Chemical weed control in seedbed sown onion (Allium cepa L.)

Chemical control of weeds in seedbed sown onion (Allium cepa L. cv. Geza 20) and the effect of different herbicides on onion seedlings and weed growth were investigated in two field experiments conducted at the central Jordan Valley during the 1998/1999 growing season. Weed competition reduced average onion fresh yield by 62% compared with the weed-free control. Out of 14 herbicides tested in 16 treatments, oxadiazon at a dose of 0.75 kg ai ha−1 and oxyfluorfen at 0.6 kg ai ha−1, both applied as pre-sowing and post-emergence to onion seedlings resulted in the highest seedlings yield and the lowest weed biomass. Post-emergence application of both herbicides gave a similar yield of onion seedlings to that of the weed-free control. Paraquat at 20 g ai ha−1 significantly increased yield of onion seedlings over the weed-infested control and other herbicides tested. Many of the herbicides used including pronamid, prometryn, methabenzthiazuron, diphenamid, metribuzin and pyrazon were phytotoxic to seedbed sown onion in both sites and reduced seedlings growth and stand below the weed-infested control. Oxadiazon in pre-sowing and oxyfluorfen in post-emergence application were the best in controlling many “hard to kill” weeds including Chenopodium murale, Malva sylvestris, and Cyperus rotundus, and in increasing seedlings yield, while oxyfluorfen in a post-emergence application treatment was the best of all herbicides used.