THE ORCHARD.

New Zealand Journal of Agriculture, Volume XII, Issue 4, 20 April 1916, Page 309

THE ORCHARD.

J. A. CAMPBELL,

Assistant Director, Horticulture Division.

With the fall of the foliage commences the dormant season’s work in the orchard. ' There are two main advantages of making an early start—firstly, in order to apply at the most beneficial time the autumn or early winter sprays; and, secondly, on account of the amount of general important work and numerous odd . jobs to be done in the orchard during this period.

AUTUMN SPRAYING.

The main diseases requiring early attention are die-back of the peach (Clasterosporium), San Jose scale, and woolly aphis. Redmite and the various scales and other diseases can be quite safely left until a little later in the season, when stronger mixtures can be more safely used for their control.

Die-back. — Clasterosporium is a fungus disease particularly affecting the peach and nectarine trees. The effects of the fungus are to be noticed in the form of brown spots of varying. size on the previous year's wood, gumming buds, and dead twigs. The bark of the diseased twig within the affected area becomes corky and dry, failing to expand with the normal growth of the twig in the spring. When the affected spots are large or numerous the nonexpansion of the bark results in the entire stoppage of the flow of sap and the death of the growths affected. It is from this characteristic of the disease that the common name of “ die-back originates. The bark of the diseased ; growths that survives the attacks invariably splits more or less to ’allow of expansion, the indication of which is often very noticeable on the - older wood

of affected trees, and is often erroneously deemed to be barkscorching as a result of using oil sprays. This disease becomes particularly active after the early winter rains, and is, together with a very dry summer, responsible for the heavy falling of the buds in the spring. The trouble is a difficult one to entirely eradicate, but a considerable amount of good will result from the application of a reliable fungicide applied sufficiently early in the season. The formula recommended for this purpose, in cases where die-back is the only disease to be considered, is 8-6-40 Bordeaux mixture ; but if San Jose scale is also present, lime sulphur solution, 1 in 15, is advocated in preference.

San Jose Scale. — This very minute' scale insect is extremely prolific and destructive, and for this reason every effort should be made to entirely eradicate ■it : from the orchard. For this purpose very careful and thorough work is necessary, as the process of eradication has to ■be- practically completed : during' one dormant season. It matters little how well the work may be done if it falls short of the complete extermination, ' for the insect, owing to the rapidity at which it multiplies, will still remain a . serious consideration. This scale is, as far as actual killing is concerned, far more easily destroyed, than either mussel scale or red mite, but it is far more destructive than either, as it is capable of destroying large portions of a tree in one season and wholly killing a tree in two seasons. Although the insects are sucking the life out of the tree throughout the summer, there is no doubt that the most vital period is from the time the sap of the . tree ceases to flow until the scale becomes dormant. The reason of this is that during the growing season the roots supply a sufficient quantity of sap to x keep the tree comparatively healthy despite the robbery carried on by the scale, but the moment this ceases the loss of sap becomes permanent and naturally much more dangerous. As a result, it is quite a common thing to find quite dead in the spring limbs which at the end of the growing season appeared to be comparatively healthy and well clothed in foliage.

During the height of the season there is little opportunity of adopting any very beneficial measures against this pest. There are several sprays that will destroy the young unprotected insect, but there are none having a lasting effect sufficient to destroy those that hatch out subsequently. At the same time the foliage of the tree will not withstand a mixture sufficiently strong to destroy the mature insects ; therefore the proper time to commence operations is .as soon as possible after the tree has reached the stage when comparatively strong mixtures can be used without damage.

Emulsified, oil is no doubt the best remedy for this as well as other soft-bodied insects, but, especially in the respect of the peach and nectarine, strong oil sprays are very liable to damage the fruiting-wood when applied early whilst such growths are more or less immature. Lime-sulphur, although not equal to oil, is fairly effective and much safer to apply than oil at this stage; besides, lime-sulphur is a fungicide also, and for this purpose would take the place of Bordeaux mixture.

