‘Good IPM’ the secret for mealybug in cotton
Queensland Government entomologist Dr David Murray said good integrated pest management, or IPM principles already being used by cotton growers would be the key to managing the newly-discovered Solenopsis mealybug.
Speaking on CSD’s Web on Wednesday broadcast, Dr Murray said while this species had been confirmed as an exotic incursion for Australia, now that it’s been identified in two districts, eradication is not an option, so it’s now a pest that will need to be managed by the industries that encounter it.
For cotton growers, says Dr Murray, that means good farm hygiene, promotion of predatory insects and the use of insecticides only as a last resort – well established pest management principles for all cotton pests.
“We want to go as soft as we can for the benefit of these mealybugs – naturally in the environment we’ve got some ladybeetle predators and some lacewing larvae that appear to be very important predators.”
“With the range of natural enemies that are available to us, we do not want to disrupt their activities so it’s the case in the early and mid parts of the season in particular, trying to avoid the use of disruptive insecticides – not unlike the situation for whitefly management,” Dr Murray said.
“Another part of the management is the role of alternative plant hosts – this mealybug has a very broad host range and that green bridge that allows the pest to survive from one season to the next – just as it is for whitefly, aphids and mites.”
“Work in Pakistan identified 154 plant species in 53 different families so a very broad host range on which it can be found.”
“If we provide alternative hosts that allow the mealybug to carry over from one season to the next it increases the likelihood that we’ll have a mealybug problem in the following season – so it’s removing the alternative hosts and these include volunteer cotton and other weeds,” he said.
Dr Murray said there were currently no insecticides registered for mealybugs in cotton – and to make matters worse the insects are covered in a white, waxy, water repellent powder which protects the insect from contact sprays.
“We’re currently working with the cotton industry to look at options that might be available for permit use next season and work is planned in the Burdekin in coming months to evaluate some of the new chemistry, plus petroleum spray oils that might be available for mealybugs so it’s a watch-and-wait for that information as it comes to hand.”
Dr Murray said the Solenopsis mealybug observed in cotton crops in the Emerald and Burdekin regions is native to the southern parts of the United States but have dispersed rapidly around the world – most recently causing problems in India and Pakistan.
“The mealybug is a sap sucker – so it’s not unlike scale insects, aphids and whitefly in that it’s got mouthparts that insert into the plant tissue, feeds on the juices from the plant and it extracts it’s nutrients from that.”
“With high numbers of mealybugs you get characteristic symptoms developing – crinkled leaves, distorted tips and terminal growth, smaller bolls, flowers structures distorted, and in those cases of very high densities of mealybug, outright death of the plant.”
Dr Murray said the very small juvenile mealybug, less that a millimetre long, were the main source of the insect’s spread.
“It can easily be spread by wind and rain – there’s certainly evidence of it spreading in cotton trash material in irrigation channels for instance and it can also be spread by bees and other insects, by birds, humans and machinery.”
“Assisted spread is obviously an important element of how this mealybug can disperse more widely so given that, to our knowledge, it’s contained to the Bowen/ Burdekin and the Emerald districts and we’re keen to not assist its spread further south.”
“At this stage the main emphasis is trying to limit further spread and so we’ve got the ‘Come Clean – Go Clean’ protocols that have been in place for Fusarium wilt but there will be more information on that as those protocols are evaluated further,” he said.
Dr Murray said people seeking more information of Solenopsis mealybug should look at the DEEDI Beat Sheet Blog http://thebeatsheet.com.au/mealybugs/exotic-mealybug-species-a-major-new-pest-in-cotton/
25 February 2010
Further Information:
Dr Melina Miles, senior entomologist, DEEDI,
Ph: (07) 4688 1369
Email: melina.miles@deedi.qld.gov.au
(Dr David Murray is currently on long service leave)
For full video and transcript of the interview
http://www.csd.net.au/wow/show/1459
Above: Predatory insects such as the three banded ladybug larvae, seen here attacking a Solenopsis mealy bug, will be essential in the long term management of this new pest.