IMPLEMENTATION OF A MONITORING AND RISK-ASSESSMENT SYSTEM FOR GREYBACK CANEGRUB NEAR MACKAY

A MONITORING AND risk-assessment system for greyback canegrub, Dermolepida albohirtum, was implemented on ten farms near Mackay during 2008–2010. We counted numbers of greyback canegrubs under up to 20 stools per field in a selection of fields on each farm, in each year. We also assessed disease in these grubs, surveyed fields for damage, and obtained other information necessary to make decisions on future risk of canegrub attack. We used predictive models developed in previous research to quantitatively predict infestation levels in the sampled fields, and we qualitatively estimated risk levels for other non-sampled fields on each farm. Maps showing currently effective insecticide treatments and numbers of canegrubs in the sampled fields and a report stating predicted risk levels and treatment recommendations were developed for each farm. There was a large amount of unexplained variation in canegrub numbers outside of what was accounted for by the models, but we judged the predictions as adequate, particularly when expressed as density classes (low, moderate, high) rather than actual numbers. However, the growers would have liked more certainty in the predictions. The system as delivered would be costly if supplied by a consultant – approx. $2000 per farm. Most of this cost was in sampling for canegrubs, and there may be ways to do this more efficiently, for example by using more efficient sampling schemes or by using other detection systems such as remote sensing.