The banana weevil and plant nematodes are the most destructive pests of bananas in Uganda. These pests may result in severe yield loss if uncontrolled.
During training in a past Harvest Money Expo, John Paul Buyungo, a plant doctor, outlined the most dangerous pests in bananas and how they can be controlled.
Damage and signs
- It results from larvae feeding and tunneling into banana corms and pseudostems. The adult weevil lays its eggs near the corm and on hatching, the larva attacks the underground part, boring tunnels in it.
- As weevil larvae grow in size, they make large tunnels 115cm in diameter.
- The damage weakens the plant and interferes with the uptake of nutrients and water.
- Weevil infestation of 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, leading to snapping and toppling of large or matured flowered plants.
- The banana weevil causes more damage to the cooking types than it does to the beer cultivars.
- Weevil damage may increase when plants of reduced vigor are attacked. Low vigor is a result of plants being grown in soils of low moisture and fertility levels, weeds, or intercrop competition for nutrients.
- The absence of banana weevil from higher elevations suggests that the weevil has a lower temperature threshold for larva development or adult survival.
Handling of the weevil habitat and oviposition site provides the first line of defense against the banana weevils.
Use of clean planting materials
This minimises the spread of the weevils which are mainly carried to new sites with infected suckers.
It involves clean weeding, de-suckering, pruning, manuring, and mulching, which produce vigorous plants that are more tolerant to weevil damage.
Destruction of post-harvest residues
Removal and splitting of harvesting stems into small strips and spreading them out to dry quickly reduce hiding and breeding sites for the weevil.
At planting, a certain amount of insecticides such as Furadan, Pimicid, Mocap, and Dursban should be systematically applied around the suckering of the planting hole. In the case of established plantations, the insecticides should be applied to the soil around the base of the banana stool.
Research is ongoing to develop a biological control strategy for the banana weevil using entomopathogenic fungi. Beauveria bassiana seems more promising and is being tested to be integrated with other methods of weevil control.
Damage and symptoms
Nematodes are miniature worms that live in the soil and infest plant roots.
- During their process of feeding, nematodes tunnel through the root cortex leading to expansion of the lesions around.
- The lesions collapse into large necrotic patches reddish-purple in color, a symptom known as root necrosis.
- It results in premature root death or root fracture at points where necrosis girdles across.
- This necrosis interferes with the water and nutrient exchange passage.
- The most obvious symptom of nematode damage is the toppling over of the entire plant, particularly in fruiting ones.
- In general, damage to the banana root system results in stunted growth, premature leaf drop, reduced vigor, delayed ratooning, and increased susceptibility to water deficiency.