutes; minimize plant debris around mats; remove infested stumps after harvest; apply insecticides. Also, a 10% household bleach solution treatment also is useful for disinfesting corms. Pruning the corm and lower trunk first until no “tunnels” are evident and treating with household bleach is the best for the home grower. It is very important that growers of bananas everywhere are aware of this weevil and its damage, because it is spread by people unknowingly (or carelessly) giving away suckers to home gardeners with “clean” gardens. Symptoms: banana plants fall over, even in light winds. Dirt-filled tunnels creating a labyrinth of weakened tissue in the corm and lower trunk up to about 30 cm (12 in) high.
Trigonops sp. (weevil), Polytus mellerborgi (banana corm weevil), Odioporus longicollis (banana pseudostem borer): Weevils are a major pest in Southeast Asia. Entire banana fields were destroyed by weevils in Okinawa in 1997 (Nelson, S. ).
Management: If suckers are infested with weevils, all infested material should first be trimmed with a machete. This includes trimming all roots, small suckers, and all necrotic tissues until only white, clean tissues remain. Then soak the trimmed suckers in 10% household bleach solution, let them air-dry for a few days, and plant in a new spot. Let the original field remain fallow for 1–2 years. Weevils may be trapped overnight by placing freshly cut pseudostem on the ground, with the cut surface in contact with the soil.
CATERPILLARS:
Chrysodeixis eriosoma (green garden looper). The larval (caterpillar) stage feeds on banana leaves.
Eudocima (Othreis) fullonia (Pacific fruit-piercing moth): The fruit-piercing moth is an important pest in localized areas. The adult moth punctures and feeds on ripening fruit, which may result in premature ripening/fruit drop.
Management: Natural enemies of this pest may reduce pest populations over time.
Decadarchis flavistriata (sugarcane bud moth): This is a localized insect pest (caterpillar); the caterpillar stage feeds on decaying flowers and causes fruit scarring.
Management: De-flowering prior to bagging; use of sprays of Bacillus thuringiensis (“BT”) products.
Erionota thrax (banana skipper): The banana skipper, Erionata thrax, rolls up banana leaves starting from the leaf midrib. Due to the effective biological control of the banana skipper in some locations (Hawai‘i), chemical treatments are uncommon.
Management:The banana skipper can be controlled effectively in some locations with naturally occurring biological control insect species (e.g, parasitic wasps). The best way for the homegardener to control these caterpillars, which eat extensive areas of leaves, is to recognize the damage (easy) and kill them by hand.
Opogona sacchari (banana moth): The banana moth lays eggs on senescing flowers and ondecaying leaves, pseudostems or fruit. The larvae feed on detritus and decaying plant material. They are often found feeding on healthy tissue at the interface with decaying plant parts. Moth larvae can destroy several palm species in tropical areas (e.g., Chamaedorea, areca palms, etc.).
Management: the removal of flowers and application of insecticidal bunch treatments prior to bagging appears to greatly reduce damage larval damage.
Nacoleia octasema (scab moth): The scab moth is a very significant pest of banana fruits in Samoa and many places in the southwest Pacific. The pest also attacks Heliconia in some locations, as well as Pandanus. Banana scab moth females lay eggs on banana flower bracts or leaves as the inflorescence emerges. Larvae hatch, enter the flower, and feed on the developing fruits within.
The feeding results in rough and irregular scars (brownish-black) on fruit skin. Large infestations can scar the entire fruit and cause deformed fingers.
Management: the best control is achieved by injecting an insecticide (as recommended by local agriculture authorities) into the flower after it emerges and before it starts bending downward.
A single injection, applied about one-third of the way down from the flower tip, is sufficient to provide control. Some varieties appear to be less susceptible to scab moth damage.
FRUIT FLIES
Bactrocera dorsalis (Oriental fruit fly)
Ceratitis capitata (Mediterranean fruit fly)
Fruit flies are significant quarantine pests for some destinations.
They attack ripe banana fruits.
LEAFHOPPERS
Sophonia rufofascia (two-spotted leafhopper)
MEALYBUGS
Planococcus citri (citrus mealybug)
Pseudococcus jackbeardsleyi (banana mealybug)
Dysmicoccus brevipes (pineapple mealybug)
Dysmicoccus neobrevipes (gray pineapple mealybug)
Ferrisia virgata (striped mealybug)
Pseudococcus orchidicola (orchid mealybug):
Mealybugs feed on banana leaves and fruits, but they are not a significant economic pest of Musa in most locations. Some mealybugs transmit banana streak virus (BSN).
