AgriGuide

Banana

Bananas constitute the fourth most important global food commodity (after rice, wheat and maize) grown in more than 100 countries over a harvested area of approximately 10 million hectares, with an annual production of 88 million tonnes (Frison and Sharrock, 1999).

The term banana refers to all types of bananas including cooking bananas. Bananas with all its species, varieties or hybrids belong to the genus Musa, order Zingiberales, family Musaceae. The genus Musa contains up to 40 species, with all wild species and native to South East Asia (Stover and Simmonds, 1987).

Banana (Musa species x Paradisiaca) is an important crop in sub-Saharan Africa, where besides consumption as food, bananas have cultural and medicinal values. There are many types of bananas grown in Africa, but depending on how bananas are utilised, they can be broadly grouped, as follows:

• Dessert bananas include Cavendish, Red Bananas, Apple bananas and Gros Michel. These are consumed as ripe fruits (table bananas). Most cultivars are susceptible to nematodes; Sigatoka leaf spots and Fusarium wilt although they are generally tolerant to weevil attack. Cavendish cultivars are the most popular and valuable of the dessert bananas and are traded worldwide.
• Cooking bananas include the East African highland bananas (EAHB) and many other types of plantains consumed as cooked or roasted bananas. The EAHB are said to be endemic to the East African region and grow comfortably at higher altitudes (above 1000m asl). Also, most plantains are lowland varieties and are very susceptible to weevil attack.
• Beer bananas cultivars are used mostly for production of banana juice which is directly consumed or used for making banana beer, wine or spirits.
• Multipurpose bananas include a number of improved cultivars such as the FHIA hybrids. These have multiple uses from being used as dessert bananas to juice production. They are also tolerant to nematodes.

Botany

Edible bananas contain no seeds. Reproduction is carried out via its subterranean rhizome, the shoots of which regularly form fruitful buds. The banana plant possesses a so-called pseudo-stem, which is created by the leaf sheathes. Inflorescence usually begins around 7-9 months after planting, depending on climatic conditions and type of soil.

Bananas are reproduced vegetatively. In accordance with availability, required amounts and transport possibilities, the following are suitable:

• Whole rhizomes; and
• Rhizome pieces;
• Shoots with inflorescence in the pseudo-stem; and
• Shoots lacking inflorescence in the pseudo-stem.

Using whole rhizomes is laborious. It requires a large amount of starting material and generates high transport costs. Rhizome pieces and shoots lacking inflorescence in the pseudo-stem are less expensive.

It is very important that the shoots are undamaged, and originate from nematode-free plantations. Prior to planting, the roots and any damaged spots should be removed with a sharp knife.

Methods of planting

Bananas are a perennial tropical and subtropical crop, which grow in a wide range of environments. However, the banana production systems can be divided into three broad categories depending on the number of cultivars grown and the intensity of management.

a. Backyard garden system

Banana is grown in a highly integrated system especially in peri-urban areas where land is limited. Bananas are grown mainly for food in combination with other enterprises like zero grazed animals or vegetable gardens to supplement nutritional or peri-urban market needs. This is a low input system and normally no proper pest and disease management is performed.

b. Perennial agroforestry system

Bananas are intercropped with perennial crops like coffee, vanilla, cocoa or fruit trees. Bananas serve as a middle storey shade crop, but also provide food for household needs. Any surplus is sold to the market. Different cultivars are normally grown together depending on the location and the intended use of the bananas. The plants are not replaced until they die of senescence or pests and diseases. This is a low input system and many pests and diseases are either partially controlled or not controlled at all, making banana production highly vulnerable. However, it is the most common production system in most banana producing areas in Africa.

c. Commercial plantation

This is performed as “single cultivar” monoculture system, comprising dessert banana cultivars which have good export potential. Management of these plantations is characterised by careful selection of cultivars/varieties and very often intensive use of synthetic fertilizers and pesticides. Well-defined crop cycles usually last 2 to 5 years after which all plants are uprooted and replaced.

