How to handle banana pests

Those who involved in banana farming are familiar with pests, whereas those who intend to start will know them with time. They are insects or other creatures that thrive by eating parts of the banana plant such as the roots, corm, stem, leaves and any other part.

When they do that, they weaken the plant as they take away nutrients thus leading to significantly reduced yield, toppling or falling off of the plants and damage to the plantation. They therefore need to be better managed to ensure that we have healthy plantations.

BANANA WEEVIL
This is one of the most devastating well known pest. It lays its eggs in the corm and when they hatch into larvae, which look like large maggots, they eat the corm and lower part of the stem.

They bore holes in the whole foundation of the plant. In this process, they take vital nutrients which would otherwise make the plant stronger and yield better. The larvae mature into adults which then mate and lay more eggs.

Weevil infestation in young plants causes stunting, disruption and delay of fruiting, and sometimes leads to plant death. Heavily infested plants produce small bunches, and have reduced resistance to drought and strong winds which makes them to topple.

The banana weevil causes more damage to the cooking bananas than the beer bananas.
Poor management such as no desuckering and no pruning encourages weevil attack and damage. Control methods include management of the sites where the weevil lays her eggs. These methods requires no extra input.

1. Use of clean planting material: Disease- and pest-free tissue culture seedlings minimises the spread of weevils, which are mainly carried to new sites with infested suckers.
Clean suckers are obtained from tissue culture nursery operators, companies or agents. Other practices using conventional suckers have been proven to be ineffective. This is especially when corms to be used as planting materials are already infected and if methods of disinfecting them have not been done properly.

2. Good husbandry: This involves weeding, desuckering, pruning, manuring and mulching, which produce vigorous plants that are more tolerant to weevil damage.

3. Destruction of post-harvest residues: Removal and splitting of harvested stems into small strips and drying them reduces hiding and breeding sites for the weevil. It also exposes weevil eggs and larvae to desiccation and death.

4. Trapping: Two types of traps, pseudo stem and disc-on-stump, are used. The first is made from pseudostem pieces split into halves and placed against a banana plant with split surface on the ground.
The second, on the other hand, are made by cutting harvested stump, 15-25 cm above ground level and then placing a pseudo stem sheath or banana leaves on top of the stump. The weevils attracted to these traps are collected and destroyed. Traps remain effective for about one or two weeks and are renewed whenever ample supp1y of pseudostem pieces are available.

5. Use of mixtures of ash, urine and insecticidal plants: Traditionally, farmers have used ash in banana fields to enhance soil nutrients and control weevils. Farmers are now using mixtures prepared by adding various levels of ash, urine, tobacco, capsicum, phytolacca and other weed species.

The method and rates of application vary from farmer to farmer. But the most common one is use of a 14-day fermented mixture at one to two cups (500 ml-1,000 ml) per banana stool. While the practice is recommended and encouraged, its field efficacy, economics and scalability are still unclear.

Apart from cultural practices, chemical control can also be employed. This can be done at planting if one is planting corms or traditional suckers. In case one is using tissue culture seedlings, there is no need to apply chemicals at planting because the seedlings are disease and pest free.

In case one is using conventional suckers, an insecticide such as Furadan, Pimicid, Mocap and Dursban should be systematically applied around the sucker in the planting hole.

In the case of established plantation, the insecticides should be applied to the soil around on the base of the banana stool. The chemicals can also be applied on the traps to kill the weevils that have already been attracted to the traps. It is extremely important for a farmer to seek advice from experts before applying such chemicals for weevil control.

NEMATODES
Apart from weevils, the other most damaging banana pests are the nematodes. They are minute worms (cannot be seen with a naked eye) that live in the soil and infest plant roots damaging them significantly.

Nematodes eat off the roots leading to rotting and weakening grip of the plant in the soil. They are responsible for the short lifespan of banana plantations in central Uganda where they are rampant, and also for migration of bananas to western, where their incidence is still much lower. When the roots are eaten by these microscopic creatures, they die. This interferes with water and nutrient uptake by the plant.

The most obvious symptom is the toppling of the entire plant, particularly fruiting ones. In general, damage to the root system results in: stunted growth, premature leaf drop, reduced vigour and delayed ratooning, small and poorly filled bunches, and increased susceptibility to water deficiency and stress.

Management strategies
The perennial nature of banana (growing over years) and the subterranean (below ground) and endoparasitic (within plant tissues) nature of nematodes makes control of the pest very difficult. However, a number of control measures have been employed but their success against nematodes is influenced by various environmental and plant-based conditions.

Some of the control measures include the following:

1. Use of clean planting material: The spread of nematodes across and within regions is attributed to transfer and planting of infested planting material (suckers) and can be avoided by using nematode-free or tissue culture seedlings.
Field suckers can be cleaned by corm paring followed by treatment with a nematicide (a chemical that kills nematodes) to some extent helps those planting conventional suckers. However, this has its limitations.
The use of tissue culture plantlets significantly delays infection by nematodes and increases the lifespan of banana plantations in central region, where nematodes are a big challenge.

2. Crop rotation: Rotating bananas with non- or less favourable hosts lead to decline in nematode populations in a field.
Root crops (cassava and sweet potato) have to be proved potential rotation crops against nematodes.
After a rotation crop or fallow, the next banana crop then is started with a low or no initial infestation of nematodes in the soil.
This is effective where farmers have come to terms with the fact that bananas can also be grown and re-grown after some seasons/years.
This is a standard practice in some countries such as Taiwan where bananas are grown for one year, then they are destroyed by a typhoon the following year, and re-planting is again done. In that country, banana is therefore more or less a seasonal crop.
Farmers (especially in the Central region) should therefore not give up giving up once the field goes.
Allow the fields to fallow or plant a rotation crop, and the nematodes to disappear for one year, and then re-plant bananas using tissue culture seedlings again, and you will be in business.

3. Soil amendments and mulching: Well managed (mulched, weed-free, manured) plantations and backyard garden plants (constantly receiving household wastes) have a long period of good productivity. In addition to enhancing vigorous plant growth, mulches may affect soil nematode populations through the benefits of organic matter and by altering the micro environment.

4. Chemical control: For quick and efficient impact on nematode pests, chemical nematicides offer the best alternative. The use of nematicides is only feasible in commercial plantations.
Their use in the subsistence production systems is not economically justified. Chemicals are hazardous to man and the environment, and may negatively affect natural enemies of many pests.
As with the banana weevil, the nematode population should be regularly monitored to justify the implementation of appropriate nematicide treatment.
Some chemicals act as insecticides as well as nematicides, for example, Furadan and Mocap so the application procedures for control of the banana weevil will also work for the namatodes. Apart from weevils and nematodes, other banana pests include termites, monkeys (for farms near forests), and some ants.

In the next articles, we shall look at the different types of bananas and the cost-benefit analysis of a banana farm as a business venture respectively.

The writer is chief executive officer, NSIGOTECH Tissue Culture Laboratory.
E-mail: [email protected]

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