MITES
Phytonemus pallidus (cyclamen mite): Mites (see photo below) can build large colonies during dry weather, primarily on the undersides of Musa leaves. Their feeding damage can cause large, dry, brown patches of necrosis on banana leaves. Generally, they are not economic pests and transmit no other diseases.
SCALES
Abgrallaspis cyanophylli (armored scale)
Aonidiella aurantii (California red scale)
Aonidiella inornata (inornate scale)
Aspidiotus destructor (coconut scale)
Chrysomphalus dictyospermi (dictyospermum scale)
Coccus hesperidum (brown soft scale)
Coccus viridis (green scale)
Diaspis boisduvalii (boisduval scale)
Eucalymnatus tessellates (tessellated scale)
Hemiberlesia lataniae (latania scale)
Icerya aegyptiaca (Egyptian fluted scale)
Ischnaspis longirostris (black thread scale)
Pinnaspis buxi (ti scale)
Saissetia coffeae (hemispherical scale)
Steatococcus samaraius (steatococcus scale)
The coconut scale (Aspidiotus destructor) causes a localized discoloration and yellowing of plant tissue. It is classified as an armored scale; feeds on underside of banana leaves, in circular colonies; can attach to petioles, peduncles, and fruits. The damage can occur at all stages of the plants. Attacks on suedo-stems, leaf petioles and leaf cause stunting of the plants. Infestation of fruit bunches causes deformed fruits which are unmarketable. Severe attacks can kill the plants. Damage on fruit trees cause leaf fall, stunting and dieback of the plants. Scale presence on fruit cause blemishes, fruits are deformed and unmarketable. Secondary effect of the CSI is development of shooty mould on plant surfaces, especially on leaves, which curtails photosynthesis. Sweet excretion attracts ants, which drive away the natural enemies of the scale and assist in spread of the crawlers.
Management: Scales are controlled with sprays of insecticidal oils. Ants tend these insects and feed on the honeydew produced by them. Biological control of CSI is the long term solution. In countries where the scale is present, the pest population is controlled by introducing natural enemies. Natural enemies of other scale insects may adapt to feeding on A. destructor as it colonizes new areas. The scale is attacked by a few specific and a large number of non-specific parasitoids and predators. Predators rather than the parasitoids play a significant role in limiting CSI populations (Waterhouse and Norris, 1987). The most common are the coccinellid beetles, Chilocorus spp., Cryptognatha nodiceps, Pseudoscymnus anomalus , Rhyzobius spp. and Telsimia nitida. Parasitoids are not very well studied and known, but Aphytis spp. and Encarsia spp. do contribute significantly in the maintaining of CSI populations in the field.
THRIPS
Thrips can scar, stain, or deform banana fruits by feeding on the fruit skin. Thrips are small, winged insects that feed on banana flowers and/or the tender green skin of developing fruits. Thrips outbreaks can occur during periods of dry weather.
The following thrips species are important pests of Musa in the Pacific region:
Chaetanaphothrips signipennis (banana rust thrips): Feeding by rust thrips creates areas of reddish-brown “rust” that develop on the banana fruit, especially where two adjacent fingers touch; skin cracking can occur, leading to severe damage. The damage is caused by thrips feeding on young, developing green banana fruits.
Management: monitor rust thrips activity; apply approved insecticides to soil, plant, and fruit; use thrips-free planting material; destroy neglected or abandoned plants or banana plantations; cover the developing bunches with perforated polyethylene sleeves.
Elixothrips brevisetis banana (rind thrips)
Hercinothrips femoralis (banded greenhouse thrips)
Thrips hawaiiensis (Hawaiian flower thrips):
Corky scab is caused by populations of the flower thrips (Thrips hawaiiensis) feeding on young, developing, green banana fruits. They cause a superficial corky scarring on the banana fruit skin; the scab is patchy, discolored, and raised.
Management:
Monitor the crop for flower thrips populations; spray registered insecticides; keep plants moist with overhead irrigation during dry periods.
