La taille hivernale et ses contraintes en Viticulture Agro-Synergique ?

Winter pruning and its constraints in Agro-Synergic Viticulture?

Remember that the vine is a liana that grows naturally at the edge of forests by climbing trees to form foliage. A method of cultivation of this type still exists today quite sporadically in certain regions of Italy and Portugal for example, but for all that the development of the branches must be controlled to ensure regular and accessible production. Pruning has therefore always been one of the most important jobs.

For vines, annual dry pruning absolutely controls the future harvest; the winegrower is first and foremost the one who knows how to prune. The best date for this operation has been much debated by agronomists since ancient times. In climates with mild winters fall or late winter, in harsher climates spring. But we can also reserve pruning at the very beginning of the rise of the sap to avoid the risks incurred by white frost. The damage from this is all the more harmful the earlier the pruning was done.
We must therefore take into account climatic hazards and adapt to the context of each year. But very often it is not these technical choices that are in question but the possibilities of the workforce. Columella and Pliny express it very clearly "When the extent of our possessions prevents us from choosing our time, it will be necessary to prune the parts of our vineyards that are the most vigorous during the cold, the leanest in the spring or during the autumn" declares the first to us after having very carefully considered all the technical consequences of the different calendars; while Pliny deplores early spring pruning “this practice arose from the distribution of tasks in large estates and not from a legitimate haste of nature”. The changes in the climate in our region encountered in recent years now strongly influence our decisions on this subject. If we statistically counted an episode of critical spring frost (with more or less total loss of the harvest) every ten or eleven years, we have recently experienced a significant increase in the frequency of these calamitous episodes (2007, 2017, 2021, etc.) due on the one hand to the disappearance of harsh winters which slowed down the start of vine growth in spring, and on the other hand to the modification of continental polar air flows which now reach us more easily until May, the famous period of the “ice saints” (Saint Mamert, Saint Pancras and Saint Servais, traditionally celebrated on May 11, 12 and 13).

We are then no longer dealing with spring frosts (radiative -1 to -3°C), but with winter frosts in spring, by advection of cold polar air (-6°C), which hardly leave of hope when they arise on these dates…
Agro-Synergy does not impose a pruning system but only a simple principle which is to promote the development and maintenance of the vines in place for as long as possible while being able to ensure qualitative and profitable production. It is therefore essential that the pruning carried out firstly allows the vine to develop as harmoniously as possible by guaranteeing easy sap flow. It is also essential that pruning allows the vine to age as long as possible to allow its root system to best exploit the potential of its terroir in all its depth: a foot bruised by pruning does not take long to die .
We traditionally use the so-called Doctor Guyot 2 size, rather simple and rarely double because it is too productive for us, which is the classic size in the region. The Guyot size is a mixed size on a short frame. The stump is made up of a trunk extended by an arm (the upper branch) and a spur (the lower branch, courson or cot) with two eyes. The length of the arm depends on the vigor of the strain. After having assembled the trunk, the training pruning of the vine consists of pruning the branches in order to give its structure to the stump. There
Annual pruning consists of removing the fruiting wood and pruning the spurs. This wand and spur pruning allows us to consider adaptive pruning in two stages to reduce the risk of frost.

We prune from December/January because the size of the vineyard does not allow us to prune the entire surface on a date that would suit us perfectly, as Pliny already mentioned. Then, we first prune the wand and the course longer, that is to say leaving a number of buds much greater than necessary, without bending the wands before the first days of May, so that the budburst of the first buds located at

top of the wand inhibit the development of those at the base (phenomenon known as acrotonia from the Greek akros, at the end, and tonos, tension), that is to say those which are useful to us size in " engagement"). Undisturbed, they are naturally better protected from the risk of frost. This old technique is relatively effective, but it condemns us to pruning (quickly) a second time, to folding and attaching the sticks then (very) quickly as soon as the risk of frost becomes a priori lower, with a mobilization of hands. work more
important and therefore more costly (but still less costly than a drastic loss of harvest...) at the end of April in Bordeaux.
Guyot pruning, like all systems, has advantages and disadvantages. The simple Guyot is first of all an easy-to-implement technique which allows a minimum reduction in the elongation of the framework, well suited to vines planted at high density. It ensures correct fruiting for less fertile grape varieties, and can lead to high production in others which are easily controlled by reducing excess buds at pruning or in spring (disbudding). But the simple Guyot also has certain disadvantages. It first contributes to the premature aging of the strain: wounds of
Too much pruning generates deep necrosis detrimental to the circulation of sap which can also promote wood diseases. Simple Guyot encourages the accumulation of vegetation in the center of the vine if disbudding is not carried out well at this location and production at the end of the stick if it is too long or excessively disbudded with possible heterogeneity in the maturation of the bunches. .
But it is possible to limit the main negative aspects of simple Guyot pruning using simple actions:
- By balancing the size: you must try to distribute the wood on the stump while keeping
when possible, a stem on the side opposite the wand. Two spurs can thus be preserved, especially on old vines. On a vine visibly
unbalanced, we can even keep during disbudding a “greedy”, a shoot of the year, on the unfed side, to prune it to the bud the following winter.
- By avoiding shaving the wounds, and always favoring removal on time (before the shoots are hardened if done manually). Leaving snags at the waist will limit deep necrosis due to drying cones. Their length must be at least equivalent to the diameter of the cup, but not excessively so as to limit the number of gourmands. They can be disposed of one or two years later when they are dry.
- Respecting vigor: pruning a vigorous stump too short is detrimental, just as much as pruning a weak stump too long. Subsequent thinning may be necessary in relation to a production objective, especially on relatively young and fertile vines.
- By observing the position of the eyes on the spur before pruning: the first eye must be below, in order to preserve the flow of sap and to make all the pruning wounds on the top. This is possible because on a vine with normal vigor, both eyes of the course develop, but much more rarely the base eye located on the crown. If only one frank eye is left, most of the time the opposite eye of the crown develops. We can therefore adapt the length of the stem according to the positioning of the eyes, but this observation delays the pruner somewhat.
- By renewing the stump or cutting back when possible: if we notice that the top of the stump is degenerating, it is advisable to keep a well-placed sucker, and to cut it back to two eyes one year in case of vigor insufficient. When cutting the trunk above the trunk, always keep a sufficient snag, and protect the large wound made with a putty for example (mechanical protection, in particular against Eutypa lata spores).

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