FRUIT TREES AND THEIR ENEMIES SPRAYING CALENDAR BY SPENCER PICKERING, M.A., F.R.S., AN» FRED. V, THEOBALD, M.A. , MARmALL. HA\!ILTON, KENT & CO.. LTD. PmOE 716 Net ^^^ % §, ^. '^xli pkarg P^5 N C STATE UNIVERSITY D,H. HILL LIBRARY liillll This book is due on the date indicated below and is subject to an overdue fine as posted at the circulation desk. EXCEPTION: Date due will be earlier if this item is RECALLED. [ 4 1998 150M/01 -92— 941680 ^JLf' BY SPECIAL APPOINTMENT TO H.M. THE KINfi. JAMES VEITCH & SONS, m. invite inspection of tiieir very fine and extensive stocks of FRUIT TREES both in open quarters and in pots. Bush Fruits, Grape Vines, Fig Trees, etc., cultivated at LANQLEY, near SLOUGH . AND . FELTHAM, MIDDLESEX Please write for full particulars and Illustrated Catalogue to JAMES VEITCH & SONS, Ltd. Royal Exotic Nursery, CHELSEA, LONDON Telephone-" 1642, WESTERN." Telegrams-" VEITCH, CHELSEA," a Established 1848. 2d. WEEKLY. "^f^^J-^ WEEKLY, 2d. The Journal of Horticulture AND HOME FARMER. THE LEADING HORTICULTURAL JOURNAL The career of THE JOURNAL OF HORTICULTURE (now in its 60th year), extending over a period distinguished for the phenomenal development of gardening, is W1TH = OUT A RIVAL in the United Kingdom. The crisp, in= telligent style of its articles maintains for the "Journal" a position which is unique. It is of GREAT UTILITY to ADVERTISERS as an effective medium for bringing their specialities before the public. TERMS OF SUBSCRIPTION. Year, 10/6; Half =year, 5/6 ; Quarter, 3/=, post free. Spccii)ie7i Copy and Scale of Charges for Adveriiseinents OH application. Office : 12 Mitre Court Chambers, Fleet St., London, E.C. FRUIT TREES AND THEIR ENEMIES WITH A SPRAYING CALENDAR SPENCER U. PICKERING, M.A., F.R.S. DIRECTOR OF THE WOBURN EXPERIMENTAL FRUIT FARM FRED. V. THEOBALD, M.A. VICE-PRINCIPAL AND ZOOLOGIST OF THE SOUTH-EASTERN AGRICULTURAL COLLEGE Price is. 6d. net ; Postage zl^d. LONDON SIMPKIN, MARSHALL, HAMILTON, KENT & CO., Ltd. 1908 Richard Clay & Sons, Limited bread street hill, e.c., and bungav, suffolk. IPROPERn 1 N. C State i^ikg CONTENTS GENERAL REMARKS ON SPRAYING I CHARACTERISTICS OF INSECTS . . 4 FUNGI . . 9 SPRAYING .... . 12 >> APPLIANCES . i6 )> MATERIALS . 20 PESTS OF APPLES . 62/ )j CHERRIES . . 78 5) CURRANTS . . 79 )J GOOSEBERRIES . . 81 5> NUTS . '^ / )J PEACHES . . 85^ >J PEARS . . . . 86 5? PLUMS . 8S )> RASPBERRIES . 93 )J STRAWBERRIES . . 94 n VINES . 95 n FRUIT TREES IN GENERAL — BIRDS, FROST 96 SPRAYING CALENDAR . 104^ TABLE OF WEIGHTS AND MEASURES . no — INDEX • III ZO-bZ\ FRUIT TREES AND THEIR ENEMIES This little volume is the outcome of suggestions which have frequently been made to the writers, that a Spraying Calendar is, at the present moment, much needed by fruit growers and gardeners. In the writing, the work has grown somewhat beyond the limits of a mere calendar, though it is still confined within very modest bounds, and does not profess to give more than a brief and popular account of such fruit tree pests as are more frequently met with in this country, as well as of the commoner insecticides and fungicides used in combating them. The spraying of trees has now for many years been recognised abroad and in our colonies as an operation indispensable to fruit-growing, if clean fruit and heavy crops are to be obtained ; and in many cases such spraying is even enforced by law. No doubt the necessity for spraying is not, and may never be, so great in this country as it is elsewhere ; our variable climate, the smallness and highly mixed character of our plantations, as well as the large number of different varieties grown, whilst being disadvantageous in many ways to fruit production, indirectly benefit it, by fl C. State Colleg 2 FRUIT TREES AND THEIR ENEMIES militating against the spread of fruit pests. But this must not be taken to imply that spraying can be dispensed with in any well-managed garden or orchard; and the efficient treatment of the fruit trees often involves applying a similar treatment to the neigh- bouring hedgerows and forest plantations ; for these act in many cases as the breeding-grounds for the insects which attack the fruit trees {e.g. the winter moth, lackey moth, little ermine moth, scale-insects, etc.). It is only during the last few years, however, that the necessity for spraying has begun to be generally recognised in Great Britain, and the eagerness dis- played to make up for lost leeway is calculated to lead to an indiscriminate dosing of fruit trees with anything and everything which may be put on the market. Unfortunately, the Board of Agriculture has no experiment station where such matters can be investigated, nor has it even a department for dealing with horticultural subjects, so that the fruit grower can look for no authoritative advice from that quarter, and is left very much at the mercy of the enterprising advertiser. Spraying, to be successful, must be done intelli- gently. The grower must know what to spray for, what to spray with, and when to do it. To spray a tree without any definite object is like giving a man physic without knowing what is the matter with him, or whether anything is the matter at all. Some acquaintance with the commoner diseases of trees is essential ; and, for that reason, it appeared that a spraying calendar, without any description of some FRUIT TREES AND THEIR ENEMIES . 3 of the commoner pests for which the spraying is done, would be somewhat useless. It is not, however, always easy to identify an insect or fungus from a mere description of it, and, whenever a grower feels doubt on the subject, he should send a specimen for identi- fication to some authority on entomology or on plant diseases. INSECTS A KNOWLEDGE of the life-histoiy of an insect or fungus is essential whenever it is a question of de- stroying it, for there is often only one period in its life when it is vulnerable, or when we can get at it so as to attack it with success. Generally speaking, there are four distinct stages in the lives of all insects : (i) the egg, (2) the larva, maggot, grub or caterpillar, (3) the chrysalis, nymph or pupa, and (4) the perfect insect or imago. The true pupal stage is absent in the case of mites and spiders, whilst in that of some insects, such as aphides and leaf-hoppers, there is no pupal stage similar to that existing in the case of a moth, where the pupa is quiescent, and does not feed. Those insects which have a quiescent pupal stage, for the conversion of the caterpillar, maggot or grub into the adult form, are said to undergo a " complete metamorphosis," and beetles, sawflies and flies undergo such a change, as well as moths. Aphides, scale- insects, leaf-hoppers and bugs undergo what is called an "incomplete metamorphosis," wherein the changes between the larva and adult are gradual, the insect in the pupal stage resembling that in the larval stage, except that '' wing-buds " appear, these giving place at the next moult to fully developed wings, and the insect then becoming perfect. During 4 INSECTS 5 the pupal stage in this case, the insect is active, and feeds throughout it, and these insects, therefore, are injurious all their lives. In the other cases, where the pupa is quiescent, damage is done during the larval and adult stages (beetles), or during the larval stage only (moths and sawflies). True caterpillars have a pair of jointed legs on each of the first three segments of their bodies ; the fourth and fifth segments have no legs, and on the next four segments, as well as on the last, or anal, segment, there are pairs of soft pro-legs, or sucker feet. In the case of "looper-caterpillars," this arrangement is modified, there being only one pair of pro-legs in addition to the anal pair, and these are on the ninth segment. False caterpillars, as the larvae of sawflies are called, have always more than four pairs of pro-legs. With moths and butterflies the insect can rarely be attacked when in the perfect state ; it must be dealt with, either in the winter, by destroying the eggs and chrysalids, or in summer, by destroying the larvae. In the former case, a strong insecticide can be used, for the trees are then devoid of foliage, and the substances selected should have, if possible, the twofold property of not only destroying the eggs, etc., but of removing moss, lichen and dead bark from the trees, thus reducing the number of lurking-places available for harbouring insects and their eggs; indeed, this is often the chief w^ay in which winter washes are beneficial ; for insect eggs are generally so resistant, or so well protected, that they cannot be destroyed by such washes without injuring the trees. For cleansing properties in a winter wash, we rely mainly on 6 FRUIT TREES AND THEIR ENEMIES caustic substances, such as caustic soda or caustic lime, but the destructive action may often be en- hanced by the addition of some other substances, notably paraffin oil. For summer treatment, a much weaker insecticide