WHITEFLIES
Whiteflies are Musa leaf parasites and generally do not damage banana fruits directly. They feed on the leaf undersides; they are sap-feeding insects that deposit honeydew on the surface of the banana fruits and leaves in the canopy below them. This sugary deposit on leaves and fruits can lead to the growth of sooty mold fungi, which use the honeydew as a food source. Sooty mold can lessen fruit quality and reduce overall leaf photosynthesis. Whiteflies may be tended by ant species that feed on the honeydew and protect the insects. Whiteflies may be controlled effectively in some locations with naturally occurring biological control insect species.
Aleurodicus dispersus (spiraling whitefly): The spiraling whitefly is a sap-sucking insect causing tissue damage and discoloration; it excretes honeydew, which is a substrate for the growth of sooty mold on the surface of plant organs
Management: Natural enemies of the spiraling whitefly may keep this pest in check locally; foliar sprays of insecticidal oils can reduce whitefly populations.
GRASSHOPPERS
Valanga excavate (large short-horn grasshopper)
Valanga nigricornis (Javanese grasshopper)
OTHERS
Leptoglossus australis (leaf-footed plant bug)
Proutista moesta (erect-winged blue plant hopper)
Lamenia caliginea (derbid planthopper)
Lamenia caliginea (a fulgorid planthopper)
Siphanta acuta (torpedo bug)
DISEASES IN THE PACIFIC REGIONS
The most significant disease of bananas in the Pacific is black leaf streak, caused by the fungus Mycosphaerella fijiensis. Bunchy top, a viral disease caused by the banana bunchy top virus (BBTV), has also emerged as a major problem for banana plantations in Hawai‘i and the Pacific Regions.
BIOTIC DISEASES
Biotic diseases are infectious and caused by plant pathogens.
DISEASES CAUSED BY FUNGI
Fungi are the most important and prevalent pathogens of banana. All banana plant organs are attacked by fungi. Fungal diseases cause the greatest pre- and postharvest production losses and account for a large share of plantation management expenses.
Leaf diseases:
Phyllacora musicola (black cross) (see photo below): Black-cross is a distinctive but relatively minor leaf disease of banana. The disease is found in Australia, Indonesia, the Philippines, and the southwestern Pacific. Symptoms are most evident on the undersides of older leaves, scattered about the leaf or occurring in large groups. The lesions are black and star-shaped, with four cardinal points and elongated along the leaf vein axes.
Management: Specific control measures for this black cross are usually not warranted;
‘Cavendish’ varieties are resistant.
Pseudocercospora fijiensis (syn. Mycosphaerella fijiensis) black sigatoka, black leaf streak: A debilitating and contagious leaf disease caused by the fungus, Mycosphaerella fijiensis. It is globally distributed and epidemic in many locations and is the most important disease of Musa worldwide. Symptoms develop as follows: reddish-brown streaks (1–5 mm long and 0.25 mm wide) appear initially on the undersides of the third or fourth youngest leaf; streaks develop into elongated spots with gray or tan centers and dark brown to black margins; lesions may be surrounded by yellow halos; lesions may coalesce to form large, blighted areas of leaves in parallel with leaf veins, or bands of dark streaks, causing leaves to turn brown and wither. Significant defoliation may occur; a banana plant may have only a few or no green (disease-free) leaves upon flowering. The cost of disease management is high. Bunch yield loss can be significant.
Management: A combination of cultural and chemical practices is recommended: field sanitation, host nutrition and sound cultural practices; fungicides; de-trashing (deleafing); pruning; ensuring good drainage and canopy aeration; plant nutrition; resistant cultivars. The indigenous Fe‘i banana of Pohnpei, ‘Karat’, shows good resistance to black leaf streak in that region. The best way for the homegardener to control the disease is to destroy the severely diseased leaves or remove them and place them topsidedown on the ground to reduce the chance of spore dispersal into the banana canopy.
Pseudocercospora musaea (syn. Mycosphaerella musicola) sigatoka, yellow sigatoka: Yellow sigatoka was formerly of greater importance in the Pacific than the similar black sigatoka. Symptoms are yellowish streaks on leaves, enlarging into narrowly elliptical gray spots with dark brown borders, up to 15 mm long and 5 mm wide. Leaves may turn gray or brown and hang from the plant, defoliating it. Bunches are small due to the presence of relatively few, healthy leaves at flowering.
Management: see black sigatoka.
Cladosporium musae (cladosporium speckle): Cladosporium speckle is a leaf spot disease of minor importance to most banana varieties and locations. Symptoms are variable among regions, affecting older leaves. Control is usually not warranted. Other fungi may also cause leaf speckle, such as Acrodontium simplex.
