Part 5 (1/2)
In fighting it every scale must be destroyed or thousands more are soon born. In order to be able to use a strong enough mixture of lime and sulphur to destroy them by smothering or choking the spray must be applied on the dormant wood in the spring or fall or both.
Thoroughness is most essential.
7. THE OYSTER Sh.e.l.l SCALE, although it is essentially the same in its habits and in its methods of sucking the sap from the tree is not as bad a pest as the San Jose scale because it is less prolific, there being but one brood a year. Still this scale often destroys a branch and sometimes a whole tree. The ”lice” winter as eggs under the scale and hatch in late May or early June. After crawling about the bark for two or three days, the young fix their beaks into it and remain fastened there for life, sucking out the sap. By the end of the season they have matured and secreted a scaly covering under which their eggs for the next season's crop winter. A smothering spray like lime and sulphur applied strong when the trees are dormant will practically control this scale. But the young may be destroyed in summer by a contact spray such as tobacco leaf extract or whale oil soap.
8. THE LEAF BLISTER MITE is a small, four-legged animal, so small as hardly to be visible to the naked eye. It pa.s.ses the winter in the bud scales and as soon as these begin to open in the spring it pa.s.ses to the tender leaves which it punctures, producing light green or reddish pimples according to the variety of apple. These later develop into galls or blisters of a blackish or reddish brown color and finally result in the destruction of the leaf. Trees are sometimes practically defoliated by this pest, and this at a time when a good foliage is most needed. Inside of the galls eggs are deposited and when the young hatch they burrow in all directions. In October the mites abandon the leaves to hibernate in the bud scales again. A strong contact spray of lime sulphur when the trees are dormant destroys the young mites while they are yet on the bud scales, which is practically the only time when they are vulnerable.
9. APHIDES, or plant lice, are of seasonal importance. Although nearly always present, it is only occasionally that they become so numerous as seriously to damage mature apple trees. But they are more often serious pests on young trees where they should be carefully watched.
Their presence is determined by the curled and distorted condition of the terminal leaves on the under side of which the green or pinkish lice will be found. Eggs deposited in autumn pa.s.s the winter in this condition, hatching in the spring about the time of the beginning of the growth of vegetation. From these winter eggs females are hatched which bear living young, which may also bear living young and so on for several generations until autumn, when eggs are again deposited for the winter stage.
Fortunately weather conditions together with parasitic and predaceous insects hold them more or less in check. Because of the difficulty of getting at the underside of the curled leaves where these lice mostly work they are extremely hard to control. Lime and sulphur when the trees are dormant destroy as many of the eggs as it comes in contact with. A tobacco extract is quite effective as a contact spray in the growing season. The trees must be closely watched and if the lice appear in any considerable number they must be promptly attended to or serious damage is likely to result.
These are by no means all the insect pests which the fruit grower has to combat, but they are usually the most important. Canker worm and tent caterpillars often do great damage in unsprayed orchards, but they are easily controlled by an application of a poison as soon as they appear. The same is true of other caterpillars and leaf eating worms. Apple tree borers are frequently serious, especially in young orchards, where the trees should be regularly ”grubbed” and the borers dug out or killed with a piece of wire. They may be prevented to some extent by painting the tree trunks with a heavy lime and sulphur or some gas tar preparation.
DISEASES.--Although not as numerous as insects, the diseases which attack the apple inflict great damage and are fully as difficult to control. They are caused by bacteria and by fungi which may be compared to weeds growing on or in the tree instead of the soil. If either of these works within the plant, as is sometimes the case, it must be attacked before it enters. It is very necessary to be thorough in order to control these diseases. Weather conditions influence nearly all of them materially. Of those which attack the apple tree or fruit we have selected three as the most serious and the most necessary for the grower to combat, namely, (1) apple scab, (2) New York apple tree canker, and (3) fire blight. To these should be added in the South and middle lat.i.tudes, sooty blotch and bitter rot.
Baldwin spot is also frequently serious in some seasons and localities.
(1) THE APPLE SCAB, commonly known among growers as ”the fungus,” is the most important of our common apple diseases and is most evident on the fruit, although it attacks the leaves as well. In some seasons the fruit is made almost unsalable. This disease lives through the winter on old leaves. In the spring about blossoming time the spores are scattered by the wind and other agencies, and reaching the tender shoots germinate and enter the tissues of the plant. Their development is greatly dependent on the weather. In a season in which there is little fog or continued damp or humid weather, they may not develop at all, but where these conditions are present they frequently become very virulent.
Spraying will be governed by the weather conditions, but the mixture must be applied very promptly as soon as it is evident that it is likely to be necessary and must cover every part of the tree to be effective. The object is to prevent the spores from germinating, the spray being entirely a preventive and in no sense a cure. The disease most frequently first manifests itself on the tender new growth and on the blossoms. Two mixtures have been found to control it, namely, Bordeaux and a weak solution of lime and sulphur. One or other of these should be applied just before the blossoms open, just before they fall, and when necessary two and nine weeks later.
