GRAPE SCALDING

Otago Daily Times, Issue 22498, 16 February 1935, Page 5

GRAPE SCALDING

Strong sunshine is the. source of a great deal of trouble in the amateur’s vinery. This jlnoy seem a curious statement, in view of the fact that genial warmth is conducive to strong, healthy growth, but a point which- is. often overlooked is the increased necessity for care in the regulation of the ventilation of the house and the content of. atmospheric moisture. Scalding of the berries, which is very prevalent in a season such as the present, is not a disease. It is the direct result of neglect of these two essential points. A mild attack, it is true, may only mean a few odd berries in each bunch being affected, but even those wijl completely ruin the appearance of the bunches. On the other hand, the entire crop may easily be lost if some effort ia not made to protect the berries, and—an even more vital point—the health: of the vine itself may be seriously' impaired if the foliage is badly affected, as the leaves will be crippled before they have complcted their natural function.

The cause of the trouble is extremely simple. Even in high summer there is a considerable drop in temperature during the hours of the night: - After the house is shut down in the evening, this gradual decrease in heat results in the condensation of , the moisture suspended in the .atmosphere,, with the result that the fruits become dewed over by the early morning. If the sun is allowed to strike on the moisture-laden berries for even a few moments in the early, hours of the day, the /any drops of water will focus its rays after the manner of a lens cr magnifying glass. The result is the burning and destruction of the delicate tissues of the skin of the berry at that particular spot. Damage soon, leads; to decay, which, in its turn, spreads rapidly, and may easily give rise to further, and more serious troubles, unless the injured berries are immediately removed. . ' It ■ is the only course to prevent the possibility of ■damaging ; hitherto uninjured berries. On the other hand, it is a i simple matter to prevent scalding from making an appearance. All that is necessary is to open the ventilators -before the sun has gained any power, and so allow the condensed 1 moisture to re-evaporate into the atmosphere. The awkward point is that during the summer months this will require to be done about 6 o’clock in the morning. Neglect on even one occasion will prove fatal, as evaporation is impossible while the house is closely shut down. The other alternative, and one which will appeal to business men, is to leave a little air on the house overnight, and so maintain a constant current.

Coolhouse vines will not suffer in any way from this overnight ventilation, providing it is not overdone! Far more trouble.is-caused through extremes, for it must be admitted that ventilation, like watering, is one of those simple tasks which actually require years, of experience before they can be properly performed. , The main aim should be to prevent harmfuf fluctuations by in-, creasing,’ the. (amount. ■of .. air admitted by comparatively small but frequent openings of the ventilators. Another point which must be watched is the avoidance of draughts. If a cold wind- is blowing, only the fee side vents- must; he’ bpened, and during such wiaather-it. : ii ueually' advisable to keep the • side sashes closed. On no account must any attempt be made to prevent scalding by maintaining; a hot, dry atmosphere; a vine is never'nappy under such‘'conditions, Which are also an invitation to attack from insect pests. The floor of the house should be in the morning, at mid-day, and again before closing down; and, in ‘ addition, ,the water trays should be .kept constantly filled. Discretion will, of course, have to be used in accordance with the weather conditions. During dull, damp periods,' it is much easier to maintain the necessary moisture content in the air, and spraying can he accordingly cut down. On the other hand, if fire heat is being used, even more will h® necessary than in a cool house, but on no account must the pipes be sprayed -while the heating is turned on. The volume of steam resulting from so doing could not but injure the foliage and the young berries, , When the fruit commences to ripen a brisker and drier atmosphere is essential, and ventilation, too, must be greatly increased. The plants will soon show resentment if spraying is carried out to excess by the cracking and splitting oi the berries. This is due to the fact that sugar is in-the process of formation in the fruit. By means of endoemotic action the sugar will absorb moisture through the skin of the berry, in exactly the same manner as a lump of sugar will absorb any liquid with which it comes in contact. If too much is absorbed in this manner and the flesh becomes overcharged the skin of the berry is unable to stand the strain. Some varieties are much more susceptible to this injury than others, being thinnei skinned. The kind Madresfield Court is specially addicted; Black Hamburgh, the amateurs’ grape, has a tougher' skin. In some cases the scalding of the foliage in particular is caused, by the rods being trained on wires or trellis in too close proximity to the glass. It is a great mistake to have the wires so arranged that the leaves are actually touching the roof, and immunity will never be achieved until the wires are-lowered to at least six or seven inches trom tue panes. The acknowledged distance in vineries is nine inches. . ■ Another fairly common trouble in amateur vineries is mildew, a fungoid growth which will quickly spread over the entire house if it is not arrested at the outset. The first signs appear in the form of a white powder resting on tne leaves. This disease has the ot rendering the berries incapable of further swelling, with the result that the skins soon split open. The cause of the trouble is difficult to determine, but there is no doubt that certain atmospheric conditions are extremely favourable to its development. It is always a more potent danger during cold, damp,, sunless periods, and if ventilation is neglected during such times to such an extent that the atmosphere becomes stagnant, it is more than likely to make an appearance. Overspraying 'is also a frequent cause, in® most effective and simple remedy is to dust over the vines with flowers of sulphur, which, after a few days, must be forcibly sprayed off with clean ram water to prevent the berries from being spoilt. Throwing sulphur on some lumps of freshly-slaked lime is also helpful, as the fumes so dispersed will attack the fungus, but on no account must the sulphur be burnt in the house.

While on the subject of faulty grapes, mention may be made of shanking, a condition in which the tiny footstalk (or shank) of the berry dies, and the grape fails to mature, but remain acid and red or “foxy’' in colour. This trouble is generally attributed to the roots getting into a cold subsoil, or, in-any case, getting into ill-heath. The remedy in such a case is the troublesome and delicate one of uncovering the roots, lifting them, and replanting. This is work for the dormant period. Yet another trouble is associated with over-cropping; in this case, the berries dp not shrivel, but refuse to become a rich purple, remaining “red,” and they are also deficient in flavour and acid. The vine should be lightly cropped for a season or two.—D. T. M., in Amateur Gardening.