Challenges to banana production in Africa

Production of bananas in Africa is, however, threatened by many challenges, including:

• Pests and diseases are the main threat to banana production. Traditional banana cultivars have been severely damaged by a wide range of pests and diseases, resulting in heavy yield losses. For example, bacterial wilt and Fusarium wilt are serious threats in many sub-Saharan African countries leading to 100% losses. Nematodes, banana weevils, Sigatoka leaf spots and banana bunchy top virus disease have also caused immense damage to plantations. Most farmers lack information on proper management of these infections so they continue to spread them unknowingly.
• Low productivity is mainly due to poor soil fertility management, water conservation and husbandry practices. In highland areas, banana plantations are not terraced and yet many trees are cut out of the garden. Running water from uphill washes down the topsoil and mulch. Bananas require good soil moisture. Many suckers are left per banana stool, pruning and removal of male buds is either done late or not at all. Crop cycles are not regulated whereby the same garden of bananas is left for a long time without rotation or replanting. Suckers for establishing new gardens are carried with all their roots from one village to another, thereby spreading pests and diseases.
• Hailstorm and wind damage can affect bananas production. Bananas have shallow spreading roots, weak stems and leaves. This makes them very susceptible to strong winds and hailstorms especially during the fruit bearing stage. This is a common problem in monoculture banana plantations where trees are cut for other purposes and in highland areas.

Improving management of banana pests and diseases

Bananas are susceptible to a wide range of pests and diseases. Some of these pests and diseases are highly destructive and very contagious (easily spread), and once introduced they are persistent and difficult to eradicate.

The severity and occurrence of pest outbreaks and plant damage depends on the prevailing environmental conditions, specific banana cultivars, and the specific disease or pest. However, most of these can be managed and controlled by implementing organic production practices.

The main approach in organic pest and disease management in banana production is prevention and proper management of infections to restrict spread and multiplication. With proper implementation of cultural practices (e.g. soil fertility improvement, crop rotation, use of resistant varieties and clean planting materials, proper sanitation in the field and rouging of infected plants) many of these pests and diseases can be effectively managed. This is also necessary because most the destructive diseases cannot be eradicated by direct control methods.

Establishing a new banana garden

A site with deep, well-drained and fertile soils, preferably rich in organic matter is good for banana production. It will encourage the development of strong plants that can tolerate infections. A newly opened land without signs or history of nematodes or the devastating Fusarium wilt and bacterial wilt diseases is preferred.

If the site has been used for production of bananas in the last two years, it is highly recommended to remove all remaining banana plants and corms. Normally such remnants harbour a lot of pests and diseases. The remnants should be transferred into another field (not of bananas), chopped and spread to dry or composted.

The land should then be planted with a legume crop (like beans) or left to fallow with a legume green manure cover crop for 1 to 2 years. This will ensure that any remaining pest or disease infections are completely removed before introducing new banana plants.

All perennial weeds should also be removed and destroyed before planting because bananas are very susceptible to weed competition. Some of the existing trees at the selected site should be left during land clearing in order to protect the young banana plants from wind and strong direct sunshine.

Selection and preparation of planting material

Sound management of banana pests and diseases begins with a careful selection and handling of pest and disease free and, where possible, resistant planting materials. The right cultivars and varieties should be selected with respect to the disease problems prevalent in a given location.

Some cultivars are resistant to certain diseases like Cavendish and highland cooking bananas, and varieties like FHIA 17 (Cavendish variety), FHIA 23 (Gros Michel variety) are resistant to the devastating Fusarium wilt (Panama) disease. Clean planting materials of superior banana cultivars that are resistant to diseases exist, and can be obtained through local extension officers and research stations. It is advisable to plant different cultivars and/or varieties in the banana plantation. In case a variety or cultivar is attacked by certain pests or diseases, then the whole field will not be wiped out.

Bananas are propagated using suckers or corms from the mother plant. Generally, well treated suckers/corms are highly recommended because they are free of pests and diseases. Suckers for planting should be carefully selected and prepared to minimise spread of pests and diseases. They must be obtained from pest and disease free plantations. Sword suckers are preferred because they are usually less infected with nematodes and weevils than bigger suckers.

