Herbicides are the primary method used to control barnyardgrass  (Echinochloa crus-galli) in rice. As a result, this troublesome weed has evolved resistance to at least 9 modes of action globally and at least 7 modes of action in the United States. Loyant^TM is a new rice herbicide being developed by Dow AgroSciences which contains Rinskor^TM active, the second herbicide in a new structural class of synthetic auxins in the arylpicolinate herbicide family. This new herbicide provides broad-spectrum post-emergence control of broadleaf, grass, and sedge species at low use rates with an alternative mode of action for rice. A field experiment was conducted in 2014 and repeated in 2015 to evaluate potential plant-back restrictions for soybean following an application of Rinskor. The experimental design was a randomized complete block with a two factor factorial treatment structure comprised of Rinskor applied at 30 and 60 g ai ha^-1 at 56, 28, 14, and 0 days prior to planting soybean. The concentration of Rinskor acid in soil at the time of planting was determined by collecting 5 soil cores at a 15-cm depth in each plot at the time of planting and quantified in the laboratory using LC-MS/MS. Visual estimates of soybean injury were highest 21 days after planting when Rinskor was applied 0 days before planting.  These injury assessments corresponded to the highest concentration of Rinskor acid recovered from soil at the time of planting. Conversely, soybean injury was reduced when Rinskor was applied at increasing intervals before planting. By the end of season, soybean injured by Rinskor had not recovered and there was stand loss. Soybean yield was similar to the non-treated control when 30 or 60 g ha^-1 of Rinskor was applied 56 days prior to planting whereas all other treatments significantly lowered yield.  The replant interval following an application of Rinskor will likely be determined by several factors including soil moisture, amount of herbicide applied, and the crop selected for replanting. These results support a relatively short replant interval for soybean after Rinskor application compared to other herbicides commonly used in rice. It appears unlikely that there will be rotational crop restrictions when planting of soybean the year following a Rinskor application in rice.

 

^TMTrademark of the Dow Chemical Company (“Dow”) or an affiliated company of Dow. Loyant^TM is not registered with the US EPA at the time of this presentation. The information presented is intended to provide technical information only.