Pruning in the vineyard: the suckering machine

Suckering consists of the elimination of unfruitful shoots. Although there is a chemical pruning technique, the most common technique adopted in vineyards is the one that includes the use of mechanical suckering machines, crucial tools for improving and speeding up operations

Suckering is one of the operations of green pruning usually done to manage the foliage of vines, which consists of the elimination of fruit-bearing shoots that start from the trunk, and in part, from the head of vines, commonly called suckers. These shoots grow on the old wood from the dormant buds or the shoots of the rootstock and exploit to their advantage the nutritional elements, which are instead useful for the growth of the fruiting shoots. Their uncontrolled proliferation would therefore risk dispersing most of the plant's nutritional potentialities. The control of suckers generated in the lower part of the trunk is an entirely mechanized operation which, according to the climatic trend, characteristics, and variety of the grape, is usually done between April and June. The best moment to act is when the shoots born from the latent buds of the trunk are still in the "vitreous phase", that is, they are not yet wholly lignified and have a length between 10 and 20 cm.

Although with most of the varieties, a single intervention is enough, with some of them (ex. Merlot), it is, however, necessary to intervene at least a couple of times a year. In any case, anticipating suckering too much usually means having to repeat it, as the plant would generate new suckers to replace the ones removed. On the contrary, postponing it when some of them have started to lignify would, in most cases, partially frustrate the success of the operation. Suckering also has a sanitary significance; in fact, it is now well established that suckers favor the onset of primary infections of cryptogamic diseases, such as especially downy mildew or black rot of the vine (also known as Black-rot). This is because primary infections usually start from an inoculum in the soil and the shoots at the base of the trunk are the most exposed during rainy periods.  As suckering is an essential operation for maximizing the plant's productive potential and facilitating the subsequent cultivation practices, nowadays, many manufacturers offer the winegrower different types of machinery capable of performing suckering in different ways. 

The traditional suckering carried out manually with scissors (nowadays mostly electric or pneumatic) and carts facilitators is the only one that allows operating simultaneously on the trunk and at the center of the plant. Unfortunately, the extreme slowness of its execution has a significant limitation that makes it quite expensive. For example, to remove the suckering from a hectare of Merlot vines with about 2500 plants present, it is necessary to employ an expert person for about 20-30 hours, and in these times, the availability of a good level of human resources is more and more a problem.  However, the benefits of this technique can be summarized in the great precision of the work carried out and the possibility of carrying out chequering simultaneously.

The alternative that ensures minimization of working time is suckering using chemical products such as glufosinate-ammonium, carfentrazone-ethyl, pyraflufen-ethyl, or pelargonic acid. Chemical suckers are quite a simple machinery, almost always equipped with a straddling frame (to operate simultaneously on both sides of the row) at the ends of which are fixed two or more pairs of nozzles enclosed in a containment casing to limit the drift of the sprayed product outside the casing. Its effectiveness is usually implemented using brushes or flexible vertical sheets placed at its base, which also allow the distribution on the suckers the product inevitably collected from the casing walls. The productivity of these pieces of equipment is really high. It is, in fact, common practice to proceed at 5-6 km/h, that is to say, to reach productivity, net of the maneuvers at the end of the field, even slightly higher than one hectare/hour (in vineyards with planting system at 2.5 meters).  Even though the last evolutions of these types of machinery are also equipped with systems to recover the product that has not been targeted and to reuse it without dispersing it in the environment, the use of chemical suckering is actually banned in the organic regulations and in any case not appreciated by many winegrowers. It also has the advantage, since it uses at the same time active herbicidal principles, of allowing in the same step also the carrying out of (chemical) weeding in the under-row. Instead, its limits are caused because it cannot be used on plants less than four years old.

The technique most often adopted in vineyards is the one using mechanical suckers, that is, machinery capable of drastically increasing the operator's productivity as opposed to manual suckering and being profitable even under the strict limitations of organic regulations. This is a relatively large family of machinery produced by many Italian manufacturers, whose marketing, however, began in France in the early 70s of the last century. The first models were machines equipped with two counter-rotating cylindrical brushes with a vertical axis, equipped with flagella made of flexible materials and operating at about 300/500 rpm. Later, there were also machines equipped with overhanging frames and models using rotors with a horizontal axis instead of the vertical axis.  On the other hand, the type of flails used is different, but they all have in common the high flexibility of the materials necessary to minimize damage to the vine shoots.  In order to carry out an accurate job, it is common practice to work in the field with this machinery at speed between 2 and 4 km/h, from this it derives productivity which in the same conditions already considered above is from a little less than 0.5 ha/h up to a little less than 1 ha/h.

