Maximising the resistance of sugarcane to soldier fly : SRDC final report BS61S
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Infestations of soldier fly (Inopus spp.) cause losses to sugarcane in areas from Innisfail to New South Wales. Cane losses attributable to soldier fly in Queensland in 1995 were estimated at 24 000 t, and the annual cost of soldier fly infestations to farmers and millers probably exceeds $1M. The number of farms affected by soldier fly at Mackay is increasing, and the pest has recently appeared at Ayr where it has not been recorded previously. During the late 1950s and early 1960s, losses attributable to soldier fly in Queensland were up to 80 000 t of cane per year on a much smaller assigned area. The pest was subsequently controlled by the application of dieldrin, but this chemical is no longer available and alternatives have not been found. With the loss of dieldrin, there is a high potential for a disastrous increase in losses.Cane losses could be reduced by agricultural practices that maximise the resistance of sugarcane to soldier fly attack, eg growing varieties that are inherently resistant to soldier fly and managing conditions for crop growth.Past observations suggest that varieties of cane may respond differently to soldier fly (Moller, 1965). In a previous glasshouse experiment, two clones responded differently when exposed to a range of densities of soldier fly larvae (Samson et al., 1993). This indicates that screening commercial varieties for resistance may be feasible, and varieties could be recommended for planting in soldier fly-prone areas.Environmental factors also may influence the response of cane to soldier fly. Untested observations suggest that germination of cane setts is more likely to be affected if autumn planting is late, and ratooning is more likely to be affected if harvesting is early (Moller, 1968). Such changes may reflect different effects of temperature on development rates of plants and insects, as has been measured in some other agricultural systems (eg Samson and Geier, 1983). Planting or harvesting date, soil moisture content, and fertiliser application could be manipulated to reduce cane losses, if their effect on the interaction between soldier fly larvae and cane was understood.The development of practices for maximising the resistance of sugarcane to soldier fly would have multiple benefits within an integrated pest management program. Not only would crop losses be reduced directly, but additional time would also be available for natural enemies of soldier fly to build up and exert control before crop damage reached unacceptable levels.