Tolpyralate is a new 4-hydroxyphenyl-pyruvate dioxygenase (HPPD)–inhibiting herbicide for weed control in corn. Previous research has reported efficacy of tolpyralate + atrazine on several annual grass and broadleaf weed species; however, no studies have evaluated weed control of tolpyralate + atrazine depending on time-of-day (TOD) of application. Six field experiments were conducted over a 2-yr period (2018, 2019) near Ridgetown, ON, to determine if there is an effect of TOD of application on tolpyralate + atrazine efficacy on common annual grass and broadleaf weeds. An application was made at 3-h intervals beginning at 06:00 h with the last application at 24:00 h. There was a slight TOD effect on velvetleaf, pigweed species, and common ragweed control with tolpyralate + atrazine; however, the magnitude of change throughout the day was ≤3% at 2, 4, or 8 wk after application (WAA). There was no effect of TOD of tolpyralate + atrazine on the control of lambsquarters, barnyardgrass, and green foxtail. All weed species were controlled ≥88% at 8 WAA. There was no effect of TOD of tolpyralate + atrazine application on corn yield. Results of this study show no evidence of a TOD effect on weed control efficacy with tolpyralate + atrazine.
Nomenclature: Atrazine; tolpyralate; barnyardgrass; Echinochloa crus-galli (L.) P. Beauv.; common ragweed; Ambrosia artemisiifolia L.; green foxtail; Setaria viridis (L.) P. Beauv; hemp sesbania; Sesbania herbacea (Mill.) McVaugh; lambsquarters; Chenopodium album L.; redroot pigweed; Amaranthus retroflexus L.; sicklepod; Senna obtusifolia (L.) H.S. Irwin & Barneby; velvetleaf; Abutilon theophrasti Medik.; corn; Zea mays L.