The relationship between numbers of Heterodera schachtii and sugar beet yields on a mineral soil, 1978‐81

SUMMARY In a 4‐yr field experiment on a mineral soil infested with beet cyst nematode (Heterodera schachtii) the relationship between root yield of sugar beet (y) and initial population of H. schachtii (Pi) fitted the equation: y=y min +(y max ‐ y min) ZPi‐T y min = 7·7 t/ha, y max = 39·4 t/ha, 2 = 0·99938 and T= 0 eggs/100 g soil. From this information and that obtained during a recent survey of 2766 beet fields, the total national root yield loss caused by H. schachtii was estimated as approximately 10 000 t/annum on mineral soils and (assuming a similar yield loss relationship on all soil types) 30 000 t/annum on organic soils. No consistent differences in efficiency of extracting cysts were found between the Fenwick Can and the flotation column. A bioassay technique was as effective as cyst extraction techniques in identifying infested soils.