The work of IFV shows that although certain alternatives to herbicides, such as glyphosate, are possible and even effective, they have technical and economic consequences for farms. A demonstration.
Anticipated consequences of glyphosate withdrawal.
Chemical in–row weed control is often based on a strategy that combines systemic, post-emergence products with pre-emergence products. This allows a large proportion of the flora to be kept under control with little intervention and at reasonable cost. Since the withdrawal of the Marketing Authorization (MA) for amitrole in December 2015, glyphosate is the only systemic post-emergence herbicide. Should this be withdrawn, strategies using only foliar weed control would not be sustainable, especially with regard to the emergence of plant cover in early spring. In this case, we can envisage either mixed strategies or a complete halt in the use of herbicides. IFV has assessed the alternatives available to winegrowers to establish where they stand technically and economically.
What alternatives are available?
Alternatives to chemical weed control are tillage, various thermal solutions, the use of biocontrol products, and electricity. The common characteristic of these alternatives is that they only act on the leaves of the targeted weeds, which means their effect is less long-lasting and repeated intervention is required. Only electrical weeding devices, prototypes of which are being tested by IFV, enable the entire root system to be acted upon: they create an electric arc that passes through the plant from the leaves to the roots. Thermal weeding techniques, while effective, require a lot of energy and time. They are more suited to superficial soils which are sensitive to erosion and where mechanical weeding is undesirable. Biocontrol (nonanoic acid) has the advantage of being easy to use compared with conventional herbicides, but effective application of it is technically demanding (climatic conditions, spray quality, young weeds). It is too costly to be used alone all year round, but can be used as a complement to in-row weeding. The most suitable alternative technique as it stands is therefore mechanical weeding, the difficulty of which must be taken into account.
What would be the economic consequences for the farms?
Adding alternative techniques into vineyard maintenance routines increases work times because tillage requires precise work around the vine trunk, at a much lower speed than for the application of herbicides, and with a higher frequency of intervention. In-row equipment is technically complex (settings, etc.) and requires training to avoid damaging the vines or mechanical breakage. Finally, agronomic impacts are to be expected because in most cases a return to tillage, however superficial, interferes with the root network. It is estimated that between 10 and 15 hectares can be managed by mechanical weeding with one tractor-tiller-driver unit dedicated to these operations. To weed larger areas, the solution is to combine hoeing the row as much as possible with other work such as trimming, mowing, etc. To make this possible, it is best to use a side-mounted frame, which frees up the 3-point linkage at the rear of the tractor. This eliminates the specific costs of the time needed for in-row weeding. Simplified tools such as clod-breaking rotary tillers provide a very high work rate.
In conclusion, there are effective alternatives in terms of efficiency, but they have a high cost, including that of training, which should not be neglected. Electricity is a promising avenue to explore in the years ahead because of its mode of action on weeds.
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