July 2011 Douro Insider

Although the end of June was destructively hot, almost as soon as the new month got underway there was a complete reversal of the broad-scale meteorological picture which came to dominate the weather in Portugal during most of July.  Very high pressure over the Azores combined with a thermal depression on the Iberian Peninsula caused strong winds to blow inland from the northwest for a large part of the month.  These maritime winds are typically very cool, meaning that the north of the country in particular was considerably fresher than might have been expected.  This was especially so at night.  It also explains why there was such a pronounced north-south divide when it came to temperatures: as the air currents blew southwards over the land they gradually warmed up and as a result the further south they got, the better the weather.  This led to the highly unusual situation whereby Faro was often the hottest city in the country. 

Another characteristic of maritime air masses is of course that they are humid, and this in itself brings a certain instability to weather patterns.  Thus conditions felt relatively changeable, although in spite of this it never actually got round to raining.  It was predictably gusty, especially in the afternoons.  Presumably this wind was in part responsible for keeping down the night-time temperatures, which loitered somewhere in the region of 15º C for most of the month.  It was only in the last seven days that this curious weather system finally broke up and allowed the daily maximum to creep up to more normal heights for this time of the year.  The last week was therefore the only part of the month that really felt like a typical July, and registered temperatures above 35º every day.  This general scenario was fairly standard across the Douro, and the usually considerable spatial differences were much reduced.

The uncommon direction of the prevailing winds resulted in a mean temperature of 23.9º in Pinhão that was almost one degree below average (24.7º).  This was probably no bad thing.  Looking back over the past few months, this part of the year can basically be summarised by a very hot early spring turning into a cool early summer, with April and May much warmer than average, and June and July notably cooler, mercifully (see the graph).  There is no denying that the fact that it was not particularly hot helped the vineyards in what was another very dry month.  The whole region remained completely rain-free, with 0 mm of precipitation to report.  Incidentally, the situation was exactly the same in July last year, and also in five out of the last 10 years.

The usual graph of cumulative precipitation shows a very flat orange line indicating that there has been no rainfall of any significance for quite some time.  In fact we have had fewer than 20 mm in the whole of the last three months and this is of course insufficient to penetrate deep enough into the soil to be of any use to the vines.  In spite of the scarcity of water the vines are still looking strong, even if the cumulative total (at 234 mm) is less than two thirds of the expected value (369 mm).  This is due to the fact that every month so far in 2011 has been drier than average.

The most significant point of note in the vineyards this month was obviously that veraison came extremely early.  Observations from one of the experimental blocks at Cavadinha have always provided our phenological frame of reference as this particular parcela contains various combinations of the most important Douro castas (varieties) on a range of different rootstocks.  The ‘average’ date of veraison this year (when half the berries on half the bunches have changed colour) came as early as July 9th (and it was even earlier at some of the other quintas).  It is hard to put this date into perspective: it is barely even on the same page as last year (22nd July) and a two week difference is a huge amount when we are talking about the vegetative cycle of a grapevine.  With regards to the ‘normal’ date for veraison, we do not even have an average for comparison.  This is because the Touriga Nacional in particular tends to colour later than the other varieties, and often it has not quite reached 50 % by the start of the August holidays.

The fruit initially changed colour very quickly (which is usually considered to be an encouraging sign, indicating that the vines are in good health) but cooler conditions mid-month meant that the higher vineyards (and the later castas) suffered from a sluggish sort of semi-stagnation and ended up actually taking rather a long time to finish.  As it turned out, this year the Nacional was some 10 days later than most of the other varieties.

Veraison is a particularly significant time for the técnicos (viticulturalists) as well.  It is welcomed throughout the viticultural world, and duly greeted with the breathing of a collective sigh of relief.  This is because it marks the point at which the grapes become virtually immune to powdery mildew.  As the threat of downy mildew has long since passed by this stage, veraison means an end to worrying about fungal diseases, and for the first time since budburst we can start to think about putting the sprayers away.

This is not to say that the grapes are entirely safe, however, as natural phenomena remain a threat, as might some insect pests (although by early August it will be too late to use many of the insecticides anyway).  There also remains the (fortunately low) risk of bunch rotting fungi such as botrytis attacking closer to the harvest, but in any case a weight is lifted from our shoulders at least for a while.  In retrospect, it has been an extremely difficult year so far for Douro viticulture: we have pretty much experienced the full scope of tribulations.  Míldio (downy), oídio (powdery), hail, sunburn and unpredictable insect pests have all made their presences uncomfortably felt this season, and led to considerable losses of potential production.  Generally, however, these are issues of quantity and not of quality, and a reasonable harvest can still be predicted for the best looked after quintas.  The quality of the fruit promises well too.

Activity in the quintas starts to wind down a little in July, with almost all the vineyard workers starting their holidays in the last week of the month, and some even earlier.  They will not be rejoining us until the very last days of August, or perhaps the start of September, so it is important that we leave everything perfectly ready for the summer break.  This means that despontas are a major focus of our efforts this month, not only for practical reasons (unimpeded passage through the vineyards, exposure of the fruit and so on) but also for aesthetic ones.  There will be plenty of tourists visiting the Douro over the summer and we wouldn’t want to give a bad impression.  Shoot trimming at this time of the year can be effective for an extended period if the weather is hot and dry, as we would expect.  Ideally the removal of the shoot tips should put an end to this season’s vegetative growth, ensuring that the vines’ resources are henceforth redirected into ripening the fruit fully and evenly.

The increasing heat and continued drought also made July an excellent time for dealing with weeds in the vineyards, whether along the rows themselves or on the taludes (soil banks of the terraces).  If necessary a last mowing of the cover crops will ensure that there is no further vegetative growth before the autumn rains, and the cut grass will form a protective mulch on the surface of the soil, helping to keep in humidity.  Finally, in one or two parcelas (vineyard blocks), we sprayed against insect pests: cicadela (a kind of leaf-hopper) has already caused some problems, and traça (the European grapevine moth) is always a risk.  To keep these treatments to a minimum the applications are targeted very specifically by both location and casta, and even then only after a careful evaluation of the risk level has been carried out in the parcelas in question and indicated that spraying will be necessary.  The timing is also critical, and this is determined by monitoring the growth cycle of the pests, something we do as a matter of course in every quinta.

2 thoughts on “July 2011 Douro Insider”

    1. Hi, thanks for the kind words. You can easily catch up on back issues of the Douro Insider by using the menu tab at the top of the page, if you like.

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