The aims and objectives of the topping interventions
There is no doubt that one of the most important summer operations in the vineyard is the topping of the shoots. The trimming of the vineyards can be carried out in three large phases: in the pre-floral, in the herbaceous berry and in the ripening of the berries. In the first phase (prefloral), the topping has the purpose of reducing the glucidic antithesis between the shoots and the flowers, and thus allows a regular enlargement, especially in the vines subjected to dripping. In the second phase, the topping is used to reduce the interference of the shoots and the hares, so as to pass more easily into the rows and allow to hit the bunches more easily with the anti-parasite products. In fact, the abundance of the feminine and shoots has negative repercussions in the development of the bunches. In the third phase of berry ripening, the topping is intended to allow the bunches to receive an abundant amount of light (it is essential above all for northern red wines). As a result, it partially replaces the flaking.
The geometry of the cut: monofilary and two-wire toppers
In the topping operation the ratio between the number of leaves and the bunch, or, better, between the surface of the leaves and the bunch should be respected. Consequently, 5-7 leaves must be left above the last bunch, which is not easy to achieve by trimming machines. Trimming manually, however, requires the use of labor estimated at around 30-40 hours per hectare, while the use of machines reduces times to 1-4 hours per hectare. Various types are available on the market, which are divided between two-wire and single-row machines, depending on the geometry of the cut. In fact, in the first case the trimming machine can operate simultaneously on the opposite sides of two adjacent rows: this implies a double productivity compared to single row machines, but it is also true that often the slope of the ground makes it impossible to use two-wire machines. For this reason, unilateral machines are more widespread in Italy than bifilar.
Cutter bar and shears with scissor blades
A second classification can be made based on the cutting system. The cutter bar machines, for example, are based on reciprocating motion blades. For reasons of lightness of compactness, generally one of the two elements is fixed while the other is moved by a crank rod system. In other cases, the moving blades run on a guide to which the counter knives are fixed. The major drawback of the system is caused by a certain tendency to refuse vegetation by folding it backwards while the trimming machine advances. For this reason the feed speed cannot be high (2-4 km / h). On the other hand, in models with scissor blades, four or more knives remain fixed and radially oriented while two rotate. The particular positions of the latter means that a scissor cut effect is created between the fixed and rotating knives. The advantage of this system is the total absence of the phenomenon of rejection of the vegetation that allows high speeds of progress (4-8 km / h).
Trimming machines: rotary knife toppers and accessories
While in the previous systems the cutting of the shoots was entrusted to the insertion of the same between two parts in relative movement with each other, in the case of the trimmers with rotating knives there is no element of contrast. The need to keep the shoot in position during cutting is entrusted to the rigidity and inertia of the same, also in relation to the very high rotation speed given to the knives. The type of cut thus made is the least satisfactory one. In fact, if in the first two systems the presence of a striking pattern causes the net cut of the shoots (an important factor for its rapid healing), using machines with rotating knives there are much higher percentages of frayed cuts. The advancement speed of these machines is around 5-6 km / h. A recently introduced accessory is a packer consisting of swivel rubber arms arranged horizontally under the cutting elements: it has the function of conveying the falling, more internal vegetation, in the area of action of the blades.