Soybean plants exposed POST to 2,4-D can have reduced seed yield depending on the dose and time of exposure, but it is unclear how 2,4-D affects specific yield components. Objectives were to quantify soybean injury, characterize changes in seed yield and yield components of soybean plants exposed to 2,4-D, and determine if seed-yield loss can be estimated from visual assessment of crop injury. Ten rates (0, 0.1, 1.1, 11.2, 35, 70, 140, 280, 560, and 2,240 g ae ha−1) of 2,4-D were applied to Becks brand 342 NRR soybean at three soybean growth stages (V2, V5, or R2). The soybeans were planted near Lafayette, IN and Urbana, IL in 2009 and 2010 and near Fowler, IN in 2009. Twenty percent visual soybean injury was caused by 29 to 109 g ha−1 2,4-D at 14 d after treatment (DAT) and 109 to 245 g ha−1 at 28 DAT. Nonlinear regression models were fit to describe the effect of 2,4-D on seed yield and yield components of soybean. Seed yield was reduced by 5% from 87 to 116 g ha−1 and a 10% reduction was caused by 149 to 202 g ha−1 2,4-D at all application timings. The number of seeds m−2, pods m−2, reproductive nodes m−2, and nodes m−2 were the most sensitive yield components. Path analysis indicated that seeds m−2, pods m−2, main stem reproductive nodes m−2, and main stem nodes m−2 were the most influential yield components in seed-yield formation. Seed-yield loss was significant (P < 0.0001) and highly correlated (R2 = 0.95 to 0.99) to visual soybean injury ratings. A 10% seed-yield loss was caused by 35% soybean injury observed at 14 DAT, whereas a 10% seed-yield loss was a result of 40, 19, and 15% soybean injury observed at 28 DAT when soybean was exposed to 2,4-D at the V2, V5, and R2 growth stages, respectively.
Nomenclature: 2,4-D; soybean, Glycine max (L.) Merr.