TWO years after an outbreak of the exotic Solenopsis mealybug devastated parts of the 2009-10 Central Highlands and 2008-09 Burdekin cotton crops, a new research project is under way to develop a management strategy for the pest.
While insect pressure generally has been low this season in the Central Highlands where the Solenopsis mealybug (Phenacoccus solenopsis) caused widespread alarm in early 2010, the small white, sucking insects are still present in the region and in other pockets of Queensland, including at Byee in the South Burnett.
Department of Employment, Economic Development and Innovation (DEEDI) senior research scientist and entomologist Dr Moazzem Khan, Toowoomba, is leading the three-year research project funded by DEEDI and the Cotton Research and Development Corporation (CRDC) with development and extension work being undertaken by DEEDI cotton extension officer Susan Maas, Emerald.
The focus of the project, including on-farm trials throughout Queensland, is to determine the impact of Solenopsis mealybug on cotton growth and yield, and determine in-crop and cultural control or management tactics consistent with an integrated pest management (IPM) approach.
Since Solenopsis mealybug reared its head in Queensland, a number of natural predators, particularly Cryptolaemus ladybird beetles (a type of ladybird native to Australia), whose larvae look like an oversized mealybug, have helped keep the pest in check.
Dr Khan said one element would not eliminate the problem, and so the impact of the beneficials combined with other initiatives, including farm hygiene and the enforcement of the 'Come Clean Go Clean' protocol to disinfect farm machinery moving between areas, would need to be ongoing.
"We will be looking at mealybug damage, categorising it and quantifying it, so we can develop action thresholds for the mealybug to determine when they can be sprayed and with what chemical," Dr Khan said.
"We also will be looking at the different management options including chemical options that fit into existing IPM, so that it's less disruptive and we can utilise beneficials at their maximum levels.
"Cryptolaemus beetles, as well as other ladybirds and lacewings, are all mealybug predators, and we'll be examining the interaction between these predators, chemicals and the damage so we can determine the optimum time to spray to maximise the beneficials.
"In the South Burnett at Byee, we had an outbreak last year which we have been monitoring.
"It was on three properties last year, and this year on two more new properties, and we're running some trials on one of those properties evaluating chemicals and assessing damage.
"In Central Queensland, nobody is spraying and nobody is panicking because they know if they keep the system healthy and maintain the beneficials, the beneficials can take care of the mealybug.
"Obviously, you have to keep monitoring populations and if a population suddenly goes up, then you have to intervene," Dr Khan said.
He said it was still not known what prompted the Solenopsis mealybug outbreaks in Queensland.
To date, they have not been found in the cotton-growing areas of NSW.
"We cannot really pinpoint why there was an outbreak, but we do know they can be transmitted by wind, rain and floodwater, and it's possible floodwater brought it to Byee," Dr Khan said.
"We did some monitoring in winter 2011 at Byee, and found that the mealybugs slowed down in growth but still were doing well.
"Besides having a wide range of host plants, mealybugs can also live in the soil and hit a plant at seedling stage, but they have to be there in big numbers to show damage."
In Emerald and the Burdekin, Solenopsis mealybug has been recorded from a range of common weed species on farms such as pigweed, sow thistle, bladder ketmia, native rosella, vines (cow, bell and potato), crownbeard and volunteer cotton.
In cotton, adults and nymphs pierce and suck the sap from both soft and hard plant tissue.
India and Pakistan have been battling the Solenopsis mealybug since it was first identified in 2004 in those countries.
However, Dr Khan said natural predators and parasitoids were also helping to control the pest, with Pakistan importing Cryptolaemus beetles to add to its beneficials.
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