Combining chemical and mechanical weeding in wheat

The European Union wishes to reduce by 50% the use of phytopharmaceutical products by 2030, including herbicides. It implies therefore to adapt weed management strategies in cultivated crops. Among the possible levers, with the technical and technological development, mechanical weeding is again becoming very popular. In particular, different tools can be used in cereal crops, including harrow or rotary hoe. In this context, an experiment aiming to assess different weed control strategies on soft wheat crop was implemented over three consecutive years (2018-2021). The objective was to evaluate to which extend it is possible to reduce herbicide quantities when mechanical control iss applied. The experiment was built on a split-plot design with three factors: (i) mechanical weeding, (ii) herbicides and (iii) rate of herbicides. Mechanical weeding consisted of 0,1,2 and 3 passes of harrow applied during the tillering phase (at regrowth after winter period), at stem extension (Z30) and f
irst node (Z31). In addition, a pass of rotary hoe at the tillering stage and a pass of rotary hoe at the tillering stage coupled with two passes of harrow (the following day of rotary hoe and at stem extension (Z30)) were applied. Regarding the use of chemical herbicides, grass- and dicot-weeds control agents were separately applied and also different rates of herbicides were applied (zero, half and full dose). Quadrats of 0.5 × 0.5 m were marked out to record the number of weeds and to identify them down to the species level before and after every weeding event. Additionally, in 2021, weeds and crop biomass were measured at the flowering stage of wheat. Results showed that mechanical weed control did not significantly reduce grass weed populations. On a dicot type flora, the mechanical weed control treatment combining one pass of rotary hoe with two passes of harrow seemed to result in the highest weed reduction among mechanical treatments (-48±19% compared to the con
trol without regulation which exhibited an increase of +12±16% between the first and last measurement in 2020-2021). However, mechanical weeding did not reach out the efficacy of chemical weed control, which appeared to reduce weed numbers by 55-85%. In order to avoid the use of broadleaf weed herbicides in the long term, improved efficacy of mechanical levers is required. Other combinations of chemical and mechanical weed control will be also tested in the future.