must be used, or the foliage of the tree will be injured. With moths — the damage being done by the insect when in the caterpillar or larval stage — the method of attack is generally based on poisoning its food, rather than on destroying its body by corrosive substances. This applies only, however, to caterpillars and false caterpillars which feed by biting the leaves ; when we have to deal with sucking insects, such as the aphis (green-fly or black-fly), poisons are ineffective, for the insect punctures the leaves and extracts the juices, and these juices cannot be poisoned. In that case the insecticide must be one which acts externally on the body of the insect, either by corroding it, or by stopping up the breathing apertures in its body. It will readily be seen from this how essential it is to have a knowledge of the life-history of the insect. But more than this is required ; we ought to know the exact action which the various insecticides have on it at various times in its life-history, and in many, it may be said in most cases, our knowledge on this point is very deficient, and can only be increased gradually by very extended and laborious investigations. Every individual case has its own complications ; thus the larval stage of an insect is generally divided into various sub-stages, the grub moulting (often five times) and changing its nature, and in some of these stages it may be more sensitive to poisons, or less protected INSECTS 7 by external hairs, than in others. It does not neces- sarily follow that the earlier stages of the insect are those in which it is most sensitive, but it would appear that, as a rule, poisons are most effective in the earlier stages, and corrosive substances most effective in the later stages. Of the poisons in use, those containing arsenic are, perhaps, the most prominent ; these, as is well known, are very deadly to animals, as well as to insects, but in many other cases it is found that substances which act as virulent poisons to vertebrate animals, have little or no effect on insects. This is so with many of the vegetable poisons ; of these there seem to be only a few which can be successfully used as insecticides, the most conspicuous being nicotine (tobacco), quassia, and hellebore, to which may be added pyrethrum, when used as a fumigant. Some recent work, however, has indicated that paraffin oil, when used in a suitable form and of a suitable strength, is more efficacious than the mineral or vegetable poisons mentioned above, though considerable more work is still required to determine the relative merits of paraffin and the compounds containing arsenic. Whether paraffin acts as a poison or as a corrosive agent does not appear to have been established ; probably it acts as both, and it may also act by blocking up the breathing orifices of the insects. Soft-soap is another substance which acts in this way. In the case of red spider and mites, sulphur, or compounds containing sulphur, are often very efficacious, but they seem to be uncertain in their action, and preference is now being given to paraffin emulsions for the destruction of these pests. 8 FRUIT TREES AND THEIR ENEMIES A large number of insects which prey upon trees pass a portion of their existence in the earth, the cocoons or grubs being in many cases buried during the winterat the depth of a few inches below the surface. Tillage of the soil is one way in which much good can be done in such cases, for it brings to the surface the various insects, and exposes them to destruction by birds. On the other hand, the growth of grass and weeds under fruit trees is very injurious, for, not only does it seriously interfere with the health and vigour of the trees, but it also affords facilities for the harbouring of many insects. For similar reasons, all prunings, dead leaves and rubbish should be cleared away from under the trees, and burnt, for they are often infested with the eggs and cocoons of insects, as well as with fungus spores. The direct destruction of insects by applying in- secticides to the soil is a branch of the subject about which little or nothing is known at present. With the exception of certain proprietary articles, the only substance used to any extent is carbon disulphide, a very volatile and inflammable liquid, which is in- jected into the soil round about the roots of the trees, by means of a syringe specially adapted for the purpose. Vermorel has lately devised an apparatus for the destruction of moths and other night insects, consist- ing of an acetylene flame, which gives a brilliant light, surrounded by a tray holding paraffin. The moths are attracted by the light, and fall into the paraflin. It is known by the name of the " Meduse " lamp, and is sold at i8j-. 6d. FUNGI Besides insect pests, the fruit grower has to con- tend with fungoid diseases. A fungus is a plant of the lower order (C7yptoga?;is), which differ from the higher plants by possessing no flowers, and by producing none of the green colouring matter {cJdoropJiyll) which characterises the leaves of ordinary plants. It forms seeds, however, known as spores, and also roots, in the form of exceedingly fine filaments, known as the mycelium or hyphcBy or, more commonly, as spawn. It is this mycelium by which the damage is done to trees attacked by a fungus ; the hyphae make their way through the wood, etc., breaking down the cells of which it is composed, and thus destroying the plant. This renders it practically impossible to apply any remedy once a tree has been invaded by a fungus, unless we can remove the whole of the part attacked ; and our efforts, therefore, must be directed to preventing the fungus from seeding, and propagating elsewhere. The seeds, or spores, which are microscopic in size, are produced in several ways. The mycelium itself in some cases becomes converted into a chain of spores, but the more usual process is for it to send out a number of branches, each bearing at its end a spore, or a receptacle containing many spores {conidia spores). The summer spores of a fungus are formed in this way, and the masses of spore-bearing filaments or 9 lo FRUIT TREES AND THEIR ENEMIES branches produce the appearance of a downy covering over the object attacked, familiar to us in the form of mildew or mould. The branches and spore receptacles constitute, in the larger fungi, the portion of the plant which is commonly called the fungus itself, such as the puff-ball, mushroom and toadstool. The mycelium of a fungus also produces other spores, known as perithecia^ which are often formed inside the host plant, and these are enclosed in a tough, leathery receptacle, which renders the destruction of them very difficult. These are the winter, or resting spores, and they are capable of resisting the most intense cold without being injured, and may remain unchanged for years, starting into activity only when they find themselves placed under favourable circum- stances. This, as a rule, is in the spring. A fungus, however, besides reproducing itself by means of spores, does so, also, more directly by means of its mycelium, parts of this becoming changed, and hardened into what is called sderotm, In which con- dition it passes the winter, and develops in the follow- ing year, spreading Itself through the soil and attacking fresh plants. Fungi which attack living plants — pai^asites — are, naturally, of more importance to the fruit grower than those which feed on dead tissue — saprophytes ; but the two classes sometimes merge into each other, and a fungus which is usually a saprophyte may, under altered conditions, become a parasite, and attack living plants. In some cases, also, a parasitic fungus only reaches the seeding stage on the dead wood of the plant which it has killed. FUNGI II Moulds and mildews are commonly differentiated from other fungi by being confined more to the surface of the host plant, their mycelium penetrating only a short distance into the substance of the leaves, shoots, etc. For the destruction of fungus spores, the fungicide must be applied either in summer or in winter, according as it is the summer spores or winter spores which have to be attacked. One essential to the successful dealing with the summer spores is to do the spraying on the very first appearance of the disease : in most cases, however, such spraying results only in a checking of the attack, for the mycelium is not destroyed by it, and a renewed formation of spores occurs later on, necessitating a repetition of the spraying operation. Besides spraying the trees in winter for the destruc- tion of the winter spores, it is very important that all dead leaves, shrivelled fruit, and prunings should be collected and burnt, for it is on them that the spores are generally found. All wounds should be attended to and tarred, for in many cases it is through some wound that the fungus spores gain an entry into the tree; unfortunately they may enter through wounds too minute to be