Drechslera gigantean (eye spot)
Leafspots:
Cordana musae (cordana leafspot)
Curvularia sp.
Phyllosticta spp.
Hendersonia toruloides
Helminthosporium sp.
Cordana leaf spot is a common but minor leaf spot disease on most banana varieties but can be severe on plantain varieties. Symptoms are pale brown, oval patches on leaves, surrounded by bright yellow halos. The disease may be controlled with the same fungicides used to control the
sigatoka diseases.
Fusarium oxysporum f. sp. cubense (Panama disease, fusarium wilt): A lethal disease caused by races of a soil-borne fungus,
Fusarium oxysporum: It is a devastating disease of banana worldwide. Infection occurs through roots and progresses to the pseudostem. Symptoms are internal stem necrosis (reddish or reddish-brown xylem), root and rhizome rot, yellow leaves, plant wilting, and plant death. Plants may die during flowering or during periods of moisture stress. The fungus may survive decades in soils.
Management: Largely preventive, by planting resistant varieties or pathogen pathogen- free materials (preferably tissue-cultured plants) in non-infested soil.
Pythium root rots:
Pythium arrhenomanes
Pythium aphanidermatum
Pythium sp.
Marasmiellus inoderma (stem rot)
A sometimes-severe pseudostem disease occurring in marginal soils (soils with poor nutrition or physical structure, low in organic matter, high in clay) or poorly drained or wet areas where M. inoderma occurs. The causal fungus is able to penetrate leaves, pseudostems, or roots to cause the following symptoms: decay and withering of outer leaf sheaths/blades; leaf stunting; cracked pseudostems; slow plant growth; plant stunting and death; and narrow pseudostems. White mushrooms often appear along the cracks in the affected pseudostems. Alternative hosts of M.
inoderma include coconut, rice, taro, and maize.
Management: Selection and use of disease-free planting material; moderate irrigation; fertilizers; soil improvement (compost, mulch); removal and destruction of diseased plants; promote conditions for vigorous plant growth.
Fruit diseases
Colletotrichum musae (anthracnose): A spot, rot, or blemish of ripening banana fingers. Initial lesions are roughly lens-shaped to circular and sunken and brown. The spots turn black, enlarge, and merge eventually; the spots become deep depressions covered in pink fungal spore masses. The splash-borne fungus, Colletotrichum musae, the spores of which infect the green banana fruits well before ripening, causes anthracnose.
Management: Regular cutting and removal of overly necrotic banana leaves (>50% necrotic) near bunches and throughout the field; careful fruit handling to minimize abrasions and wounds; keep fruit as cool as possible to slow down the disease; prompt ripening; on-time harvest; good packing house hygiene (e.g., clean water and equipment); prompt cooling of fruits to appropriate storage temperature after processing.
Colletotrichum musae, Nigrospora sphaerica, or Fusarium spp. (black end): Black decay of the finger stalk and the adjacent part of the finger; usually confined to the banana peel.
Management: Good plantation and packinghouse hygiene and ventilation; mulch dead leaves in field; keep packing house free of plant debris, rejected fruit, and other trash; de-hand bunches in clean water; use sharp de-handing knife for good, clean cut surfaces; keep fruit as cool as possible after harvest (both before and after ripening).
Ceratocystis paradoxa (syn. Chalara paradoxa) (ceratocystis fruit rot): Crown rot, stem end rot, and tip rot of green or ripe fruit. Crowns are soft, black, and water-soaked; dark fungal growth may develop in a mass; stem ends and skin may turn black. Fungal growth may cover the fruit skin with a white to greenish-black color; the pulp may rot and fingers may drop or ripen.
Management: Good packing house hygiene (clean and disinfest the packing house regularly; do not allow rotting fruit to accumulate). See also management for black end.
Verticillium theobromae and Trachysphaera fructigena (cigar end rot): A finger tip rot, dark brown to black; the fruit pulp is characteristically dry and fibrous or stringy; spore masses occur on the lesions, gray and powdery.
Management: Frequent removal of dead flowers from banana fingers, followed by bagging of bunches with perforated polyethylene sleeves; removal of bracts and dead flower parts that may accumulate in the sleeves after bagging; field sanitation; field cultural practices (de-leafing, pruning) to modify the environment (promote canopy aeration and exposure to light); packinghouse sanitation; culling of infected fruits before placing them in a wash tank; fungicide sprays.
