CORRECTTREATMENT

Hokitika Guardian, 27 May 1932, Page 8

CORRECTTREATMENT

OF DEVITALIZED APPLE-TREES

(M. Davey, Orchard Instructor, Mupua, In. N.Z. Journal of Agriculture).

Throughout the commercial fruitproducing districts of New Zealand, and especially in those areas where orchards haVc been established on hilly or second-cfass land, there exist a large number'' of individual apple-trees which have declined in vigour, ceased their development of wood growth, and whose carrying-capacity shows no profit over the Cost of production. In most cases this class of tre© can be avoided ' by judicious treatment and special treatment and special attention from the time at which full cropping commences. When debility has Jjeen established for some considerable period, correction or rejuvenation of the tree is more difficult and often a slow process. However, it is seldom that the condition cannot be materially modified if not entirely eliminated. Generally speaking, the direct cau-e or causes of debility are not difficult to ascertain and remedy. The chief factors operating comprise the following —(1) Insufficient nutrition; (2) neglect to maintain a healthy condition of foliage ; :(3) overcropping; (4) lack of- conservation of soil moisture; (5) indifferent drainage. These subjects will be briefly dca/t with seriatim.

nutrition

In cases coming under this heading it is recommended that special treatment with manures be the first aim, with the object of stimulating and increasing the green tissues throughout the tree represented by its annual extension of growth and the leaf, system. To achieve this object recourse must be made to fertilisers .rich in nitrogen and of a highly soluble nature. Ranking first among such manures are sulphate of ammonia and nitrate of soda. On present market values sulphate of ammonia commands consideration, providing a,s it does the maximum nitrogen content at the lowest unit cost. An effective and not excessive application of 41b.' to 61b. of this fertiliser per tree in early winter may he expected to gverti’y stimulate growth during the ensuing season. The acidifying effect of the manure may be no disadvantage; but if such is considered to be the case a top-dressing of lib. of filtrate of soda applied in early spring will tend to neutralize this effect. When a pronounced extension of growing terminals has been realized, and the foliage has -shown a marked Micrenso in leaf surface, a return to complete fertilizers is advisable ; phos-phat-ic manures stimulate the ro°tsystem, while potassic manures tend t.o tone up the tree and refine the fruit.

MAINTENANCE- OF A REA-LTHY x LEAF SYSTEM. ■

Neglect to maintain a healthy condition of foliage is probab'y one of the Host common and serious causes oi debility in apple-trees, and does not appear to exercise the minds, of orchardists to the extent. that is warranted. Although most instances of spray burn are attributed to the caustic nature of the compounds applied, in very many instances miming is only secondary to the impoverished condition of tho foliage previous to the application the spray. Failure'to appreciate the devitalizing effects of .heavy infestations of red-mite and apple i'eafhopper nitty be regarded as one oi the weakest links in commercial fruitgrowing in the past. Until recently adequate control of these two insects has been costly and difficult, but with the advent of emulsified oils which can be used with safety during the late summer the position has been greatly relieved.

Practical experiments carried out by the Horticulture Division during the last two seasons with summer applica-

tions of emulsified oils have established the fact chat not omy can effective controls be obtained, but that other benefits are also derived. It has been indicated that one application of oil causes a partial if not entire suspension of feeding by the insects, enabling the leaves to accumulate and restore a substantial amount of the depleted chlorophyll. The freshening of the foliage also suggests that excessive transpiration is partly suspended by the film* of oil covering the leaves. ft is all important that orchard ists who.se sole anxiety in the past has 1 •?('•' to keep the fruit free from deposition of red-mite eggs should realise that the maintenance of a generous and vigorous leaf system for the natural period subsequent to leaf fall is mi important factor in hui'ding up t.h<' development of fruit buds for ■ following .season. Where red-mite l® preveAmt—and it is common in most district's subject to dry climatic conditions—orchnrdisls are oariiestlv recommended to consider rpp'icatious of oil sprays to each varr-ty immediale'y after harvesting that variety, and 1 Iv? minimise' tho adverse effect-' rel'env 1 to.

iPKKVE\TI()X OF OVHKL'ROPIMX(j, It may bo truly said Unit overcrop ping i.s a. fruit In.' source of uep.ecu.i of tile vigour of many lives, kcilcm.mil will remind one of the fact, that Lae modern apple-tree i.s a highly .developed organism, vastly different in many respects to its original parent. Commencing life buihli d or grafted n lo tile root, ol oilier Se'eeled varieties, it is handicapped at the start by an interrupted root-system, I ’rim- to me'. interference with the original type by selection and liybiid'Zation |be l it was approximately une-louili ui tiesize ol lh.it mm produced mi nm l i,i.;l. i a v.uuue,. To be cmui.imil

with these radical changes in type, control or limitation of the crop oecomes a necessity for the commercial orchard ist.

Apple-trees, unfortunately, in common with a great number of other plants, become more fruitful as vigour declines, rendering it incumbent on the grower to offset this tendency by preventive measures'. In advanced stages of debility th c most effective and rapid measure is to entirely remove at pruning period all fruit spurs, cutting hack to within £in. of the branches from which the spurs have grown. This may appear an extreme or drastic- process, but experience shows that entire removal of crop .is seldom attained, many fruits being produced on adventitious growths the first season the tree will be carrying a quantity of fruit equal to the amount produced prior to treatment. Where debility is not so far advanced ..or pronounced judicious thinning at fruit set may be sufficient; reduction of the clusters, or thinning to one fruit per cluster, should serve the purpose. It may', be noted that in most instances a reduction of fruit spurs during the dormant season, and consequent limitation of blossom, will often effect a more prolific setting of fruit than would occur if no restriction of bloom had been imposed.

CONSERVATION OF MOISTURE.

Dealing with lack of sufficient moisture, it should be borne in mind that the roots of plants absorb most food substances in liquid, form by the process termed osmosis. When the moisture content falls below a given point the function of osmosis is greatly reduced or ceases. With sufficient moisture many insoluble plant nutrients which occur in the oil are made soluble and available to the tree by tire action of soil acids. Also, organic acids secreted by the roots, and which act a® solvents of insoluble matter, are impotent in the absence of moisture. For these substantial reasons it- may be accepted that a uniform and sufficient moisture content is essential to healthy growth. In most instances weak trees are shallow-rooted, and for that reason it is imperative that an effective mulch he in order to bring the action of capillarity close to the surface.

ADEQUATE DRAINAGE

The importance of adequate drainage need hardly he stressed when one considers the influences brought to bear by it on the soil. The penetration of plant-foods to the subsoil -is largely dependent on the percolation of. rainfall':*-' Drainage raises the temperature of the ground, thereby causing an early spring growth of the tree. Aeration of the soil, which follows displacement of surface water, is essential to those micro-organisms which exert considerable beneficial influences on the plant. Indifferent drainage allows accumulation of substances which are toxic to plant-life.