noticed, such as those made by the woolly aphis, and the destruction of pests of that description is, therefore, one of the best ways of keeping the trees free from the attacks of fungi. There are practically only two substances effectual in destroying fungus spores — potassium sulphide, and copper, the latter being generally used in the form of one of its sulphates. SPRAYING From what has already been said, it must be evident that spraying will always have to be adapted, both as regards the date of the operation and the substances used, to the nature of the pest to be dealt with. The idea of having some one substance which will cure all the ills to which a tree is liable, is just as unlikely of realisation, as is that of some panacea for all the diseases to which human beings are prone. Never- theless, a simplification of the treatment of trees is highly desirable, and this has been attempted in the present treatise. Instead of giving all the remedies which have ever been recommended for each individual pest, the most promising one or ones (in the opinion of the authors) have alone been mentioned ; and, where a number of equally efficacious remedies appear to exist, preference has been given to that which is applicable in other cases as well. It must be borne in mind that by far the greater number of pests have not yet been made the subject of careful study from the point of view of the best means of destroying them, and, till that has been done, all recommendations must contain a consider- able element of uncertainty. Growers who are sufficiently interested in the matter to wish to make themselves acquainted with the evidence on which 12 SPRAYING 13 the various recommendations are based, should consult the reports in which the experiments have been described : meanwhile, it is well that they should look with some distrust on such remedies as are recommended only on the strength of casual or isolated trials, for any one making such trials is not unnaturally apt to be misled into attributing real merit to some form of treatment which owed its success merely to chance or exceptional circumstances. Still more should growers hesitate to spend their money on proprietary articles of unknown compo- sition, until the virtue of such articles has been thoroughly established by general experience : and it is well to remember that exaggerated praise in advertisements is not required, when the article advertised possesses real merit of its own. Although the remedies recommended for each pest have been limited to the lowest possible number, all the ordinary remedies in use have been included in the list of spraying materials, together with the in- structions for making them. Spraying, being a necessary part of the routine of fruit-growing, and being, moreover, an expensive part of it, all large growers should make it their business, if only for economy's sake, to acquire sufficient knowledge and skill to make their own insecticides. With smaller growers and gardeners it is otherwise, and the difference in the cost of buying or of making the insecticides, would hardly be counterbalanced by the probable superiority of these substances when made by the skilled chemical manufacturer. In many cases a certain latitude may be allowed in. 14 FRUIT TREES AND THEIR ENEMIES the proportions taken when making an insecticide ; but unless the alteration is based on actual knowledge or experience, it is well not to attempt it ; for too often such alterations may result either in injury to the trees, or in the failure of the spraying to effect its purpose. Still more should growers not attempt to mix various insecticides together, unless they are thorough masters of the chemistry of the substances concerned. Such haphazard mixing will generally result in the destruction of the valuable properties of one or all of the substances in question. Above all, it should be remembered that it is mere waste of money to spray, unless the spraying is done thoroughly. One thorough spraying may succeed in destroying a pest, where several slipshod sprayings will have no permanent effect whatever. Every portion of the tree should be thoroughly wetted. If heavy rain falls soon after trees have been sprayed, the work may have to be done over again ; but a certain amount of rain is often beneficial, as it prevents the wash from drying up too quickly, and helps to distribute the liquid over parts which might otherwise not have been wetted by it. Spraying, it should be remembered, is rather a cura- tive than a preventive measure. There is no good in spraying a tree if there is nothing on it to be destroyed ; indeed, there may be positive harm in doing so ; for, though spraying, when required, results indirectly in improving the trees and the crops, by destroying pests attacking them, yet the substances used may of themselves be injurious to the plant, and the continual use of them often causes damage. Spraying a healthy SPRA YING tree is very much the same as giving medicine to a healthy man. There arc exceptions to this rule, perhaps, but they are chiefly exceptions only in appearance, and apply to cases where the insect or fungus is so widely distributed that its presence may be regarded as a certainty. APPLIANCES The character of the appliances used for spraying is a matter of considerable importance. The chief points to be aimed at are to have a machine sufficiently powerful to send the liquid to the top of the highest trees in the plantation, and to secure a very fine and even distribution of the liquid. An ordinary garden syringe, even with the finest rose-jet attached, gives much too coarse a spray, and is a very wasteful, and, therefore, expensive piece of apparatus : when a syringe is used, one specially designed for spraying, such as the " Abol " syringe, should be selected. The various knapsack sprayers, of which there are several forms on the market, are the most convenient for use in gardens, and in small plantations of an acre or two. They generally hold about three gallons, and are strapped on to the back of the workman, who with one hand works the handle of a pump fixed inside the sprayer, whilst with the other he directs the jet of liquid, which is forced out through a tube attached to it. One of the first forms of knapsack sprayer — Vermorel's Eclair — is still, perhaps, the best on the market. It costs about 30J-. The knapsack sprayers, however, are not sufficiently powerful to deal satis- factorily with thick liquids, such as lime-wash. The form of nozzle fitted to the jet is,. naturally, a i6 APPLIANCES 17 matter of importance, and whenever a nozzle becomes worn, so as to give too coarse a jet of liquid, a new one should be substituted for it. Nozzles designed for dealing with clear liquids, or with those containing solids in a minute state of division, are not suitable for washes containing much lime, for they soon become clogged or worn. A coarser nozzle should be used in such cases, or if the nozzle is adjustable, as some of them are, the opening may be enlarged. There is generally an arrangement for clearing the nozzle whenever it becomes choked. Where an exceptionally fine spray is required, a pneumatic sprayer or " mistifier " may be used, from which the liquid, instead of being forced out by a pump, is ejected by means of compressed air. Small hand-sprayers, holding two or three quarts, are made on this principle, and they will be found exceedingly useful for spraying one or two trees, and also for use in greenhouses, and for experimental purposes. They cost about 22s. Larger machines, made on the same principle, are obtainable. For spraying on a more extensive scale, more powerful and complicated appliances are required ; but it would be beyond the scope of the present work to enter into a description of them, and any attempt to do so might involve preferential mention of the various engineering firms who devote their energies to this subject. Two points which require attention in spraying should be mentioned : the one, that many of the liquids used contain insoluble substances which tend to separate out, either sinking to the bottom, or rising 1 8 FRUIT TREES AND THEIR ENEMIES to the top, and therefore, if the Hquid is not con- stantly agitated, a very unequal distribution of material results. Some of the more recent machines contain an automatic agitator, which is worked by the pump itself : in the case of the knapsack sprayer, the motion of the man who carries it is generally sufficient to keep the liquid shaken up. The second precaution is that the sprayers after use should always be thoroughly washed out, pumping water through them for the purpose, as many of the liquids used corrode the metal and the rubber of the valves. Spraying machines are now to be had with wooden, instead of metal tanks, and these present the advan- tage of it being possible to use the tank for making Bordeaux mixture, instead of having to make this in a separate vessel. It is