Vine Pruning

Climate resilience Vine pruning and training

Vine recutting is a very common technique, used to form a new trunk with a young shoot. The advantage is that the well-developed root system of a vine in production is preserved. Moreover, the recut vine will return to production much faster than a young replant. The effectiveness of this technique is very good for combating eutypa dieback (BNIC-INRA Bordeaux, 1989). The effectiveness against Esca and Black Dead Arm is partial because some of the recut vines may express symptoms again in the following years. Several complementary methods exist within the same plot. Thus, recutting can be:

preventive, performed before the first symptoms of wood diseases appear
curative, used on vines showing symptoms.

The success of recutting depends on many factors:

the grape variety,
the development stage of the disease: recutting works better when done early.
the region

Implementation

In the vineyard, recutting can be implemented in different circumstances. It can be justified on healthy vines but presenting factors favoring the development of wood diseases. Also, when vines show the beginning of the first symptoms of wood diseases or even on fully diseased vines. We distinguish two types of recutting techniques depending on the situation:

« the classic recutting », performed on a vine in production using a shoot that has grown spontaneously,
« the forced recutting » performed using a shoot that grew after decapitating the old trunk.

Implementation on symptomatic vines: forced recutting

It is possible to recut a vine, thus replacing the old diseased trunk with a shoot that will form a new healthy trunk. This helps to improve yield, and can slow the spread of the disease by eliminating a potential source of inoculum in the plot. However, reinfection is not guaranteed to be avoided. Moreover, the pruning wounds made for recutting must be protected by applying fungicides (Smart, 2015), or by a biocontrol agent. It is possible to decapitate vines before harvest, as soon as the first symptoms of wood diseases are visible. Indeed, recutting seems more effective when the disease is not in the apoplectic form but rather in a slow form and at the beginning of symptom expression. If diseased vines have been marked, they can be cut during winter. Grape varieties may react differently to decapitation and have different capacities to produce shoots in spring. A particularly important element is to cut the vine below the necroses caused by wood diseases, to remove all the diseased wood constituting the inoculum and also to apply fungicides on the wound. If decapitation is done in winter, the decapitation wound must be protected to limit the penetration of fungi.

Steps of forced recutting

Perform this technique on suitable plots, on a grape variety that produces enough shoots.
Remove the symptomatic part of the trunk by sawing it at the base, below the last necroses (with a saw or chainsaw). Protect the wound (by applying a fungicide or a biocontrol agent) and wait for spring.
In spring, select a well-developed shoot at the base of the trunk. Be careful not to select a rootstock sucker.
Stake the shoot. If necessary, protect it from chemical weed control or mechanical weeding, with sturdy stakes or plastic sleeves.
Perform shoot thinning, adapted to the pruning of a young plant.
Prune the plant like a young plant, performing formative pruning adapted to the pruning system in place.

Results of this technique

This technique is very effective against eutypa dieback. For Esca and Black Dead Arm, this technique is more effective when vines are affected by the slow form. Indeed, if they are affected by the apoplectic form, some of the recut vines express symptoms again within the following two years. New trunks can be free of diseases of the wood if decapitation was done low enough, below the cankers and necroses caused by pathogenic fungi.

Implementation on healthy vines: preventive recutting

This technique consists of recutting before observing symptoms of wood diseases. It aims to rejuvenate trunks, to prevent the appearance of wood diseases. This can be done on a whole plot or only on some vines depending on several parameters. When a young plot (less than 15-20 years) begins to show symptoms of wood diseases, it means that the wood of most vines contains necroses of wood diseases and presents altered sap flow paths, so the mortality rate will increase in the following years. In these plots, it is possible to restore sap flow and eliminate inoculum by performing a massive recutting of the plot. For this, it is best to select a shoot located as low as possible on the trunk, to remove as much inoculum as possible (SICAVAC, BIVC, 2015). In this situation, the original trunk can be preserved and continue to produce as a double trunk, it can even serve as a stake for the young shoot until it forms a new productive trunk. It is interesting to perform recutting on an entire plot because maintaining recut vines requires specific manual work, similar to the maintenance of a young plantation. It is easier to manage recutting when it is done uniformly on a plot. It is also possible to recut preventively only some vines, by performing spot recutting when vines showing factors favoring wood diseases are identified. As in the previous case of forced recutting, during preventive recutting, pruning wounds must be protected.

