Soybean and tobacco response to sublethal rates of herbicides used along roadsides

Abstract Herbicides are one of the primary tools for vegetation management along roadsides. However, the drift of particles and vapors from herbicide applications along roadsides can cause damage and yield loss in adjacent sensitive crops. The objective of this research was to investigate the response of soybean [ Glycine max (L.) Merr.] and tobacco ( Nicotiana tabacum L.) to sublethal rates of five herbicides [sulfometuron‐methyl, indaziflam, triclopyr, triclopyr + clopyralid, and 2,4‐dichlorophenoxyacetic acid (2,4‐D) + dichlorprop] commonly used along North Carolina roadsides. Each herbicide was applied at four rates (0.01×, 0.05×, 0.10×, and 1× of the field rate) and at six different timings (18, 12, and 6 weeks before planting or transplanting, at planting or transplanting, and 4 and 8 weeks after planting or transplanting). Field studies were conducted at the Sandhills Research Station near Jackson Springs, NC, in 2022 and 2023. In soybean, triclopyr applied post‐planting caused the greatest injury and yield loss, up to 100% when applied at the full dose (1×), while indaziflam was most damaging at or before planting. In tobacco, triclopyr followed by 2,4‐D + dichlorprop applied post‐transplanting caused the greatest injury and height reduction, whereas indaziflam caused mild visual injury (≤28%) and minimal height reduction across all timings. Crop damage generally increased with rate; however, injury, height reduction, and yield loss were occasionally observed even at the lowest rate (0.01×). These findings demonstrate that herbicides commonly used for roadside vegetation management differ in their potential to injure soybean and tobacco crops, underscoring the importance of informed and cautious herbicide selection to minimize the risk of off‐target injury when these crops are grown near roadsides.