Recommendations to farmers for preparing planting seedlings

• Planting materials should be prepared in the field from where they are being obtained to limit the transfer of infections into new fields.
• Remove all leaves, outer leaf sheaths, roots, dead parts of the plant and pare the corm (trim off part of the corm) to eliminate weevils, weevil eggs and nematodes. Any brown and black spots that may appear on the corms should also be removed until only white corm tissue remains.
• It is recommended to treat the suckers to clean them of any infections. This is done by soaking the suckers in soapy water over night to eliminate weevil eggs and nymphs. Alternatively, the suckers can be treated by soaking the base of the plant in hot water (about 60°C) for 10 minutes. This will kill all nematodes in the outer layers of the sucker. A 10% household bleach solution (100ml of solution in 1lt of water) is also useful for disinfesting corms. Submerge the base of the suckers into the solution for about 20 minutes. Treated suckers should be planted within one week to avoid being re-infected.

Recommendations to farmers for planting a banana garden

Farmers should be advised on how to set up a banana garden by following these simple guidelines as:

• Mark out rows with a spacing of 3m*3m (10f*10f) to get the proper plant population of 450 plants/acre. This helps to avoid competition between banana plants and limits spread of pests and diseases from one plant to another.
• Dig out planting holes 60cm*60cm*60cm (2f*2f*2f) while placing the top soil and subsoil on separate sides of the planting hole. This ensures that during planting, the top soil mixed with manure/compost will be used for refilling the hole.
• Plant bananas at the beginning of the rainy season so newly planted plants receive enough water for quick establishment. When planting, do not completely fill the planting hole. Leave a shallow basin of about 1ft to enhance harvesting water for the young plant. Later during growth, this also provides a conducive environment for producing new suckers away from the mother plant.

Routine management practices

Some management practices are helpful in both strengthening the growing banana plants and in minimising the spread of pests and diseases. However, these practices need to be routinely applied together as a package as leaving one practice may undermine the benefits achieved from the others.

a. De-suckering

Competition between suckers depletes soil fertility very fast and results in weak plants which are very susceptible to infections. About 3 to 4 suckers should be maintained per stool in order to ensure strong plants and good yields. Any extra suckers should be removed when they are still young. Suckers at different growth stages (mother, daughter and granddaughter) on the opposite side of the mother plant, should be chosen, also to avoid competition for light. De-suckering should be done well, so that pruned suckers do not grow up again. The sucker pseudostem should be cut off near its corm and the sharp point of the knife twisted into the growing point to kill off the sucker permanently. During this operation, care must be taken not to harm other daughter plants.

In the course of time, the banana plants tend to grow away from the original space whereby the gaps between the plants become smaller. At this point, it is necessary to remove the plants that stand close to each other. If the original pattern of the banana plantation becomes completely distorted, then the plantation should be cleared and newly planted.-

b. De-leafing

Old leaves and sheaths are susceptible to infections and can host infections if not removed in time. Removal of old leaves helps in management of the Sigatoka leaf spots, limiting its spread to young leaves and plants, while the removal of old sheaths eliminates hiding places for adult banana weevils. In addition, old leaves that hang downwards shield the young plants from sunlight. It is recommended to remove all old leaves and sheaths that have attained natural senescence and use them as mulch.

It is, however, important that enough leaves are left on the plant to produce a good quality bunch. The average number of leaves per banana plant should be 8 to 10 leaves at flowering and 4 at harvest. Complete de-leafing of the plant prior to harvesting is not recommended as this starts the ripening process, before the plant is actually ready.

c. Cutting off male buds

Removing the male buds early also helps reduce the spread of diseases like the banana bacterial wilt, which can be transmitted by bees collecting nectar from the banana male buds. Care should be taken not to damage the hands of the bunch while removing the male buds. Male bud removal also encourages quicker development of the young bunch.

