Practice Abstract 36 - Stem and bulb nematode in field beans - background

Short title (native language): 
Stem and bulb nematode in field beans - background

Short summary for practitioners (native language): 
Stem and bulb nematodes are slender, transparent and virtually microscopic. They can be found in large numbers within the stem or leaf tissue or in seed, by microscopic examination. Ditylenchus gigas is the most common and damaging species in field beans, but Ditylenchus dipsaci can also be present. The nematodes can be seed-borne and can also survive in the soil in a free-living form. The main routes of infestation on farms are from the use of infested seed, infested bulbs or contaminated soil.
This pest is one of the most important problems in UK field beans. Following introduction and establishment in soils, nematodes remain viable for many years, placing future crops at risk from damage, which is often first seen as plants reach flowering stage. Earlier symptoms may be found at any stage.
Plants may be stunted, stems thickened and twisted. Leaves become thick and brittle with bronze discolouration and stems may swell, twist and break. Pods fail to fill evenly, and seeds become black and shrivelled as they mature. Single affected plants in a field may indicate a seed source, more general crop damage indicating a field infestation. Multiplication of nematodes is enhanced in a wet spring and crop loss can be substantial. Infested seed is unsuitable for planting, but beans are still usable in animal feed compounds and blemish-free produce may still be suitable for export.
If a field has been infested, ten years should elapse before beans are grown.