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18 August 2020 Time-of-day effect on weed control efficacy with tolpyralate plus atrazine
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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.

© The Author(s), 2020. Published by Cambridge University Press on behalf of the Weed Science Society of America.
Nicole M. Langdon, Nader Soltani, Alan J. Raedar, David C. Hooker, Darren E. Robinson, and Peter H. Sikkema "Time-of-day effect on weed control efficacy with tolpyralate plus atrazine," Weed Technology 35(1), 149-154, (18 August 2020).
Received: 25 March 2020; Accepted: 4 August 2020; Published: 18 August 2020

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