Monday, 28 December 2015

Vine Grafting in Sherry Vineyards

The European species of vine, known as Vitis Vinifera or “the wine bearing vine”, has many enemies. The two most deadly are Oïdium, a fungus, and Phylloxera Vastatrix “the destroyer”, a tiny aphid which kills Vinifera vines by sucking the sap from their roots. Both of these plagues originated in the United States where various species of native vines had grown for millennia but had, over time, developed resistance to Phylloxera. Sulphur is effective against Oïdium.

Pure white chalky Albariza
During the 1860s attempts to deal with Oïdium in the vineyards saw the import to Europe of large numbers of resistant American vines, however nobody realised they were also importing Phylloxera, which was all but invisible to the human eye. Its effects were first observed in Europe in 1863 as vines mysteriously died, and by the turn of the century it had ravaged most of the vineyards causing economic chaos. Jerez was visited by Phylloxera in 1894, but by then the answer had been found: grafting Vinifera scions onto resistant American rootstocks.

Injerto en yema or bud graft
This was not as easy as it sounds. First of all every Vinifera vine had to be uprooted, burned and replaced with American vines which had to be selected carefully for their ability to grow happily in alkaline albariza soil and to accept the graft. Many old Vinifera grape varieties were lost for their inability to do this, but gradually the vineyards were restored with the Palomino coming out most successfully. While grafting cured the vines it could not get rid of Phylloxera however, and therefore this process must still be undertaken every time a new vine is planted.

Injerto en espiga or stem graft
Young “portainjertos” or rootstocks are planted in wintertime so they can take advantage of the rainfall which will help develop their roots. The rootstocks in current use are usually crossings of the American vines Vitis Berlandieri for its root structure and tolerance of albariza, and Vitis Riparia to help with the graft. This takes place in August and September when a small piece of the stem of the rootstock is cut out and a Palomino bud is inserted tightly. This is called “injerto en yema” or a bud graft. Then the graft is wrapped with raffia leaving the bud peeping through and covered with soil for protection. By next spring the graft should have taken and the raffia will be removed. If it hasn’t taken another graft called “injerto en espiga” or a stem graft will be carried out. Successful grafting is later followed by pruning to organise the vine for full production in its fourth year. It is amazing how much work – or “graft” - goes into a bottle of Sherry!

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