May 2008 Douro Insider

May started a little curiously, with the weather still undecided (as it has been for most of the year so far) but it was changeable in a different way from April.  Rather than fluctuating from one extreme to another from week to week, there were a number of days that, at breakfast time, appeared to have little idea as to what they were going to do until dinner.  There were often spells of overcast skies bringing with them some light showers but these gloomy patches were broken up by sticky, sunny spells that tempted out the  first snakes of spring.  Whilst precipitation was not especially high by the usual standards, it trickled in consistently throughout the month (particularly in the second half), a slow but steady stream that ensured that the air remained decidedly humid and, coupled with the cloudy conditions, might have favoured powdery mildew had precautions not been taken.  Unfortunately things didn’t really clear up in time for flowering and by mid-month a heavy depression could be found camped broodingly over the Iberian peninsula for about a week or so.  Thus things remained variable but thundery, basically quite grey but with plenty of showers.  In any case, it is turning out to be quite a challenging spring as far as the treatments go.

Whilst on the subject of flowering, it is worth making a few points of a phenological nature.  The first thing to appreciate is that temperatures were quite a bit lower than average (as we shall see in due course) which meant that the mean date for full bloom didn’t come until the 25th May, a full week later than last year.  All in all the conditions were not favourable by any stretch of the imagination: rain and overcast skies prolonged the period of flowering and created considerable heterogeneity on three levels: within single bunches, between bunches on the same vine and between different plants in the vineyard.  All of these are potential indicators of poor fruit set but fortunately first impressions after flowering suggest that the vines have held up rather better than expected in the majority of quintas.  At some of the cooler properties there has been a notable loss of fruit, however.  This is not always bad news, as a smaller crop is easier to ripen, and more concentrated fruit often results.

As if these difficulties were not enough, they came on the back of two considerable hailstorms.  The first, on the 9th, hit the Vilariça valley but coming as it did so early there was luckily very limited damage done to the embryo bunches.  Much more destructive, though, was the hail that struck the Mirandela region on the 24th of the month, piling up as deep as 8 cm on the ground in places.  Although not technically within the Demarcated Region, there is much vineyard in the area and both vines and olive trees were badly hit.  It also turned out to be a miserable month for apiculturists, apparently.  Beekeepers in the damper parts of the Douro complained that their charges were dying from starvation.  In spite of the spectacular abundance of wild flowers, it appears that their nectar was to remain just out of reach of the poor hungry bees since they are not able to fly in the rain.

In spite of this insistent, low-level trickling of drizzle, the actual volume of precipitation was really quite modest, at least right up until the end of the month.  Going into the last week the total figure was still below 20 mm.  For a while it seemed as though the drought of February and March had returned but then finally, as if trying to get back on track, there came a very wet spell to wrap up the spring.  It is worth noting that according to records in Pinhão, May actually has a higher average rainfall than both March and April.  This year that was not exactly the case due to the extremely wet April we had – but instead May brought more rainfall than both February and March did.  The final total figure, at 51 mm, was almost spot on the average which stands at 54 mm.  As usual, the cumulative rainfall status and evolution of temperatures this year are shown in the graphs below.

The figures show that, principally as a result of April’s efforts, we are still fractionally ahead of the expected values for total precipitation (around 10 %  over the mean figure for this time of year).  If we consider that temperatures (and, by implication, evapotranspiration) have been amenable, we are not in too bad a position as we head towards the warmest part of the year.  May’s average temperature in Pinhão was 16.5º C, one full degree below the mean.  The absolute maximum for the month, at 30.1º, also illustrates that we were not too hot in the vineyards compared with some years that have been endured in the past.  The evenings were pleasantly refreshing, with the mercury dropping below 15º on every night but two.  Furthermore, there were only five days on which the temperature reached 25º or above.

May is usually a busy time in the vineyards of the Douro as a combination of pleasant temperatures, some fair degree of sunshine and regular waterings to freshen up the vineyards often conspire to produce very rapid vegetative growth.  Furthermore, these factors also contribute to the development of fungi, and sporadic treatments are normally called for.  Thus virtually all the work carried out involves controlling the foliage of the vines (canopy management) and occasional spraying.  Note that without effective canopy management being implemented first, the entire vine treatment programme can be put in jeopardy.  Firstly because drooping shoot tips from adjacent rows can become entangled across the mid-row space, thereby restricting access for people and machinery.  Furthermore, overgrown canopies have reduced air circulation and a more humid internal microclimate, thereby encouraging the development of fungal diseases.

What this tells us is that at practically every quinta in the region without exception there were three activities that dominated totally.  The first two, shoot positioning (between the wires) and shoot thinning (see the explanation of despampa in last month’s report) are concerned with creating and maintaining a workable and aesthetic vineyard, whilst the other is much less romantic but at least as necessary.  It is, of course, spraying the vines with fungicides.  One of our best defences against downy mildew is simple copper sulphate – a long-standing friend of viticulturists around the world, and approved for use in organically-grown cultures.

The vines and the fungal diseases were not the only things to bloom in the spring weather.  The cover crops were also doing beautifully where they had been sown in the vertical plantings.  We generally use a mixture of leguminous and gramineous species, principally clovers, rye grass and oats.  The balance between nitrogen-fixing species and nitrogen-consuming species can be adjusted for each location according to the vigour of the vines.  The nature of these species is always to try to flower as early as possible (and indeed, it is in our interests that they lay down a decent seed bed for next year) but, left unattended, this stage normally comes too early for our liking as the plants atrophy soon after flowering, thereby reducing their beneficial effects.  In order to control this we normally mow them for the first time as soon as the flowers begin to open.  Removing the first flowers temporarily slows down this process and thereby lengthens the cycle of the plants by a few weeks.  Now that the ‘second’ (or completed) flowering was finishing, it was time to mow for a second time to ensure that the cover cops dry up definitively.  This is so that, as the summer starts to become hotter and drier, we can be sure that they are no longer consuming any water.  The cut grass now lies on the surface of the soil where it acts as a mulch.  It breaks up the flow of air over the soil whilst simultaneously providing localised shade, two factors that are important to reduce evaporation.  At the same time, the blanket of organic matter continues to reduce the erosional impact of any raindrops that might still fall.

All of the aforementioned jobs (but particularly the canopy management, much of which is necessarily carried out by hand) are particularly labour-intensive, and for this reason very little else was going on in the vineyards in May.  As ever there was some limited ploughing here and there, principally for weed-control, and one other job of some considerable importance.  In our new plantations (vineyards planted this year) hand watering of the vines will soon be required.  The arid climate of the Douro makes it impossible to establish a vineyard without giving the vines some extra water in their first year (since their root systems are totally undeveloped).  So water-retaining basins were dug at the base of each of the young rootlings in the 2008 plantations in preparation for the hosepipes.