Management of specific pests and diseases

Banana weevils and nematodes are the most important pests of bananas, attacking nearly all banana cultivars. On the other hand, banana has a multitude of diseases which can cause significant yield losses if not well managed.

For example, the black sigatoka, bunchy top disease, streak virus disease, and the highly devastative bacterial wilt and Fusarium wilt (panama) diseases.

Pest management

a. Banana weevil (Cosmopolites sordidus)
The Banana weevil is a very damaging banana root borer. The larvae bore into corms, suckers, and roots and lead to extensive root destruction. This leads to stunted plant growth and eventually premature toppling of the plants and plant death.

Recommendations to farmers for management of the banana weevil

• Use clean planting materials for planting new banana plantations;
• In heavily infested gardens, crop rotation is highly recommended. Progressively destroy the garden and remove all banana plants and their corms. Chop them to dry or compost them and plant other crops in the field for 1 to 2 years. Make sure all corms/roots are destroyed;
• Ensure field hygiene. It is a common practice to split the pseudostem after every harvest. The stem is split open and the sheaths are spread out to dry so that weevil eggs and larvae are destroyed. The sheaths should, however, be laid about 2ft away from the banana stool, like any other mulching material in a banana plantation. Do not move banana residue material (pseudostems, corms, sheaths) from one field to another to limit transmission of weevils;
• Trap the weevils. Laying traps to catch banana weevils and killing the weevils collected from traps can be an effective method of controlling weevils especially in small gardens. The weevils are mobile at night and can be trapped by baiting the field with slices of banana pseudostems. Traps should be cleared every 3 days so that they do not become a breeding ground for the weevils. All trapped weevils should be picked from the baits and destroyed or fed to poultry.
• Keep the banana stool clean. Mulching materials or any debris should not be put close or within the stool to deny weevils a hiding place. Also, any banana plant remains from infected gardens should not be used as mulch in clean banana gardens.
• Use natural pesticides, such as wood ash, tephrosia leaf dust, chilli preparations with animal urine, tithonia leaf extract, and neem oil. These materials should be applied at the base of the plants around the stool and around infected pseudostems. However, it is important for certified organic farmers to check with their certification body before using any factory-made products for weevil control.

Also, it would be useful to have working groups on field identification of banana pests and diseases. Extensionists can organise field visit with farmers to different banana fields and identify any observable signs of pest or disease problems. Ask the farmers to analyze the signs of infection and identify the pests or diseases.

b. Nematodes
Radopholus similis and Pratylenchus goodeyi are the most damaging nematode species on bananas. Nematodes are microscopic (not visible with the naked eye) pests, which feed on banana roots. They destroy the roots and reduce uptake of water and nutrients. With damage to the roots, plants will lose stability and topple down.

It is, however, hard for farmers to distinguish between damage caused by the nematodes and the banana weevils. Nematode attack will cause the plant to topple down with all the roots exposed (the whole plant is uprooted) while weevils will cause the plant to break from the base at the soil level. New fields become infested with nematodes when suckers from infected fields are used; nearly all suckers will be infected with nematodes in an infected field. Cooking bananas and plantains are particularly susceptible to nematodes.

Recommendations to farmers for management of the banana nematodes

• Use clean planting materials to ensure that no infections are introduced into the new fields;
• Crop rotation is highly recommended;
• Increase soil fertility by adding of compost in planting holes, top-dressing with organic manures and mulching with organic materials increases soil life activity and has a negative effect on soil pests like nematodes. It encourages establishment of stronger plants that are less susceptible to toppling as a result of nematode infestation.
• Field hygiene. Besides planting materials, nematodes can also be spread through soil carried on farm tools, farmers shoes/feet and banana residues, mainly corms. Therefore, ensure that cleaning is done of all tools and farmers shoes/feet before entering a healthy garden. Banana corms should not be shared between gardens to limit the spread of nematode infections.

