Mechanical intra-row weed control at early growth stages in medicinal and aromatic plants using the example of parsley (Petroselinum crispum (Mill.) Fuss) and lemon balm (Melissa officinalis L.)

Abstract

Weed control in medicinal and aromatic plants (MAP) is particularly challenging as many species have a low competitiveness at early growth stages. Intra-row (within the row) mechanical weed control is most challenging since crops may be damaged as well. Here we compared five different devices for mechanical intra-row weeding (finger, torsion and rotative weeders, tine harrow, ridger share) in lemon balm and parsley, focusing on the critical stage of crop establishment. In total, eight field trials were carried out in 2020 and 2021 at two experimental farms of the University Bonn in the west of Germany. The devices were tested in replicated trials after optimising the settings on test plots. Data on weed control efficacy (WCE) and crop damage were analysed with ANOVA. The average WCE was 66 % and had a high variability ranging from 0 % to 100 %. Tine harrows could be applied most often and at earlier growth stages, followed by finger weeder. Highest crop damage was noted after use of rotative weeder. Yield decreasing effects were only significant in two cases and tended to be lower in transplanted than in sown lemon balm and parsley. However, due to variable operating conditions a consistent ranking of weeding devices was not possible. We conclude that despite significant technical progress during the last two decades, a complete replacement of herbicides is difficult at present, unless weed control is carried out manually. Further research is needed to ascertain under which environmental and management conditions mechanical intra-row weeding is most effective in the field, and how these techniques can be best integrated with other weed control methods.