THE RELATIONSHIP BETWEEN NUMBERS OF HETERODERA-SCHACHTII AND SUGAR-BEET YIELDS ON A MINERAL SOIL, 1978-81

In a 4-yr field experiment on a mineral soil infested with beet cyst nematode (H. 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[tons]/ha, y max = 39.4 t/ha, Z = 0.99938 and T = 0 eggs/100 g soil. The total national root yield loss caused by H. schachtii was estimated as .apprx. 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.