Impact of Adjuvants and Nozzles on Palmer amaranth (Amaranthus palmeri S. Watson) and Waterhemp (A. tuberculatus (Moq.) J. D. Sauer) Control Using Mesotrione and Rimsulfuron + Thifensulfuron-Methyl

Abstract

Limitations on the available herbicide portfolio for weed control have led to weed control failures, while application techniques such as proper selection of nozzle types, adjuvants, and herbicide selection have been suggested as one of the ways to maximize efficacy. A greenhouse experiment was conducted at the Pesticide Application Technology Laboratory of the University of Nebraska-Lincoln located in North Platte, NE, USA. This study sought to evaluate the effects of mesotrione (MES) and rimsulfuron plus thifensulfuron-methyl (RIMTHIF) in tank mixtures with five adjuvants (ammonium sulfate – AMS, crop oil concentrate – COC, drift reducing adjuvant – DRA, methylated seed oil – MSO, and nonionic surfactant – NIS) sprayed with three different nozzle types, XR (Extended Range), AIXR (Air Induction Extended Range), and TTI (Turbo TeeJet Induction) on common waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer) and Palmer amaranth (Amaranthus palmeri S. Wats.) control. Applications were made when plants were 10-15 cm (14-16 BBCH) tall using a three-nozzle spray chamber (Generation 4 Research Sprayer; DeVries Manufacturing, Hollandale, MN, USA), calibrated to deliver 94 L ha-1 at 276 kPa. Following applications, plants were returned to the greenhouse for 28 days under the same growth conditions previously described. The aboveground biomass was harvested using clippers and oven-dried at 65 °C to constant mass, and dry weights were recorded. Selected nozzles did not influence efficacy. Adjuvant effect was significant for both species, while the interaction between herbicide versus adjuvant was significant for common waterhemp. Regardless of adjuvant, the highest biomass reduction (95%) was obtained by spraying MES associated with RIMTHIF, while herbicide pooled together provided 92% biomass reduction of Palmer amaranth. The MSO and NIS adjuvants provided biomass reductions of 98% and 97%, respectively. In general, all adjuvants increased the biomass reduction of common waterhemp in comparison to the solutions without adjuvant for MES and MES plus RIMTHIF herbicides. Conversely, RIMTHIF alone or associated with adjuvants produced the same biomass reduction, ranging from 91% to 96%. Our results suggest spraying tank mixtures of MES and RIMTHIF for successful Palmer amaranth and waterhemp control, whereas the MSO and NIS adjuvants can increase efficacy. Our results indicate possible alternatives to commonly used herbicide such as glyphosate, glufosinate, and dicamba for obtaining satisfactory weed control