11 April 1997


Confused about scab control? Rebecca Austin seeks the advice of an expert

SHEEP scab is one of the most serious welfare problems producers may encounter in their flocks, warns Peter Bates, head of entomology at the Central Veterinary Laboratory.

Since deregulation in 1992, outbreaks have risen dramatically. At the same time there have been an increase in other ectoparasites, such as keds and chewing lice, which were previously suppressed by compulsory dipping.

This can cause confusion when diagnosing an ectoparasite outbreak. Mr Bates therefore warns producers to identify accurately suspected ectoparasites before treating against scab.

When a producer has diagnosed scab correctly, there are a bewildering array of treatment available:

&#8226 Organophosphate (OP)-based dips

&#8226 Synthetic pyrethroid (SP) dips

&#8226 Systemic injectables.

"Reading the label will tell you which product is effective against sheep scab, and whether it protects against reinfestation as well as killing active scab. Remember the sheep scab mite can live off the host and remain infective for 15-17 days."

Approved dip formulations – licensed prior to 1992 – containing the OPs diazinon or propetamphos or the synthetic pyrethroid, flumethrin, are guaranteed to protect against reinfestation for at least three weeks on sheep with 1cm (0.4in) of wool. "In reality this is considerably longer on full fleeced sheep," says Mr Bates.

Sheep dipped with one of these approved dips can return to an infested pasture, yard or barn directly post dipping without risk of reinfestation.

Dips licensed after 1992 – such as high cis cypermethrin – are no longer required to offer protection against scab. Dipped sheep therefore cannot be returned to infested pasture after dipping.

"Many flocks owners cannot use OP dips for medical reasons and the debate over their safety continues," says Mr Bates. "Non-OPs are one option for these producers. But strains of the mite have now been identified as resistant to the SP dip flumethrin – possibly brought on by the inappropriate use of SP pour-ons which are ineffective against the mite."

Plunge dipping is time consuming and labour intensive and can be stressful to sheep. Also, dip disposal may constitute a hazard to the environment.

Systemic injections, such as ivermectin, can overcome these problems. They are also effective anthelmintics.

"Ivermectin has been licensed for scab control in sheep for a number of years. When two injections are given seven days apart it is effective at curing scab, but offers little or no protection against reinfestation. Again, sheep should not be returned to infested pasture," says Mr Bates.n

Sheep ectoparasiticides

NameCompanyChemicalUseWithdrawalActive against

period (meat)TicksMitesB/flyFliesLiceKeds

Synthetic pyrethroid

CrovectCrownCypermethrinPour-on3 days****

Crovect DipCrownCypermethrinDipNil****

ProvinecC-Vet VPCypermethrinPour-on3 days****

Provinec DipC-Vet VPCypermethrinDipNil****


VectorYoungsCypermethrinPour-on3 days****

CyporYoungsCypermethrinPour-on7 days****

Spot onMallinckrodtDeltamethrinSpot-on3 days*****



All seasonsMalinckrodtDiazinonDip14 days*****

Diazinon dipDiversey LeverDiazinonDip14 days*****


All SeasonsBayerDiazinonDip35 days*****

Osmonds GoldBimeda UKDiazinonDip14 days*****Fleece

Paracide PlusBattle Hayward

and BowerDiazinonDip35 days*****

Summer fly dipBattle Hayward

and BowerDiazinonDip35 days*****

Topclip flyNovartisDiazinonDip35 days*****

& Scab

Flyte 1250YoungsPropetamphosDip21 days*****

SeraphosCrownPropetamphosDip21 days*****

Ectomort CentenaryYoungsPropetamphosDip14 days*****

Natural compound

BanflyArnoldsCitronella OilTopicalNil*




Ivomec InjectionMSD AgvetIvermectinInjection42 days**(nasal bots) for Sheep

Oramec DrenchMSD AgvetIvermectinOral drench14 days*(nasal bots)

PanomecMSD AgvetIvermectinInjection42 days**(nasal bots)


TakticHoechst RousselAmitrazSpray21 days***


Summer fly creamBattle HaywardDiethyltoluamideTopicalNil*

and Bowerlotion

Insect growth regulator

VetrazinNovartisCyromazinePour-on3 days*


NegasuntBayerPropoxurDusting28 days*


 Basic scab control

&#8226 OPs diazinon and propetamphos and the SP flumethrin guaranteed to protect against reinfestation for at least three weeks post dipping.

&#8226 Sheep dipped with above products can be returned to mite-infested pasture, yard or barn post dipping.

&#8226 Dips licensed after 1992, such as high cis cypermethrin, no longer required to protect against scab.

&#8226 Sheep dipped with the above cannot be returned to infested pasture, yard or barn post dipping.

&#8226 Strains of sheep scab mite now found to be resistant to SP dip flumethrin.

&#8226 Systemic injections can overcome problems of time, labour, stress and polluting environment.

&#8226 Ivermectin effective at curing scab, but does not protect against reinfestation. Also an effective anthelmintic.