Bio-pesticide to target emerging cotton pest

A naturally-occurring fungi is being used to control green mirids.

A naturally-occurring fungi is being used to control
green mirids.

NSW Department of Primary Industries (DPI) researchers have come up with an environmentally friendly treatment for an insect which is emerging as one of the cotton industry’s biggest pests.

Chemicals used to control the insect, green mirid, in the 2005-2006 season are estimated to have cost growers $38 per hectare or a total of $11.7 million, excluding application costs.

Since 2001, DPI Principal Research Scientist, Dr Robert Mensah has been working with two fungi which are showing great promise as a biological insecticide to control green mirids in both transgenic Bollgard® and conventional cotton crops.

This season, a large scale trial using a new formulation of the fungi has controlled green mirids to the same level as a commonly used chemical insecticide.

Dr Mensah said efficacy and performance of the fungal insecticide would improve with improved knowledge of formulation and application techniques.

One of the two fungi being tested is showing more promise, and this will be produced in large quantities and undergo large scale commercial trials in 2006-07, before being commercialised.

He added that 'since the commercial release of transgenic Bollgard® cotton in 2003, sucking pests – particularly green mirids – have emerged as major pests.

'About 40 percent of all insecticides used on Bollgard® transgenic cotton crops in the 2003-04 and 2004-05 seasons were to combat green mirids.

'Green mirids are difficult to control because they are highly mobile, difficult to sample accurately and the source of the population is difficult to determine.

'They also seem to have few effective natural enemies.'

Dr Mensah said there was concern that green mirids could develop resistance if the reliance on insecticides against green mirids continues at this rate.

'In addition, the insecticides applied against green mirids will also disrupt natural enemies and flare up other pests such as aphids and mites.'

Dr Robert Mensah

Dr Robert Mensah

Dr Mensah and his colleagues at the Australian Cotton Research Institute at Narrabri screened 30 fungal isolates before narrowing down the most promising ones for field trials.

The fungi produce spores which, when applied to crops, either attack the insects directly or are picked up from the crop surface by the insect, and then germinate and invade its body tissue. The insect dies within 3 to 7 days.

Dr Mensah said a fungal insecticide is considered to be a bio-pesticide and hence does not affect the environment in the same way as synthetic insecticides.

'The use of the fungus will minimise or reduce the use of synthetic insecticides which are not environmentally friendly', he said.

Further information

Dr Robert Mensah, NSW DPI, Narrabri on 02 6799 1500 or robert.mensah@dpi.nsw.gov.au.