Online learning: Treatment—Application methods

The failure of lice eradication can often be attributed to poor application. Choose the right method for your situation and ensure that equipment and operators are up to the job.

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.

Treating sheep for lice
Introduction to lice treatments.

Backline application
Introduction to backline treatments.

Off-shears backline treatments
Details on applying off-shears backline treatments.

Immersion (plunge and cage) dipping
Introduction to dipping (includes video).

Plunge and cage dipping
Details on how to dip sheep.

Shower dipping
Introduction to shower dipping (includes video).

Shower dipping
Details on how to shower dip sheep.

Long wool treatments
Introduction to long wool treatments (includes video).

Hand-jetting sheep for lice control
Details on how to jet sheep effectively.

Avoiding dermo at dipping
Management to minimise the spread of dermatophilus when sheep are dipped.

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. What do you first need to consider when choosing an application method for treating lice?
  2. When should most backline treatments be applied?
  3. What are some disadvantages of backline products?
  4. Why is it recommended to not use backline treatments on sheep that have not been cleanly shorn or those with dermo?
  5. What issues need to be considered when applying backline products to pregnant or lactating ewes?
  6. Under what situation is resistance to lice treatments most likely?
  7. How can incorrect dosing affect effectiveness and development of pesticide resistance?
  8. What types of product cannot be applied with a manual backline applicator?
  9. Describe two ways of applying a backline product that help to ensure it is applied evenly and in the correct position on the sheep.
  10. When dipping sheep, regardless of the equipment to be used, what must be achieved if the lice treatment is to be effective?
  11. What do the following terms mean in relation to dipping?
  12. What is the minimum swim length of a plunge dip and how many times should the sheep be dunked during the swim?
  13. If a large number of sheep are to be dipped, after how many sheep should the dip be emptied and cleaned?
  14. What are the advantages of cage dipping?
  15. Can diazinon be used in all cage dips?
  16. Both pressure at the nozzles and flow rate are essential for effective shower dipping. What pressure and flow rate should be achieved?
  17. As a quick guide to see whether an existing shower dip might deliver enough pressure to be effective, what minimum height should the bottom sprays reach (when turned on alone)?
  18. How long do the top sprays of a shower dip (supplying the minimum pressure and volume) need to run to effectively wet sheep?
  19. Can lice be eradicated with long wool treatments?
  20. Effective jetting requires what pressure at the handpiece?
  21. What handpiece is preferred for both effectiveness as well as ease of use?
  22. What is dermo?
  23. What can be added to many dipwashes to limit the spread of dermo?
  24. What management can be done to limit the spread of dermo?

Answers:

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

In addition to attempting to answer these questions, there are a number of videos you should first watch:

Hand jetting, Plunge dipping and shower dipping

 

1. What do you first need to consider when choosing an application method for treating lice?

The choice of application method is dictated by two primary factors:

  • The chemical group to be used: some can only be applied by particular methods
  • The availability of suitable equipment: existing equipment found on many farms does not deliver the chemical treatment effectively.

Beyond these factors also consider labour required and the speed and ease of use.
 

2. When should most backline treatments be applied?

Most products must be applied within 24 hours after shearing. As with all lice control treatments, it is essential that every sheep is treated according to the label directions for dose rate and application pattern.
 

3. What are some disadvantages of backline products?

Some disadvantages of off-shears backline treatments are:

  • Most must be applied within 24 hours after shearing (seven days for some products, but 24 hours is recommended).
  • For some products, 6 weeks or longer is needed for all lice to be killed, so lice can be present for some time after treatment.
  • There is an uneven distribution of chemical around the sheep. Most of the product applied stays on the backline. If not applied correctly, low concentrations of insecticide in areas distant from the site of application may be insufficient to kill all lice.
  • The uneven concentration of chemical on the sheep increases the likelihood of development of resistance to the pesticide.
  • Backline treatments are not recommended for, and likely to be ineffective on, sheep that are not cleanly shorn or that are affected by ‘dermo’.
     

