IPM of mirids in Australian cotton: Why and when pest managers spray for mirids

Abstract

Integrated Pest Management (IPM) aims to maintain pests below an economic threshold to avoid yield loss without resorting to unnecessary insecticide applications, rather than eradicate all pests in a crop. However, convincing growers to spray only if pest numbers exceed a threshold can be difficult, especially if the threshold changes in response to external factors, as in the case of mirids. The aim of this work was to establish if the mirid thresholds were adhered to by growers, and if not, when they were relaxed. The results showed that pest managers in this survey were following the guidelines recommended for mirid management, but in a conservative manner. Pest managers accepted the threshold for mirid numbers developed for visual surveys, but not the threshold developed for beatsheets. When retention rate and mirid numbers were low, the fruit retention threshold was used to trigger a spray application; but there was no evidence that high retention rates were used to withhold a spray application. There was a high reliance on Fipronil (Regent) to control mirids. This chemical accounted for 63% of the insecticides in the 2006/2007 survey, and was often applied multiple times to fields at low rates. There was no cost to yield in following the mirid thresholds, vindicating the recommended thresholds for mirids. The ultimate aim of this work is to support the further development of IPM in cotton. A discussion of IPM revealed that the cotton industry in Australia is well positioned to support and further develop IPM in cotton, especially given its policy to develop Best Management Practice (BMP). However, differences in interpretive knowledge by the stakeholders appeared to be inhibiting the development of mirid IPM. This common problem in multi-disciplined groups may account for the reluctance of pest managers to adjust their mirid threshold in respect to sampling method.