Grafting is a thousands-year-old practice which was used ever since Roman times, and illustrated in the Georgics and by Columella and Varrone. In the XIV century, Crescenzi explained how it could be used to replace cultivars, and also to have wild varieties bear fruit or bring forward the fruit-bearing process.
In viticulture grafting is an irreplaceable practice in producing two-part plants which are resistant to phylloxera. Only two versions are used: the bench graft performed in the nursery and followed by forcing, and the field graft performed on rootstock.
Bench grafts are defined as whip and tongue, omega and multiple notch grafts. They are easy to perform, and as they are followed by forcing they offer high returns.
In the ‘80s grafting began to be used on plants in production with the intention of changing the cultivar or replacing clones which had been shown to be unsuitable in achieving objectives.
The grafts carried out on adult vines can be with dormant or vegetative buds depending on the moment in which the scions are collected. There are four types of graft carried out in the field.
Carried out on “wild” rooted cuttings planted in autumn or spring. The double cleft graft is used: the best time is the end of August, when semi-woody scions are collected and grafted immediately.
A double cut in the wood forms the saddle in which the suitably stained scion sits.
Raffia is used to hold the graft in place, with sealing occurring over the following days. If environmental conditions are favourable, the yield is very high, and there is no danger of detachment.
If practised on adult plants, this can be affected by the environmental conditions. Cold spells can be a challenge, and at times it can be subject to detachment, even several years after its execution.
If practised correctly in early spring on seedlings with the same or a slightly larger diameter than the scions, it offers satisfactory, long-lasting results.
The T-Bud graft
This technique is used on adult plants, and it offers a very high rooting percentage due to the degree of contact between the cambia of the scion and the stock.
The period in which it can be performed is very short, lasting approximately 40 days around flowering.
Expert hands and eyes are required to cut the bud correctly and place it in the most effective position. The graft must be tied using tape with the correct tension in order to help the bud take.
Chip Bud graft
This is unquestionably the technique which requires the greatest experience, but at the same time it offers the best results in terms of growth.
The technique can be used starting from two months after bud burst, and it adapts well to smaller sizes, such as renewal spurs.
It is complementary to the previous technique, and good grafters know how to choose which one is best suited to each single plant.
Financial and Regulatory Aspects
The practice is permitted under the regulations governing the sector, which allow a grafted vineyard to enter into production the following year with 70% of the maximum yield. There are no constraints relating to clones, while all the varieties provided for regionally and by the regulations can be used.
The change is subject to certification by the agricultural authorities, who must receive the application 30 days before the work is carried out, and must be informed on conclusion of the work.
The cost-effectiveness can be clearly seen by comparing top-grafting with uprooting and replanting, considering that the unproductive period in the case of the former is just one year, while in the case of the latter it is two years.
The removal of an existing vineyard and the replanting of a new one entails a two or three-year loss of production, and the cost of removing posts, wires and old plants, and of materials and labour involved in returning to production.
The cost of the top-graft includes a one year loss of production, the work involved in executing the graft, and running costs.
In terms of both cost and production, the second year after grafting - when production is limited under the regulations to 70% - can be considered equivalent to the third year after replanting.
The cost of top-grafting is therefore around 35% of the cost of uprooting and replanting.
With top-grafting you can:
change cultivar or clone rapidly, losing just one year of production;
obtain plants which are immediately balanced and able to produce wines with high quality potential;
change the pruning and training system over a short period of time;
rejuvenate old stock, excluding the distal side of the vine-stock which is no longer functional due to the necroses resulting from renewal cuts;
adapt clones to the environment and requirements;
keep the plant alive in the event of a failed graft, with the possibility of regrafting;
maintain perfect continuity between the vessels of the scion and the trunk, meaning no detachment after-effects;
obtain plants which are mechanically stable and suitable for harvesting mechanically.