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Beyond the Bale : June 2017
Lice management strategies on late pregnant or lambing ewes are complex. Dipping heavily pregnant ewes may not be possible and many backline treatments take six weeks or more to kill all lice. After a backline treatment and before it has killed the lice on the ewes, lice can spread from the ewes to any untreated newborn lambs. The lice can then spread back to the ewes after the protection from their treatment has worn off. A lengthy lambing period exacerbates this problem. Further complexity arises from differing product claims: variations in periods of protection against new infestations, how soon after shearing they must be applied, and whether or not they can be used on unshorn lambs. Attention to the product label is required. Selection of ewe and lamb treatments needs careful consideration to avoid starting a new infestation in lambs or failing to eradicate an infestation in ewes. The LiceBoss Ewe-Lamb Treatments Tool can assist your decision. TREATING LICE ON PREGNANT AND LAMBING EWES When lice are found in late pregnant ewes or ewes that have lambs at foot, lice management strategies are complex. The LiceBoss Ewe-Lamb Treatments Tool can help woolgrowers to choose an appropriate treatment strategy for these ewes and lambs. TREATMENT OPTIONS FOR EWES Long wool treatments of ewes will not achieve eradication and these ewes remain a potential lice risk. Dipping is best done at least six weeks before lambing with ewes in good condition while ewes are able to move safely through a dip. It also reduces the risk of treatment failure from carry over of lice from ewes to early born lambs. But dipping must also occur two to six weeks after shearing (ideally, between weeks two and four). If ewes are not in good condition or lambing is imminent, a backline treatment must be used after shearing (most within 24 hours, one up to seven days after shearing), but these often require six weeks to remove all lice. Insect Growth Regulator (IGR) products require even longer and it is recommended that lambs born to IGR-treated ewes be treated in the first three months of life. Unless you are certain of their effectiveness against the lice on your property, avoid using chemicals to which chemical resistance is known. Knowing protective periods of a product may be useful when treated ewes contact untreated lambs, or when treated lambs contact untreated lousy ewes. Few products have protective period claims: some IGR products claim protection from reinfection for 12 weeks after treatment. One neonicotinoid-based pour-on product claims to protect treated sheep from reinfestation for a period of four weeks. See Table 1 below for more information about chemical groups and their method of application. Also check that withholding periods can be met before using a product. The meat withholding period (WHP) and Export Slaughter Interval (ESI) will restrict the choice of chemicals when treated sheep or lambs are to be sold for slaughter for the domestic or export markets, especially in prime lamb flocks. CHEMICAL GROUP REGISTERED METHODS OF APPLICATION OFF SHEARS/SHORT WOOL LONG WOOL OFF SHEARS BACKLINER SHORT WOOL DIP BACKLINE UPTO6 MONTHS BACKLINE UPTO10 MONTHS BACKLINE UPTO12 MONTHS HAND JET UPTO6 MONTHS HAND JET UP TO 10.5 MONTHS HAND JET UPTO12 MONTHS NEONICOTINOID YES NO NO NO NO NO NO NO SPINOSYN YES YES NO YES YES YES YES YES ORGANOPHOSPHATE YES YES NO NO NO NO NO NO PYRETHROID YES NO YES YES NO NO NO NO INSECT GROWTH REGULATORS YES YES YES NO NO YES NO NO MACROCYCLIC LACTONE YES NO NO NO NO YES YES NO MAGNESIUM FLUOROSILICATE, SULPHUR AND ROTENONE NO YES NO NO NO NO NO NO TABLE 1. CHEMICAL GROUPS AND METHODS OF APPLICATION REGISTERED FOR THE TREATMENT OF LICE IN BREEDING EWE FLOCKS YES indicates that there is at least one product from this group registered for this purpose. Check the LiceBoss Products Tool available via www.liceboss.com.au/tools NO indicates that there are no products from this group registered for this purpose. Note: Despite products being registered for control of lice on sheep, not all will be effective. This is due to the development of resistance to certain pesticide classes in some lice populations. Treatments applied in long wool will not eradicate lice. Re-treatment off-shears or in short wool after the next shearing is recommended. ALWAYS CHECK THE LABEL CLAIMS BEFORE CHOOSING A PRODUCT 42 ON FARM