Online learning: Treatment—Pesticide treatments

Choose the right chemical to eradicate lice, but also consider the various withholding periods, which could restrict your choice.

Structured reading

For those who like to see all the information and simply read through it in order. Each heading is a link to a page of information—the dot point provides a summary of the page.
Tip: Keep this page open and open the links in new tabs.

Chemical group
An introduction to chemical groups.

Sheep lice treatments—chemical group characteristics
Details on chemical groups.

Sheep lice control for ewes and lambs
Factors to consider when choosing a treatment

Ewe-lamb Treatments Tool 
An interactive tool to assist producers determine the best course of action including choosing the right chemical to use when treating pregnant or lactating ewes.

Question and answer

For those who prefer a problem based approach to learning, answer the following questions.
Each of the questions below links further down the page to the answers.

Questions:

  1. List the 7 different chemical groups of current (2104) lice treatments.
  2. Resistance is already known to be present to what two groups?
  3. Describe the four intervals or periods that apply to lice treatments.
  4. When can two lice treatments be mixed together?
  5. What detrimental effect can come from using a combination product for both lice and worms? (Currently there is one product with abamectin for both lice and worms).
  6. Can lice be eradicated if all sheep on a property are not treated at the one time?

Answers:

You can also click on each question below to go to WormBoss pages with related information.
 

1. List the 7 different chemical groups of current (2104) lice treatments.

  • Neonicotinoid (Imidacloprid)
  • Spinosyn (Spinosad)
  • Organophosphate (OP: temephos, diazinon)
  • Macrocyclic lactone (ML: abamectin, ivermectin)
  • Magnesium fluorosilicate/sulphur (MgFSi, sulphur, rotenone)
  • Insect growth regulator (IGR: diflubenzuron, triflumuron)
  • Synthetic pyrethroid (SP: cypermethin, alphacypermethrin, deltamethrin)
     

2. Resistance is already known to be present to what two groups?

Resistance is known to have developed to pyrethroid and to IGR pesticides in some sheep lice populations. These pesticides will not adequately control populations containing pyrethroid- or IGR-resistant lice. Resistance to either group is not restricted to any particular geographic region. Resistance can be suspected in pyrethroid treated sheep if live lice are present later than 6 weeks post-treatment. Resistance to IGRs should be suspected if live immature lice are seen on sheep later than about 10 weeks after treatment.
 

3. Describe the four intervals or periods that apply to lice treatments.

  • The Wool Harvesting Interval (WHI) is defined as the time from application of a chemical to when the wool can be harvested to satisfy Australian environmental requirements (also includes crutching).
  • The Wool Rehandling Period is the time between treatment and when wool/sheep can be safely handled without the need for protective clothing.
  • The Meat Withholding Period (WHP) is the time from chemical application to when an animal is slaughtered for domestic use.
  • The Export Slaughter Interval (ESI) is the time from chemical application to when an animal is slaughtered for export.
     

4. When can two lice treatments be mixed together?

Under no circumstance should products be mixed or label rates altered in an attempt to improve the effectiveness of lice control. There are many different effective products from a number of different chemical groups currently available on the market. Mixing chemicals or increasing rates will not make up for a failure in lice biosecurity or inadequacies in application technique.
 

5. What detrimental effect can come from using a combination product for both lice and worms? (Currently there is one product with abamectin for both lice and worms).

When applied as a backline lice treatment, abamectin will move into the bloodstream and affect sheep worms as well. Abamectin remains an important drench chemical, although resistance in worms has been reported in all Australian States. If considering using abamectin for lice control, producers should consider the possible impact of this treatment on their drench resistance management strategy; the abamectin drench component can be at risk of faster resistance development if its use is not really warranted at the time of the lice treatment.
 

6. Can lice be eradicated if all sheep on a property are not treated at the one time?

It is easier to eradicate sheep lice on farms with one main shearing than it is on properties where mobs are shorn at different times (split shearings).

Similarly, flock management becomes more complicated where pregnant ewes or ewes with lambs at foot need to be treated for lice. This is because backline treatments and insect growth regulator products take some time to bring about the death of all lice. During this time, if there is contact with other untreated sheep, there is the potential for lice to spread.

Where split shearings occur, it is critical that treated mobs are kept separate from untreated sheep for the period specified on the label. Managing ewes with lambs at foot or ewes due to lamb soon after treatment is more complex.

 


Links to the learning topics