Diseases Of Vines
disease vine leaves eggs insect fungus grapes phylloxera root caused
DISEASES OF VINES. The organic diseases which affect the vine may be divided into two categories, those caused by insects and those caused by parasitic fungi.
Diseases Caused by Inseets. - Kaltenbach in 1874 enumerated thirty-two species of insects which injure the vine ; and since then others have been added to the list. We here deal only with the most important. Amongst those which attack the leaves and young buds a small beetle, Anomala vitis, one of the Searabteida, does great harm in some parts of southern Europe by devouring the soft tissue of the leaves. A genus of weevils, Otiorlcynehus, contains several species which are injurious to the vine, chiefly by the adult beetle devouring the buds. 0. mucus, hirticornis, picipes, nigritus, ligmcstici, and sulcatus are all reported from various places as doing much damage ; the larva of the last-mentioned species attacks the roots of the vine, causing the shoots to be small and ultimately bringing about the death of the plant. Fortunately the members of this genus have no wings, so that the damage they cause is to a great extent localized. The same kind of injury is mused by a small Chrysomeleous beetle, Eumo/pus vitis. The larvae of several Lepidoptera attack the vine in the same way, destroying the young buds. Amongst these Nania typiea, Agrotis tritici, and A. pronuba may be mentioned. The larva of Tortrix pillcriana in the early spring weaves the young vine leaves together, and, enclosed in this nest, devours the soft tissue at leisure. The imago emerges from the chrysalis in July and shortly alter lays its eggs upon flu; upper surface of the vine leaf. After a few weeks time caterpillars emerge and continue their work of destruction. Lethrus cephalotes, one of the Scarabxidx, is very injurious in vineyards which have a dry sandy soil. The beetles live in pairs in holes in the ground ; during the summer the beetle bites off the small young shoots and drags them away to its hole, where it is believed they serve as food for the larva. In this way very serious damage is caused to the vine plants. Rhynehites betuleti, a weevil, also does much damage to the young shoots and leaves. The grapes are attacked by the caterpillar of a moth, Conehylis ambiguella, which lays its egg in the young fruit ; and in a similar way the larva of Graptolitha (Cemehylis) botrana attacks the flowers and fruit. The larva of the cockchafer, ilfelolontha vulgaris, also does much damage by biting through and devouring the roots. Coccus vitis is a small scale insect of reddish brown colour, with irregular black spots in the female, which lives in the bark of old or neglected vines and weakens the tree.
By far the most destructive of all insect pests which attack the cultivated vine is Phylloxera vaslatrix. This much-dreaded insect :+ belongs to the family Apkida! or plant lice of the order Hentiptc•. The genus contains several species which live upon oak trees. Their proper 'home is in North America ; but they have been found in English vineries since 1863. The symptoms of the disease first appeared in France about the same time, in the neighbourhood of Tarascon. From the department of Gard the infection spread south to the sea, and east, west, and north, till the south-eastern corner of France was thoroughly infected, Another centre of infection nose• a few years later near Bordeaux in Gironde, whence the disease spread till the whole of the southern half of France was more or less severely attacked. The parasite was first discovered in France in the year 1868. The Phylloxera has spread to Corsica ; it has appeared here and there amongst the vineyards of the Rhine and switzerland ; it is found in Spain and Portugal, Austria, Iluiwary, Daly, and Greece ; and in 1885 its presence was discovered in Australia (Victoria), at the Cape of Good Hope, and in Algeria. I knee it is no exaggeration to say that with very few exceptions its distribution is co-extensive with that of the cultivated grapevine.