Early recutting according to Richard Smart

Early recutting according to Richard Smart has several objectives:

preserve healthy vines
restore yields before crop loss
manage wood diseases in the vineyard at an early stage of infection.

Steps of early recutting

Assess infection by wood diseases by counting vines showing foliar symptoms as well as dead and missing vines. The timing of assessment depends on the predominant disease in the vineyard. For eutypa dieback it can be done in spring and for Esca and Black Dead Arm it can be done at the end of summer, before harvest.
Assess disease risk: depending on the grape variety, there is different sensitivity to wood diseases.
Combine the risk and infection status of the plot to decide on the management strategy.

Depending on the plot risk (sensitivity of grape varieties, overall management) and the current infection rate of the plot, 4 management strategies are proposed by R. Smart:

Strategy 1 - low risk, low infection: remove dead vines and keep shoots on vines showing symptoms of wood diseases and recut these vines.
Strategy 2 - low risk, medium infection, medium risk: assessment before harvest to early identify symptomatic vines. Perform recutting of symptomatic vines as well as adjacent vines (if there is spread by foci of wood diseases symptoms).
Strategy 3 - low risk, high infection or medium risk, medium and high infection or high risk, low and medium infection: same strategy as strategy 2, but all trunks will be recut over one or two years.
Strategy 4 - high risk, high infection: prune very short in winter, decapitate all trunks in spring to recut all vines. Replace dead and missing vines, or those that could not be recut.

Results of this technique

The presence of shoots at the base of the trunk is a key factor for the success of a recutting strategy, and depends on several factors:

The grape variety: some varieties are not suitable for recutting because they produce too few shoots.

Examples of suitable varieties: Colombard, Merlot, Gewurztraminer, Auxerrois Examples of unsuitable varieties: Ugni Blanc, Riesling, Portugieser…

The training system: chemical shoot thinning is not favorable to shoot regrowth. Likewise, very rigorous shoot thinning every year is not favorable to the development of buds sprouting from old wood.
Age of the vines: the younger the vine, the more shoots it produces. With age, the number of dormant buds at the base of the trunk decreases. It is therefore better to consider recutting on not too old vines. On vines less than 20 years old, results are very good.

Helping the vine produce shoots at the base of the trunk

If buds are present at the base of the trunk, it is possible to help them burst by removing excess bark covering them and making a superficial notch (2 mm deep over 3-4 centimeters long at the base of the trunk).

Cost

Part of the economic losses related to symptoms of wood diseases can be compensated by implementing techniques that limit damage, such as recutting for example. Overall, implementing preventive techniques to combat wood diseases is profitable. Indeed, using preventive techniques early allows to extend the profitability period of a plot. The cost of techniques used to sanitize or prevent wood diseases on a vine (recutting, regrafting…) will always be lower than the cost of replacing the plant. The earlier preventive techniques are implemented, the greater the long-term benefit will be. The profitability of recutting depends notably on the price of wine and the remaining years of production of the plot. Recutting is justified if the plot's lifespan is at least another ten years, if the wine price is above €0.8 per liter, and if the recutting success rate is above 20%. When recutting works with 60% success (symptomatic vines becoming asymptomatic), the cost of recutting is €3/vine. Replacing a vine by a replant costs €9.

Sources

This article was written based on the PDF document: "Vine recutting: A practice applied in the field to limit damage caused by wood diseases" published within the framework of the National Vineyard Decline Plan.

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