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Vine Fungi

Many species of Fungi have been recorded as living on Vines in Europe and in North America, and there exists almost a special literature upon these parasites. They vary greatly in their destructive powers; and some species have ravaged the vineyards of both Continents. Inquiry into the best methods of contending with the parasites, and of saving the Vines from complete destruction, has thus been powerfully stimulated. In vineries in the British Islands, these pests have not caused so great harm as where the Vines are cultivated on a large scale; yet, even in Britain, the harm done is sufficient to render some notice of them desirable in this work. Of the hundred or more species that have been recorded as growing on Vines, only those that give rise to serious disease are mentioned below.

Vine Mildew is the name given when the leaves and stems become covered with a whitish or greyish coating, either in patches, or over large portions of the plants. Such an appearance is caused by more than one Fungus. The best-known are Oidium Tuckeri (which has long been known in Europe, and which was at one time most injurious in the vineyards of France, and also in those of Madeira), and Peronospora viticola, the latter a Fungus brought in recent years from America to France, on imported Vines.

Oidium Tuckeri was first described by the well-known botanist, Rev. M. J. Berkeley, from specimens sent to him, in 1847, by Mr. Tucker, a gardener in Ramsgate. It was detected in France in 1848. By 1851 it had spread to all the vineyards in Europe; and in the next year it was observed in Madeira. The Fungus shows itself as a thin, pale layer or coat on the leaves and on the young twigs, and even occurs on the fruits. The diseased parts often become pale, and more or less distorted; the coat becomes thicker; then the spots become brown, and the parts die. An examination with the microscope shows that the surface of the part is covered with the filaments of the Fungus creeping over the epiderm cells of the diseased spots, and that from the side of each filament of the Fungus little suckers are pushed into the epiderm-cells, and absorb food from them for the Fungus. From the other side of the filaments erect branches arise, each formed of a row of cells, of which those at the ends of the branches (conidia) are oval, and break away, to produce the Fungus again when they fall on suitable situations on the Vine leaves or branches. No other mode of reproduction has yet been detected in this Fungus, though it undoubtedly belongs to a more fully-developed form, such as is described under Mildew and Oidium. Mr. Berkeley has suggested that it may belong to the very common Erisyphe communis. Plants suffering from its attacks have a mouldy, disagreeable smell. Another Oidium (O. Balsamii), with more slender conidia, sometimes occurs on Vines. The Fungus spreads rapidly in a moist, warm atmosphere, and is greatly checked in dry air, and also by very heavy rain, which washes away the spores.

All dead leaves and stems should be removed and burned, to destroy the conidia. Flowers of sulphur form a complete and thorough cure, as they destroy the parasite without injuring the Vines. The sulphur should be dusted on the Vines in early spring, after the stems have begun to push forth, then again when the blossoms have opened, and lastly, when the grapes are beginning to ripen. To prevent any taste of sulphur being perceptible in the ripe fruits, the third dusting must not be too late. The green organs to which sulphur is to be applied should be moistened, to make the powder adhere. Peronospora viticola had been known, from 1834, as a parasite on almost all the Vines of North America; but it was imported into Europe only in 1878, on plants brought to replace the European Vines destroyed by Phylloxera. It has now spread widely through France and Algeria. The diseased leaves, about August, show patches of irregular form, and whitish in colour, which soon become brown and dry. The tissues of the leaf are traversed by mycelium, furnished with small haustoria, or suckers, for taking food from the cells; and the white spots bear myriads of erect, fruiting branches of the Fungus (see Peronospora), each repeatedly divided into three, less often into two, branches. The terminal branches are short, and on the tip of each is an egg-shaped spore. In the spore there grow five or six smaller spores (zoospores), which escape by the bursting of the cell-wall of the spore, and can swim about in dew-drops and moisture of any kind; and at last the zoospores settle down on the leaves, push a slender tube through the epiderm, and give rise to a new plant. The diseased plants produce defective crops of fruit. The grapes also may be attacked. The resting, or sexual, spores of the Fungus have been found in Vitis aestivalis; they have a thick, smooth, yellow coat.

Vines grow more healthily in well-watered than in dry soil, and are therefore better able to resist the attacks of the parasite; but a close, moist atmosphere is hurtful, as it encourages the growth of Moulds. The fruiting threads may be destroyed by dusting the plants with a mixture of sulphur and quicklime; but the internal mycelium renders a thorough cure very difficult. Probably the best preventive of the disease is burning dead leaves, stems, prunings, &c.

Several other species of Fungi have been recorded as very destructive in the vineyards of France, Germany, and Italy; but they have not been observed to be hurtful in England, and therefore require but brief notice here. The roots have been found destroyed by four different Fungi, viz., the Rhizomorpha stage of Agaricus melleus (Figs. 193 and 194) (see Pinus, FUNGI), Dermatophora necatrix, Roesleria hypogaea, and an imperfect mycelium enveloping the lateral roots, and called by Persoon Fibrillaria xylotricha. These Fungi differ in details of their attacks on the Vine roots; but they all kill the roots, usually beginning with the younger ones; the leaves turn yellow and fall off; and the Vines perish, though some continue to exist in a sickly state for one or two years, if left untouched. Against these root-parasites, the only effectual remedy is to remove and burn the diseased plants, taking the utmost care to remove all fragments of wood, &c., from the soil, to prevent the disease from reaching healthy subjects. No cure is known for plants already attacked by any of these Fungi.

Another disease very fatal in European vineyards assumes the form of dark spots on the young shoots and leaves, on the flower-stalks, and on immature fruits. At first the spots are round, brownish pustules; but they soon extend, and often become confluent. The centre becomes ashy-grey or pinkish-grey, owing to the outpouring of minute, oval conidia through the torn epidermis; but the rest of the spot becomes nearly black. It is surrounded by a narrow, brown border. All the surface tissues of the spot are hardened, and are full of the mycelium of the Fungus; and the conidia or spores are produced on the surface of the mycelium, but below the epidermis, through a tear in which they escape when mature. This Fungus is known as Gloeosporium ampelophagum. Those parts of the Vines on which it grows are killed or seriously stunted, and even the plants themselves may be killed in bad attacks. When it grows on the flower-stalks, the entire clusters of fruit are destroyed. When it occurs on the grapes, they seldom come to ripeness. The disease has attracted much attention; and it is said that an effectual cure for it has been found in the employment of a solution of sulphate of iron (10 to 15 per cent.) in water, applied in winter, with a pretty large brush, to all parts of the branches. This solution destroys all spores of Fungi, but does not seem to injure the bark of the Vines. As a preventive measure, all prunings and dead leaves should be carefully removed from the surface of the soil, lest they might spread infection among the healthy plants in the following spring. In Saccardo's great work, the "Sylloge Fungorum," many other Fungi are noted as parasitic on Vines, some of which (Fusarium Zavianum, Pionnotes Biasolettiana, &c.) are occasionally more or less hurtful. Probably one or other of the remedies indicated above would prove suitable against these parasites, as well as against any others that may in future be met with in vineries in Great Britain.