Whether it is a mechanical or chemical suckering, in both cases, it is not possible to avoid a subsequent manual finishing work, whose entity in vineyards with about 2500 plants/hectare is estimated around 4-8 hours/ha, with the highest values to be attributed to cases where it has been previously operated with chemical suckering. In this case, it is sometimes necessary to manually remove the basal shoots dried by the active ingredient used but which still remain physically stuck to the trunk.  It is therefore clear that, in general terms, the wide gap in productivity between the two methods should be slightly adjusted downwards. It should also be noted that for breeding systems such as the GDC, there are suckers that offer a suckering kit with an additional hydraulic tilting roller to clean the high bending of the stump. This is extremely useful to reduce, and sometimes even eliminate, the need to complete the operation manually.

Anyway, to make a wise choice, it is essential to consider the various characteristics of each machine, since according to the rotation systems or the materials used, the cost of suckering can change substantially because of the necessary periodical replacement of the materials subject to wear. Furthermore, it is also important to evaluate the actual hydraulic requirements since these are rather demanding tools from this point of view.  Therefore, it is important to choose a machine that best suits the tractor already existing on the farm to try to avoid (when possible) having to purchase a machine with its hydraulic power unit operated by a cardan shaft. It is, therefore, necessary to know in the first place the requirements in terms of the hydraulic capacity of the suckering machine, that is, how many liters of oil per minute it needs to provide its maximum performance. Then, it is necessary to verify that the tractor distributors are actually able to provide this capacity.  However, it is necessary to pay a lot of attention when making this check and also contact the manufacturer or the dealer of your choice because the data declared by the manufacturer, i.e., the maximum flow rate of the hydraulic pump, do not always correspond to the flow rate actually available from a single distributor. Moreover, it would be better to check that the required flow rate is available at a lower engine speed than the maximum one (the speed at which the declared flow rate is available), so that it is then possible to work in the field keeping the engine at partial speed, with all the advantages that this entails in terms of consumption, noise and tractor wear. Typically, mechanical suckers use a supporting frame made of steel and/or aluminum, which, using hydraulic adjustment devices, allows the machine to adapt to different working environments. Furthermore, compared to the first models of the '70s, nowadays, almost all of them are equipped with a protective cover that prevents the operator from being hit by processing residues.

For greater convenience, the suckering machines are preferably coupled to the tractor's front using anchor plates or are carried by the front lift. A particular commercial success has been achieved by models equipped with an overturned U-shaped frame, which enables the operator to work on both sides of the row simultaneously. However, models carried by the rear lift and operating in a rear-lateral position are also quite common, even if there are some models carried ventrally, which, being fixed to the central part of the tractor, allow to keep the center of gravity of the yard more central, and for this reason, they are appreciated in the most sloping areas.  As for chemical suckers, the use of mechanical ones is not recommended on young vines (less than 3-4 years old) because they could tear the stump when it is still not very woody.  In any case, to avoid debarking, it is advisable to use soft flails and to operate at a low speed.  Sometimes, to carry out combined operations, the suckering unit can also be mounted on the frame of harrows of different types, of milling machines, or machines for mowing. 

Mechanical suckers can be divided into two different categories depending on the operating principle on which they are based. In fact, there are those with vertical axis rotors and those with horizontal axis rotors.  Both have a hydraulically-controlled supporting frame, which is often overhanging and carries one or two rotors equipped with synthetic material flagella of various thicknesses and with different mechanical properties.  Usually, rotors are always hydraulically driven by the tractor, and the kinetic energy given to the scourges allows them to detach the suckers from the trunk. However, Horizontal-axis suckers have been introduced more recently. They allow an effective mechanical weeding action of the under-row but are less fit for certain types of farming.  However, the horizontal axis rotors also facilitate the coupling of the suckering machine to other machines for inter-row management, contributing to reducing the number of interventions necessary for the management of the vineyard and, therefore, to the decrease in the degree of soil compaction.

Hydraulic suckers, depending on the shape of the rotor frames, can be adapted to different forms of cultivation, including simple or double Cortina, Casarsa, high cordon, GDC (Geneva Double Courtain), low spurred cordon, Guyot, awning, and pergola.