Fusarium spp., Verticillium spp., Colletotrichum musae, and Acremonium sp. (crown rot): A blackening and rotting of the cut ends of banana fruit hands. As the fruit ripens, the rot advances down into the fruit stalks, contributing to fruit rot and premature ripening. A whitish-gray fungal growth may be present on the surface of affected crowns. Numerous fungi are associated with this disease.
Management: Good packing house hygiene (e.g., clean water in the wash tank); approved fungicides; rapid cooling of fruit after de-handing; refrigeration of fruit at not less than 13°C (55°F) during storage and sale.
Phyllosticta musarum syn. Guignardia musae (freckle): A relatively minor fruit disease in the Pacific. However, the pathogen also infects Musa leaves, which can serve as a source of disease for fruits. The symptoms are raised black pinpoint spots, occurring in groups, on leaf or fruit surfaces. The disease may render fruit unmarketable.
Management: Choice of banana variety (‘Cavendish’ is resistant); periodic and regular de-trashing (removal of diseased leaves, especially near developing or unprotected bunches); bagging of bunches; fungicides.
Sooty mold: A patchy, black, sooty surface mold on green or mature banana fruits. Sooty mold is the surface growth and spores of fungi, which use as their food source the sugary excretions of sap-feeding insects such as aphids, mealybugs, scales, and whiteflies. Management: Bagging of the developing bunches to block access of insects to fruit and to block fruits from deposition of sooty mold from insect-infested leaves surrounding the bunch; bunch sprays of copper fungicides; insect control methods; soak bananas in 1% bleach solution for a few minutes in a postharvest wash tank.
Deightoniella torulosa (swamp spot, speckle, black tip) (refer to photos below): A widely distributed disease but rarely a severe problem in maintained orchards; symptoms are reddish brown to black speckles on fruit skin or black fruit tips; overall, considered to be a common but minor disease that is dependent on poor air circulation within Musa plantations or habitats.
NEMATODE DISEASES OF BANANA
Banana nematodes are microscopic roundworms that live as soil-borne parasites of roots. The root-knot nematodes (Meloidogyne spp.) and the burrowing nematode (Radopholus similis) can significantly weaken root systems, reduce yields, topple plants before harvest, make plants more prone to wind knockdowns, reduce fertilizer uptake and utility, and reduce the banana-growing lifespan of a given piece of land. Nematodes are managed with avoidance, clean (nematode-free) planting material, heat treatment of planting material, pre-plant soil fumigation, crop rotation, mulching and composting, fallow, chemical nematicides, plant propping, fertilizer use, and varietal resistance. Following are the principal plant-parasitic nematodes associated with banana, in order of their relative threat to Musa production and/or as plant quarantine pests:
Radopholus similis (burrowing nematode): This is a major banana root pathogen, causing lesions to roots and rhizomes, banana decline, yield losses, and toppling; the nematode has relatively wide non-Musa host range.
Management: Nematode-free rhizomes are required to prevent large losses and dissemination of the nematode; nematicides; in severe infestations, bunch-bearing plants must be supported to prevent toppling before harvest; composting and mulching; soil treatment before planting; crop rotation; fallow. Meloidogyne sp., Meloidogyne incognita (root-knot nematodes)
Infection leads to swelling and galling of banana roots. Galled roots may crack and rot. Plants rise from the soil (“float”) and can topple during bunch development coupled with wet weather or water draining through the field. Rootknot nematodes can make a field unusable for commercial
banana production after 5 years.
Management: Avoidance; nematicides; cultural practices; nematode-free planting material; composting and mulching; soil treatment before planting; crop rotation; fallow.
Other nematodes
Helicotylenchus spp. (spiral nematode)
Rotylenchulus reniformis, Rotylenchulus sp. (reniform
nematode)
Pratylenchus coffeae (lesion nematode)
Tylenchorhynchus sp. (stunt nematode)
Criconemoides sphaerocephalum (ring nematode) Criconemella sphaerocephala
Hoplolaimus sp.
VIRUS DISEASES OF BANANA
All banana viruses are transmitted in infected planted materials. After planting, the viruses are usually spread further by aphids.
