Sheep Dipping, Dusting, and Spraying

New Zealand Journal of Agriculture, Volume 97, Issue 6, 15 December 1958, Page 519

Sheep Dipping, Dusting, and Spraying

By

J. E. DUNCAN,

Wool Supervisor, Department of Agriculture, : Wellington

A BIG revolution in sheep dipping methods has taken place in the past 10 years ** or so. Recent technical advances have been so rapid that there has been some justification for farmers being confused about their obligations in regard to control of lice and keds. This article reviews development of new methods and materials and clarifies farmers' obligations under recent amendments to the Stock Act.

UP to the end of the war sheep were dipped by “plunging or immersion”, to quote the Stock Act, in some sort of dipping bath containing a poisonous liquid. The poison had to be sufficiently concentrated to kill lice and keds, but not the sheep. Most of the dipping materials at that time in favour were based on arsenic, though carbolic and derris dips were also used, either alone or in combination. None of these dipping materials was renowned for its lasting properties in the fleece, so it was very desirable that neighbours should dip about the same time to minimise the chance of clean sheep becoming reinfested from parasite-infested sheep on adjoining properties. At that time the Stock Act provided for dipping all longwool sheep between 1 January and 31 March in the North Island and 1 January .and 30 April in the South Island. Early or pre-lambing shearing was then little practised.

After the war new dipping materials, such as “Gammexane” (BHC) and DDT, became available. Their greater effectiveness and longer-lasting powers changed the whole picture. Farmers now had at their disposal new and lethal weapons in the continual war of attrition against lice and keds.

Power Spray Dips At about the. same time new methods of ; dipping became available in the power spray dips which had just appeared from Australia, where they originated. Power spray dipping greatly reduced the hard labour of dipping, speeded it up enormously, and converted it from one of the hardest

and dirtiest jobs on the farm to a relatively easy routine operation. It also markedly reduced the losses of sheep and economised in dip. There was much to be said in its favour, provided it was used intelligently and the equipment was kept in good order. To legalise this new practice an amendment to the Stock Act was passed in 1947 which included power spraying under the definition of dipping: “. . . or to spray sheep with such a preparation by means of an effective pressure spraying apparatus.” Pre-lambing Shearing Problem About 10 years now passed without any radical changes in dipping practice; merely minor improvements in material, equipment, and methods. However, during this same period pre-lambing shearing gained greatly in popularity, particularly in some South Island districts and this created another problem. To comply with the

Stock Act farmers were obliged to dip between 1 January and 30 April, but if the ewes had been shorn in August, they would be carrying too much wool by that time for effective dipping, particularly if they were to be spray dipped. This led to a further demand for an amendment to the Act, and this was passed in 1955, legalising dipping (including power spraying) from 1 October to 30 April throughout New Zealand. It also included all sheep, not just longwool sheep. The next radical change occurred only a couple of years ago. A Canterbury firm imported a number of American dusting machines and demonstrated sheep dusting throughout New Zealand. These machines used a very finely ground dust containing dieldrin as the active ingredient. In this new chemical lay the secret of their success. As early as 1948 Americans had tried dusting for control of keds without achieving a 100 per cent kill of parasites, because at. that time the three modern chemicals dieldrin, aldrin, and diazinon were not available. These three have the unique property of being able to dissolve in the wool grease and diffuse downward ■ to skin level, where the parasites spend most of their time; hence their almost unbelievable effectiveness. In New Zealand dusting, right from its inception, was permissible for blowfly control, but it could not be accepted as a legal substitute for dipping until carefully controlled official trials carried out by the Department of Agriculture had proved its effectiveness beyond doubt. These trials had

to be extensive and thorough and therefore took some time, so it was not until recently that dusting was officially recognised. New Spraying Technique Almost parallel with the development of dusting a new type of spraying technique became available. In power spray dipping, developed a decade earlier, a large volume of dip at moderate pressure was applied to the sheep and the run-off was recirculated. The new idea was to use a low volume at high pressure, or a moderate volume at moderate pressure, and not recirculate any fluid which dripped off the sheep. The situation was further confused by reference to the process .by various names such as misting, foaming, fogging, and tip spraying. Tip spraying is the only reasonably accurate description, as only the tips of the staples of wool are wetted. Like dusting, the treatment depends for its success on the active ingredients mentioned, which can diffuse down the wool to skin level. With the existing wording of the Stock Act there was no legal barrier to the use of the various kinds of tip spraying machines, and many firms and even individual farmers started making them. A great variety is now available, with a similar range of effectiveness in their ability to apply sufficient active ingredient to each sheep. From the farmer’s angle dusting and tip spraying are no doubt very attractive, with their speed, ease of use, economy, and potential effectiveness.

However, both these methods are wide open to abuse; much more so than the older methods. There are often-quoted examples of organisms developing an immunity to various chemicals, such as micro-organisms no longer susceptible to penicillin and houseflies immune to DDT. It will be a great pity if lice and keds develop a similar immunity to the new insecticides as a result of half-hearted and ineffective use by careless operators, possibly using badly designed equipment.

Treatment Period Specified

The latest amendment to the Stock Act does something to prevent ineffective use by restricting dusting and spraying to a 3-month period immediately after shearing. This means that with shorter wool there will be fewer parasites and a better chance of the insecticides reaching them. The amendment, passed on 18 September 1958, also extends the dipping period from 1 August to 30 April to cater for those who favour pre-lambing or early shearing. Those who still use plunge dips (baths of various kinds) can dip at any time within this period. Dusting and spraying can also be carried out at .any time within the period, provided they are done within 3 months of shearing.

Authorities in several Australian states have for some time been recommending “off-shears” dipping as the most effective method, because the parasites are reduced to their lowest numbers immediately after shearing and there is so little wool that the remainder are easily reached by dips, dusts, or sprays. Before conventional dipping or power spraying is done a period should be allowed for shear cuts to heal or there is a risk of infection from the dirty wash. With dusting or tip spraying, however, only clean material is applied to the sheep, so it is not unduly risky to carry out the operation literally “off-shears” and save another muster.

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