hardly necessary to mention that spraying can- not be done efficiently on a windy day. Even on a calm day it is not always a pleasant operation, especially when caustic washes are being used, and great care should be taken to prevent the workmen from being injured by these. The men should be provided with waterproof capes, broad-brimmed hats, and india-rubber gloves ; and it is well to have a basin of vinegar and water handy to neutralise the alkali, in case any of it gets on to their faces or hands. When spraying lime-washes, the men should be pro- vided with coloured glasses, and these should also be worn while making up any washes with caustic soda, as if the strong alkali splashes up into the eyes, the consequence may be serious. Powders are distributed on trees by being blown on APPLIANCES 19 to them by means of bellows. A knapsack apparatus designed on this principle is procurable, as also are other more powerful appliances, some of which are worked by horse-power. It is important that the powder used should be in a very fine state of division, and that it should be quite dry : on the other hand, the trees should be slightly wet, so that the powder may stick to them. The dusting of trees, therefore, is best done in misty weather, or after a heavy dew. Liquids may be injected into the soil by means of a Vermorel's injector, which is a syringe with a long, sharp nozzle, which can be thrust into the soil to various given depths. MATERIALS Arsenical preparations. — These are used for the destruction of caterpillars, etc., by poisoning their food, the application of them being generally made to the trees when just coming into leaf. Great care must be taken in using them, as they are intensely poisonous, to both man and beasts. Work in this country and in America has shown, however, that the use of arsenic compounds is not, under ordinary circumstances, attended with any danger of poisoning the fruit, or the herbage under trees in grass orchards ; but they should not be applied within three or four weeks of the ripening of the fruit, nor during the blossoming of the trees, otherwise bees visiting the flowers may be poisoned. Arsenical compounds must, also, always be used in an insoluble condition, for, when soluble, they are injurious to plant-life, scorching the leaves, and even killing the plant. None of the compounds in use are absolutely insoluble, and, con- sequently, a little scorching of the foliage is liable to occur in some cases. Considerable preference has been given of late to the arsenates as compared with the arsenites. The compounds in most general use are the following — I. Aceto-arsenite of copper : Paris green. — It is best for the grower to buy this, instead of trying to make MATERIALS 21 it himself. It is sold as a dry powder, or as a paste containing 70 to 80 per cent, of the powder ; the paste is much the more convenient and safe for hand- ling. Paris green nearly always causes some scorch- ing of the leaves, often to a serious extent ; this miy be diminished, though not altogether prevented, by the addition of lime, which neutralises any free arsenious acid which may be present. (i) Paris green paste . . v to i oz. Lime i oz. Water 10 galls. Put the paste in a small pail, and stand it on a stool in the centre of a tub ; while stirring the contents of the pail with a flat piece of wood, pour water into it, and let this overflow into the tub ; the water will carry over only the finer particles, leaving all lumps behind in the pail ; these are broken up by further stirring. The lime (see p. 36) may then be added to the mixture. It should be kept well stirred during use. 2. Arsenite of calcium (^Arscuite of lime : London pur-ple). (2a) White arsenic ... 2 ozs. Quicklime ... 4 ozs. Water .... 10 galls. Slake the lime (p. 36), add the powdered white arsenic to it, and boil the mixture with one quart of the water for half-an-hour ; then add the rest of the water. London purple is a waste product from dye works, and contains about 75 per cent, of calcium arsenite. 2 2 FRUIT TREES AND THEIR ENEMIES It generally contains, also, much soluble arsenic, and to prevent this from scorching the foliage, lime must be added. The quantities recommended are — (2/;) London purple . . . f oz. Lime . . . . f oz. Water .... 10 galls. These quantities represent a much weaker liquid than those given for the arsenite in the formula {2a). London purple does not, on the whole, seem to be so efficacious as Paris green, and the danger of scorching the foliage with it is greater. 3. Arsenate of lead : Gypsine. — This may either be made by the grower, or bought in the form of a paste. It is generally made by mixing together solutions of arsenate of soda and acetate of lead (sugar of lead), but care must be taken that these are mixed in the right proportions, otherwise the foliage will be scorched, the scorching being more serious if it is the arsenate of soda which is in excess. There are at least two different arsenates of soda on the market^ and the proportions to be used depend on which of these is bought. (3^) Arsenate of soda, if " pure " or " crystallised," . 3^ ozs. Acetate of lead . 7 ozs. Water .... 10 galls. (3^) Arsenate of soda, if **dry," " crude," or " commercial " 2 ozs. Acetate of lead . 7 ozs. Water .... 10 galls. MATERIALS 23 The arsenate of soda and the acetate of lead are each dissolved separately in 5 gallons of the waten and the solutions mixed together. The dissolving may be effected most conveniently in this, and in all other similar cases, by tying the solid in a piece of sacking, and hanging it in the water, so as to be only just immersed below the surface. The above proportions will ensure there always being an excess of lead present, and, as different samples of sodium arsenate are liable to contain less arsenic than those on which these proportions are based the excess of lead may be considerable. It is more economical, therefore, to add the lead acetate gradually to the arsenate, examining the liquid between suc- cessive additions, by allowing it to settle, and adding no more of the lead as soon as further additions fail to produce any further cloudiness. The strength of the wash mentioned above is the greatest which should be used, and weaker prepara- tions are generally effective : the actual quantities in the 10 gallons may be reduced to one-half or one-quarter of those given, but both materials must be reduced in the same proportions, the weight of lead acetate being always double that of the crystallised sodium arsenate, or 3^ times that of the crude sodium arsenate. Fur- ther details as to the arsenates of lead will be found in the Sixth Report of the Woburn Experimental Fruit Farm. A ready-made arsenate of lead of American origin is now on the market, in the form of a paste (Swift's arsenate), containing half its weight of dry arsenate, and growers would find it more satisfactory to use 2 4 FRUIT TREES AND THEIR ENEMIES "^ this, or similar preparations, than to make the material 5^ themselves. It should be mixed up with water in the (2 same way as Paris green paste. The proportions to % be taken are- { ^ (3<:) Lead arsenate paste . 3 to I2 ozs. I '^^ Water . . . . lO oralis. i<^ 4. Arsenate of calciinn. — Tlus has been suggested as a cheap substitute for arsenate of lead ; but it seems to be somewhat less effective than the lead salt. (4) Arsenate of soda, " crystallised " 3^ ozs. (or if " crude " arsenate, 2 ozs.) Quicklime • • • • Si ozs. Water 10 galls. Dissolve the arsenate in the whole of the water, then add to it the lime, previously made into a milk (see p. 36). Bordeaux mixture. See Copper sulpJiate. 