Changes in Soybean Yield Components in Response to Dicamba

CORE IDEAS: Dicamba off‐target movement to sensitive soybean is a major concern. Soybean has the ability to compensate through increased branching when exposed to dicamba during the vegetative growth stage. The reproductive growth stage of soybean was the most sensitive growth stage to dicamba off‐target movement. Yield predictions were greatly improved using measured growth parameters. Soybean [Glycine max (L.) Merr.] containing a genetic trait that confirms resistance to dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) has provided growers with an alternative method of control for broadleaf weeds that are resistant to Group 9 and 14 herbicides. These applications of dicamba have resulted in significant off‐target movement and injury to susceptible soybean. Soybean plants can exhibit dicamba symptoms on leaves in the upper canopy and the terminal bud, leaf petioles, stems, and pods. Using symptoms of leaf cupping or leaf crinkling to forecast yield loss may cause unnecessary concern and place growers in a predicament in regard to the economic value of crop inputs for the remainder of the growing season. With regard to soybean yield components, exposure to 0.6 g ha⁻¹ dicamba reduced main stem height 47% for V3–V4 and 11% for R1–R2. The reduction in main stem height for 0.6 g ha⁻¹ dicamba resulted in a 53% reduction in main stem pod production compared with the nontreated control for the V3–V4 application timing, but only 11% reduction for the R1–R2 application timing. Main stem height reduction was observed for 0.6 g ha⁻¹ dicamba at V3–V4, but was accompanied by an increase in the number of lateral branches and lateral branch pod production. With seed per pod unaffected by dicamba, total seed production and yield following 0.6 g ha⁻¹ dicamba at V3–V4 was equivalent to the nontreated control. At higher dicamba rates, seed yield reduction was attributed to production of fewer nodes and seed per plant.