John C. Fluttert, Nader Soltani, Mariano Galla, David C. Hooker, Darren E. Robinson, Peter H. Sikkema
Weed Technology 36 (4), 523-530, (9 June 2022) https://doi.org/10.1017/wet.2022.45
KEYWORDS: atrazine, effective dose, HPPD inhibitor, PS II inhibitor, tolpyralate
Tolpyralate is an herbicide that is usually mixed with atrazine for broad-spectrum weed control in corn. Previous research has provided information on the effective dose (ED) of tolpyralate applied alone and in a 1:33.3 mixture with atrazine; however, tolpyralate is commercially applied at a dose of 30 to 40 g ai ha–1 with a minimum of 560 g ai ha–1 of atrazine. Therefore, five field trials were conducted over 3 yr (2019 to 2021) to determine the ED of atrazine to complement 30 g ai ha–1 of tolpyralate to achieve 80%, 90%, and 95% control of seven weed species 2, 4, and 8 wk after application (WAA). Tolpyralate was applied alone and in a mixture with atrazine doses ranging from 50 to 2,000 g ai ha–1. At 8 WAA, the ED of atrazine for 95% control of velvetleaf, common ragweed, common lambsquarters, and wild mustard was below the minimum label dose of atrazine on the commercial tolpyralate label, ranging from 430 to 520 g ai ha–1, which supports the use of the minimum label dose of atrazine. In contrast, redroot pigweed required 1,231 g ai ha–1 of atrazine to complement tolpyralate for 95% control 8 WAA. At 8 WAA, barnyardgrass and a mixture of green foxtail and giant foxtail (Setaria spp.) were not controlled by 80%, 90%, or 95% with tolpyralate applied alone or co-applied with any dose of atrazine evaluated in this study. The results of this study conclude that tolpyralate + atrazine is highly efficacious on several weed species at atrazine doses of 40 to 130 g ai ha–1 below the label dose of 560 g ai ha–1, but the use of the higher dose of tolpyralate or another herbicide may be required to improve control of redroot pigweed and grass weed species.
Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) P. Beauv.; common lambsquarters, Chenopodium album L.; common ragweed, Ambrosia artemisiifolia L.; giant foxtail, Setaria faberi Herrm.; green foxtail; Setaria viridis (L.) P. Beauv.; ladysthumb, Persicaria maculosa Gray; redroot pigweed, Amaranthus retroflexus L.; velvetleaf, Abutilon theophrasti Medik; wild mustard, Sinapis arvensis L.; corn, Zea mays L.