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While the damage caused by primary cotton pest Helicoverpa has been drastically reduced in cotton, the industry is still troubled by secondary pests, such as green mirids, which are becoming a greater threat.

In order to manage the risk of mirids becoming a primary pest Dr Mary Whitehouse of CSIRO and Cotton CRC has been conducting surveys which aimed to benchmark current management techniques and identify those most effective at controlling mirid damage.

“Minds are a difficult pest to manage because pest managers report no clear-cut relationship between crop damage and mirid numbers, which makes it harder to know when, or indeed if, it is appropriate to apply insecticides”, said Dr Whitehouse.

Nevertheless, there are guidelines indicating when growers should spray for mirids to avoid yield penalty. These include monitoring the percentage crop retention (which should always be above 60%) and mirid number thresholds. The thresholds vary with respect to the growth stage of the crop, the climatic zone, and the techniques used to sample the mirids (sampling techniques include beatsheets and visual searches).

“The surveys revealed that many crops are being sprayed below threshold, which suggest that many pest managers are not confident in these thresholds (particularly when they sample mirids using beatsheets) and so they opt for “insurance sprays”.

According to Dr Whitehouse, the survey showed that spraying for minds below threshold levels provided no yield advantage.

“The results from the survey validate the current recommended thresholds. Emphasis needs to be placed on giving pest managers the confidence in mirid thresholds so that they will adjust their interpretation of their counts according to sampling technique.

“Installing greater confidence in the thresholds would reduce the amount of unnecessary sprays, reduce costs, and the risk of flaring secondary pests.

For more information or an interview please contact Dr Mary Whitehouse on 6799 1538.