VINE-CULTURE UNDER GLASS.

New Zealand Journal of Agriculture, Volume XXVI, Issue 3, 20 March 1923, Page 172

VINE-CULTURE UNDER GLASS.

( Concluded.)

W. H. TAYLOR,

Horticulturist, Wellington.

DISEASES AND PESTS OF THE VINE. Powdery Mildew (Uncinula necator). This fungus appears in the form of greyish patches of mould on leaves and young shoots. Where neglected the whole surface of the leaves may become covered with the mould. On the berries it at first appears as a white powder, like lime, but when much developed the mould looks like a grey felt, completely enveloping the berries. Powdery mildew is known to most grape-growers by its old name of Oidium Tuckeri. While one of the most destructive vine-diseases when allowed to run its course without effective check, it is yet not feared by expert growers. Probably no crops are grown entirely free from mildew, but where the vines are under expert management infection is of a trifling character and easily controlled. The frequent cases of crops being ruined by this disease are entirely due to mismanagement. Attacks are most likely to occur during the early period of growth, when leaves, shoots, and fruit are all young and tender. If the attack is severe, and is not checked, it will persist during the whole season. Autumn attacks are also common, occurring in houses which have been free from the disease till that time. This is accounted for by the increased atmospheric moisture and longer nights at that time. In such circumstances, if the vines have been allowed to make a considerable amount of young growth, as is frequently the case, this is fist attacked, the mildew then quickly spreading to the older leaves. Attacks at this time are of no particular consequence, however, as they do very little harm. The spores of powdery mildew are present everywhere, but they develop only in circumstances suitable to their growth. The conditions that favour germination of the spores are excessive cold on tender vegetable surfaces. In vineries attacks usually occur in the morning, and are caused by the sun, or more frequently newly admitted air, reaching tender growth wet with the condensed moisture that collects during the night. This causes sudden evaporation of the moisture; which lowers the temperature on the affected surface nearly to freezing point. Infection can be prevented by avoiding these conditions.' The top ventilators should be opened before the sun shines on the roof in the morning, so as to promote a slight movement in the atmosphere of the house. This movement will increase as the temperature rises. The moisture on leaves and berries will. thus be slowly dispelled, so that all will be dry before the sun gains much power. The bottom ventilators should be kept closed till the vines are dry, as admitting bottom air while moisture remains on the vines is the most frequent cause of mildew. Cold draughts may be caused by leaving open spaces where rods planted outside pass through the wall of the house. These spaces should be blocked with sacking, or by other means. Any other open spaces, such as occur under the plates, should be

stopped, and the glass should be kept in good repair. In medium climates the bottom ventilators can be kept closed till colouring begins, and this course is best. In warm districts it cannot be done, but in no case should they be opened before the foliage is dry. If these precautions are taken, and provided the aspect of the house and other conditions are suitable for grapes, mildew will not be a serious trouble. Mild attacks are always likely to occur, however, and should be watched for.

A dusting of dry flowers of sulphur, applied on the first sign of the disease, will control it. The sulphur must be quite dry, and, before use, should be placed between folded paper and well rolled with a dry bottle or rolling-pin. Sulphur - bellows may be necessary in large vineries, but for small houses the best plan is to carry the sulphur on a sheet of paper, and, holding the paper under a bunch or leaf — whichever has to be treatedlift a fair amount of sulphur and let it fall on the affected bunch or-leaf. A slight jar will then cause most, of the sulphur to fall back to the heap on the paper ; but sufficient for the purpose will cling to the fungus. This method ensures an ample dusting being quickly applied ; it arrests the progress of fungus not yet visible to the unaided eye, and no sulphur is wasted.