5. Cai'bolzc acid {Phenol). — This has been very thoroughly tested both in this country and in America, and the conclusion arrived at is that its value as an insecticide or fungicide is too slight for it to be recommended for use. It has been tried in the form of a I to 2 per cent, solution in water, as well as in con- junction with glycerine, soap, lime, etc. Some of the much-advertised insecticides recently placed on the English market consist largely of carbolic acid. 6. Carbon disulphide. — This is a very volatile and inflammable liquid, which is used for preventing insects from destroying stored grain, and also for the destruc- tion of insects in the soil, being then injected with the MATERIALS 25 syringe mentioned on p. 19. The quantity to be used in such cases is from 2 to 4 ozs. to each tree, dis- tributing this at three or four points at a distance of a foot or two from the stems. The ground should not be too dry at the time of appHcation, and the nozzle of the syringe should be thrust down to about six inches below the surface. In the vaporous condition, carbon disulphide does not seem to injure the roots of plants, but it does so when liquid, probably owing to the intense cold produced by its evaporation ; conse- quently, if the end of the injector is felt to strike one of the roots, it should be withdrawn and inserted elsewhere. Ants' nests may be destroyed by pouring half an ounce of carbon disulphide into the nest through a hole made in it, and then stopping up the hole. A second application is needed about two weeks after the first, as the sulphide does not seem to kill the pupae. Copper compounds. — With the exception of Paris green, described above, the compounds of copper are used as fungicides only. A great number of different preparations have been investigated, some consisting of the carbonate, but the majority of the sulphates in some form or another. Copper sulphate itself can be used only on trees when they are dormant, for it is acid in its reaction, and destroys the leaves. For summer use, therefore, the copper sulphate is con- verted by the addition of lime into a basic sulphate, which is insoluble, but which by the action of the carbonic acid of the air, gradually liberates small quantities of the ordinary sulphate, sufficient to act on the fungi, but not sufficient (as a rule) to result 26 FRUIT TREES AND THEIR ENEMIES in any material damage to the leaves. This basic sulphate is known as Bordeaux mixture. The injury to the leaves, which sometimes results from its use, is generally due to its having been improperly made, either by not adding enough lime to precipitate all the copper, or, possibly, by adding too much, the caustic lime being then the substance which causes the scorch- ing : but, even when properly made, some scorching is still liable to occur under certain weather conditions. This cannot be obviated without preventing the liberation of the ordinary sulphate from it, and on this its fungicidal properties depends. 7. Copper carbonate. — This, dissolved in ammonia, forms a fungicide known as Cupram. There are various formulae for making it : one is — Copper carbonate . . • I4 ozs. Strong ammonia ... 16 liquid ozs. Water to make up to . . 10 galls. Dilute the ammonia with 12 pints of the water, and shake it up with the carbonate till this is all dissolved ; then add the rest of the water. This has not proved to be such a satisfactory fungicide as Bordeaux mixture, but the danger of scorching the foliage with it is less. 8. Copper stdpJiate {Bhce vitriol, Bluestone). — For dormant wood the proportions recommended are — (8) Copper sulphate . . . J to i lb. Water . . . .10 galls. For the method of conveniently dissolving it, see p. 23. MATERIALS 27 A wooden or stoneware vessel must be used for the solution, as it acts on iron and zinc. 9. Copper basic sulphate {Bordeaux mixture). — A number of different compounds are formed when lime is added to copper sulphate, according to the proportions used, but they all behave similarly in reproducing by exposure to air a certain amount of ordinary copper sulphate, which acts as a fungicide ; but the proportion of this which is thus reproduced varies in different cases, so that some of the mixtures are much more effective than others, or, what comes to the same thing, the same degree of effectiveness may be obtained at the expense of different amounts of copper taken. The amount of lime used in making Bordeaux mixture can only be regulated accurately when used in the form of the clear solution known as lime-water (see p. 37). The instructions for making Bordeaux mixture with this are — (9^:) Copper sulphate . . .10 ozs. Lime-water . . . .8^ galls. Water to make up to . .10 galls. Dissolve the copper sulphate separately in about half a gallon of the water. Put about half a pound of quicklime, previously slaked (see p.'36), in a tub with 12 to 15 gallons of water; stir this up once or twice, and then leave it to settle. When the liquid is quite clear, run S^- gallons of it off into the solution of copper sulphate. Add whatever extra water is required to make the whole up to 10 gallons. The lime-water may vary a little in strength, so that it is absolutely necessary to test the mixture to 2 8 FRUIT TREES AND THEIR ENEMIES make sure that the whole of the copper has been thrown down : therefore, before adding the additional water, ladle out a little of the mixture, and add one or two drops of it to a weak solution of potassium ferrocyanide in a white saucer (the ferrocyanide may be obtained from any chemist) : if there is any brown coloration, the copper has not all been thrown down ; a little more lime-water must then be added, and the test repeated. Another test for unprecipitated copper consists in immersing the blade of a knife in the liquid, and seeing whether it becomes stained : but this test is neither very delicate nor reliable. Bordeaux mixture made with lime-water in this way is as efficient as that made in the ordinary way (No. 9<:), though the latter contains two-and-a-half times as much copper sulphate. It also presents the advantages of being much finer in texture, and, therefore, less liable to settle to the bottom of the liquid ; it also contains no particles of solid lime, which wear the spraying nozzles, and cause loss of material, by being easily knocked off the leaves, and, further, it exhibits its fungicidal action at once after it is applied, instead of necessitating a certain time to elapse before such action begins, as in the case of the ordinary mixture. Bordeaux mixture may be emulsified with paraffin oil, and thus gives us a combined fungicide and insecticide of great efficiency. The mixture should be made exactly as described above, and then the paraffin added, and churned up with it by a few strokes with a syringe fitted with a rose-jet. This has been named Bordeaux Emulsion. MATERIALS 29 Bordeaux Emulsion. {gb) Copper sulphate . . . 10 ozs. Lime-water . . . . SJ galls. Water to make up to nearly . 10 galls. Paraffin (solar distillate) . 22^ ozs. The amount of paraffin may be varied from 16 to 24 ozs., but with 22J ozs., as above given, the quantity is just sufficient (if it is the solar distillate recom- mended on p. 43) to buoy the copper sulphate up, so that it neither sinks nor rises in the liquid, thus obviating all need for keeping the liquid agitated during use. Bordeaux emulsion of ten times the above strength is sold by some manufacturers, and only requires diluting to be ready for use. It should, however, always be re-churned, either before or after dilution, in case it has not been properly emulsified. A few cases where foliage has been seriously scorched owing to the omission of this precaution, have been reported. Mere shaking of the emulsion is not sufficient. For making Bordeaux mixture in the ordinary way, the following formula may be taken — {gc) Copper sulphate . . i lb. 10 ozs. Lime . . . . .Mb. Water to make up to . 10 galls. The copper sulphate is dissolved in nearly the whole of the water, and the lime, previously slaked and made into a milk (see p. 36), is run into it through a piece of sacking, or through the strainer belonging to the spraying machine. The lime should be added 30 FRUIT TREES AND THEIR ENEMIES gradually, and the addition stopped as soon as the green-blue colour of the precipitate changes to a full blue. It is not safe, however, to rely on this change of colour, as it is not always well marked, and it is better to test the liquid at intervals with ferrocyanide, as described above, during the addition of the lime. If the lime is quite fresh, and if the slaking has been carefully done, it will be found that little more than half the quantity mentioned in the formula will suffice to precipitate the whole of the copper. Bordeaux mixture made with milk of lime may be emulsified with paraffin in the same way as that made with lime-water, though it does not make such a perfect preparation. Both the Bordeaux mixtures here described are equivalent in fungicidal value to that known in America as the ** normal" or '' vG'' mixture. In England, weaker mixtures are often used, and, if such are required, the amount of copper sulphate may be reduced, reducing that of the lime in the same pro- portion. The writers, however, have rarely found any serious injury to be done to the foliage by mixtures of the ''normal" strength, when carefully made. Many recipes recommend the use of a large excess of lime, under the mistaken impression that it will prevent scorching : this is not the case. A full in- vestigation of the nature and action of Bordeaux mixture will be found in the Eighth Report of the Woburn Experimental Fruit Farm. Caustic winter washes. — These should be used only on the trees in the dormant state, the object of their use being to remove moss, lichen and dead bark, MATERIALS 31 all of which tend to harbour insects, and to" protect their eggs ; but some caustic washes, especially those containing paraffin, will also destroy, by their chemical action, the eggs of certain insects (mussel scale, etc.) as well as some chrysalids of caterpillars. The caustic substances used are caustic soda or caustic lime : the latter, being a much less powerful agent, figures also in certain preparations used in summer. Winter washes may be used at any time between the fall of the leaf and the swelling of the buds in the following spring ; but they seem to be generally more effective when applied late in the winter, say, February or March. It is well not to defer the operation too long, however, for bad weather may then occur and render it impossible. One thorough winter-washing every second or third year should be sufficient to keep the trees clean. 