THE IMPACT OF ROOT-KNOT NEMATODES (MELOIDOGYNE SPP.) ON LEGUME CROPS GROWN IN ROTATION WITH SUGARCANE

IN A FIELD TRIAL at a site near Mackay, the performance of nine legume crops was assessed at two planting times in a sandy soil infested with two species of root-knot nematode (Meloidogyne javanica and M. incognita). Sugarcane was harvested in mid-November, the fallow legumes were sown 4 and 12 weeks later, and the severity of nematode galling on roots was assessed 7 weeks after planting. Final nematode population densities were measured at 14 weeks. Roots of mungbean, lablab and the soybean cultivars Leichhardt, Melrose and YY were damaged by root-knot nematode at both planting times but, because rootknot nematode populations declined rapidly when soil was bare fallowed following the sugarcane harvest, galling was less severe in the second planting than the first. Peanut, velvet bean, cowpea (cv. Meringa) and soybean cv. Stuart showed little or no nematode damage at either planting time. Final nematode population densities on mature legume crops generally reflected the severity of galling. Nematode numbers were high (more than 1000 root-knot nematodes/200 mL soil) following most of the susceptible crops, whereas populations following peanut, velvet bean and soybean cv. Stuart were no greater than in adjacent plots under bare fallow. These results demonstrate that root-knot nematode damage to fallow legumes in sandy soils can be minimised by reducing nematode numbers with a bare fallow of at least 2 months, or by growing legumes such as peanut and velvet bean, which are relatively resistant to root-knot nematode.