4. Why is it recommended to not use backline treatments on sheep that have not been cleanly shorn or those with dermo?

If wool is left too long, or if dermo lesions are present, product dispersal over the skin will be reduced and lice control compromised. Unless sheep are shorn cleanly and are free from dermo, do not use any backline product. These sheep may need to be dipped or culled.
 

5. What issues need to be considered when applying backline products to pregnant or lactating ewes?

Do not treat ewes while leaving their lambs at foot untreated. If the ewes had lice then some may have spread to their lambs. The lambs will then transfer the lice back to the ewes as the pesticide concentration declines.

Do not treat ewes less than six weeks before lambing unless all of the lambs born will be treated with a product registered for the control of lice on unshorn lambs. Backline products take several weeks to control lice. Depending on the product there can still be live lice present on the ewes for six or more weeks after treatment. These will infest lambs if they are born within this time. Refer to the Ewe-lamb treatments tool for further details.
 

6. Under what situation is resistance to lice treatments most likely?

If lice are not eliminated from a flock, it is unwise to use the same product group to treat the sheep in the next year. Most resistance occurs where the same product group is used repeatedly for a number of years. If treatment is necessary every year, then rotate product groups to reduce the likelihood of resistance development. If resistance is a problem and alternative backline product groups are not available, dipping may be necessary, as it achieves a better distribution of chemical over the sheep.
 

7. How can incorrect dosing affect effectiveness and development of pesticide resistance?

Read the label to determine the correct dose. Dose rates for all registered backline products are determined by the weight of the sheep being treated. Clearly, knowing the weight of the sheep is essential for correct dosing. Weigh a few of the largest sheep in the mob and set the dose for all sheep to that indicated for the heaviest sheep. Underdosing is a major cause of failure with backline products and increases the likelihood that resistance will develop. Most off-shears backline products are applied as low-volume doses, so even a millilitre or so underdosing can represent a significant percentage of the dose. If there is significant variation in sheep weights, it might be worthwhile to draft the mob into two or more weight classes and adjust dose rates according to the heaviest sheep in each class.
 

8. What types of product cannot be applied with a manual backline applicator?

Usually, labels also stipulate the applicator and nozzle that should be used to apply specific products and warn that drench guns are not suitable. Some applicators apply a wide band of product while others apply multiple stripes via a T-bar nozzle. Most off-shears backline products that are sold as ‘ready-to-use’ are applied as low-volume doses that can be comfortably delivered by manual applicators. The exceptions are the high-volume aqueous diazinon-based products that must be pre-mixed before application. With doses as high as 225 ml per sheep, manual applicators cannot be used. Instead, gas pressure applicators such as the Genesis Power Doser™ or NJ Phillips Powermaster™ Pour-On must be used.
 

9. Describe two ways of applying a backline product that help to ensure it is applied evenly and in the correct position on the sheep.

  1. It is sometimes easier to work from the back of the race to the front and apply the product from the tail to the poll. The operator is out of sight of the sheep so they move less than if the application starts from the poll. It is critical that the treatment is applied as directed on the label. Usually this means evenly down the centre of the back, so any movement of the sheep that results in a distorted application line may require extra product applied to cover the other side.
  2. Some producers recommend setting the applicator to half the correct dose and applying two stripes to each sheep, one from the poll to the middle of the back and the other from the tail to the middle, slightly overlapping the first strip. This helps ensure that the correct dose is delivered and that there is no wastage if the applicator is not quite empty on reaching the end of the sheep. Neither is there an untreated area at the tail or the head if the applicator is emptied too early.
     

10. When dipping sheep, regardless of the equipment to be used, what must be achieved if the lice treatment is to be effective?

Irrespective of the apparatus used to dip sheep, it is essential for lice control that all sheep are wet to skin level at all sites on the head and body.
 

