Studies on the relation between density of Longidorus elongatus and growth of sugar beet, with supplementary observations on Trichodorus spp

SUMMARY Longidorus elongatus attacks sugar beet on light sandy soils in the West Midlands. Severely damaged plants may die or recover, producing fanged roots. Up to 335 L. elongatus /200 g of soil were found around attacked seedling plants and were often visible to the unaided eye on the roots of freshly lifted plants. Five experiments were made and regressions computed of yield of beet, total numbers of plants and numbers of normal and fanged beet on L. elongatus numbers. Between 24% and 50% of roots per 100 L. elongatus / 200 g were killed or became fanged. Corresponding figures for loss of plant were between 7.5% and 33%. Estimated loss of yield varied between 0.8 and 7.3 tons (2.0–18.3 t/ha)/acre/100 L. elongatus /200 g, the former where the potential yield was high and the latter where poor growing conditions hindered recovery. Large numbers of Trichodorus occurred in two trial sites and there is some evidence of competition between the two genera. Significant negative regressions for Trichodorus spp. were obtained in one trial suggesting a loss of 12% total and 17% normal roots per 100 Trichodorus spp./200 g.