Root lesion nematode
The root lesion nematode Pratylenchus coffeae is a major pest of bananas.
Pratylenchus coffeae is probably native to the Pacific and the Pacific Rim countries, but now has a worldwide distribution.
Nematodes by themselves can only move about 1 meter per year. But unintentional movement may occur in planting materials, on equipment, through irrigation water, etc. Once introduced, eradication of R. similis from the soil is virtually impossible and populations will build up more or less rapidly after planting. Therefore, prevention of infestation and spread should be a priority.
Tissue-cultured plantlets are the only planting material source guaranteed to be absolutely free of nematodes and should be the only method allowed for the introduction of banana plant material into virgin land.
If tissue-cultured materials are difficult to obtain, planting materials from clean nursery blocks can be used. For the set-up of clean nursery blocks, check the status of the soil in the nursery area (e.g. no prior history of banana growing) and prevent movement of nematodes into the nursery area on tools, vehicles and footwear. The area can then be planted with tissue-cultured plantlets, and suckers can be collected from these clean blocks.
Conventional planting materials can be cleaned and pared prior to planting. All diseased tissue, characterized by necrotic lesions, is cut from the corm. Do not carry out the paring in the new planting site and clean your knife or machete in between paring of different corms. However, nematodes located deep within the cortex in non-necrosed tissues may escape removal. Sun exposure of pared material for 2 weeks may further reduce the nematode population, but such techniques cannot be applied to small suckers which are quite fragile and need to be replanted rapidly. Paring followed by hot-water treatments (52-55°C for 15-20 minutes) has been a common and effective practice, but it is labour intensive and requires careful monitoring of temperature and exposure time as these are is critical to be efficient and to limit the negative effects on the plants. Planting material disinfestation using chemicals can also be achieved by dipping plant material in a nematicide solution, e.g. cold fenamiphos (100 ml of Nemacur® 400 in 100 l of water) for 10 minutes. Thoroughly clean and trim all planting material for optimal adherence of the nematicide. Make sure that the dip is fresh and strictly follow the label recommendations in the use of the product. These products are very toxic; properly dispose the remaining dip solution by applying it to plots where nematode treatment is required. The technique known as “pralinage” is a significant improvement over dipping. This involves the use of a nematicidal mud mixture which permits instantaneous coating of the plant. It is recommended to use either bentonite (15 kg in 100 l of water + 400-500 g of active ingredient) or a natural clay (proportion of clay to be mixed with water must be adapted). This method has the advantage that the treated material can be removed immediately from the dip and there is much less splashing of dangerous chemicals.
Other preventive control measures include strict quarantaine measures, cleaning of machinery and equipment, avoidance of contaminated irrigation water and removal of plants with symptoms.
Instead of focusing on reducing the nematode infestation, an alternative is to avoid or minimize the damage caused by the nematodes. Yield losses may be reduced through propping or guying of pseudostems to avoid toppling. Application of amendments (mulching, manure, agricultural wastes) or any other measures that improve soil fertility and root development may increase plant tolerance to nematodes. Adding of organic materials also improves the microbial activity and thus acts as a natural biological control. Improved drainage is also an important factor in reducing nematode damage in high-rainfall regions.