With wind, hail and lightning, the tremendous storms earlier this week in the western Cape have significantly affected some Cape vineyards. Overall it’s not clear just how much damage was caused, and of course it varies from place to place. There was some hail – which can obviously wreak havoc, shredding leaves and tender young stems and bashing the flowers that right now are showing on many vines as minuscule and scarcely noticeable precursors of the harvest to come in three or four months. But it seems the hail was generally not as much a problem as the powerful winds. Not only can the wind dislodge the flowers and break stems, it can effectively burn or sandblast the soft shoots.
I was vineyard-visiting in the Swartland and Olifants River districts on Tuesday, a day or more after the worst of the weather, and even there, in the more southerly parts, damage was to be seen in exposed vineyards. Of course, in the dryland vineyards of these parts and elsewhere, farmers who had just a bit of welcome rain, with no “collateral damage” (as the military might call it) will be pleased. It was actually rather strange being in this dry but beautiful part of the world and seeing it for the first time in my summer experience darkened by lowering clouds, and driving though occasional rainshowers – mostly too small to be of much use, sadly. The picture alongside is of a valley (with more rooibos tea and wheat in it than grapes) somewhere northwest of Clanwilliam (my knowledge of the geography of that area is shamefully vague).
Things were much worse for more vineyards closer to the coast down south. I believe that young vines at Cape Point Vineyards suffered seriously, and parts of Constantia must also have been affected. It is with very young vines that the damage can be most serious – but if shoots even on mature vines break off at their base, not only is the forthcoming harvest affected, but the vine can lose its bearer for the following season, and you’re two years behind.
In parts of the Helderberg area of Stellenbosch, “it was the worst damage I’ve ever seen”, a distressed viticulturist told me. “The wind just took handful of shoots and pulled them out of every vine. The growth tips are burnt black and a lot of the bunches were scorched. This does not only destroy the crop for this year, but you have no “tappie” to prune next winter and it therefore also affects your crop for next year.”
Parts of Stellenbosch at least also seem, incidentally, to be enduring a lot of downy mildew this year, and more humidity is not going to help.
One bright side is that, where young leaf growth was ripped up but there was not too serious damage to the vine structure or to the nascent bunches of grapes, growth will be enormously stimulated – by the lightning. This is always for me a fascinating thing, the nitrogen boost that lightning gives to plants, and I used to think it on a par with other bits of moonstruck nonsense that one occasionally hears in vineyards. But this is real science, I’ve learnt.
The story goes something like this: Nitrogen is, of course, the most abundant element in air. The huge amount of energy released when there’s lightning can break the strong bonds between nitrogen atoms, and cause them to react with oxygen. Nitrous oxide results, and then nitrogen dioxide, which dissolves in water to product nitric and nitrous acids. The next stage is to release hydrogen, forming nitrate and nitrite ions.
And lo and behold, these can be used by plants and micro-organisms; and vines can get a good green boost. Sadly, many of them are going to need it at this early stage of harvest 2010. Viticulturists and vineyards workers will also, inevitably, have a great deal more canopy management to do as a result. But the real problem caused by the storms is for those whose canopies have been seriously set back – or made a bit irrelevant by destruction.