Banana bunchy top virus (BBTV) (bunchy top): This is the most serious virus disease affecting banana and plantain in Asia. It has been present in the region since the last century, and probably much earlier than this. Initial symptoms are dark green dots and streaks (“Morse code” streaking, up to 25 mm in length) on the veins of banana leaves. As the disease progresses, leaves become progressively smaller, erect, and brittle, with pale, ragged, necrotic margins. The most conspicuous symptom is the “stacking up” or bunching up/rosetting of leaves; the disease name derives from this reduced internode distance between leaves of affected plants. Symptoms can appear on plants of all ages, although young plants, when infected, may not bear fruit. Banana varieties vary somewhat in their reaction to the disease. Disease is spread by planting infected material or by insect transmission of the virus between plants. The banana aphid, Pentalonia nigronervosa, is the sole insect vector of BBTV and can transmit the virus by feeding on banana leaves, petioles, or pseudostems. P. nigronervosa is specific to Musa spp.
Management: Aphid (Pentalonia nigronervosa) scouting and management or spot-treatment (kerosene, mineral oil, soapy water, or conventional insecticides); field surveys for symptomatic plants; complete eradication of diseased plants and mats; use of virus-free planting material; tissue culture; and effective regional and international plant quarantine are important to control bunchy top. Once a region has been contaminated with BBTV, eradication is very difficult. Prevention of the disease is a key component to its management. There are no known resistant commercial banana cultivars, and there appears to be more than one strain of the virus. However, in Hawai‘I the ‘Dwarf Brazilian’ cultivar is more tolerant of bunchy top than Cavendish cultivars. The virus has a limited range of vectors, and is found in only a few species. Apart from abaca, the main spread is from banana to banana. This means that the eradication of infected plants is an effective control measure.
Banana streak virus (BSV) (banana streak): This virus was only identified recently, being first described in Africa in 1974 in the Ivory Coast (Lassoudière 1974), following previous reports of a mosaic disease in Africa thought to be caused by a strain of cucumber mosaic virus (CMV). Despite the fact that these first recordings of BSV were from Africa, in a relatively short period of time, the disease had been observed or identified in most banana and plantain producing areas of the world. This suggests that the causal agent, banana streak virus (BSV), has been widely distributed for many years, and that its geographical origin is still uncertain. It is clear that in the past the symptoms caused by BSV were confused with those caused by CMV. Indeed photographs of what is almost certainly BSV infection have even appeared labelled as CMV infection in reference texts.
The virions of BSV were first isolated in 1985 (Lockhart 1986) and are bacilliform in shape (ca 30 x 120 nm), containing a dsDNA genome of ca 7.4 kbp. A high degree of genomic and serological heterogeneity between BSV isolates has meant that indexing can be problematic. The virus is transmitted in a semipersistent manner by mealybugs and also through vegetative planting material. Long distance spread is primarily due to the use of infected planting material, including micropropagated plants. The mealybug vector can spread the disease locally, though this is thought to occur very slowly and over short distances. The use of infected planting material can also be responsible for local spread. It has been reported that the disease may be seed transmitted and this possibility is being further investigated.The late diagnosis is probably because it is a highly variable virus, which makes detection and indexing difficult. The virus is widespread, and has probably existed for a very long time. Symptoms (see photos below) tend to be more severe in poorly managed plantations. The symptoms consist of a combination of chlorotic streaks (broken or continuous) and narrow lesions on leaves. As the leaves age, the yellow streaks may turn brown and necrotic, resulting in a pattern of fine black streaks running parallel to leaf veins. Diseased plants may be stunted and have smaller bunches. Banana streak is transmitted by mealybugs.
Management: Control the disease through the use of virus-free planting material and eradication of diseased plants. Banana plants infected with BSV may periodically show no symptoms and therefore should be kept in quarantine for a period of 9 months or more. A startling recent discovery has been that all banana and plantain species contain segments of the DNA of this virus. When virus-free varieties of banana are propagated by tissue culture, the integrated DNA of the virus in the DNA of the plant sometimes becomes activated. As a result, the new plants are infected with BSV.
Cucumber mosaic virus (CMV) (banana mosaic): Banana mosaic is a disease of relatively minor importance to banana. Symptoms included yellow streaks or flecks on leaves in a mosaic pattern, leaf yellowing, and leaf mosaic. CMV is distributed worldwide and has perhaps the widest host range of any plant pathogenic virus.
Management: Unlike banana bunchy-top, both the virus and its vectors occur on a wide range of plant species. It is found in common crops such as bean, cucumber, pepper and tomato. Eliminating the sources of virus outside the crop is important in controlling this disease.
