Efficacy of directed post-plant herbicide application with a shielded nozzle for control of weeds in onion

Weed weights at 30 DAT were all significantly lower than those in unweeded plots of the treatments, the highest weed weights and poor weed control efficacy were obtained from plots treated with glyphosate applied at 2 weeks after planting with no follow-up hand weeding (treatment 2). Lowest weed weights and greatest weed control efficacy were obtained from plots treated with two herbicides and two handweedings (treatment 1), interrow cultivation (treatment 3) and stale-seedbed treatment (treatment 5). Adequate weed control was obtained from plots treated with glyphosate applied at 3 weeks after transplanting with one follow-up handweeding (treatment 4). Crop yields in plots with glyphosate applied with a shielded nozzle at 3 weeks after transplanting and followed by one handweeding (treatment 4) were comparable to yields of plots treated with farmers' practice of two herbicides and two hand weedings, interrow cultivation and stale-seedbed plots. Highest yields were obtained from plots treated with stale-seedbed technique, confirming results obtained from studies on this treatment conducted in previous years. Lowest weed control costs were obtained from plots treated with postplant glyphosate application with a shielded nozzle. Because of lower weed control costs, net income obtained from plots treated with glyphosate at 3 weeks after transplanting and followed by one handweeding were higher than net incomes from plots treated with interrow cultivation and comparable, but lower than, net incomes from plots treated with farmers practice of two herbicides and two handweedings. Highest net incomes were obtained from the stale-seedbed treated plots. Low yields and negative net income from plots treated with postplant glyphosate at 2 weeks after treatment with no follow-up handweeding were due to poor weed control during mid season. Apparently, this treatment controlled weeds early in the season but did not provide adequate control throughout the rest of the cropping season.