Sheep parasites
Integrated pest management to control blowflies and lice
Dave Jordan, Department of Primary Industries and Fisheries
Revised by Geoff Knights, Department of Primary Industries and Fisheries and
Bob Armstrong and Wendy McLeish, former employees
of the Department of Primary Industries and Fisheries
Key points
- Surveys have shown that most treatments applied less than six months before shearing are likely to leave unacceptable levels of pesticide residues on wool.
- To reduce pesticide residues on wool producers should minimise the use of blowfly and louse treatments in the six months before shearing and avoid them altogether in the three months before shearing.
- Integrated pest management (IPM) is designed to maximise control of blowflies and lice while minimising reliance on pesticides and residues on wool.
- The use of effective pesticides according to label instructions, withholding periods and export slaughter intervals when combined with IPM practices normally result in acceptable residue levels.
Introduction
Parasite infestation in the Queensland sheep flock from blowflies and lice causes significant economic loss through reduced efficiency of production. Management of blowflies and lice currently relies heavily on the use of pesticides.
While pesticides start breaking down on the sheep's back from the time they are applied, when the sheep is shorn some pesticide remains on the wool until it is processed; it is then discharged into the environment as scour effluent or sludge.
There are global, government and wool industry concerns about the environmental impact of pesticides in wool scour effluent. This means that producers may no longer be able to rely heavily on pesticides for the control of external parasites. Pesticide residues are also likely to have an impact on the future marketing of Australian raw wool and the price received for it.
It is necessary therefore to ensure that pesticide treatments result in minimal residues on wool while maintaining effective control of blowflies and lice.
What is integrated pest management?
Integrated pest management (IPM) is a systematic approach to controlling blowflies and lice with the primary aim of reducing reliance on pesticides by using preferred alternative management methods. An IPM program includes consideration of animal welfare, environmental, economic and occupational health and safety concerns.
IPM program
Blowfly control and lice control are often considered separate issues, but in terms of residues they both contribute to the total pesticide load on wool and so benefit from an integrated management program.
An IPM program calls for planning of the year's management activities and involves a number of components. They are all based on applying good management and husbandry practices that integrate:
- timing of shearing
- timing of crutching
- mulesing all sheep
- docking lambs' tails to the correct length
- keeping mobs separated
- quarantining introduced sheep (including rams and sheep returned from adjoining properties)
- achieving complete musters
- regularly inspecting the flock
- recording all pesticide treatments.
Blowfly control
A number of management activities aimed at minimising pesticide use are specific to blowfly control. They include:
- monitoring climatic conditions to predict blowfly activity
- monitoring blowfly populations through trapping
- reducing blowfly populations through trapping
- catching, clipping and treating individual blowfly struck sheep
- preventive jetting or backlining of susceptible sheep (such as weaners and hoggets) at the start of the blowfly season
- targeted jetting of specific areas on the sheep if a flywave is expected (such as pizzle of wethers, breech of ewes, poll of horned rams);
- controlling internal parasites.
Breeding and selection programs are a major factor in improved host resistance to blowfly strike. Whenever possible rams - the major contributors to the genetic pool - should be purchased from a stud that has blowfly resistance as one of the selection criteria in its breeding program.
Struck sheep and sheep with fleece rot should be culled from the flock. Strong host resistance should be maintained through good nutrition, disease control (vaccination), worm control and by minimising stress.
Lice control
If a flock is infested with lice the aim of treating with a pesticide is to eradicate them from the property. The job should be done correctly the first time so that the flock does not need to be treated again in that wool growing season.
This requires effective treatment of all sheep (including pets, rams and killers) after shearing using either a backline product off-shears or plunge or shower dipping within six weeks. To successfully eradicate lice it is essential to achieve complete musters.
To further minimise pesticide use the flock should be kept free of lice so that they do not have to be treated at every shearing. If possible, shear all sheep at one annual shearing or, if split shearings are unavoidable, ensure that mobs are kept separate.
Monitoring is essential to determine whether or not sheep are infested with lice. Producers should check each mob using the visual inspection technique at least four times a year, such as at crutching, lamb marking, drenching and before shearing.
General control principles
Even when producers have used all management and husbandry options to their fullest, they are sometimes confronted with specific blowfly and lice problems that require identification and treatment. The aim is to use some general control principles so that pesticide residues on wool are minimised at the next shearing. These include:
- treating with an effective pesticide as early as possible after shearing
- minimising the use of pesticides in the six months before shearing
- avoiding the use of pesticides altogether in the three months before shearing
- using the most effective and safest method of pesticide application
- ensuring the equipment is operating to the manufacturer's specifications.
Other factors to consider
Parasite resistance
Significant resistance has been detected in blowflies and lice to the organophosphate (OP) and synthetic pyrethroid (SP) chemical groups respectively. Resistance of lice to SPs is widespread and it is highly recommended that producers not use an SP unless susceptibility is assured and they do not intend to market their clip to a sensitive market such as the European Union (EU).
Effective application
Pesticides will perform as claimed only if they are applied correctly. Devices not designed for the application of modern pesticides and not recommended by the manufacturer (such as fire fighting pumps and spray races) should not be used under any circumstances.
The key to effective jetting is the depth of penetration by the pesticide into the wool. Hand jetting is the most effective method as it achieves maximum penetration. Automatic jetting races (AJRs) simplify and speed up treatment but may not be as effective, in which case repeat treatment may be necessary.
Individual treatment of struck sheep
Treating individual blowfly struck sheep is preferable to treating entire mobs because it minimises pesticide residues across the whole clip. Catch any affected sheep and clip the wool from the struck area close to the skin and for at least 50 mm into unstruck wool. A registered dressing should then be applied. Pesticides from the IGR or spinosyn group are recommended.
Conclusion
In Queensland the incidence of blowfly strike is highly dependent on seasonal conditions and varies greatly from region to region and year to year. Because of the potentially devastating effects of blowfly strike on their flock many producers use a yearly strategy of preventive pesticide treatment, even though severe flywaves may happen only one or two years in ten. The effective implementation of a blowfly management strategy based on IPM principles would ensure that widespread pesticide use in long-wool sheep would be necessary in only those years.
Ineffective eradication of lice after shearing resulting in re-treatment of sheep in long wool is one of the major sources of pesticide residues on Queensland wool. Efficient off-shears or short wool application of an effective pesticide for lice control has the potential to dramatically alter the situation to such an extent that eradication can be achieved. Eradication enables producers not to treat - thus minimising residues on wool and production costs - and to rely on IPM practices to prevent reinfestation.
Further information
For further information contact DPI&F on 13 25 23 (Queensland residents) or 07 3404 6999 (non-Queensland residents) between 8 am and 6 pm weekdays, or e-mail callweb@dpi.qld.gov.au
The book Blowflies and lice information manual: A practical approach to producing low residue wool (Qld Government Publications) takes you step-by-step through best practice management of blowflies and lice following an integrated pest management approach to reducing pesticide use and residues on wool.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries, Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Last reviewed 03 March 2005