Use of pathogen-free planting material and control of alternate hosts (weeds, legumes, cucurbits, members of the Solanaceae, such as tomato).
BACTERIAL DISEASES IN THE PACIFIC
Ralstonia solanacearum race 2 (biovar 1) (moko disease): Moko disease is a wilt of banana and cooking banana (especially Bluggoe [ABB Group]) common in Central and South America (moved there in seed pieces). There is no known resistance to Ralstonia solanacearum among edible bananas (‘Pelipita’ ABB and FHIA-03 have some resistance where the insect-transmitted form exists; the absence of a male bud and/or “dirty stem” below the bunch provides useful control). Insect transmission of the bacterium enables the disease to spread rapidly in some locations.
Management: Control of the disease is difficult and expensive. Methods include quarantine; routine plant inspection and destruction of diseased plants; variety selection; tool disinfestations; destruction of neighboring plants (adjacent to diseased areas); prompt removal of the male flower bud after the last female hand has emerged.
Erwinia spp. (rhizome rot): This disease is caused by a bacterial genus known for its ability to cause soft rots on a wide range of host plants and tissues. These bacteria infect banana plants through leaves and pseudostems, causing the following symptoms: wilting or death of leaves before fruit has ripened, vascular discoloration, and internal rot of the pseudostem (usually accompanied by a characteristically foul odor) (see photos below)
Management: Cultural control tactics such as planting of disease free material, and prompt identification and eradication of diseased plants (preferably by burning).
ABIOTIC DISEASES OF BANANA IN THE PACIFIC
Abiotic diseases are noninfectious and include nutrient deficiencies and environmental disorders.
Common nutrient deficiencies and abiotic conditions of Musa in the Pacific
Nutrient deficiency symptoms are common for banana grown in Pacific island soils. In some cases, deficiency symptoms may appear as a group because several elements may be lacking (e.g., N, K, Ca, and B). The symptoms are usually both preventable and correctable with choice of location, improved soil characteristics and fertility, and the use of amendments and fertilizers
Boron (B): Chlorotic streaking of leaves, oriented perpendicular to and crossing the primary veins; leaf malformation; interveinal chlorosis. Foliar malformation may result. This deficiency can develop slowly over time.
Calcium (Ca): General dwarfing; reduced leaf length; reduced rate of leaf emission; leaves are undulated; tissue near midrib thickens, may turn reddish-brown. Fields should be limed periodically; correctable with calcium nitrate.
Iron (Fe): General chlorosis of the entire lamina of young leaves; retarded plant growth; small bunches. Apply iron compounds to soil; foliar sprays of Fe using naturally occurring or manufactured iron-containing compounds.
Magnesium (Mg): Marginal chlorosis of older leaves; violet-colored marbling of petioles; fruit may have defective flavor and not ship well; symptoms are reduced by use of magnesium sulfate.
Nitrogen (N): A generalized yellowing of leaves; rose-colored tints on petioles and leaf sheaths; stunting; rosetting; slender pseudostem; small petioles and leaves; reduced life span of leaves; notable reduction in yield. Banana is more sensitive to a lack of nitrogen than any other element; problem is compounded by dense stands of weeds or grass.
Potassium (K): Rapid yellowing of oldest leaves, which then turn orange and dry up; leaves may become tattered and fold downward; leaves are crumpled in appearance; bunches are poorly filled; correctable with potassium fertilizers such as potash.
Sulphur (S): Leaves are chlorotic and reduced in size, with a thickening of secondary veins; undulating leaf edges; necrosis along edge of lower leaves. Correctable with sulfate fertilizers such as ammonium sulfate, potassium sulfate, and magnesium sulfate.
Zinc (Zn): Rosetting and stunting; chlorotic, strap-shaped leaves; leaf chlorosis in stripes or patches; abnormal bunch and hand characteristics; symptoms may be more severe in sandy soils
Abiotic fruit disorders
Abiotic fruit disorders reduce fruit quality and may reduce fruit grade or render fruit unmarketable.
Chilling injury: A necrotic flecking just below the surface of the green skin and pulp of the banana fruit, caused by exposure of banana fruits to temperatures below 13°C (55°F). Management: Avoid refrigeration at below 13°C (55°F).
