Diseases that Affect Vineyards

Throughout the year, the vines are watched carefully for disease, which may break out at any moment, particularly when the weather has been damp or sunless. Diseases are of four types and may be caused by deficiencies in the soil, fungus growths, insects, or viruses. There is only one disease in the first category - chlorosis. This is usually caused by an excess of calcium in the soil, which makes the leaves turn yellow and wither.

It can be cured by sprinkling the vines with an aqueous solution of iron sulphate stirred up with linseed oil, or by injecting an iron sulphate solution into the soil, but it is very rare in the sherry area despite the nature of the soil. Any condition affecting the leaves of the vine is inevitably serious. The sugar which eventually accumulates in the berries is first formed in the leaves. The plant breathes through them and they protect the grapes against sunburn.

Evaporation of water from the leaves cools the vine at the height of summer. There are only two diseases of any importance caused by fungi: oidium {uncinula necator, uncinula americana, or uncinula spir­alis, formerly known as oidium tuckeri); and mildew (plasmopara viticola, formerly called peronospora viticola). These, however, are very serious indeed unless spotted and checked at once.

Oidium is indigenous to North America, and was first observed in Europe by one Tucker, who found it in a hothouse at Margate in 1845. A London gardener named Kyle found the remedy a year later. The vineyards at Chiclana were attacked in 1852, and the disease spread rapidly, reaching Jerez in 1855. It was not fully checked until 1858, and there was not another good vintage until 1861.

In the meantime, the yield of the sherry vineyards was drastically reduced, and the French vineyards were devastated at much the same time. The old established shippers sold less wine at higher prices, but there were upstarts of no integrity who were only too willing to satisfy the demand by importing inferior, though not dissimilar, wines from other parts of Andalusia.

When a vine is attacked, the first symptom of oidium is a dark stain on the stem, and it is known locally as cenizo, or ash, owing to a fine ash-like powder that covers the grapes soon afterwards, turning them sour and rotten. The fungus requires a minimum temperature of about fifty degrees and generally starts growing in damp weather, so it is likely to appear after rain at any time between the flowering of the vine and the vintage, though strong and well-pruned vines are less susceptible to attack than others.

Spraying helps to keep it under control, but the only real remedy, as discovered by Kyle, is powdered sulphur. Mildew grows under similar conditions, though it fails to germinate if the temperature approaches a hundred. When it attacks vines, white stains like icing sugar appear, often at the edges of the leaves, and gradually spread inwards. It also affects the grapes.

When it infects young fruit it is known as \"grey rot,\" but when it attacks fruit that is almost ripe a different color is produced and it is known as \"brown rot.\" Unfortunately there is no sign of infection until it has taken a firm hold of the grapes, and by that time it is incurable. It is very rare today, though, as it is prevented by spraying with some such spray as Cuprosan or with the old Bordeaux mixture during the dangerous summer months.

Evaporation of water from the leaves cools the vine at the height of summer. There are only two diseases of any importance caused by fungi: oidium and mildew. These, however, are very serious indeed unless spotted and checked at once.