10. Caustic soda. {Soda: Sodium Jiydroxide). — This must not be confused with carbonate of soda or washing soda, both of which are practically useless for cleansing trees. By far the most convenient form in which caustic soda is sold is that known as " powdered " ; it is obtainable in tins holding i lb. and upwards, and is of 98 per cent, purity. If a less pure article is used, the quantities in the following recipes must be increased accordingly. It must be remembered that caustic soda is exceedingly in- jurious to the skin, and may cause considerable injury : the precautions requisite in using it have already been mentioned (p. 18), and it is only necessary to add that the solid absorbs both water and carbon dioxide very eagerly, so that the tins of it 32 FRUIT TREES AND THEIR ENEMIES must be kept tightly closed, or it will deteriorate and cake together. A solution of it prepared for spraying should be exposed to the air as little as possible. The strength to be used is — {\0(i) Caustic soda (98 per cent, purity) . . 2 to 2^7 lbs. Water . . .10 galls. The water should be stirred while the soda is shaken in, or the latter may cake together at the bottom. The smaller proportion — 2 lbs. — is sufficient to effectively remove moss and lichen from the trees under ordinary conditions, but a still smaller propor- tion will be only partially successful. By increasing the amount to 2\ lbs. the action on scale is con- siderably increased, but the risk to the workmen using it is proportionately greater. It appears that in the case of scale, the action does not consist of a direct destruction of the eggs, but of a softening, and subsequent glueing of the covering scale to the bark, which results in imprisoning the insects when the eggs hatch. A 2 per cent, solution is not strong enough to do this with certainty, though it is generally effective. Caustic potash is just as effective as caustic soda, when equivalent chemical quantities are used, which means using about three parts of the potash instead of two parts of the soda ; but, as potash, is much clearer than soda, there is no object in making the substitution. Many of the recipes still in circulation recommend substituting for half of the soda an equal MATERIALS 33 weight of " crude " potash, that is, of potassium car- bonate or potashes : this is a great mistake ; as the carbonate has little or no detergent or insecticidal value, and the use of it means so much waste of money, and a reduction of the strength of the wash below that at which it is efficient. The efficiency of a caustic winter wash as an in- secticide has been found to be much increased by the addition of paraffin, and such mixtures are to be re- commended in preference to the simple caustic wash. The mixture is known as the Woburn Wash. The substances used for incorporating the paraffin with the soda are either soap, basic sulphate of copper, or basic sulphate of iron. When soap is used attention should be paid to the brand, for with some soaps the addition of soda will cause the entire separation of the paraffin, and with others, the soap will separate in big clots, which clog the nozzles of the machines. The Chiswick Soap Co. sell a brand (The Woburn Soap) specially adapted for the purpose. The recipe for this waste is — (10/;) Soft soap . . . \\h. Paraffin (solar distillate). 5 pints. Caustic soda . . . 2 to 2J lbs. Water .... 9^ galls. Dissolve the soap in the water (hot or cold) : churn the paraffin up with it (p. 46), and then shake the soda into it. The soda converts the soft soap (potash soap) into hard soap (soda soap), and this, together with the paraffin, tends to rise to the surface, so that the 34 FRUIT TREES AND THEIR ENEMIES mixture has to be stirred continually while being used. The necessity for stirring is almost obviated when basic sulphate of copper is used instead of soap, and the wash obtained has the further great advant- age of being a fungicide, as well as a detergent and insecticide, for it practically contains Bordeaux mixture. The recipe for it is — (lor) Copper sulphate . \\ lbs. Quicklime . . . i to A lb. Paraffin (solar distillate) 5 pints. Water ... 9J galls. Caustic soda . . 2 to 2J lbs. The first four ingredients are mixed exactly as in 9^, and the caustic soda is then shaken in. Testing the liquid to see if all the copper is precipitated is not necessary in this case. A wash precisely similar to the above, except that it possesses no fungicidal properties, may be made by substituting iron sulphate (which is much cheaper) for the copper sulphate. The amount of iron may also be reduced, if necessary, taking — {\od) Iron sulphate lib. Quicklime . ilb. Paraffin (solar distillate) 5 pints. Water 9i galls. Caustic soda 2 to 2I lbs. The lime in the above (but not in the copper wash) may be dispensed with, by adding some of the soda to the iron sulphate before the addition of the paraffin ; MATERIALS 35 but the resulting emulsion is not so fine as when lime is used. When the wash with iron is used, it turns browai on the trees, owing to the formation of rust. This does no harm whatever. For the iron and copper washes a special paraffin oil (solar distillate, p. 43) should be used ; with the soap wash any oil will do, at any rate, so far as making a successful emulsion is concerned, but with solar dis- tillate it is probably more effective than with ordinary lighting oil. The iron emulsion, and also the soap emulsion, may be bought in a concentrated form, requiring only dilution and the addition of the soda to be ready for use. Re-churning, however, is advisable, as mentioned under Bordeaux mixture (p. 29). II. Lime. — As a winter wash, lime is in many respects inferior to caustic soda : it is much less energetic, and, to remove moss and lichen effectively, the strength must not be reduced below lo per cent.; it is advisable, indeed, to raise it up to 20 per cent. : its action in destroying scale, even when used at this strength, is generally less than that of the caustic soda wash, and it appears to be diminished, rather than increased, by the addition of paraffin oil. Such strong lime-washes, moreover, cause much wear of the spraying apparatus, and the whitened appear- ance of the trees is considered by many to be objec- tionable. On the other hand, lime-washing is held to be the only means of diminishing the attack of birds on fruit buds, and, when salt is mixed with it, a wash is obtained which has been found to prevent the hatching of the eggs of the apple-sucker {Psylla) : for 36 FRUIT TREES AND THEIR ENEMIES that purpose, however, it is best applied a few weeks before the buds expand, when it must be regarded rather as a spring, than as a winter wash : an apph'ca- tion at that date would be too late to prevent the depredations of birds. In every case where lime is mentioned in this volume, the weights refer to that of the quicklime, and in every case this quicklime should be slaked before anything further is done to it. Failure in obtaining satisfactory results with preparations of lime are nearly always to be traced to want of care in starting with quite freshly burnt lime, or in slaking this. Quicklime is an oxide of calcium, which com- bines chemically with one-third of its weight of water to form calcium hydroxide, or slaked lime, a compound corresponding with caustic soda. The combination oc- curs only slowly at first, but much heat is developed by it, and if this heat is not dissipated, the whole becomes very hot, and then the action proceeds rapidly, the lime all crumbling up into a fine powder. If too much water is added at first, the rise of temperature is pre- vented, and the slaking takes place very slowly and imperfectly, hard lumps of unslaked lime being left in the product. In slaking, therefore, only just enough water should be added to wet the lime, without any actual water being left over ; and, if the lime does not become very hot, and crumble up in about ten minutes, a fresher sample should be procured. Air-slaked lime should never be used, for that always contains an unknown proportion of carbonate (chalk), which is useless for insecticidal purposes. After the lime has been properly slaked, it may MATERIALS 37 easily be mixed with more water in any proportions, such a mixture forming a iiiilk-of-liine : in using this, it should always be run through a piece of sacking or a strainer, to get rid of any grits which may be present. The milk consists chiefly of the fine parti- cles of lime suspended in the water ; when these are allowed to settle, a clear