Field trials were conducted to evaluate the effect of planting configurations (raised bed and no bed) and reservoir tillage on onion (Allium cepa) yield and grade when a cereal grass or cool-season broadleaf species was used as a companion crop. Total onion yield, the number of plants harvested, percentage of single centers, and cull-sized bulb yields did not differ among planting configurations. However, planting onion seed in raised beds with reservoir tillage resulted in more large-diameter bulbs compared to planting without a bed configuration. Raised beds also had fewer small-sized bulbs than the non-bed configuration. Companion crop influence on onion yield and grade varied among environments (location plus year). In general, canola (Brassica napus) as a companion crop increased the yield of small-sized bulbs and decreased total yield and the yield of large-sized bulbs. These results were attributed to poor canola control from the initial bromoxynil plus oxyfluorfen application because each label restricts application until onions have reached the two true-leaf stage. Onion yield and grade with barley (Hordeum vulgare) as a companion crop was similar to that of onion with no companion crop except during 2002 (Carrington) when rain delayed the postemergence grass herbicide application and lowered onion yield.
Field studies were conducted at Absaraka, Carrington, and Oakes, N.D., in 2005 to evaluate early season broadleaf weed control and onion (Allium cepa L.) injury with herbicides applied preemergence to the crop. DCPA is a common preemergence herbicide used in onion. However, DCPA can be uneconomical in most high-weed situations, or the usage may be restricted due to possible groundwater contamination. Potential substitutes evaluated were bromoxynil, dimethenamid-P, and pendimethalin. Main broadleaf weeds were redroot pigweed (Amaranthus retroflexus L.) and common lambsquarters (Chenopodium album L.). In general, all herbicides, except bromoxynil, provided acceptable broadleaf weed control 4 weeks after treatment. The highest herbicide rate provided greater weed control compared with the lowest rate for each herbicide. However, onion height was also reduced with the highest herbicide rate. In addition, the two highest rates of dimethenamid-P reduced the onion stand compared with the untreated. A postemergence application of bromoxynil + oxyfluorfen + pendimethalin to onion at the four- to five-leaf stage controlled the few broadleaf weeds that escaped the preemergence treatments and provided residual control of mid- and late-season germinating broadleaf weeds at two of the three locations. Intense germination of redroot pigweed during July at the Oakes location reduced onion yield with all treatments compared with the hand-weeded check. In contrast, total onion yields with all herbicide treatments except the high rate of dimethenamid-P were similar to the hand-weeded check at Absaraka and Carrington.