If mildew is not effectually checked in its early stages it may, during the stoning - period, become epidemic, involving the whole surface of the vine, fruit, leaves, and young bark. In such cases dusting with sulphur would have but little effect. ; more drastic treatment must be given. Mix a good handful of sulphur with sufficient milk (skim-milk will answer) to make a thin paste, beating out all lumps. Place the mixture in a kerosene-tin and fill up with tepid water ; the water must not be more than tepid or the milk will curdle. About an hour before the sun leaves the roof of the house in the evening close all the ventilators and thoroughly syringe the whole of the vines and the walls of the house with the solution. The solution must be kept well mixed, this being done by discharging . the syringe back into the tin now and again, and thrusting it nearly to the bottom of the tin each time of charging before pulling up the piston.. Open the- top ventilators before daybreak the next morning so as to dry the vines before the sun reaches them. On the evening of the second day after treatment close up the house again and thoroughly syringe the vines with clean tepid water. The writer has proved this method to be completely effective in getting rid of the worst attack of mildew. This treatment cannot, however,. be recommended for use earlier in the season while the foliage is tender, as burning would be sure to result. Vine Sclerotinia . (Sclerotinia Fuckeliana). The Department’s Biologist has reported ripe grapes received from Auckland ; to be affected by this disease. On the leaves the disease shows as a mouse-coloured, fluffy mould. Ripe grapes are caused to shrivel to dark purple-coloured mummies, which remain attached to the stems. As the disease cannot occur except in a very damp atmosphere, which should not be allowed, it is not considered necessary to describe the fungus fully. Where it occurs, the conditions of the house should be altered by proper ventilation. The mould form of the disease can be checked by 'spraying with liver of sulphur at the rate

of | oz. to a gallon of water. All dead leaves and wood pruned off should be collected and burned, and the house thoroughly cleaned. These precautions should be taken even in the case of vines not affected by disease. Grape-spot, 1 This disease, which rarely attacks any but thin-skinned white grapes, is stated to be probably caused by the fungus Gloeosporium' fructigenum. Brown spotswhich increase in size, rupture the cuticle, and cause a rotappear on ripe grapes. Once a berry is attacked there is no remedy, and affected berries should be cut off. It is not practicable to spray ripe grapes, therefore the only remedy is to increase the ventilation and prevent as far as is possible an accumulation of moisture during the night. This involves keeping late growths from crowding the trellis. • ■ ’ Shanking. Sometimes the footstalks of the berries and even the stems of the bunches wither ; they are then said to have shanked. This trouble is not caused by a disease proper, but by a cultural defect. Shanked berries fail to colour or ripen properly, and are sour and uneatable. Different opinions are held as to the exact cause of shanking, but all agree that it is a root trouble, and that it is induced by the roots being in sour soil. Sour soil need not necessarily be wet soil, though excessive wetness will cause shanking, and should be remedied by attention to drainage. Roots growing down into cold subsoil may be the cause, and they should be encouraged to remain nearer the surface. Again, when the . vines are furnished with leaves very thin in texture shanking may be expected. All these things result in, or are the result of, an imperfect balance between root and top. Where there is too much organic matter in the soil soft spongy roots are formed which cause an excessive growth of soft foliage early in the season. Later on these spongy roots die, leaving the vines with insufficient roots to feed a gross leafage. The remedy is to restrict root-action by rigid and timely suppression of early lateral growth, in the manner described in the section of this series on routine management. . In this way the formation of spongy roots is checked, and the results which would arise from their loss later on are not experienced. Cases are recorded where shanking had been extensive for a number of years, but had since been avoided by the simple means indicated above. Scalding. Scalding occurs both on leaves and on berries, in some cases being extensive and causing serious losses. This affection, like shanking, is usually spoken of as a disease, but this is not correct, as no pathogen has been found in either case. Scalding, or scorching, may be due to the direct action'of the sun or to variations in temperature. When occurring on leaves it is in nearly all cases due to the action of sunrays on damp foliage ; it may occur at any time of the day. If foliage is allowed to crowd up against the glass the passage of air is prevented, and the leaves remain wet till dried by sun-heat ; burning is sure to take place in such circumstances. To a lesser extent leavesmay be burnt by the focusing of sun-rays through faults in the glass. The common glass used is full of such faults, and it is rare that some