11. What do the following terms mean in relation to dipping?

a) Charging

The addition of product at the dilution rate indicated on the label at the beginning of dipping.

b) Stripping

The selective uptake of pesticide from the dip solution at a faster rate than the removal of water. As a result, the chemical is removed faster than the dip wash, which gradually decreases in concentration as dipping proceeds.

c) Constant replenishment

The ‘constant’ addition of fresh pesticide solution from supply tanks into the dip sump during dipping to maintain a constant volume (and concentration) of dip wash. Advantages of constant replenishment are less fluctuation in dip concentration and no interruption of dipping to replenish or reinforce the dip.

d) Reinforcement

The regular addition of pesticide, but not water, to the dip. Reinforcement replaces the pesticide removed from the dip wash by stripping.

e) Topping up (Replenishment)

The addition of water and pesticide to the dip to replace the dip wash taken out by the sheep. If product label directions say so, topping up should occur after reinforcement, every time the dip volume drops to no less than 75% full.

f) Dipping out

The addition of product only (reinforcement) towards the end of dipping to minimise the amount of used dip wash for disposal. By reinforcing without topping up, dipping out allows the dip volume to drop to 50% full. To determine when to start dipping out, estimate the rate at which wash is being removed from the dip. Calculate how many sheep will take the dip to half its initial volume. Keep the dip at full volume until that number of sheep remain, then begin dipping out. Reinforce when the dip falls to 75% of its initial volume. Continue to dip out until the dip reaches half its initial volume then stop dipping and clean the dip. A dip must not fall below half of the initial level even when dipping out. The dip level should never be low enough to allow the sheep to walk in the dip.
 

12. What is the minimum swim length of a plunge dip and how many times should the sheep be dunked during the swim?

To achieve effective wetting of sheep and ensure eradication of lice by plunge dipping, the swim length should be at least 9m. The sheep should be dunked twice, not including the ‘splash’ entry, to completely wet the head and neck, with a preference towards backward dunking. A large spray nozzle can be used to replace one dunk and would be advantageous in maintaining dip wash circulation.
 

13. If a large number of sheep are to be dipped, after how many sheep should the dip be emptied and cleaned?

The dip should be emptied and cleaned when one sheep has been dipped for every 2 litres of the dip's working volume (e.g. for a 10,000 litre dip after 5,000 sheep have been dipped irrespective of how many times topping up has occurred).
 

14. What are the advantages of cage dipping?

Cage dipping is an extremely efficient means of treating large numbers of sheep quickly. Most cage dips are operated by contractors, and a single operator with good dogs can dip several thousand sheep in a day.

Cage dipping is physically less stressful on sheep than plunge dipping.
 

15. Can diazinon be used in all cage dips?

‘Richards’ design cage dips operated by ‘Richards-trained’ staff are able to use diazinon to dip sheep for lice. This is because of several unique design features that protect the operator from exposure to dip spray or splash. It is illegal to use diazinon in any other cage dip design or plunge or shower dips. However, there are effective, safer to use alternative products available.
 

16. Both pressure at the nozzles and flow rate are essential for effective shower dipping. What pressure and flow rate should be achieved?

The most important factor affecting sheep wetting is the volume of dip wash delivered from the nozzles. This is determined by pump pressure, the diameter of delivery pipes and the spray nozzles. The pump should supply at least 142 kPa, maintaining high flow rate to the nozzles at this pressure. Some producers have modified their shower dips with larger diameter pipes to increase the volume of dip wash delivered. Common causes of low pressure are worn impellors in the pump or low pump speed.

Check the flow rate and pump pressure. A bucket placed anywhere on the floor of the dip should be filled at a rate of 2 litres per minute. The rotation speed of the top arm should be about 5 revolutions per minute (rpm). High speeds (i.e. above 12 rpm) do not wet sheep thoroughly.
 

17. As a quick guide to see whether an existing shower dip might deliver enough pressure to be effective, what minimum height should the bottom sprays reach (when turned on alone)?

