Pests and diseases

The vine is a plant which is sensitive to several pathogenic diseases. We could say that the finer the variety of grape, the bigger the risk to the vine and clusters of grapes.To a certain extent, this is easy to understand as fine wines come from grapes with very subtle and delicate skins and are, therefore, soft and fragile. In varieties of grapes with hard, herbaceous skins, maceration produces wines which are not very fine but the hardness of the skin protects the grape from external attacks.

In addition to being susceptible to attack by different bacteria, fungi and insects, different eras have had an important influence. The second half of the last century was noteworthy for two new diseases which settled in European vineyards: Oidium and Phylloxera.

Recently (during the last decade) diseases have appeared in the vineyards of the Rioja which, although not devastating, are new in the sense that they are of recent appearance and their incidence is important; namely, Virosis and the Acari.

From viruses to butterflies of the vine (from the pyralid caterpillar) there is an enormous variation in size. The butterfly of the pyralid caterpillar is, at least, a million times bigger than the viruses which exist in some vineyards. This is general in all vinegrowing areas and the situation in the Rioja shows variations in accordance with its microclimates and varieties.

To describe the most typical diseases which affect the vineyards of the Rioja, we shall start with the smallest, the viruses, which have little importance but are of scientific interest. It is believed that they do not only affect the quality of the wine but also the productivity of the vine.

Their size is several thousandths of a millimetre and their presence can be diagnosed by low grape yields, changes (in some cases) in the colour of the leaves and by the length of the canes or production of double canes. The Rioja vinegrower is not disturbed by the presence of these viruses with respect to the quality of his grapes, but the effects they have on yield are indeed important. We do not know how long these viruses have existed in the vineyards of the Rioja. We only know that their presence has just been noticed. New plantations of vines tend to be made with guarantees of absence of these viruses.

The next largest pest is a bacteria, one thousandth of a millimetre in size, which produces necrosis or the death of some tissues of the vine, delaying budding, producing black spots in the wood or in the medulla of the cane, even on its outer part, and by giving very small clusters of grapes. This is not an old disease. Its occurrence is not important but we have mentioned it as a rare and interesting case; there are very few bacteria which attack vines. This disease is easily overcome and eradicated by disinfecting the shears and cuts when pruning the vine. It is a disease which attacks the red Garnacha of the Rioja which, in general terms, is a very resistant variety to other diseases.

Larger in size than bacteria, there are moulds and fungi which attack the vine and are known in the vinegrowing world as "Cryptogams". We name the most important diseases: Oidium and Mildew. The size of these fungi is variable and difficult to describe with precision. They range from a few thousanths of a millimetre in spores to a tenth of a millimetre in filaments.

Oidium is a new disease in Europe and has existed here only since the middle of the last Century. It comes from North America and its effect was felt intensely in the Rioja at the end of the 19th Century. The risk of infection has been constant since then but the disease is easily contained by spraying sulphur powder on the leaves and clusters. The powder reacts with the sun'heat producing sulphurous vapors which kill the fungi growing on the outer surface of the leaves and clusters. Should the fungi not be destroyed, the effects would be disastrous. It attacks the leaves producing granulation and greyish pilosity on the bunches. Vinegrowers call this "cenicilla" or "powdery mildew"; it cracks the skin of the grape, preventing ripening.

Another very important cryptogamous disease is Mildew. Its importance derives from the penetration of the delicate interior of the vine, growing inside, and thus remaining highly resistant to treatment.

Vinegrowers combat this disease with care by using copper sulphate compounds. The important question is when to treat. This disease is a constant risk and occurs when there is a high level of humidity and heat. Sometimes, sporadically, as in 1972, it causes extreme damage and can destroy entire areas of vineyards. Not only do the green parts in the vine die but the trunk also becomes contaminated. Thus, in 1972, due to the rapid invasion of mildew during the month of June, thousands of hectares of vines were destroyed in Spain.

The vineyards of the Rioja, due to their semi-humid nature, are prone to mildew, but the vinegrower has sufficient knowledge and means to deal with it. Mildew attacks the leaves, first producing an oily patch and later destroying it completely. The same thing happens to the bunch of grapes.

Moulds can also attack bunches during the ripening period and during the harvest. This occurs with the Botrytis mould, which grows on soft grapes destroying the bunch and producing musts with deficient colouring and which are highly oxidable. The resulting wines have un unstable colour.

Acari are enemies of the vine and have appeared in the Rioja within the last ten years. The climatic irregularities of this period have produced cold Springs with hesitant budding allowing these acari, red spider, yellow spider and acariosis, to proliferate easily, devouring tender buds and incipient leaves during May. At first, at the beginning of the seventies, their impact was considerable. In the Rioja we were afraid of an escalation of damage due to acari. Despite everything, little by little the Rioja vinegrower, by means of treatment of pruned wood during the winter, has been able to control this pest. Today, it does not represent a danger, although the risk still exists.

The largest of the pests which attack vines are insects.

Several types of insect attack the vineyards and there are few variations between the different vine-growing areas with respect to the importance of these aggressors.

Phylloxera is extremely important. This has affected, devastated and left its mark on all the vineyards of Europe.

As in the case of Oidium, it came from North America. Both invasions first affected Britain and then crossed the Channel to the Continent. Phylloxera reached Spanish vineyards by sea. Through Oporto and Málaga in 1880 it began to penetrate the peninsula. However it had already arrived by sea in Bordeaux and the South of France: from there it also extended to the Rioja and Cataluña. The first outbreak in the Rioja was in 1899 in the vineyards of Sajazarra, in the Rioja Alta. It was detected by technicians of the Enological Laboratory of Haro

Vinegrowers took rapid corrective action by means of American vine stocks which are resistant to phylloxera. Rioja varieties of European vines were grafted on these rootstocks.

Phylloxera has two living forms: one which attacks the roots, piercing them, creating knots causing them to lose vitality; the other, an aerial form, with wings, which pierces the leaves, producing galls or bumps, causing the green parts to disappear if the attack is intense. This plant louse represented the most disastrous invasion of vineyards and is latent in all existing vineyards in the world. The only means of combating it is the creation of plants with American vine roots which withstand the root-attacking type and an upper European part of the vine which provides quality grapes and resists the winged version of phylloxera more than American vines.

Another important insect which offers a possible threat to Rioja vines is the vine pyralid caterpillar. In Spring their larvae appear among the roughness in the bark of the trunk and devour tender shoots, even incipient clusters of grapes, and then change into chrysalises, from which butterflies emerge. This insect is easy to control.

Pests and diseases affect Rioja wine both in quality and quantity. The first effect of a disease in the Rioja is to reduce production. A more intense attack can also delay ripening, producing wines with a "green" taste, little colour and a low alcohol level, therefore not appropriate for long ageing, always desirable in Rioja wines.

These are the general effects, but the attacks to which vines are submitted to during the ripening period, such as Botrytis moulds, can reduce the yield, concentrate the sugar, produce less wine but with a higher alcohol content. There is, however, the inconvenience of colour alteration. Every year, technicians have to face the dilemma of the harvest, namely, to pick early without Botrytis and with little sugar, or later, when the grapes have more sugar but Some Botrytis mould. The choice is simple, harvest late and try to treat Botrytis in the bodega.