amount of burning does not occur from this cause, but never to a harmful extent. Berries exposed to the direct rays of the sun may also be scorched, this generally occurring near or during the ripeningperiod. Scorching also takes place when the'vine-leaves are very thin, and cases are met where considerable damage has been done in this way. Leaves ,of a flimsy texture are unable to withstand the heat of the sun, and burning results. This condition is due to a want of plant-food ; it can be. remedied by supplying what the vines need. Another cause of this condition is dryness at root and an arid atmosphere, resulting in semi-starvation with consequent feeble leafage, which is bound to scorch. _ It would perhaps be better to speak of these occurrences as “ scorching," which it really is, rather than as “scalding"; they are not-the affections usually meant by authorities when speaking of scalding. Scalding proper occurs during the stoning-period, and sometimes causes very serious losses. It has been previously stated that the stoning-period is a critical time. The berries, during the three or four weeks of stoning, make practically no increase in size, x and are very susceptible to injury, so that any attempt to force them into growth is likely to result in damage being done. Scalding in this case is not due to, direct sun-rays, for berries that the sun cannot reach are scalded. It is due to a wide range between' day and night temperature, combined with atmospheric moisture. Damping-down should therefore be reduced to a minimum, and a little top air should be left on all night, except during bad weather. More air should be given very early in the morning to dispel moisture and, above all, to prevent a sudden rise in temperature. During the day the temperature should be kept as low as is consistent with proper ventilation. The greatest danger is a sudden rise of temperature in the morning. Warted Leaves. This is a very common affection, occurring mostly in the warmer districts. The leaves affected are usually of a gross character, indicating that the roots are in rich soil. Such leaves are heavily charged with water, and are very susceptible to injury. The damage is done by sudden evaporation of moisture from the gross foliage, usually caused by a current of cold air admitted before the foliage has dried. The leaves have a rough surface, covered with warts or intumesences. Aerial Roots. It is not uncommon to see vines with bunches of aerial roots hanging down from each spur. The cause may be a warm and moist atmosphere combined with lack of proper ventilation. In most cases, however, it is due to faulty root-action, the roots having got down into cold soil. This again may be due to poor drainage. In any case it is not a desirable state and should, if possible, be put right. Mealy Bug (Dactylopius adonidum). This insect is aptly described by the common name applied to it, the term “ mealy bug " serving to distinguish it from any other grapevine pest. The rapidity with which the insect propagates, and itshabit of depositing its eggs under the bark, beneath the scales of buds, and in crevices in the building, particularly the rafters, make it the

most difficult of all insects to get rid of. In small vineries it should not be a continuous pest, as it is possible to clean it out. The case of large houses is different ; it would be impossible to devote the necessary time to the pest if the same means were adopted that are applicable to small houses. The mealy bug has been the subject of more writings than probably has any other insect, and a good many recommendations have been made for its eradication. A number of different dressings for the rods have been recommended, such as washing with soft-soap or with paraffin, and dressing with a mixture of coal-tar and clay. Although these recommendations are well authenticated, and have been put into practice with good results, yet cases have occurred of the rods being killed by each one of them. The fault, however, has not been in the dressing, but in the method of application. A vine-rod is very porous, and, unless protected by ' its bark, is capable of. soaking up anything of a penetrating nature. It is a general custom to scrape off all the bark which it is possible to remove, but, as pointed out earlier in this series, only that bark .which is hanging loose may safely be detached ; all that is firmly attached should remain. Bark is often scraped off because it is thought the bug gets under it, but the insect cannot get under unless the bark is loose. If a natural covering of bark is left, a fairly strong dressing may safely be applied. It appears, however, that there is danger in the use of strong dressings, and it is therefore best to avoid them. Scrubbing the rods with hot water has been found by many growers, including the writer, to be effective. First remove loose bark and loose scales around the buds ; then scrub the rods with, a fairly stiff brush, using water at a temperature of about 130° F., which is hot enough to kill the bugs but will not injure the buds. In bad cases the rods should be scrubbed twice —at the time of pruning, and again a few weeks later. Before the buds begin to move, dress the rods with a solution of Gishurst’s compound oz. in a gallon of water, applied with a paint-brush. All prunings and leaves should be carefully collected and burned, and everything needful done to thoroughly clean the house, ,so as to get rid of bugs that have fallen to the ground. The rods must, of course, be taken down for cleaning ; before tying them up again thoroughly and forcibly spray the,whole interior with a solution of kerosene emulsion at a strength of 1 in 12. The wires of the trellis should be rubbed with a rag soaked in kerosene. While the vines are in growth keep at hand a tin containing a little kerosene and an old tooth-brush. When a bug is seen touch it with the brush just wetted with kerosene, and it will be instantly killed. Tedious methods are not possible in large houses, however, and for these fumigating with hydrocyanic-acid gas appears to be the only way to get rid of the pest. This gas is of a deadly nature, and human life is endangered by any carelessness. It is therefore best to avoid its use where other methods can be made effectual. A good deal of care in its use is necessary while the vines are in growth, as it can easily kill tender foliage, either of the vine or of other plants, and can also injure the berries. In theory, damage from its use can be avoided, but it proves to be difficult in practice. It is noticed that authorities in England now advise its use only after the grapes have been cut, and this is, no doubt, the wisest course. . As fumigation does