The symptoms of the disease, by means of which an infected spot may be readily recognized, are these. The vines am stunted and bear few leaves, and those small ones. When the disease reaches an advanced stage, the leaves are discoloured, yellow or reddish,with their edges turned back, and withered. The grapes are arrested in their growth and their skin is wrinkled. If the roots are examined, numerous fasiform swellings arc found upon the smaller rootlets. These are at first yellowish in colour and fleshy ; but as they grow older they become rotten and assume a brown or black colour. If the roots on which these swellings occur be examined with a lens, a number of minute insects of a yellowish brown colour are observed ; these are the root- forms radicol a) of Phylloxera (fig. 1); they observed. The head bears small iced eyes and a, pair of three-jointed antenna', he first two joints being short and thick, the third more elongated, with the and cut off oblb Ludy and slightly hollowed out. Underneath, between the legs, lies the rostrum, which reaches back to the abdomen. The insect is fixed by this rostrum, which is inserted into the rout of the vine for the purpose of sucking the sap. 'the abdomen consists of seven segments, and these as well as the anterior segments bear four rows of small tubercles on their dorsal surface. These root-dwelling insects are females, which lay parthenogenetic eggs. The insect is fixed by its proboscis, but moves its abdomen about and lays thirty to forty yellow eggs in small clusters. After the lapse of six, eight, or twelve days, according to the temperature, the lame: hatch out of the eggs. These are light yellow in colour and in appearance resemble their mother, but with relatively larger appendages. They move actively about for a few days and then, having selected a convenient place on the young roots, insert their proboscis and become stationary. They moult five times, becoming with each change of skin darker in colour ; in about three weeks they become adult and capable of laying parthenogenetic eggs. In this way the insect increases with appalling rapidity : it has been calculated that a single mother which dies after laying her eggs in March would have over 25,000,000 descendants by October. If, however, the insect were content with this method of reproduction, the disease could be isolated by surrounding the infected patches with a deep ditch full of some such substance as coal-tar, which would prevent the insects spreading on to the roots of healthy vines. The fertility of the parthenogenetically-produced insects would also diminish after a certain number of generations had been produced.
As the summer wears on a second form of insect appears amongst the root-dwellers, though hatched from the same eggs as the form described above. These are the nymphs, destined to acquire wings; their body is more slender in outline, and at first they bear well-marked tubercles. After several moults the rudiments of two pairs of wings appear, and then the insect creeps up to the surface of the earth, and on to the vine. Here it undergoes its fifth and last moult, and appears as a winged female, capable of reproducing parthenogenetically. The winged form has a slender body with distinct head (fig. 2). The eyes are Nvell developed, with numerous facets ; the anteume have three joints, the terminal one shaped like that of the root-dwellers. The wings are transparent, with few ne•vures, and are well adapted for flight. The anterior pair reach far beyond the end of the abdomen ; the posterior are narrower and not so long. These winged forms are about 1 mm. long. They fly about from July till October, living upon the sap of the vine, which is sucked up by the rostrum from the leaves or buds. They lay their parthenogenetically-produced eggs in the angles of the veins of the leaves, in the buds, or, if the season is already far advanced, in the bark. In very damp or cold weather the insect remains in the ground near the surface, and deposits its eggs there. The eggs are very few in number and of two sizes, small and large (fig. 4, b and c). From the larger a female (fig. 3) is hatched in eight or ten days, and simultaneously, for the first time in the life-history of the Phylloxera, a male (fig. 4) appears from the smaller egg. Neither male nor female has wings ; the rostrum is replaced by a functionless tubercle ; and there is no alimentary canal. The female is larger than the male and differs from it and the other forms in the last joint of the antenna'. The life of those sexual forms lasts but a few days, and is entirely taken up with reproduction. The female is fertilized by the male and three or four days later lays a single egg - the winter egg - and then (lies. This egg is laid in the crevices of the bark of the vine, and as it is protectively coloured it is almost impossible to find it. Here the winter eggs remain undeveloped during the cold months ; but in the following spring, as a rule in the month of April, they give birth to a female insect without wings, which resembles the root-dwelling forms, but has pointed antennae. These forms are termed the stock-mothers ; they creep into the buds of the vine, and, as these develop into the young leaves, insert their proboscis into the upper side. By this means a gall is produced on the under side of the leaf. The gall is cup-shaped, and its outer surface is crumpled and covered with small warts and hairs. The opening npou the upper surface of the leaf is protected by similar structures. Within this gall the stock-mother lives and surrounds herself with numerous parthenogenetically-produced eggs, - sometimes as many as two hundred in a single gall ; these eggs give birth after six or eight days to a numerous progeny (gallicola), some of which form new galls and multiply in the leaves, whilst others descend to the roots and become the root-dwelling forms already described. The galls and the gall-producing form are much commoner in America than in the Old World.
