FIGHTING INSECT PESTS.

New Zealand Herald, Volume XLVIII, Issue 14690, 26 May 1911, Page 10

FIGHTING INSECT PESTS.

THE USE OF SPRAYS, BY'BIKEXE. Having in the previous article discussed the structure and life histories of injurious insects, in so far as it assists in the application of remedial measures, wo aro now in a bettor position to consider the various substances used for insect destruction. Since the use of washes is the most general method employed, let us consider such washes as have been found efficient in common practice. The types of washes employed may bo divided into six, namely, (1) arsenical washes. (2) resin washes, (6) kerosene washes, (4) sulphur washes, (5) soft soap and quassia washes, (6) caustic washes.

Arsenical Washes. Tho common arsenical washes are arsenate of lead and paris green. Such washes aro of use only for poisoning leaf-eating insects (pear slug), and larvro (e.g., codlin moth larva-). As to the respective merits of the two washes, arsenate of lead seems to be the one most in popular favour, perhaps on account of it having a. lesser tendency to burn the leaves. Paris green is used" largely throughout America, and, if properly mixed and carefully applied, its scorching propensities are much reduced. If lib to ljlb Swift's arsenate of lead bo dissolved in 100 'gallons of water, a very cheap and efficient wash is obtained. Stronger solutions may be employed without damaging the foliage, but the above strength is sufficient to kill most insects. Swift's arsenate of lead costs about Is 6d per lb. The important points to remember with regard to these washes are: — Tho wash must be evenly mixed. The trees must be sprayed with as fine a spray as possible. Two or three light sprayings are better than one drenching. Do not spray when the- sun is out, as there is liability of leafage scorching. Never spraywhen the blossom is out, as it damages the blossoms and kills the bees. For the codlin moth larva, spraying just after tho blossom has fallen lodges some of the poison in the calyx. It is this that the larva) has to bito through when it enters the apple. Resin Washes. Resin washes are used principally for scale insects, e.g., apple mussel scale, and their object is to fix the scale to the tree in the early spring, and so prevent the egress of the young huvce scales from beneath the parent scale, and also to burn awr.y certain of tho soft scales. A resin wash made up from the following recipe is found to be very efficient: Resin 241bs, caustic tod.i 51bs, fish oil three pints, or 4ilbs soft soap to 100 gallons of water. Less soda is required if soap is used. First crash tho resin by pounding it in a sack, then put it in tho cooking vessel and add two-thirds of a gallon of water to every pound of resin. Boil the caustic soda, and then add the oil. Mix well, and while still very warm add the resin and stir well until the resin has completely dissolved. The mixture, which is at first creamy, later becomes coffee-coloured and clear. Continue boiling for ten minutes after this coffee-coloured stage is reached, and then add warm water to make the mixture up to 25 gallons. When using, dilute this solution with three times as much water as concentrated wash, and apply tho mixture warm —about 130deg. Fahr. Only apply when tree is dormant, as it burns the foliage.

Kerosene Emulsions. Kerosene forms nix excellent insecticide and insectifuge, more especially *if used with soft soap in the form of an emulsion, in which, the kerosene 13 more evenly distributed when mixed with water. This wash i 3 almost universal in the treatment

of the various species of aphides. It is only useful oil soft-bjodied insects, and has no effect on scales. In .the former it dissolves the wax, as on woolly aphis, and -, then destroys the whole skin. The chief difficulty in the destruction of aphides is to get the- fluid on them, as they are often hidden in the interstices of the bark. It is well, therefore, to. use a strong force pump and as fine a spray as possible. The Woburn kerosene emulsion is probably the best in use. Dissolve £oz of soft soap in a pint of warm water; to this is added gradually two pints of kerosene, and, while so doing, the mixture is churned with a garden syringe. One minute's' churning is quite sufficient to make a permanent emulsion. The emulsion may be made cold, but the water is generally heated to make the.soft soap : dissolve more quickly. This emulsion must; be diluted with- 15 times its bulk of water before it is applied to green leaves.

Using Caustic Soda. Experiments have shown that the addition iof 2. per- cent solution' caustic soda caused a complete mortality of the eggs of apple mussel scale. Its use is therefore indicated with the keroseno emulsion for this pest. Wetting the trees 24 to 48 hours after spraying with emulsions causes a large increase in the mortality of scales. The effect of the water is to bring the keroseno and soap into solution again after drying, and this acts as a second dose to the pests. The branches of the trees should, if possible, not be made dripping wet, ae if this is done much of the solution falls to the ground and is lost. Experiments with the emulsion-soda wash have shown that wetting increased the mortality of the scales from 55 to 88 cent. , Pure kerosene has also been used with kucccss, but this must not be applied when the tree is in leaf, nor in hot weather, when the sap is moving freely in the tree! The estimated cost of spraying an orchard with pure kerosene is from a. halfpenny to twopence per tree, depending on the "size and state of the trees treated.