A rough guide to correct pressure is that the bottom spray should reach 30 to 40 cm above the top of the dip when run alone.
 

18. How long do the top sprays of a shower dip (supplying the minimum pressure and volume) need to run to effectively wet sheep?

To wet sheep thoroughly they need to be showered using the top nozzles alone for about 12 minutes. Unless you are prepared to shower for this length of time do not use a shower dip as eradication is unlikely to be achieved. Merino sheep look wet much sooner than they are actually wet to the skin where the lice will be. Nozzles must be clean and checked regularly for blockages during dipping.
 

19. Can lice be eradicated with long wool treatments?

Jetting long wool sheep to reduce louse infestations is only a stopgap measure to minimise wool damage until shearing. Lice numbers will be reduced, but the infestation will not be eradicated.

A thorough off-shears, or short wool treatment will need to be applied post-shearing to eradicate lice. Moreover, jetting woolly sheep can cause high insecticide residues in the wool at shearing. Because lice are likely to be present all over the sheep, treatment must target more areas than simply the back. Jetting fluid needs to penetrate to skin level around the neck and sides of infested sheep.
 

20. Effective jetting requires what pressure at the handpiece?

The pump should be checked before use to ensure it is operating efficiently and adequate fuel should be available. The pump must be capable of delivering 700 kPa (100 psi) at the handpiece while still returning enough jetting fluid via the recirculating hose to provide sufficient mixing in the sump. When the jetting fluid has been mixed, the pump should be started and the handpieces held below the surface of the fluid in the sump in the ‘on’ position for about five minutes. This will provide thorough mixing and ensure the hoses are full of jetting fluid, not just water. If two operators are jetting in side-by-side races, the pump must be able to deliver 700 kPa at each handpiece and still provide recirculation.
 

21. What handpiece is preferred for both effectiveness as well as ease of use?

Either a sickle-shaped wand (Figure 1) or the Dutjet® wand (Figure 2) may be used, although the Dutjet is preferred for ease of use and effectiveness.

The Dutjet wand has a metal shroud covering the T-shaped delivery tube. The tube has three big bore jets. The shroud has an angled back edge that opens the staple as the wand is drawn along the back of the sheep. This places the jets directly over the opening in the wool so that fluid is directed onto the skin.

dermo

22. What is dermo?

‘Dermo’, or more correctly, dermatophilosis, is a skin infection of sheep and occasionally other species, and is also called ‘lumpy wool’. It makes sheep highly susceptible to flystrike, difficult to shear cleanly, interferes with the distribution of backline products, and is highly contagious when wet sheep come into close contact. The disease occurs when the bacterium Dermatophilus congolensis gains access to skin and causes inflammation with exudation of protein and serum from skin, which goes on to form the scabs.
 

23. What can be added to many dipwashes to limit the spread of dermo?

Zinc sulphate heptahydrate is registered as a bacteriostat to minimise the spread of dermo between sheep during dipping, but will not have any effect on active lesions. Product labels carry directions for the addition of 10 kg of zinc sulphate heptahydrate per 1000 litres of dip water (1% solution). Some dipping product labels suggest adding chlorhexidine disinfectants (e.g. Hibitane®) for general dip hygiene, but these have no registered claims against the spread of dermo.
 

24. What management can be done to limit the spread of dermo?

An alternative approach to using zinc sulphate is to improve management around dipping to avoid dermo spread e.g. don’t hold wet sheep closely together in yards for extended periods, don’t truck wet sheep or choose not to wet-dip in years when the risks of dermo and subsequent losses are greatest.

When dermo risk is high:

  • Cull infected sheep if only a small proportion is affected.
  • If affected sheep can be clean-shorn, choose a backline lice treatment. See Short Wool Tool.
  • Use good dipping management. See Plunge and cage dipping LiceBoss Note.
  • Consider adding a bacteriostat to the dip.

 


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