Disease management

a. Bacterial wilt

Bacterial wilt is the most destructive banana disease, attacking all types of bananas. It is caused by Xanthomonas campestris pv. Musacearum. Infected plants show premature ripening and staining of fruits, yellowing of leaves, the male bud dries prematurely and a pus-like liquid flows when the stem is cut. The infection is spread when farm tools and infected plant parts are moved from infected to healthy gardens. It is also spread by pollinating bees visiting male buds of infected plants and passing the infection to male buds of healthy plants.

To effectively manage the bacterial wilt disease, participatory and community action is normally necessary. Local leaders, NGOs, extension and research staff can be very helpful in mobilising communities to implement strict quarantine practices.

Recommendations to farmers for management of the banana bacterial wilt
The disease can also be managed by employing the following measures:

• Destroy all plants showing symptoms of bacterial wilt. At the very first show of any signs. Cut the entire plant and heap to rot or bury, to limit the spread of the disease. All tools must be disinfected by flaming them over fire or by cleaning them with Sodium hypochlorite or any other bleach solution.
• Use clean planting materials. Use tissue materials or treat banana suckers to ensure that no infections are introduced into the new fields.
• Crop rotation. After uprooting all banana material from the infected plot; grow other crops for a period of at least 2 years, followed by re-cultivation with pest-free banana planting materials.

b. Fusarium wilt

Fusarium wilt is caused by the soil borne fungus, Fusarium oxysporum f.sp cubense (Foc). It spreads mostly through infected suckers, soil attached to plants, tools and shoes/feet. As the disease disrupts the plant’s water vessels, leaves become yellow progressing from old to young leaves. The leaves then collapse at the petiole forming a skirt around the plant. Vascular tissues (pseudostems, corm leaf stalks), will also show discoloration to yellow, pale and dark red lines (i.e. infected vessels).

Gros Michel and apple bananas are highly susceptible to Fusarium wilt. The fungus can survive in the soil for many years (up to 30 years) and is thus very difficult to control. Fusarium wilt can be distinguished from Bacterial wilt by the absence of symptoms in young suckers of less than 4 to 5 months of age.

Recommendations to farmers on management of the banana Fusarium wilt

Always use resistant cultivars or varieties - This is the most cost-effective and sustainable method of controlling the Fusarium wilt in the field. Resistant varieties include: Cavendish, FHIA 17, FHIA 23 and other hybrids.
Field hygiene. It is recommended to destroy infected gardens; remove all banana plants and their corms. Chop them to dry or compost them to limit the spread of infection. Plant the field with other non-susceptible banana cultivars (cooking bananas, Cavendish, or other hybrids). Select new clean fields for replanting with clean banana planting materials. Ensure that proper cleaning is done of all tools and farmers shoes/feet (dipping in a 10% Sodium hypochlorite solution) before entering a healthy garden. Banana corms should not be shared between gardens to limit the spread of nematode infections.

c. Black sigatoka

Black sigatoka is also called Black leaf streak (caused by fungus Mycosphaerella fijiensis). It is the most important leaf disease that reduces yields. The disease causes severe discolouration and leaf necrosis, reducing the effective photosynthetic area dramatically and leading to poor fruit formation and small fingers.

As the pathogen can be spread by wind or water, it becomes difficult to control.

Recommendations to farmers for management of the Sigatoka leaf spots

Sigatoka leaf spots can be managed by applying the following cultural practices to improve host resistance and minimize the spread of infection:

• Improve soil fertility - Enhancing plant nutrition has been found to reduce leaf spot impact. A fertile soil encourages quick growth of the banana plant before significant leaf tissue is destroyed by the pathogen.
• Maintain proper spacing. As banana trees grow and produce suckers, there is a possibility of the space between neighbouring plants to reduce. It is important for the farmer to regulate the space between plants such that plant leaves from adjacent plants do not touch and rub against each other. This will limit the spread of sigatoka leaf spots.
•  Ensure field hygiene. Remove old leaves and mulch them in non-banana gardens to limit infecting young leaves and plants and banana leaves and stalksshould not be shared between gardens to limit spread of infections.