1845; in 1848 it appeared at Versailles; by 1851 it had spread
through all the wine-producing countries of Europe, being specially
virulent in the lands bordering on the Mediterranean; and in the
following year it made its appearance in Madeira. Like the Phylloxera
(q.v.; also Wine), the mildew is in its origin probably American.
The disease is characterized by the appearance of a mycelium forming
white or greyish-white patches 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 hyphae composing the mycelium
are provided with haustoria which project into the cells of the
affected part (fig. 3).
Some of the hyphae which project from the leaf bear spores (conidia), which are constricted off one at a time, and by their means the fungus is distributed (fig. 2, 3). The perithecia are only produced exceptionally in Europe, but this stage of the life-history is common in the United States and causes a widely spread disease among the American vines. The mildew is in its turn attacked by a fungus of the same tribe, Cicinnobolus Cesatii, which lives parasitically within the hyphae of its host, and at times even succeeds in destroying it. The means which have proved most efficacious, both as a remedy and a preventive of this disease, is to scatter flowers 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 Plasmopara viticola, which has also been introduced from America to Europe. 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 hyphae. 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," "pech" or "brenner." This disease is caused by the parasitism of Sphaceloma ampelinum, one of the Pyrenomycetous fungi (fig. 4). 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 surrounding tissue enlarges, so that the spots appear as if sunk in depressions, and bear a considerable resemblance to hailstone wounds. Later the spots on the leaves often drop out. The berries do not shrivel up as those do that are affected by the black rot. The mycelium of Sphaceloma grows just beneath the cuticle of the vine, through which it soon bursts, giving rise to a number of minute hyphae, 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 m what form, would probably afford some useful indications as to the method that should be adopted to combat the disease. Anthracnose 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 preventive to its attacks the copper sulphate sprays and a solution (50%) of iron sulphate have 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.
 |
| |
|
Fig. 4.—Charbon or Anthracnose of Vine, caused by Sphaceloma ampelinum. 1. Portion of twig with discoloured patches, caused by the fungus.
2. Fruit attacked by the fungus (reduced).
|
Fig. 5.—Black Rot of Grapes, Guignardia Bidwellii. 1. Grapes attacked by the fungus; the fruit becomes black, hard and shrivelled.
2. Fructification of the fungus, entire and in section; the latter shows the asci containing as cos pores, much enlarged.
3. Single ascus, more enlarged, showing the eight contained spores.
|
From Hartig's Lchrbuch der Pftanzenireitkheilen, by permission of Julius Springer.
Fig. 6.—Rosellinia (Dematophora) necatrix.
A great deal of confusion still exists with regard to this disease. A similar disease which of late has frequently been found in England, and which is ascribed to the fungus Gloeosporium ampelophagum, is very similar to it. In their mode of attack, in the symptoms they produce, and in the result upon the grapes and the vine the two fungi are so much alike that for practical purposes they may be regarded as identical. Massee recommends that the shoots should be dredged with flowers of sulphur at intervals of ten days, while the disease continues to spread, a small quantity of quicklime in a finely powdered condition being added and the quantity of lime being increased at every application, not so as to exceed the sulphur, however. The iron sulphate solution should be used while the vines are in a dormant condition, and diseased parts should be cleared away and burned.
The black rot, like the Uncinula and Plasmopara, is also American in its origin. It has been known and observed there since 1848, but appeared for the first time in France in 1885. The disease is caused by a fungus, Guignardia Bidwellii (fig. 5) (Phoma uvicola), one of the Pyrenomycetes, and by some authorities it has been considered to be a further stage in the life-history of Sphaceloma ampelinum. The fungus is most conspicuous on the grapes, but the leaves and stems are also affected. The grapes are not assailed until nearly full-grown, when a brownish spot appears, which spreads over the
