About 3200 ha of rice (cv. Starbonnet) are grown on the impermeable clay flood plain soils of the lower Burdekin River in north Queensland. Some growers adopt a continuous cropping schedule, pla nt ing summer crops in December and January and winter crops in June and JUly. Others rotate with field crops such as maize , sorghum and soybeans. Poor growth of rice was first observed in 1976 and has recurred every year, diseased patches gradually increasing in size and number until about 100 ha are now affected. The disease occurs in both summer and winter crops, but is most common and more severe In the summer crop. Seedl ings emerge and grow normally for a few weeks but decl ine symptoms appear soon after permanent water is app lied , when plants are 10-15 cm high. Diseased plants are stu nted and chlorotic, with short discoloured roots and necrotic root tips . The roots of severely affected plants may be only 1-2 em long, Since diseased plants lack vigor, the stand decli nes unti l relatively few plants remain. Sedges (Cyperus spp .) become dominant and water birds tend to cong regate in diseased patches, adding to crop losses. Badly affected areas yield little or no grain. Init ial stud ies by local agronomists and extension off icers failed to identi fy the cause of the poor growth. Poor management . particular crop rotations , inadequate nutrition , salin ity of irrigat ion water and root feed ing insects were not consistently assoc iated with the disease. Subsequently, needle nematodes (Paralongidorus sp .) were found in the root zone of declining rice plants. Populations of 100-1000 needle nematodes per 200 ml soil occurred around the roots of