liquid is left, retaining a small portion of the lime actually dissolved in it : this is lime-iuater \ it contains rather more than one- thousandth of its weight of lime. On exposure to the air it becomes cloudy at the surface, owing to its absorbing carbonic acid, and forming chalk. For use on a small scale, where additional expense is not a consideration, it will be found very convenient to take pure slaked lime, which may be bought at any chemist's for ^d. to 6cL the lb. It forms a fine, impalpable powder, and its use obviates the necessity of any straining, or even of mixing it with water before adding it to sulphate of copper or iron. It should be kept in a well-closed bottle. The weights of quick- lime given in the above formulae may be taken to apply equally to pure slaked lime, for though the latter contains 27 per cent, of combined water, allowance has been made, in giving the weights of quicklime, for the presence of considerable impurity. When a lime-wash is sprayed or painted on to the trees, the deposit of lime soon becomes converted into one of chalk, and it gradually flakes off. The addition of various substances has been tried so as to prevent this flaking, but without much success ; some improve- ment will be obtained by adding to each 10 gallons of lime-wash either 3 lbs. of flowers of sulphur, or 38 FRUIT TREES AND THEIR ENEMIES 5 pints of solar distillate (churning this up with it), or I lb. of water-glass. In the case of sulphur, a certain amount of chemical combination occurs, analo- gous to that occurring in the lime-sulphur-salt washes mentioned below: where solar distillate is used, the effectiveness of the wash on scale is diminished, whilst in the case of water-glass, the results seem to be very uncertain, there being sometimes an increased ad- hesiveness of the wash, sometimes the contrary. Lime-sulphur-salt washes are applied in winter to trees, but more as insecticides and fungicides, than as detergent agents. They will be considered under Sulphur Compounds (p. 53). 12. Lime-salt wash. — This is recommended for the destruction of psylla, and should be applied a few weeks before the buds open. (12) Lime . . . . 15 to 20 lbs. Salt . . . . 2 „ 3 lbs. Water-glass . . . ^ „ i lb. Water .... about 8 galls. Slake the lime, and mix it with half the water ; in the rest of the water dissolve the salt and the water- glass (sodium silicate) ; mix the two. It is not known yet what the mechanism of the action is in the case of this wash, especially as to the part played by the salt. The amount of this latter has recently been raised from 2 up to 3 lbs., and, if the action depended on it, it might be raised still further, even up to 10 lbs. ; but it is stated that very little advantage has been gained by raising it to 4 lbs. The lime appears to act MATERIALS 39 to a certain extent mechanically, forming a coating over the Q%^s>, through which the insects cannot break ; but it also, no doubt, acts chemically, the comparative weakness of its causticity being counterbalanced by the large proportion in which it is used, and the long time required for it to become entirely converted into carbonate. In Canada this wash has been in use for many years for cleansing trees from moss, lichen and rough bark, and also for destroying scale ; and in Nova Scotia it is being tried for reducing the attack of the leaf-curling apple aphis ; but experiments in this country show that for removing moss, etc., and scale, it is inferior to the paraffin-soda washes. As already stated, a powerful spraying machine fitted with a special nozzle is required for applying this and other lime-washes. All these lime-washes appear to delay the expansion of the blossoms for a few days, which, on the whole, is an advantage, by increasing the probability of their escaping damage from frost. But other washes also (soda-paraffin washes) have a similar action, when applied late in the winter. 13. Hydrocyanic acid {Pnissic acid). — This is a gas, and is used for destroying various insects in green- houses (scale, mealy bug, thrips, weevils, etc.), and those on young nursery stock (woolly aphis, especially) before planting out. "When used with the precautions mentioned below, and under favourable conditions, it should destroy also the eggs of these insects ; but if not, a second fumigation, in the case of greenhouse plants, will be necessary, to kill the insects hatched from the 40 FRUIT TREES AND THEIR ENEMIES eggs which survived the first fumigation. For mealy bug, this second fumigation should be done about a fortnight after the first. The gas is a deadly poison, and operations con- nected with it should never be left to the care of workmen. It is made by acting on potassium or sodium cyanide (also deadly poisons) with diluted sulphuric acid. When stocks have to be fumigated, they may be placed in a small greenhouse, or under a skeleton box covered with oiled cloth. The operation should not be done in sunshine, nor when the temperature is above 60° F. ; also, the house, earth, etc., should be as dry as possible at the time. The amount of material used depends on the cubic contents of the place to be fumigated : for every 100 cubic feet, two-thirds to one-quarter of an ounce of potassium cyanide is required, or one-half to one- fifth of an ounce of sodium cyanide, the quantity depending on the hardiness of the plants treated. For each ounce of cyanide, one liquid ounce of strong sulphuric acid (oil of vitriol), previously diluted by pouring it very gradually into 3 or 4 ozs. of water, is required. A jar containing the diluted acid is placed on the ground, and the cyanide, wrapped up in a piece of netting or wire gauze, is lowered into it by means of a string, passing over a pulley, or tied to a long stick, so that the operator may work it while he himself is outside the house. Every opening in the house should previously have been closed, except the one necessary for lowering the cyanide. After one hour, the door may be opened, but no one should go in, till time has been allowed for thorough ventilation. MATERIALS 41 Trees growing in the open may be fumigated by covering them with dome-shaped tents. The experience of both the writers of this volume has led them to state at various times that fumigation is not effectual in killing insect eggs, but further evi- dence shows that hydrocyanic acid is really fatal to eggs, provided it is applied in suificient quantity and under sufficiently favourable circumstances, though success does not seem to be a certainty. The fact that it is soluble in water accounts for many of the dis- crepancies noticed, and this would always render its application to trees while in the ground very un- certain in this country ; for the soil here is never dry during the winter. A hard frost is the best type of weather in which to treat such trees. For killing insect eggs, the maximum quantity of cyanide men- tioned above should be employed, and, if it is the potassium cyanide which is used, this must be the "lump" cyanide, which is practically pure, and not "stick" cyanide, which contains only 40 per cent, of true cyanide. The operator should also make certain that the action has been complete, for occasionally the lumps of cyanide become coated with a deposit of acid sulphate, which protects them from further action before more than half of the cyanide has been attacked by the acid. To obviate this, the cyanide should be broken up into pieces not larger than beans, and it is best not to use paper for wrapping it up, as is generally recommended, for some paper becomes converted by the acid into parchment paper, and the packet of cyanide reinains intact. Sodium cyanide dissolves more easily than the 42 FRUIT TREES AND THEIR ENEMIES potassium cyanide, and on that account is preferable to it, though it is somewhat dearer. Weight for weight, it hberates 30 per cent, more gas than the potassium cyanide. The damage done to trees by the gas is usually insignificant, and is generally confined to killing off the ends of a few shoots ; but occasionally the damage will be more serious, and trees are some- times nearly killed, even with doses not strong enough to destroy the eggs of the mussel scale. This discrepancy in behaviour is doubtless connected with differences in the water contents of the cells of the trees, which would affect the results when dealing with a gas soluble in water. 14. Iron sulphate {Copperas : Green vitriol). — This appears to have little or no value as a fungicide, and cannot, therefore, be used as a substitute for copper sulphate in this respect. Merely as a substance for emulsifying paraffin oil, however, it is an efficient substi- tute for the corresponding copper salt. (See pp. 34, 48). 