The natural enemies of the Phylloxera are few- in number : they include some inites, - /Toplophora aretala, l'hyroylyplaus phylloxera', - and the millepede Poly.renus layurus, which devours the subterranean forms. Innumerable artifices have been proposed to combat the terrible disease caused by this minute insect, but none of them seem to be completely successful. As a rule the means stiggested are to render the soil uninhabitable for the root forms by injecting certain chemical poisons. Since the importance of the winter egg in the life-history of the insect was demonstrated by Balbiani, attempts have been made to destroy these eggs by rubbing the branches with a chain-armour glove, or some such contrivance for removing the outer layers of the bark, which should be burnt. Again, certain varieties of American vines, which have the reputation of being Phylloxera proof, have been grafted on European stocks; but this has proved to be only a doubtful success as regards the Phylloxera, whilst the wine made from such vines has undoubtedly deteriorated. The treatment which has been most successful is periodically to submerge the vineyard for a period of not less than forty days. Where this plan has been tried, it has been most successful ; unfortunately the majority of vineyards are planted on Lill-sides and other places where this method of treatment is impracticable. The root-dwelling forms do not thrive in a sandy soil ; hence vines grown in a district where such soil is found usually escape the disease.
Fungoid Diseases. - The most destructive form of fungoid disease which attacks the vine is caused by a Pyrenomycetous fungus, Oidiurrz (Erysiphe) Tuelceri. The disease was first noticed in England in 1845 ; in 1848 it appeared at Versailles ; by 1851 it had spread through all the wine-producing countries of Europe, being especially virulent in the lands bordering on the Mediterranean ; and in the following year it made its appearance in Madeira. There is little doubt that, like the Phylloxera, the Oidium is in its origin American. The disease is characterized by the appearance of a white mycelium on the young leaves ; this spreads quickly and attacks the older leaves and branches, and ultimately reaches the grapes. At first these are marked only by small brown spots ; but the spots spread and fuse together, the skin of the grape is destroyed, and the flesh decays, the seed only remaining apparently untouched. The disease spreads by the mycelium growing over the epidermis of the plant. The hyphu composing the mycelium arc provided with haustoria, which project into the cells of the affected part. Some of the hyplue which project from the leaf bear conidia, which are constricted olr one at a time, and it is by their means that the fungus spreads. The perithecia have not yet been discovered in Europe. But it is not impossible that this stage of the life-history of Oidium exists in the United States in the form of Uncinula spiralis, which causes a widely spread disease amongst the American vines. The Oidium is in its turn attacked by a fungus of the same tribe, Cicinnobolus Cesatii, De By, which lives parasitically within the hyplue of its host, and at times even succeeds in destroying it. The means which have proved most efficacious, both as a remedy and a preventative of this disease, is to scatter flower of sulphur over the vines, before the morning dew has evaporated. Another method is to boil one part of lime with three parts of sulphur, and to sprinkle the mixture over the affected plants.
Another fungus which attacks vines, especially those of America, is Peronospora vitieola. The mycelium spreads through the green parts of the plant, attacking the leaves, twigs, and unripe grapes. On the upper side of the leaf, where it is first visible, it forms pale green irregular spots, which become darker in colour. On the under side of the leaf these patches are white and are composed of the spore-bearing hyph. The leaf ultimately becomes dried up and brittle. The grapes which are attacked cease to grow, turn brown or white, and ultimately dry up and fall off. This disease has been successfully treated with a spray of copper sulphate and lime, or sulphate of iron ; solutions of these salts prevent the conidia from germinating.
