Utilizing Silage Tarps, S-metolachlor, and Hand-Weeding for Weed Management in Transplanted Onions

Small farms play a crucial role in food security and agricultural diversity in the United States. Small-scale onion ( Allium cepa ) production faces unique challenges because of the crop’s susceptibility to weed competition. To address this concern, field trials were conducted at the Purdue Student Farm in West Lafayette, IN, USA, in 2023 and 2024 to investigate the effectiveness of silage tarps, S -metolachlor, and hand-weeding for weed management in small-scale transplanted onion production. The experiment tested tarping (tarped vs. nontarped) and S -metolachlor application frequency (zero, once, or twice) with or without hand-weeding. Tarping occurred after spring soil preparation, with tarp removal 5 weeks later and just before transplanting ‘Hamilton’ onions. S -metolachlor (1064 g active ingredient/ha) was applied at 2 and/or 4 weeks after transplanting (WATr), and hand-weeding was conducted at 7, 8, and 9 WATr. Tarping reduced early-season broadleaf weed emergence just after lifting the tarp compared with nontarped beds. Two S -metolachlor applications resulted in greater weed control compared with a single application when hand-weeding was not used. However, no additional benefits were observed with a second application when hand-weeding was used. Similarly, when hand-weeding was performed, there were no differences between one and two applications of S -metolachlor in end-of-season aboveground weed biomass (24 g/m 2 and 17 g/m 2 , respectively) or onion yield (7.52 kg/m 2 and 7.57 kg/m 2 , respectively). Tarping reduced early-season weed emergence, but the effects were transient. Tarping with herbicides and hand-weeding provided long-term weed control and maintained onion yield potential.