not kill the eggs, a second treatment should be given before the leaves have fallen.

Fumigating should be done towards evening, when the heat of the sun has declined ; the temperature should not be above 70° F. The house should be made .airtight, and the vines and building should be as dry as possible. After treatment, the house may be kept closed all night, but must be opened before sunrise in the morning. When opening the doors care must be taken not to breathe the air of the house, and the house should not be entered till one hour after the doors have been opened. For every 1,000 cubic feet of space in the house use 4 oz. avoirdupois of potassium. cyanide, 4 fluid oz. of commercial sulphuric acid, and 12 fluid oz. of water. Provide an earthenware basin for every 10 ft. of length in the house, the basin to be of a size proportionate to the amount of chemicals it will be required to hold. The necessary quantities of cyanide should first be weighed out and placed in pieces of tissue paper, which should then be placed in the positions where the basins will be. If the cyanide is in large lumps these must be broken until they are not larger than a filbert nut. , The water should first, be placed in all the basins, and then the sulphuric acid. The cyanide in the paper should be added last of all; begin at the basin farthest from the door, holding the breath and retreating as quickly as possible. The paper will delay the action of the acids for a moment or two. When sulphuric acid is added to the water heat is generated, and it is important that the cyanide be added before this heat declines ; if it has cooled down the generation of gas will be slower and less in volume. A good grade of sulphuric acid should be used ; low grades may contain nitric acid, which would cause burning. Red Spider (Tetr any chus telarius). This is a minute brick-red insect that attacks the leaves. If present in great numbers the vines are debilitated, as the insects suck the juices from the leaves. It is troublesome only where hot, dry conditions prevail, and in most parts of New Zealand need not be a source of trouble. The way of avoiding attacks is to supply sufficient moisture to the roots, and to prevent arid conditions in the house by damping down and syringing. The warmer parts of the Dominion are most favourable to the pest, but the very conditions that favour the spider, make it possible to use more water in the house. A number of recommendations for its eradication have been made, but so difficult is it to get rid of the spider without injuring the vines that all agree that treatment which will prevent an attack is the best course. Thrips. The thrip is a tiny, insect, dark in colour when matured. It is a sucking-insect like the red spider, but is more destructive than that pest. Like the red spider, these insects thrive in dry conditions, and treatment that will prevent attacks by spider is usually effective for thrips. If an attack occurs, fumigation with X.L. All fluid or tobacco two or three nights in succession will control it. Tobacco should not be used when the berries are ripening, as the flavour of the tobacco remains for some time. A thorough cleaning of the vines and house on the lines previously indicated is essential to the riddance of both thrips and red spider.