No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Free-living or ectoparasitic nematodes attacking plants are less well documented than are the more thoroughly investigated endoparasites. The prevalence of Docking Disorder of sugar beet in the East Riding of Yorkshire has presented an opportunity to obtain more information on ectoparasitic nematodes. Regular monthly sampling at several fields in the area over a two year period has yielded information on the bionomics of these ectoparasites. The vertical and horizontal distributions of several genera were investigated. Longidorus, Rotylenchus, Tylenchorhynchus, Trichodorus, Hemicycliophora, Criconemoides and Pratylenchus were recorded. Ectoparasites were found to be patchily distributed within each field. Different fields were shown to have different population sizes. Each genus showed a general preference for either surface or deeper soil layers. Trichodorus, Hemicycliophora and Criconemoides were depth preferring genera, while Tylenchorhynchus and Pratylenchus were found predominantly in shallower layers of soil. Several factors were investigated to attempt an explanation of these preferences for different soil layers. From these results, soil sampling techniques should take into account the distribution of nematodes in field soils in order to accurately assess the population sizes and potential crop damage. Seasonal variations in population size of the genera were followed over two years under different crops. The population dynamics were characteristic for each genus and year. Total nematode populations tended to decline during the first few months of the year, before building up as the season progressed, and fading away during winter months. The relationship between population size and soil environmental factors was examined. A Soil Environment Index was designed to interpret total population curves. Soil temperature, soil moisture, and crop growth were included in the index. Population curves appeared to show a definite relationship to the index. Microplot, pot and laboratory experiments were carried out on the movement and activity of Trichodorus and other ectoparasites. Trichodorus was shown to be capable of migrating downwards from surface inoculations in microplots, simulating the field distribution of this genus. Migration was more extensive and rapid in the presence of sugar beet roots than cereal roots. Migration was dependent on the presence of a root system. Longidorus and Trichodorus were shown under laboratory conditions to move most quickly through soils which were evenly moist and free draining, as opposed to waterlogged or dried soils. Conclusions review the practical implications of these results to agriculture, particularly with respect to the techniques of sampling for nematodes, the relevance of cropping programmes, and the problems of controlling Docking Disorder by cultural and chemical methods.

No description available.

No description available.