|Felix, Joel -|
Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 29, 2011
Publication Date: October 1, 2011
Citation: Felix, J., Boydston, R.A. 2011. Potato (Solanum tuberosum) response to simulated glyphosate drift. Weed Technology. 25:637-644. Interpretive Summary: Since glyphosate resistant crops were launched in 1996, glyphosate use has been increasing dramatically in the United States. In the Pacific Northwest, glyphosate is applied directly to tolerant crops including alfalfa, corn, and sugar beet. Glyphosate is also used pre-plant as a burn down weed treatment early in the season before planting numerous crops. Non-crop uses include applications to control weeds along ditch banks and fence lines throughout summer. Large numbers of fields planted to glyphosate resistant crops and multiple applications of glyphosate during the season increases the chance of accidental drift to susceptible crops. Off-target movement of herbicides during application may cause considerable injury to susceptible plants. The objectives of these studies were to determine injury, symptomology, chemical changes in the potato plant, and tuber yield reduction in response to simulated glyphosate drift when applied at different doses (simulating drift) and four potato growth stages. Potato foliar injury was greatest when low dose simulated drift rates of glyphosate were applied in the stolon hooking stage of potato growth (just prior to tuber initiation). The least foliar injury was observed when simulated drift rates of glyphosate were applied at the tuber bulking stage of potato growth. Potato yield and quality decreased as foliar injury and shikimic acid accumulation (measured at 1 week after glyphosate applications) increased. Potato tuber yields were least when glyphosate was applied at stolon hooking and tuber initiation stages of growth. Measuring shikimic acid accumulation in potato foliage at one week after a suspected glyphosate drift incident could be used as a predictor of potential tuber yield loss.
Technical Abstract: Field studies were conducted in 2008 in Ontario, OR and Paterson, WA to determine the effect of simulated glyphosate drift on 'Ranger Russet' potato injury, shikimic acid accumulation, and tuber yield. Glyphosate was applied at 8.5-, 54-, 107-, 215-, and 423 g ae ha-1; which corresponds to 0.01, 0.064, 0.126, 0.254, and 0.5 of the lowest recommended (846 g ha-1) single application dose for glyphosate resistant corn and sugar beet. Glyphosate was applied when potato plants were at 10-cm height, stolon hooking, tuber initiation, or bulking stage. The greatest visual foliar injury was observed when glyphosate was applied at a dose of 54 g ha-1 or greater and potato plants were at the hooking stage. The lowest foliar injury was observed when glyphosate was applied to potato plants at the bulking stage. The I50 glyphosate dose at 42 DAT was estimated to be 167 g ha-1 for potatoes sprayed at the hooking stage. The corresponding glyphosate dose to result in 50% injury for potatoes sprayed at tuber initiation, 10-cm height, and bulking stages were 129%, 338%, and 438% greater than hooking stage. The U.S. No.1 potato yield was inversely related to vine injury and shikimic acid accumulation. Shikimic acid accumulation increased when glyphosate was applied at 107 g ha-1 or greater. U.S. No.1 potato yield was reduced by 46% and 84% relative to the untreated control (55 and 76 T/ha) when glyphosate was applied at 107 g ha-1 to plants in the hooking stage at Ontario and Paterson, respectively. Tuber yields at both sites were lowest when glyphosate was applied at hooking and tuber initiation stages.