The Relationship Between Population Density of Heterodera schachtii, Soil Temperature, and Sugarbeet Yields

In two glasshouse experiments, relations between sugarbeet root dry weight (y, expressed as a percentage of the maximum dry root weight), and preplanting populations of Heterodera schachtii (P(i)) were described by the equation y = 100(Z)(P(i)-T), in which Z = a constant slightly smaller than 1, and T = the tolerance limit (the value of P(i) below which damage was not measureable). T varied with temperature; it was 65 eggs/100 g soil at 23 and 27 C and 430 eggs/100 g soil at 19 C. At 15 and 31 C there was no loss of root dry weight up to the maximum preplanting populations tested. In a field experiment in the Imperial Valley the relation between root yield (y) and P(i) was y = 100 (0.99886)(P(i) ) - 100, and the tolerance limit was 100 eggs/100 g soil.