Choke throat of banana: It is a physiological disorder of bananas. Choke throat occurs when the bunch is about to emerge from the top of the pseudostem but becomes trapped at various stages of emergence. In its most severe form the bunch fails to emerge from the top of the pseudostem and instead bursts through the side of the pseudostem (see photos below). Such bunches are worthless. In less severe cases the top 1 or 2 hands become trapped in the throat of the plant leading to badly misshapen fruit. Bunches which experience difficulty in emergence usually have several leaves closely ‘bunched’ together at the top of the pseudostem.
Choke throat is seasonal in nature. It is usually worst in the winter and early spring following cold weather. However, it can also occur following periods of waterlogging or severe water stress and following wind storms. Two factors contribute to the actual difficulty in bunch emergence: (a) due to a reduction in the elongation of internodes of the true stem bearing the bunch inside the pseudostem (pseudo = false) and (b) the stiffness of the leaf bases at the top of the pseudostem can prevent proper bunch emergence. Some varieties are more susceptible to this disorder than others. Notably Williams and Mons Mari are far less susceptible than Dwarf Cavendish. Choke throat is often associated with dwarf varieties. Dwarf off-types from tissue culture are particularly susceptible.
Management:
Select taller varieties, which are less susceptible to choke, throat, eg Williams.
Choose a warm environment, one which is well protected from frosts and strong winds. Slopes facing the north and north west are usually warmer.
Control time of bunching to avoid cold weather prior to bunching. Plants bunching in the late spring to mid autumn are less affected.
Good on-farm drainage measures including mounding of rows.
Regular irrigation to avoid water stress particularly during hot-dry weather.
Higher nitrogen rates are thought to be beneficial.
Fused fingers: The fusion of banana fingers is the result of a genetic mutation or defect, seen particularly in Cavendish varieties. Hands with fused fingers may not be marketable but are completely safe to eat.
Management: Destroy the affected plant and its suckers if found on a commercial farm; use the fused hands as animal food.
Maturity bronzing: A reddish-brown to brown discoloration of mature green bananas; fruit skin may develop cracks and scabs. The cause of this problem is unclear; however, it appears to be a physiological disorder resulting from periodic water stress. Calcium deficiency may also be implicated.
Management: Irrigate to avoid moisture stress when bunches are young. Do not allow bunches to “over-fill” before harvest.
Precocious ripening or mixed ripe: Individual fingers ripen prematurely, which could be caused by harvesting over-mature bananas; excessive postharvest storage or transit temperatures; anthracnose wound infections on fruit skin.
Management: Harvest fruit that is at a proper stage of maturity; adequate temperature control after harvest; fungicide dips of fruit; well ventilated fruit storage. This problem may occur as a result of severe leaf disease, such as black leaf streak (black sigatoka).
Sap damage: Stains on banana fruit skin, caused by contact of the sensitive green fruit surface with its own banana sap during de-handing and packing activities
Management: Avoid sloppy de-handing work; soak banana hands in clean water in a washing/de-sapping tank for enough time to allow the fresh wounds (from the cutting and de-handing process) to stop emitting the staining sap. The water in the tank dilutes the flowing sap so that it cannot damage the green banana tissue.
Senescent spots: Senescent spots, a natural part of the ripening process for Cavendish bananas, are numerous, superficial brown flecks on peels. Spots are shallow (less than 1 mm [0.04 in] deep) and do not enlarge or change color. The brown spots are caused by the death of small groups of cells in the outer peel, usually after treatment in a ripening room. The condition
is associated with the forced ripening of overly mature banana fruits.
Management: Avoid the harvest and ripening of overly mature fruit. Splitting of fingers
Longitudinal splits in fingers; ripe fingers separate from the hand. The splitting can be caused either by high relative humidity (>95%) during final fruit ripening or harvest and ripening of over-mature fruit or over-caliper fruit (bunches left on plant too long, leading to overly swollen fingers).
Management: Lower the relative humidity to 70–75% during fourth and fifth day of ripening; ensure good aeration in ripening room; restack cartons so that ventilation slots are aligned with each other; harvest fruits on time according to caliper grade. Avoid harvesting and ripening bunches with swollen fingers due to late or missed harvest.
Other pests
Wild birds, bats, and rodents not only feed on banana fruits but often construct nests within the bunch, poised to feed their young when the bananas ripen. Rats can be a serious problem; therefore bananas should be harvested just before or at the first sign of rat damage, then hung upside-down in a rat-free environment until ripe.
Reference:
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