Assessment of the pest status of Leucaena Psyllid

Summary

Four commercial sites across the range of environments in central Queensland were selected. The leucaena rows cut back to 1 m in height. Meteorological stations were established. Leucaena dry matter yield was obtained by harvesting all material above 1 m at 4 weekly intervals. Psyllid populations were controlled on half the plots by weekly insecticide spraying with 0.03% dimethoate. Psyllid numbers were counted on the remaining plots. An additional 2 sites at Rockhampton and Rannes were monitored for psyllid populations.

Data on yield loss due to psyllids was restricted to the April to August period due to drought conditions over the whole period of the study. Average loss over this restricted period was 28% which compares with average annual loss of 36% obtained by CSIRO at their 7 southern and northern Queensland sites. The estimated annual losses due to psyllids based on an estimated 30 000 ha currently planted ranged from $0. 6M to $2.2M with the annual value of leucaena to industry being $2.6M to $5.1M. If 500 000 ha were to be planted in the next 10 years or 8.3~ of the suitable land, losses would range from $10.5 to $34.0M for an industry value of $43.8 to $85.2M. The 2.75 years of field work for the project was completed in December 1992.

Useful data on leucaena DM yield under drought conditions and psyllid population dynamics were obtained. Annual edible dry matter yields at 4 sites over the 2.75 years of the study were 454 (Dingo) , 728 (Kabra) , 1+'16 (Banana) and 491 kg/ha (Blackwater). This was much lower than expected. The psyllid counts undertaken for this work and during a previous study indicate that psyllids are more prevalent in coastal districts of Central Queensland and population increases are most likely to occur with the milder weather of spring and autumn.