Predicting the slow decline of root lesion nematodes (Pratylenchus thornei) during host-free fallows to improve farm management decisions

Dynamic populations of P. thornei existed within the upper layers (<0.6 m) of the soil and these declined at a rate that could be described by the negative exponential model Y = ae−bt. The time taken for a population to decline was dependent on the initial population density at harvest of the previous host crop. Generally, between 300-600 days of host-free fallow was required to reduce a moderately high initial population of 80 P. thornei/cm3 soil to the damage threshold of 2 P. thornei/cm3. The rate of decline varied between soil layers, particularly in the surface layer (0-0.15 m), but remained constant from year to year for each layer. There was no interaction between year and soil layer. Knowing the expected rate of decline of a P. thornei population at the start of a fallow allows better management of the crop rotation to ensure populations do not continue to rise and thus reduce the yield potential of future crops.