Obtaining Maximum Effectiveness from Modern Insecticides

New Zealand Journal of Agriculture, Volume 99, Issue 5, 16 November 1959, Page 428

Obtaining Maximum Effectiveness from Modern Insecticides

Tip Spraying, Dusting, Showering, Dipping

By

J. E. DUNCAN,

Chief Advisory Officer (Wool), Department of Agriculture, Wellington

THE last five years have seen a bigger upheaval in I dipping methods in New Zealand than all the previous years of our history. The revolution is by no means finished yet, and no one can tell what the end will be. However, the objective remains the sameto achieve the most efficient way of ridding sheep of external parasites. >

THE two parties chiefly concerned are the farmer and the dip maker.

FARMER

If possible, he wants his sheep freed of parasites and protected against reinfestation for the maximum period at a reasonable cost. Preferably the operation should be easy, foolproof, and not unpleasant or dangerous to either sheep or men.

[maker |

He also seeks the most efficient material, which should be cheap and easy to manufacture, deadly to parasites but innocuous to sheep and men, foolproof, and easy to use.

If these ideals could be realised, there would be .no . problems, but because they cannot, maker and user must collaborate to get the best results. That is why the labels on dipping materials at times appear complicated or on the longside to ensure that dips are used as safely and efficiently as possible. The maker knows the nature and performance of his product better than the user. The farmer ignores the instructions at his own risk. .

Though the modern insecticides are infinitely more potent against parasites, they are not nearly as poisonous to warm-blooded animals as the old arsenical dips. In those days there was an uncomfortably small margin between killing the parasites and killing the sheep as well. Nevertheless the modern dipping materials cannot be treated entirely with impunity, and

many of the directions on the label are designed to avoid any remaining risk of poisoning. The others are mainly to ensure that the dipping material is mixed at the correct strength for best results, that the sheep are handled in a reasonable manner, that the dip is applied as effectively as possible, and that sundry other conditions are as favourable as possible. These directions can be considered under the following headings:

Ipoisoning]

Sheep may be poisoned by swallowing an arsenical dip or by absorbing it through cuts or even unbroken skin if the dip is overstrength. The modern chlorinated hydrocarbon type dips such as BHC, aldrin, and dieldrin are much less deadly when swallowed, but in concentrated form can quickly be absorbed through the unbroken skin. So can the organic phosphorus compounds such as diazinon and “Delnav”Hence the need for care on the operator’s part in handling concentrated materials and for the directions to wear protective clothing, including a mask, when using dusts. That is also the reason behind the direction to remove wet clothes at the first opportunity and to wash off concentrated dip that has come in contact with the skin. The labels - usually carry warnings against less obvious forms of poisoning, such as calves chewing empty arsenical dip packets and fish being killed by running used dip into a stream.

mixing]

Directions for mixing are generally very clearly set out and must be faithfully followed for best results. In the old days dips were mixed pretty well in a standard way to deal only with lice and keds. Now they can be mixed at various concentrations according to how they are to be applied (for example, by plunge, shower, or tip spray) and to whether prolonged protection against fly strike is desired beside killing keds and lice. Tip spraying machines

vary widely in their outputs, pressures, patterns of nozzles, and physical construction, and the concentration must match these characteristics.

Part of the arsenic in the old dips was in true solution and the strength did not progressively fall as dipping continued and the level in the bath fell. Modern dips are suspensions rather than solutions, and the active particles or droplets are progressively removed by the wool of the sheep passing

through. This is known as stripping or exhaustion. Hence the need for “replenishing” or “reinforcing” the bath or sump at frequent intervals to keep up the concentration of active ingredients. If this is allowed to fall too far, a complete kill of parasites will not be obtained, and most of the expense, time, and trouble of dipping will be wasted.

Replenishment means the raising of the level of the used wash in the bath by addition of both concentrate and water, but usually at a higher strength than the original wash in the bath or sump.

Reinforcement means the adding of concentrate only to the bath without addition of water. Both methods are to compensate for the exhaustion that has taken place, and here again the makers’ instructions must be rigidly followed.

One of the advantages of tip spraying is the avoidance of stripping, because no fluid is returned from the sheep; it is all fresh and full strength.

■ condition OF SHEEP

Dipping sheep with open shear cuts is inviting trouble in the form of a potential outbreak of blood poisoning. Nearly all dips now contain bacteriostats to prevent the infection of cuts and scratches, but there are limits to their powers, particularly when the dip is old and dirty. Before bacteriostats came into common use there had been a good deal of trouble with lameness after dipping, which was due to infection of scratches and abrasions of the feet and legs.

Bacteriostats are sometimes omitted from materials to be used in shower dips, and tip sprayers because the dip is not, or should not be, kept long enough for infection to develop. They are not required in dusts. Many dips use copper sulphate (bluestone) as the bacteriostat, and these must not be used in showers or tip sprays, as the copper sulphate would attack the metal; hence the warning on the packet.

At the other end of the scale, tip spraying and dusting sheep with long, woolover 3 months’ growth—frowned on by the makers and not allowed under the Stock Act, as results are likely to be disappointing.

Warnings are given, against driving sheep for any distance immediately before or after dipping as a precaution against their heating up and possibly absorbing enough dip to harm them. Dipping in extreme heat is similarly unwise and warned against.

[breakdown of dip|

Arsenical dips could and did work when they were very old and very dirty; what they did to fleeces and wool values was another matter. Modern dips will not stand this sort of treatment; the actual ingredients are. liable to decompose if the dip is kept too long in a dirty state. The makers warn against this and also storing the dip under extreme conditions of heat and cold, again due to the risk of breakdown or separation of ingredients. Some dips will not mix satisfactorily with hard water; if so, the containers bear a plain warning. Dips badly mixed can stain wool and endanger the health and lives of sheep. With all dips, even the old arsenical powder types, emphasis has always been placed on complete mixing and constant agitation to keep, the ingredients mixed so that every sheep gets its share of active ingredient.

general

The basic requirement that every sheep on' the property should be dipped holds today as it has always done. With modern equipment such as tip sprayers it is little trouble to deal with stragglers or with bought-in sheep after the main dipping or even to dip the whole flock twice a year if necessary.

With plunge dipping the recommended time of immersion was at least a minute, and with power sprays or showers it was several minutes,

the aim being to achieve complete wetting all over and down to the skin. With surface methods of application it is quite impracticable to give a time

limit, and complete wetting is no longer required, thanks to the wonderful ability of modern insecticides to migrate or transfuse down the wool to skin level. What is still required, however, is complete coverage, and enough of the dip remaining in the wool and eventually reaching the skin to do the job.

The latest insecticides are near-miracles of potency against parasites. Users should not unreasonably expect them to perform 100 per cent efficiently if they are abused by disregard of instructions and by attempts to break records in speed of dipping.