15. Paraffin {Petroleum : Kerosene). — Paraffin is a generic name applied to certain substances pos- sessing an analogous chemical constitution, but differing considerably in physical properties, and ranging from gases to solids. Those which are of use in the treatment of trees are all liquids, but these liquids vary largely as regards their volatility. If they are too volatile, they will eva- porate before having time to act on the pests to be destroyed ; if they are too stable, they will remain so long on the trees that the bark of these may be damaged. For general use the best oil is MATERIALS 43 one which contains only a small proportion, either of the very volatile, or very stable paraffins. One of the various products known as solar distillates has been found to answer these requirements, and is sold under the name of the Woburn Distillate. Ordinary paraffin lighting-oil will answer most purposes fairly well, but the solar distillate, besides being more efficient, possesses the further advantage of being cheaper, of not being an "inflammable" for the purposes of railway carriage, and of emulsifying well with the basic sulphates of iron and copper, whereas lighting-oil is less satisfactory in this respect. Paraffin is sometimes sprayed on to dormant trees as a winter wash ; but it cannot be recommended for this purpose. It has little or no detergent action as regards moss, lichen, etc., and it is less effective in destroying mussel scale, etc., than is a caustic wash to which 6 per cent, of paraffin has been added. It is also liable to injure the trees, especially if used in successive years, the buds and tips of the shoots being destroyed. The heavier the oil, the more marked is this destructive action. Young nursery stock may be immersed in petrol before planting for the destruction of woolly aphis, and this treatment has not been found to result in any injury to them : but no less volatile oil should be us-ed for this purpose : even a good quality lighting- oil, such as White Rose, has been found to have a very deleterious effect on the trees ; and the use of a heavy oil, such as solar distillate, will prove fatal. Apple trees may be effectively sprayed in summer 44 FRUIT TREES AND THEIR ENEMIES for woolly aphis, with a high class burning oil, such as White Rose oil, and very little damage to the foliage will result; but in this case neither the heavier oil (solar distillate) nor the lighter oil (petrol) must be used : the latter appears to destroy the foliage almost instantly. The use of undiluted paraffin — even White Rose oil — on trees in leaf, must, however, at present be considered a somewhat risky proceeding, and one which requires further investigation : it is well to apply such a drastic remedy only in cases where unimportant trees are infested, and where there is danger of the infection spreading to more valuable ones. But if paraffin is used, it should not be diluted — that is, made into a strong emulsion — under the impression that there will then be less likelihood of its doing damage, for the reverse has been found to be the case, strong emulsions causing more injury than undiluted paraffin. In spraying paraffin a very fine spray, such as that produced by a "mistifier" or pneumatic sprayer (p. 17), should be used. 16. Paraffin emulsion. — For spraying in winter, an emulsion containing 6 per cent, by volume of paraffin is recommended, and no fear need be entertained of any damage being done by it, so long as the buds are not opening. It has already been used very ex- tensively in conjunction with caustic soda {lob, loc and lod), and no damage has yet been reported, even in the case of peaches and nectarines ; in some cases, too, it has been applied to mixed plantations when the gooseberries and currants were quite green with foliage, and the damage done to them was of the MATERIALS 45 slightest description, and often not noticeable. Mix- tures containing as much as 12 and 18 per cent, have been found to be harmless to apples, while dormant ; but it is probable that the repeated use of liquids of this strength would ultimately do harm ; such, at any rate, has been found to be the case in America, though there, still stronger mixtures, often made with crude petroleum, have been used. For use when the leaves are on the trees, emulsions containing \\ per cent, of paraffin are the strongest which should be used, though an increase to 2 per cent, causes only an amount of damage to the foliage which is generally too slight to be noticeable. While the trees are in blossom, paraffin insecticides should not be used at all. For incorporating paraffin with water, special pumps are in use in America, but a much more satisfactory method is to add some substance which will emulsify the oil. In emulsification the paraffin is broken up into microscopic globules, and there must be present some substance which has the power of preventing these from reuniting: the mixture then remains per- manently milky. Soap, and also solids in an ex- tremely fine state of division, have this power, and several emulsions made with them have already been mentioned. For use in winter, paraffin emulsions are not of much service, unless mixed with caustic soda, for without the soda they will not destroy moss and lichen, and, therefore, those emulsions are preferable which are not broken up (de-emulsified) when soda is added to them. This is so with the emulsions made with basic iron sulphate and basic copper 46 FRUIT TREES AND THEIR ENEMIES sulphate, but only partially so with those made with soap, some soaps being satisfactory in this respect, and others not. A soap specially made for this purpose should be used (see p. 33). Enmlsions ivith soap. — The formula for making this when required for use as a winter wash with caustic soda, has already been given in lob (p. 33) ; but the emulsion itself may be made in a concentrated form, according to the following recipe (16^:), this stock emulsion, when required for use, being diluted in the proportion of i gallon to 9 gallons of water, and the caustic soda (2 to 2 J lbs. to the 10 gallons) being subsequently added, if required. {i6a) Soft soap .... 5 lbs. Paraffin .... 6 galls. Water . . . . 3^ galls. The soap is dissolved in the water, and the paraffin is added to it gradually, churning it up meanwhile with a syringe fitted with a rose jet. The resulting emulsion should be of the consistency of a thick cream. It is liable to de-emulsify on keeping, the paraffin separating from the rest of the liquid. If this occurs, pour the paraffin off, heat the watery liquid over a fire in the open air (in case of its catching fire), and then churn the paraffin into it again. For use in summer, it is well to increase the relative proportion of soap in the emulsion. The following may be suggested — (i6<^) Soft soap . . . 2Hbs. Paraffin . . . 16 to 24 ozs. Water . . - 9\ galls. MATERIALS 47 This emulsion, also, may be made of about ten times the strength required for use, emulsifying the soap and oil with half a gallon of water only, and adding the further nine gallons to it subsequently. Another method of making emulsions with soap is by means of what is known as Soluble Parajfi)i or Paraffiji Jelly. When soap, with a little water added to it, is heated, and mixed up with paraffin oil, a nearly clear liquid is obtained, which forms a jelly on cool- ing. As much as eight or nine volumes of paraffin can thus be incorporated with one volume of soap. When the "soluble paraffin" thus obtained is mixed with water, it forms an emulsion similar to that produced by churning the oil with a soap solution, as described above. One of the formula; most in use for making paraffin jelly is : Paraffin, 5 gallons ; soft soap, 8 lbs. ; water, i pint. A certain amount of naphthalene can be incorpor- ated with such a mixture, and a product of this nature has received the name of Paranaph. The instructions for makinGf it are — (16^) Soft soap . . 10 lbs. Water . 3 pints. Naphthalene . I lb. Paraffin . 2 pints, 13 ozs. Heat the soap and water together till the former is quite dissolved, stir into this the naphthalene, and, after removing the vessel from the fire, add the paraffin, and stir till the whole is incorporated. P'or use, one part by weight of the mixture should be diluted with 100 to 200 parts of soft water. 48 FRUIT TREES AND THEIR ENEMIES Preparations of "soluble paraffin" mixed with potassium sulphide are also made, these being recommended for use against red spider and mites, as well as for fungicidal purposes. Emulsions with basic sulphates. — The de-emulsifica- tion mentioned as occurring sometimes in the case of strong emulsions made with soap, never appears to take place in those made with basic sulphates. For use as a summer wash, that is, where caustic soda has not to be added, the emulsions, both with copper sulphate and iron sulphate, may be made, or may be bought, of a strength tenfold that required for use ; but with the washes for use in winter, it is only that made with iron sulphate which can be obtained in a concentrated form. The emulsions made with the sulphates of copper and of iron for use in winter with caustic soda have already been described under io