Wednesday 24 September 2014

Grape stars

When my team leader gave us trainees an introduction to the Fruit Department, he showed us some dessert grapes grown in a small greenhouse by the orchard, remarking that they were high maintenance, requiring: an intensive regime of pruning and trimming, fruit thinning and stripping of the bark from the stems to expose pests before treating in the winter.

Today, one of those grapevines: Vitis vinifera 'Muscat of Alexandria', was the object of extra attentions, as it was of interest to a filming crew coming to the gardens.

Vitis vinifera 'Muscat of Alexandria'
under glass at RHS Garden Wisley
As we were not quite sure why that specific plant was in the limelight, I did a bit of research. An excellent quality variety, although not high-yielding and potentially unreliable , it has been very popular in the Mediterranean from time immemorial, and used as dessert, for raisins and wine-making . Incidentally, I found it really interesting to discover that one of the synonyms for this variety is ‘Zibibbo’, from the Arab for grapes (the grapes of grapes?), which gives the name to a fortified wine from Southern Italy that was the favourite of my grandfather.

Anyway, the reason we worked on the ‘Muscat of Alexandria’ today was the sooty mould growing on the excretions of brown scales (Parthenolecanium corni), one of the glasshouse’s longstanding pests.

Sooty mould
Parthenolecanium corni on Vitis sp

Some of the leaves were completely blackened, which, besides affecting their photosynthesising capacity (and occasionally clogging the pores on the underside), was rather aesthetically unappealing.

So we washed them, bucket of water and sponge in hand. High maintenance stars indeed!

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