The effect of beet cyst nematode, Heterodera schachtii, on the yield of sugar beet in organic soils

In ten experiments on commercial sugar-beet crops grown on organic soils in 1984 - 86, a Genstat programme was used to examine the relationship between the initial population of Heterodera schachtii and sugar-beet root yield using the equation Y = Ymin + (Ymax - Ymin) Z(Pi-T) Fixing T = 200 eggs + juveniles 100 g-1 soil and Z(T) = 0.95, estimated values of Ymax varied from 49.2 - 67.1 t ha-1 (129-155% of the national average root yield for the years in which the experiments were carried out) and estimates of Ymin varied from 14.5-53.9 t ha-1 (27-94% of Ymax). The estimated average root yield loss caused by the nematode was 6.95 t ha-1.