Parasitic nematodes pose problems
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CTA. 1994. Parasitic nematodes pose problems. Spore 49. CTA, Wageningen, The Netherlands.
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Nematodes are tiny worms that abound in the soil. Many species are harmless but parasitic nematodes have a mouth styles that allows them to feed on the root systems of living plants. The feeding activity of some parasitic nematodes causes the roots...
Nematodes are tiny worms that abound in the soil. Many species are harmless but parasitic nematodes have a mouth styles that allows them to feed on the root systems of living plants. The feeding activity of some parasitic nematodes causes the roots to grow galls or nodules that cannot be rubbed off as they are part of the root itself. It is estimated that the average farmer can lose between 12% and 30% of the potential crop per year from nematode attack. Losses vary greatly according to the different nematode species, found in the soil and their numbers. Population size and the balance between species are determined by the availability of suitable host plants and are highly dependent on the local soil and climate. Tropical and subtropical zones, where agroforestry is most practiced, are particularly favourable to many nematode species and total crop losses from their attacks are not rare. Permanent agroforestry systems, where trees and shrubs are inter-planted with crops are very suitable for nematode attack. This is especially so when a tree or shrub that is an ideal host for nematode survival and population build-up is present. If this is the case crop rotation which is the preferred method of nematode control, may be rendered useless. Some species of trees and shrubs can have a negative effect upon certain species of nematode. Populations will therefore be reduced, particularly if the tree or shrub acts as a trap host (attracting nematodes and preventing their reproduction] or is an antagonistic plant, exuding chemicals that kill nematodes. In Nigeria, deliberate planting of Leucaena leucocephala during the fallow period dramatically reduced parasitic nematode populations in the soil. When the fallow was converted to L. leucocephala alley-cropped with maize, the population of parasitic spiral and root lesion nematodes remained low. In West Africa, Sesbania rostrata acts as a trap host for the Hirshmaiella spp of nematode that are prevalent in flooded areas where rice grows. However studies in Malawi suggest that Acacia, Leucaena and Sesbania spp. can act as hosts for root-knot nemtatodes, allowing the populations to build up and attack many crops that are normally included in alley or mixed cropping systems. A build-up of parasitic nematode populations can be prevented by ensuring that no trees or shrubs susceptible to the nematode species naturally found in the area are introduced or cultivated on a large scale. It is also important to ensure that the trees and shrubs which are planted come from nursery sites that are as free from nematodes as possible. A more active control strategy is to include growing trees and shrubs that trap or are antagonistic to local nematodes and avoid those which may act as hosts. ICRAF PO Box 30677 Nairobi KENYA
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