Assessment of the Integration of Mechanical Weeding for Weed Control in Sugar Beet-Growing

The aim of this research was to evaluate the potential of mechanical weeding for the cultivation of sugar beet by comparing four weed control programmes (one chemical, two mixed (chemical and mechanical) and one mechanical). Under the dry conditions of 2017, the mixed conditions displayed the best effectiveness (more than 97%), using less herbicide and costing €30/ha less than the chemical scheme, while producing a yield identical to that obtained with fully chemical protection. Conversely, the mechanical programme was ineffective (69%), especially on weeds in the crop row (23% effectiveness only); while its cost was lower (€180/ha), it led to a loss of sugar yield of 18.9% compared to chemical weed control. INTRODUCTION Plant protection products have a recognised impact on the environment (air, soil, surface water, groundwater and seawater pollution), and are toxic to varying degrees (Calvet et al., 2005). Herbicides are applied to plants at an early stage of development, and are therefore more easily transported to surface water and groundwater. According to the key indicators for the Walloon environment (DGARNE, 2014), pesticides are detected in twothirds of groundwater quality control sites, and the active substances found in higher concentrations are all herbicides. Representing 36,679 ha of land in 2016, beet is an important crop in Wallonia, but makes heavy use of pesticides (mainly herbicides): an average of 6.5 kg of active substances per hectare (Lievens and al., 2014). The control of weeds is essential in beet-growing, as the plant’s slow juvenile growth leads to strong competition from weeds which potentially has a significant impact on yields of up to 90%. More specifically, there are number of problems associated with the herbicide solutions used for beet-growing, including the appearance of resistance, in particular in fat hen (Chenopodium album) (Mechant and al., 2008) and spreading orach (Atriplex patula) (De Cauwer et al., in press), and the reduction of available active substances and authorised doses. In response to these problems, one solution for farmers is integrated weed management, in which various approaches to managing weeds are combined. In this context, mechanical weeding is a clearly identified technique which has benefited in recent years from developments which facilitate its implementation, such as camera or GPS guidance, increased working widths and the introduction of equipment for working on the crop row itself. Trials have shown that it is possible to control weeds in integrated systems combining mechanical weeding and phytosanitary treatment, even for beetgrowing, which is highly demanding in terms of weed competition (ITB, 2011, Kunz et al., 2015). However, problems remain due to lack of flexibility in the application of treatments, observed crop losses and lack of effectiveness (Pottier M., 2012; Colomb et al., 2011; ITB, 2011). Questions may be legitimately asked about the cost of implementing these practices. The available studies show variable results depending on