Multiple Applications of Reduced-Rate Herbicides for Weed Control in Onion

Abstract

Field experiments were conducted at Oakes, Absaraka, and Tappen, ND, in 2006 and repeated at Oakes and Absaraka, ND, in 2007 to evaluate early season weed control of common lambsquarters and redroot pigweed in onion with POST herbicides applied at multiple reduced rates (microrates) and to determine whether microrate herbicide treatments effectively reduced early season broadleaf weed competition, caused crop injury, or affected yield. Application rates of bromoxynil, oxyfluorfen, metribuzin, and acifluorfen were reduced to 0.25, 0.13, and 0.06× of their lowest labeled rate and applied in sequential applications (every 7 d) either two or three times. The 0.25× rate of bromoxynil (70.1 g ae/ha) provided the greatest control of common lambsquarters (95%). The 0.25× rates of bromoxynil and oxyfluorfen (70.1 g ai/ha) provided the greatest control of redroot pigweed (93 and 85%, respectively). Microrate applications of metribuzin or acifluorfen did not effectively control common lambsquarters or redroot pigweed. In 2006, no onion injury was observed. However, in 2007, applications of oxyfluorfen resulted in approximately 15% injury, regardless of the herbicide rate or the number of applications. Plants outgrew symptoms by 4 wk after treatment and were similar to the untreated plants. Onion treated with oxyfluorfen had the greatest total yield, followed by onion treated with bromoxynil. Onion treated with acifluorfen had a greater total marketable bulb yield than onion treated with metribuzin, but yield was considered poor compared to the other herbicide treatments. Three microrate applications provided greater weed control and increased yield compared with two applications across herbicides and rates. Results suggest that microrate applications of bromoxynil and oxyfluorfen will provide early season broadleaf weed control in onion.

Strip Tillage and Early-Season Broadleaf Weed Control in Seeded Onion (Allium cepa)

“…The lack of onion grade and yield differences among herbicide treatments suggests that even though the post-emergence herbicide treatments generally provided better early-season broadleaf control compared to the pre-emergence treatments, this did not compensate for the additional costs associated with multiple spray applications and the increased weather risk associated with the need for four timely spray applications. The lack of onion grand and yield differences among herbicide treatments were contrary to those reported by Loken and Hatterman-Valenti [11], but do reinforce the importance of weed control at the onion two-and three-leaf stage (mid-season herbicide application) and prior to the onion bulbing stage.…”

“…This is further complicated when a barley companion crop is planted as previously described. Recent research has shown effective early-season broadleaf weed control can be achieved by applying post-emergence (POST) herbicides at regular intervals as micro-rates when broadleaf weeds are in the cotyledon to first-true-leaf stage [11]. These applications have been effective in standard tillage systems, but have not been tested in strip tillage systems.…”

Managing Weeds with Reduced Herbicide Inputs: Developing a Novel System for Onion

“…Onion treated with oxyfluorfen (high rate, three applications) had the greatest large-grade and total yield, although total yield was similar to the yield with DCPA (Table 5) (Loken and Hatterman-Valenti, 2010). There was an herbicide by environment interaction for large-grade onion yield, which was attributed to the yield fluctuations in bromoxynil treatments due to common purslane (Portulaca oleracea) competition.…”

“…The high rate of bromoxynil (70 g/ha) applied twice or three times provided the greatest early season control of common lambsquarters (Table 4) (Loken and Hatterman-Valenti, 2010). The similar control between two and three weekly applications suggested that ideally, the producer would have seen that there wasn't an additional weed flush after the second week, thus would not have made the third application.…”

“…Effect of micro-rate herbicide treatments averaged across five locations on common lambsquarters and redroot pigweed percent control 2 weeks after the standard herbicide application to onion at the two-leaf stage. Adapted from Loken and Hatterman-Valenti, 2010.…”