Options for controlling needle nematode (Paralongidorus australis) and preventing damage to rice in northern Queensland

Options for the control of Paralongidorus australis on paddy rice in northern Queensland were evaluated in a series of field and pot experiments. Soil fumigation with 1,3-dichloropropene at 220 and 358 kglha gave excellent control in the field and increased grain yields by more than 40%. In pots, carbofuran (5, 10 and 20 kg a.i./ha) applied to soil prior to sowing or in water at the time of permanent flooding gave good control but fenamiphos and CuSO4 did not. These results suggested that the amounts of 1,3-dichloropropene or carbofuran needed to control the nematode were too high for annual treatment with nematicides to be economic. Carbofuran and oxamyl applied as seed dressings at 0.75% and 0.36% a.i. respectively were much cheaper treatments, but failed to control P. australis or reduce nematode damage to root tips. P. australis was eliminated from moist soil by air-drying, but this effect could not be reproduced in the field by deep ripping followed by cultivation to break up clods. Amendment of nematode-infested soil with straw and various sulfur-containing compounds and flooding for 6 or 12 weeks, failed to reduce nematode numbers in the subsequent rice crop, indicating that products of anaerobic decomposition did not control the nematode. However, there was a marked reduction in the percentage of root tips damaged by the nematode in the straw + sulphur treatment. Additional pot experiments investigated practices that reduced losses from P. australis but did not necessarily control the nematode. When rice was flooded 1, 2, 3, 5 or 7 weeks after sowing, the degree of nematode damage was reduced as flooding was delayed, possibly because P. australis remained inactive during the period prior to flooding. Of the 14 rice cultivars and breeding lines tested for tolerance to P. australis, several cultivars were more tolerant than Starbonnet and Lemont, the cultivars currently being grown commercially in northern Queensland. Both delayed flooding and the use of tolerant varieties showed enough promise to warrant further testing in the field.