Shikimic Acid Accumulation in Field-Grown Corn (Zea mays) Following Simulated Glyphosate Drift

Field studies were conducted in 2001 through 2003 to determine if shikimic acid accumulation could be used to accurately predict yield reductions in field corn exposed to sublethal rates of glyphosate. Glyphosate (0-0.32 kg ae/ha) was applied to corn at the V6 to V8 growth stage. Corn whorls were randomly collected up to 14 days after application (DAA), and shikimic acid accumulation in the whorls was determined using HPLC-UV. Maximum shikimic acid accumulation occurred 3-7 DAA in corn receiving 0.16 and 0.32 kg/ha. Shikimic acid accumulation 3, 5, and 7 DAA did correlate (r = 0.80-0.86) to yield losses from a sublethal application of glyphosate. Shikimic acid accumulation 3, 5, and 7 DAA was better correlated to visual injury at 14 DAA than to yield reductions. Visual injury ratings 14 DAA were a slightly better indicator of potential yield losses (r = 0.93) than shikimic acid accumulation in field-grown corn whorls (r = 0.8-0.86).