Depth distribution of Rotylenchulus reniformis under crops of different host status and after fumigation

Population densities of Rotylenchulus reniformis were investigated in 15 cm horizons from the surface to 120 cm deep in field plots under fallow, grain sorghum (cv. Asgrow 571), and susceptible (cv. DP6880RR) or resistant (cv. HY798) soybean. In 2000, population densities were monitored in non-fumigated plots and in plots fumigated pre-season with 1,3-dichloropropene (1,3-D) at 38 em depth. Fallow, grain sorghum and resistant soybean reduced the incidence of R. reniformis down to 120 cm in comparison to susceptible soybean. In 2001, population densities were monitored under cotton in these plots and in additional plots that had grown susceptible soybean cv. Vernal or resistant cv. Padre in 2000 and that were fumigated before the 2001 crop with 1,3-D at depths of 0-60, 60-120, or 0-120 cm. In 2000 non-fumigated plots, cotton fibre yields were increased by an average 35% after fallow, grain sorghum or resistant soybean compared to those after susceptible soybean. In the 2000 fumigated plots, cotton fibre yields were increased 38% after grain sorghum and resistant soybean compared to those after susceptible soybean or fallow. In plots cropped previously to susceptible soybean, fumigation at 60-120 cm deep increased cotton fibre yields by 68% compared to the non-fumigated control. Population densities in the 0-120 cm horizon were a more accurate predictor of plant damage than those at 0-30 cm. The value of R. reniformis-resistant soybean cultivar-cotton crop sequences was confirmed and the importance of their effects on deep-occurring populations of R. reniformis demonstrated.