amarchinthevines

Learning about wine, vines and vignerons whilst living in the Languedoc

Mildew

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Su mildew

As I have posted regularly in 2016, this has been a most unusual year weather wise. After no real autumn in 2015, no real winter, no true spring we have had a stop start summer in June. Yes there have been a few hot sunny days but lots of rain and cloud too with many days in the mid 20s.

Sadly, humid days in the mid 20s and cool nights are exactly the conditions favoured by downy mildew, and it has prospered in 2016. Jeff Coutelou has spent many nights out on his tractor spraying the vines to try to protect them. As an organic producer (and much more) he cannot (and does not want to) use manufactured, chemical sprays. Instead he has used sprays based on rainwater with seaweed, nettles, horsetail and essential oils of sweet orange and rosemary. These are better absorbed by the vines in the cool of the night.

P1000885

On June 3rd Jeff spent much of the night spraying only for it be ruined by a storm on the 4th which had the effect of washing away the spray from the vines. The rainwater created other problems however. The humidity in the soils created ever more favourable conditions for mildew, the disease spread. And, there was a third effect; downy mildew lives as spores in the soils and the rain splashes them onto the vines. Mildiou is not a fungus as commonly believed, it is a one celled spore which germinates in warm, humid conditions especially between 16 and 24 Centigrade.

Once the spores are on the vine they attack the new growth and can create a downy white covering. Leaves show a mottled surface with oily spots, first of light green or yellow and then turning to brown as the mildew dries out. Underneath the leaf appears a downy white or grey growth.

The big question was whether to spray with copper. This is effective against mildew but has an effect on the soils, killing the micro organisms which live in them. It is allowed for organic production as long as no more than 25kg per hectare is used in a five year period, it is a natural product. Jeff has used hardly any in the last few years and was very reluctant to start this year. His belief was that it was better to have some losses this year from mildew than lose the life in the soils for a longer period. However, as the mildew spread so quickly he was forced to relent and use a little copper.

His long nights of unpleasant work have helped Jeff to contain the problem but there have been damages. In some parcels as much as 50% of the crop is lost. Mildew thrives on the leaves but spreads to the actual grapes and destroys them. We may go into the vines and cut away damaged bunches.When harvest arrives we will have to be even more vigilant than ever to ensure that affected bunches do not make their way into the  vats and, ultimately, the wines.

Car dead bunch

Dried out leaves and grappe

Meanwhile the sprays do not kill wildlife, such as that photographed below after the treatment.

The north wind which so often helps to dry out the vines has finally started to blow, though even it was humid for much of the past fortnight. The forecast is for hot, sunny weather which will stop mildew, so the threat should now diminish but it has left the vines looking mottled and a bit sickly. After a restless winter where the sap has been constantly on the move they have been less able to resist mildew’s effects.

The wire trellises which are used in many parcels have helped to ensure that air can circulate amongst the bunches to stop them becoming too humid and prone to mildew. Everything has been done but it has been a hard fight and losses suffered.

However, all is not doom and gloom. Most of the vines are now lush with growth. Flowering (fleuraison) was very late but last week the vines made up for lost time and the small grapes swelled greatly. Let’s hope for smoother progress in the next three months.

 

Author: amarch34

I'm a recently retired (early!) teacher from County Durham in North east England. I am going to be spending most of the next year in the Languedoc leaarning about wines, vineyards and the people who care for both.

One thought on “Mildew

  1. Pingback: Let’s be Candide | amarchinthevines

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