Woolly Aphis. — Summer treatment for woolly aphis is carried out mainly with the idea of keeping the disease within bounds until the stronger winter remedies can be applied. This is the utmost good that can be expected of the summer treatment, as the eradication of the aphis is a matter that can only be attended to properly when the trees are dormant. It will also, in order to be entirely successful, require a great amount of care and supervision, and is practicable only as far as trees' up to a moderate size are concerned. . This refers .to painting the aphis colonies with strong oil emulsion, and to the renewal of treatment immediately a fresh outbreak is observed. Where . practicable this is an excellent remedy, and one which, if regularly applied to young trees, would save much labour and trouble. In respect to large trees which have long been affected, the only practicable remedial treatment up to the present is that of spraying. To what extent spraying is successful depends mainly on the material used and the manner in which it is applied. Oil emulsion is now the recognized remedy for aphis, and owing to its value in this respect many varieties of apples can now be very successfully grown in localities where similar varieties had previously to be destroyed owing to attacks from aphis.

. Although oil spraying is regularly adopted there is still a considerable difference of opinion in regard to the strength of mixture and the time of application. In this respect there has been a general tendency during the last few seasons towards increasing the strength very materially, particularly in spraying pip-fruits; but there are also undoubtedly many who still use the oil sprays at too weak a strength. Large numbers of growers strongly favour one thorough dressing of oil at the ratio of I in 8 to i in 12, applied when the trees are quite dormant, as being the most satisfactory all-round winter remedy for all sucking-insects. ■ For the' control of woolly aphis others particularly favour two applications of oil* at a■■ considerably reduced strength —1 in 25 ; the first application as - soon as the foliage has sufficiently fallen to allow of thorough work being carried out, and the other just before, the

buds burst. For general purposes I should recommend the - single application, but there is no doubt that the double application has resulted very satisfactorily in the control of the aphis.- The drawback to this method, however, lies in the fact that the spray used is far too weak to give satisfaction with either mussel scale or red mite. If the second application was increased to i in 12 ,or 1 in 15 the main . points of both ideas would be carried at the expense of a little more material on the one hand and labour on the other.

Summary.— To sum up, the sprays recommended for the control of the diseases mentioned are as follows :

For die-back of the peach, spray with 8-6-40 Bordeaux mixture as soon as possible after the foliage has fallen.

For die-back of the peach and San Jose scale, spray with lime-sulphur solution at the rate of 1 in 15 .as soon as possible after the foliage has fallen.

For woolly aphis spray with oil emulsion at the rate of I in 25 as soon as the foliage has fallen sufficiently to allow of the work being properly carried out.

PRUNING.

The pruning of stone-fruits will be well under way during May. Whether this should be done before or after spraying depends very much upon circumstances. There is no doubt that thinning out should be done only before spraying in respect to trees affected with diseases which multiply rapidly during the summer, such as San Jose scale. In this way practically all unshortened wood diseased when spraying would be cut away when subsequently pruned; whilst, on the other hand, the unsprayed tips—-the weak spot with all sprayers — pruned trees would still remain. Such unsprayed parts of an affected tree provide the main source of reinfection.

CULTIVATION

The advantage to be derived from turning up the soil in the autumn for exposure throughout the winter is very great. Not only is the soil sweetened and altogether improved in this way, but provision is also made for the full advantage to be taken of the rainfall, whilst better provision is made for the drainage of surplus water. When ploughing at this season of the year the sod should be turned in towards the trees, leaving the finishing furrow between the rows. The ploughing of steep slopes or comparatively . steep slopes, however, particularly when composed of

light soil, should be left . till the spring, owing to the danger of such soils washing out seriously during heavy rains.

PLANTING.

Fruit-tree planting can be carried out during May where land has been properly prepared and is in suitable planting condition. Before planting all trees should be dipped in a barrel or other suitable receptacle containing a ■. strong solution of emulsified oil, to ensure the destruction of the eggs of the red mite and other injurious insects.