Anthracnose is the name usually given to a disease which was formerly known as "charbon," "peck," or " brenner." This disease is caused by the parasitism of Sphaceloma ampelinum, one of the Pyrenomycetous fungi. The fungus assails all the green parts of the vine, and injures the leaves and young shoots as much as it does the grape itself. The first sign of its presence is the appearance of a minute spot, which is greyish in the centre, with a brown border. This spot increases in size ; in the stalks it assumes an oval shape, with its long axis parallel to the stalk, whilst in the leaves and grapes it is more or less circular in outline. The centre of the spots on the grapes becomes darker as the disease advances, and a red line appears dividing the dark brown border into an outer and an inner rim and giving a very characteristic appearance to the diseased plant. The berries do not shrivel up as those do that are affected by the black rot. The mycelium of Spltacelama grows just beneath the cuticle of the vine, through which it soon bursts, giving rise to a number of minute hyplia,, which bear conidia. These are minute, oval, colourless spores, which serve to spread the disease over the vineyard and from place to place. The complete life-history of this form is at present unknown ; and information as to where the fungus passes the winter, and in what form, would probably afford some useful indications as to the method that should be adopted to combat the disease. A nthracnose has been known in Europe for many years, but has only been observed in America since 1881, whither it was probably imported from the Old World. As a preventative to its attacks a solution (50 per cent.) of iron sulphate has been found very useful, as well as care in planting on well-drained soil that does not lie too low, the disease seldom appearing in dry, well-exposed vineyards.
The black rot, like the Oidium and P. vi4ieola, is American in its origin. It has been known and observed there since 1848, but appeared for the first time in Fiance in 1885. The disease is caused by a fungus, Plsysalospora Eedcccdfii, Sece. (Hama uvicula), one of the Pyrenomyeetes, and by sonic authorities it has been considered to be a further stage in the life-history of Sphaecloma. The fungus confines its attacks to the grapes, the leaves and stems beim, rarely if ever affected. The grapes are not assailed until nearly fulCgrown, when a brownish spot appears, which spreads over the whole grape. The latter at first retains its plumpness, but on the appearance of little black pustules, which first occur on the part first affected, the grape begins to shrivel. This continues until the grape is reduced to a black hard mass, with the folds of skin pressed closely against the seed. The disease does not spread from grape to grape, so that as a rule only a certain number of grapes in a bunch are destroyed. The hyplive of the mycelium of this fungus are septate, with numerous short branches. The pustules on the surface are due to fructifications, pyonidia, and spermagonia. The presence of conidia has also been recently demonstrated. The fungus passes the winter in the withered grapes which fall to the ground ; hence every care should be taken to collect these and burn them. The use of the solutions mentioned above may also be recommended as a preventative.
Among the other fungi which infest the vine may he mentioned Phyllosticta viticola and Ph. Lab•usex, which, when the attack is severe, cause the destruction of the leaves, the only part they assail. These, like the foregoing, are members of the Pyrenomyeetes. To the same class belongs also Ccrcospora nit is (Cladosporiam nit icolvm), which has club-shaped spores of a green-brown colour. This also attacks the leaves ; but, unless the season is extremely unfavourable, it does little harm.
A very disastrous root-disease of the vine is due to the ravages of the fungus Dematophora nee.atrix, which forms subterranean strings of mycelium - so-called rhizomorphs - the frnetifleation of which is as yet not known ; it forms conidia and sclerotic, however, and presents certain analogies to the Discomyeeles. The diseased roots have been confounded with those attacked by Phylloxera. The only mode of combating the malady seems to be to uproot the plants and burn them. Isolation of the diseased areas by means of trenches has also been practised. This fungus has extended its ravages considerably in southern France and Switzerland within the last ten years. (A. E. S.)