LAUSR

Abstract Pratylenchus thornei is a major pathogen of cereal and legume crops around the world, especially in the northern grains region of eastern Australia. The dominance of host species within the rotation has seen soil pathogen population densities increase. Long weed-free fallows combined with sorghum production (non host crop) to reduce population densities has been successful. However, little is known about the rate of population decline during the fallow or how long this non–host period should continue in order to reduce the population below an accepted damage threshold. The rate of decline from a range of initial starting populations (high, medium, low and very low) were monitored over a 30 month weed free fallow. Fallows were initiated in November (late Spring) for three consecutive years. Nematode population densities and soil moisture were measured at eight depths down the soil profile to 1.5 m and used to describe the rate of population decline over time in each soil layer. Dynamic populations of P. thornei existed within the upper layers (