May 2010 Douro Insider

We enjoyed a beautifully warm and sunny first weekend of the month, with real spring weather in the air.  Given how summery it felt both in Porto and in the Douro it was somewhat surprising to hear forecasts of snow in the Serra de Estrela just a day or two later.  On the other hand it was also very gusty in spite of the sun, and there might have been some considerable wind-chill.  So whilst the days were fine, for a brief period the nights were remarkably wintery and on some evenings we felt the need to light a fire again.  Perhaps this chilly spell had something to do with the easterly winds; unusually they seemed to be blowing downriver for some reason.  There was even a case of frost settling in the Vilariça valley on the night of the 4th but fortunately it caused no damage to the vines.  The press reported heavy snowfalls in Paris at the same time, so this was apparently not a localised cold snap.

It marked the start of about a week of rather cool temperatures in the Douro, particularly when compared with the hot end of April, but at least initially it stayed very bright too.  Things then turned rather nondescript and dreary.  It was overcast, there was some rain, allegedly more snow in the mountains, and eventually even a spot of volcanic ash from Iceland.  Whilst Iberia had escaped the first wave relatively unscathed, the second flourish took a different route south and was enough to close most of Portugal’s airports for a couple of days.  Things continued in this vein into mid-month: cold, windy and unsettled and some major frost damage to the vines was reported in the outskirts of Vila Real.  This appeared to coincide with some widespread flooding in central and eastern Europe which resulted in several deaths.

Eventually conditions perked up going into the last two weeks of the month – there were blue skies again and the sunny weather led to a rapid warming of temperatures.  It was really quite hot by about the 20th but there was still heavy dew falling at night in the cover crops which made it extremely slippery to work on foot.  On the steeper slopes even the tractors on tyres (as opposed to on tracks) can skid.  Winter came by again on the night of 24th bringing tipping rain and whipping winds but it turned out to be just a short interruption.  Things got better after a day or two and in the end the month finished up very hot and sunny.

As the usual graph below shows, this May this did not turn out to be one of the really wet ones.  In fact there weren’t any of the intense thunderstorms that can so often push the precipitation figures right up and so the actual total was much below average, at just 15 mm.  Records show that an amount closer to 54 mm might fall in a typical month of May.  This result finally puts an end to a run of seven consecutive wetter than average months.  In spite of this the cumulative total is obviously still very far in advance of what would normally be expected.  To date we have had 417 mm of precipitation this year, and when we consider that the mean value for this stage is less than 320 mm it turns out that we are about 30% above average.

The details presented also show that, in spite of some pretty bad weather, there were enough hot days to bring about a mean temperature just fractionally above average in Pinhão, at 17.6º C.  The difference, however, at just 0.1º, is of no significance.  Based solely on the climatic summary it would be easy to conclude that May was basically warm and fine.  In fact it wasn’t really, but the impressive last 10 or 12 days weighed heavily in the averages.

Fortunately, as far as the vines were concerned, this good weather came at an absolutely critical period.  In short, conditions over flowering were absolutely excellent.  The skies were clear, there was little wind and precipitation was negligible.  All this, combined with high temperatures and plenty of humidity in the soil, meant that once flowering started it happened very quickly indeed, and a short flowering period means more phenological homogeneity and better fruit set.  Compared with a normal year the flowers were already on the large side before flowering and, in spite of last year’s drought, this year’s shoots are quite fruitful.  If we can continue to keep on top of the disease situation for the rest of the spring these factors would suggest that we could expect a plentiful harvest come September.

In terms of the actual timing of the phenological cycle the mean flowering date in 2010 for the principal varieties was May 25th.  This is five days later than it was in 2009 but the same day as 2008.  Given that budburst was eight days later than average this year it seems likely that the relative warmth of April had helped the vines to catch up and reduce the gap.  By fruit set (on the 30th May) the lag had been cut to just four days thanks to a contracted flowering period.

In the vineyards May found us very busy, with the month’s activities basically reduced to a three-way struggle between interrelated operations.  Firstly the rapidly growing cover crops needed to be cut back.  Not only did this make access on foot through the vineyards considerably easier but it also reduces the humidity in the bunch zone affording some added protection against fungal diseases.  Foot access was required to enable the correct canopy management practices to be carried out.  Training the shoots up between the foliage wires is essential if we are to use the shoot trimmer later on in the season – for obvious reasons we cannot despontar (shoot trim) if the bunches are hanging in the mid-row space.  There was also some thinning carried out at the same time to clear out the canopy of unnecessary shoot growth.  In some extreme cases there was so much vine growth into the mid-row that the shoot positioning was carried out before the mowing, as to use tractors would have run an unacceptable risk of damage to the crop and the untamed growth would make it extremely difficult for them to operate correctly.

Only once all this had been done could the spraying programme continue.  After the relatively greater risk of downy mildew in April, the low rainfall but unsettled weather of early May swung conditions more in favour of powdery mildew.  The period immediately following flowering in particular is a critical phase, and without properly controlled vegetation the sprays simply do not penetrate into the interior of the canopy where the fruit can be found.  Additionally, the improved aeration brought about by shoot thinning is in many ways as important for disease control as chemical methods.  The timing of all these activities is obviously critical, and has been particularly difficult this spring as the growth of both the vines and the grasses has been very rapid lately.

One or two quintas still found the time to start the despontas towards the end of May, and there were also some spot applications of herbicide carried out where time permitted.  Other than that the only other activity going on was terrace wall rebuilding, an ongoing hangover from the winter’s damage.  This is often carried out by specialists who don’t do other types of work so it does not necessarily reduce the actual vineyard workforce and can continue even during hard-pressed times such as these.