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United States Department of Agriculture

Agricultural Research Service

Research Project: SUSTAINABLE CROPPING SYSTEMS FOR IRRIGATED SPECIALTY CROPS AND BIOFUELS

Location: Vegetable and Forage Crops Production Research

Title: Response of direct-seeded dry bulb onion to simulated glyphosate drift with variable rates and application timings

Authors
item Felix, Joel -
item Boydston, Rick
item Burke, Ian -

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 2, 2012
Publication Date: December 1, 2012
Citation: Felix, J., Boydston, R.A., Burke, I. 2012. Response of direct-seeded dry bulb onion to simulated glyphosate drift with variable rates and application timings. Weed Technology. 26:747-756.

Interpretive Summary: Onions are grown in fields interspersed with glyphosate-resistant alfalfa, corn, and sugar beet. Consequently, glyphosate is the predominant herbicide used to control weeds in these crops. The proximity of onion fields to fields planted to glyphosate-resistant crops increases the potential for off-target injury. The objectives of these studies were to determine crop injury, shikimic acid, and yield response of dry bulb onion to simulated glyphosate drift applied at different doses and onion growth stages.Trials were conducted in 2011 at Ontario, OR and Prosser, WA. Glyphosate was applied at six doses simulating glyphosate drift when onion plants were at the flag-, 2-, 4-, and 6-leaf stages. Onion injury was directly related to the glyphosate dose and varied with application timing. Onion foliar injury increased sharply at 21 days after treatment when glyphosate was applied = 25.8 g ha-1 to plants at the flag- and 4-leaf stage, and ranged from 24 to 99%. Glyphosate was most injurious when applied to onions at the 4-leaf and flag stages. Severity of injury increased further when glyphosate was applied at = 86 g ha-1 and eventually resulted in plant death at 860 g ha-1. Foliar injury and plant height were inversely correlated to U.S. no. 1 onion yield. Onion injury and yield displayed severe sensitivity to very low glyphosate doses especially at the 4-leaf stage. Shikimic acid accumulation increased with the increase in glyphosate dose and was negatively correlated with foliar injury, plant height, and onion yield. Measurement of shikimic acid in onion one week following a suspected glyphosate drift incident could be a useful tool for confirming glyphosate drift.

Technical Abstract: Field studies were conducted in 2011 at the Malheur Experiment Station, Ontario, OR and Prosser, WA to evaluate the effect of simulated glyphosate drift on direct-seeded dry bulb onion. Glyphosate was applied at 8.6, 25.8, 86, 290, 434, and 860 g ae ha-1 when onion plants were at the flag-, 2-, 4-, and 6-leaf stages. Onion foliar injury was directly related to the glyphosate dose and varied with application timing. Foliar injury at 7 DAT ranged from 0 to 12% for glyphosate = 25.8 g ha-1. Foliar injury increased sharply at 21 DAT when glyphosate was applied = 25.8 g ha-1 to plants at the flag- and 4-leaf stage, and ranged from 24 to 99%. The I50 glyphosate dose at 21 DAT was lowest when onions were treated at the 4-leaf and flag stages and was estimated to be 76.8 and 81 g ha-1, respectively. Onion injury severity increased when glyphosate was applied at = 86 g ha-1 and eventually resulted in plant death at 860 g ha-1. Foliar injury and plant height at 35 DAT were inversely correlated to U.S. no. 1 onion yield. Onions displayed severe sensitivity to very low glyphosate doses especially at the 4-leaf stage. Shikimic acid accumulation increased with the increase in glyphosate dose and was negatively correlated with foliar injury, plant height, and onion yield.

Last Modified: 8/22/2014
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