(2) NEW YORK APPLE TREE CANKER is usually found mainly on the trunks of old trees, but it also affects the smaller branches. Practically every old or uncared for orchard has more or less of this canker, and where it is not checked it eventually destroys the tree. This fungus is the cause of most of the dead wood found in old orchards. The surface of the canker is black and rough and covered with minute black pimples. It lives over winter and spreads from one branch or tree to another. As it most frequently enters a branch through wounds made in pruning, these should be promptly painted over with a heavy lead and oil paint. All diseased parts should be cut out and removed as soon as observed. The value of spraying for this disease is not definitely known, but it is seldom very troublesome in well sprayed and well cared for orchards.
(3) BLIGHT appears on apple trees in three forms, as blossom blight, as twig blight, and as blight cankers. It is a bacterial disease which is distributed by flies, bees, birds, etc., and cannot be controlled by spraying. The bacteria are carried over the winter in cankers on the main limbs and bodies of the trees, oozing out in a sticky ma.s.s in the spring. These cankers should be cut out with a sharp knife cutting well into the healthy bark and then was.h.i.+ng the wound with corrosive sublimate, one part to one thousand of water.
Cutting out and destroying are also the chief remedies to be used when the blight appears in the twigs and blossoms. It is not usually as serious on apples as on pears. Some varieties, like Alexander, are more subject to it than others.
CHAPTER VIII
THE PRINCIPLES AND PRACTICE OF SPRAYING
The spraying of fruit trees in the United States is of comparatively recent origin, having been a general commercial practice for less than two decades. It involves the principle of applying with force and in the form of a fine rain or mist, water in which a poison or a substance which kills by contact is suspended. The first application of the principle was against chewing insects with h.e.l.lebore. Pure a.r.s.enic was early used and soon led to the use of other a.r.s.enicals.
Our greatest fungicide, Bordeaux mixture, was discovered by accident in 1882 when it was found to control mildew in France. Up until about five years ago Bordeaux mixture as the fungicide and paris green as the poison were almost universally used. Within the last few years, however, there have been developed two subst.i.tutes which, although known and used to some extent for twenty years, have only recently come into such general use as practically to replace the old sprays.
These are lime and sulphur as the fungicide and partial insecticide and a.r.s.enate of lead as a partial insecticide.
The necessity for and the advisability of spraying have already been pointed out. There is an increasing demand for fine fruit the supplying of which is possible only with thorough spraying. In the humid East especially the compet.i.tion of more progressive sections in the West is demanding more and better spraying. There is no cure-all in this process. It does not make a tree more fruitful except as it improves its general health, but it does bring a larger percentage of the fruit to perfection. Certain knowledge is fundamental; the grower must know what he is spraying for, when and with what to combat it and how to accomplish the desired result most effectively.
Spraying is an insurance against antic.i.p.ated troubles with the fruit, and the best and most successful growers are those most completely insured. It has many general advantages also. It stimulates the grower to a greater interest in his business because of the extra knowledge and skill required. It compels thoroughness. It necessitates spending money, therefore a return is looked for. To be sure, it is only one of the operations necessary to success, but it enables us to grow a quality of fruit which we could not obtain without it.
SPRAY MATERIALS are conveniently divided into two cla.s.ses, insecticides and fungicides. An insecticide is a poison by which the insect is killed either directly by eating it, or indirectly by the caustic, smothering, or stifling effects resulting from closing its breathing pores. Direct poisons are used for insects which eat some part of the tree or fruit and are called stomach poisons. Sprays which kill indirectly are used for insects which suck the sap or juice from the tree or fruit and are called contact sprays. a.r.s.enical compounds have supplanted practically all other substances used to combat external biting insects. Two stomach poisons are commonly used, namely, a.r.s.enate of lead and paris green, but the former is rapidly replacing the latter.
a.r.s.eNATE OF LEAD is prepared by mixing three parts of crystallized a.r.s.enate of soda with seven parts of crystallized white sugar (acetate) of lead in water, but it will not as a rule pay the grower to mix his own material, as a.r.s.enate of lead can be purchased in convenient commercial form at a reasonable price. The preparation on the market is a finely pulverized precipitate in two forms, one a powder and the other a paste. These are probably about equally good and are readily kept suspended in water. Less free a.r.s.enic is contained in this form than in any other compound of a.r.s.enic, making it safer to use, especially in heavy applications. a.r.s.enate of lead may be used without danger of burning the foliage as strong as five or six pounds to fifty gallons of water, but three pounds is the usual and a sufficient amount for the control of any apple insect for which it is efficacious.
PARIS GREEN is being rapidly displaced by a.r.s.enate of lead for several reasons. It is a compound of white a.r.s.enic, copper oxide, and acetic acid. The commercial form is a crystal which in suspension settles rapidly, a serious fault. It is more soluble than a.r.s.enate of lead and hence there is greater danger of burning the foliage with it.
Moreover, it costs from twenty to twenty-five cents a pound, and the a.r.s.enate of lead can be purchased for from eight to ten cents a pound.
The amount which it is safe to use in fifty gallons of water is from one-half to three-quarters of a pound. When paris green is used alone as a poison lime should be added. Both these a.r.s.enicals should be thoroughly wet up by stirring in a smaller receptacle before they are put into the spray tank, in order to get them in as complete suspension as possible. They may be used in the same mixture with Bordeaux or lime sulphur.
CONTACT SPRAYS.--Four compounds are used as contact sprays in combating sucking insects, namely, lime sulphur, soaps such as whale oil soap, kerosene emulsion, and tobacco extract. Of these lime sulphur is the most used and for winter spraying is probably the best.