Adjuvant and nozzle effects on weed control using mesotrione and rimsulfuron plus thifensulfuron-methyl

Abstract

Limitations on the available herbicide portfolio for weed control have led to weed control failures. Application techniques such as proper selection of nozzle types, adjuvants, and herbicide selection have been suggested as one of the ways to maximize efficacy. The launch of HPPD (hydroxyphenylpyruvate dioxygenase)-tolerant crops will increase HPPD herbicide applications, while effective herbicide tank mixtures might prolong herbicide resistance evolution. Therefore, a greenhouse experiment was conducted to evaluate the effects of mesotrione (MES) and rimsulfuron plus thifensulfuron-methyl (RIMTHIF) in tank mixtures with five adjuvants sprayed with three different nozzle types, XR (Extended Range), AIXR (Air Induction Extended Range), and TTI (Turbo TeeJet Induction), on weed control. Five weed species were tested: common lambsquarters (Chenopodium album L.), velvetleaf (Abutilon theophrasti Medic.), common waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer), Palmer amaranth (Amaranthus palmeri S. Wats.), barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.), and a grain sorghum (Sorghum bicolor (L.) Moench) crop. A dose‒response study using MES and RIMTHIF was conducted to estimate the effective dose to reduce the aboveground biomass by 50% from the nontreated control (ED50). Another study was conducted to evaluate the efficacy of MES and 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 nozzle types (XR, AIXR, and TTI). The selected nozzles influenced velvetleaf, common lambsquarters, and sorghum, indicating the possibility of applying herbicides with Coarser sprays, avoiding off-target movement. Our findings suggest adjuvants are an essential factor for improving weed control over the active ingredient, up to 18.7% and 38.3% for MES and RIMTHIF, respectively. Barnyardgrass biomass reduction was greater than 98% with RIMTHIF in tank mixtures with COC and MSO compared to 65% when applied alone. Common lambsquarters had 52.1% biomass reduction when RIMTHIF was sprayed alone, while adding adjuvants to the tank-mixture resulted in biomass reduction ranging from 60.1% (COC) to 94.1% (AMS). Velvetleaf biomass reduction was 98% when the MES and RIMTHIF mixture was applied with the addition of MSO, while 87% without the adjuvant added. These results indicate that adding adjuvants in herbicide solution can improve herbicide efficacy (COC and MSO for barnyardgrass; NIS, AMS, and MSO for velvetleaf; and NIS, COC, and MSO for common lambsquaters).