Abstract
Giant ragweed is an early emerging and one of the most competitive summer annual species found in many fields throughout North America. Extensive use of glyphosate in glyphosate-tolerant (GT) crops has evolved giant ragweed populations with glyphosate resistance. Field dose-response studies were conducted to determine the influence of growth stage on the level of glyphosate resistance in a suspected giant ragweed population. In addition, efficacy of alternative pre-plant, pre-emergence (PRE) and post-emergence (POST) herbicides were evaluated in corn and soybeans for glyphosate-resistant (GR) giant ragweed control. The field glyphosate dose-response studies confirmed that the suspected giant ragweed population were resistant ranging from 14- to 32-fold resistance depending on the growth stage of glyphosate application. The 10, 20 and 30 cm tall giant ragweed had 14, 17 and 32X resistance level, respectively. The dose-response studies indicated that the 10, 20, and 30 cm tall GR giant ragweed was controlled 90% with 214, 402 and 482 g ae ha-1 of dicamba, respectively, when tank-mixed with glyphosate (1060 g ae ha-1) 21 days after treatment (DAT). All evaluated pre-plant herbicides for corn provided ≥ 90% control of the GR giant ragweed at 30 DAT; among which the best control (100%) was achieved with pre-plant application of atrazine (2240 g ai ha-1), isoxaflutole (90 g ai ha-1), and premix of flumioxazin/pyroxasulfone (315 g ai ha-1). Herbicide combinations of different site of action provided greater than 90% control of the GR giant ragweed population in a PRE followed by POST herbicide program in corn and soybean, suggesting that alternative herbicide for giant ragweed control are available.
Highlights
Giant ragweed (Ambrosia trifida L.) is a broadleaf weed species found in many fields in North America (Regnier et al, 2016)
Herbicide combinations of different site of action provided greater than 90% control of the GR giant ragweed population in a PRE followed by POST herbicide program in corn and soybean, suggesting that alternative herbicide for giant ragweed control are available
Nebraska to determine the level of glyphosate resistance in a suspected glyphosate-resistant (GR) giant ragweed population and to evaluate alternative herbicides for pre-plant, pre-emergence (PRE) and post-emergence (POST) herbicides in corn and soybeans for GR giant ragweed control
Summary
Giant ragweed (Ambrosia trifida L.) is a broadleaf weed species found in many fields in North America (Regnier et al, 2016). Giant ragweed is a summer annual weeds in field crops such as soybean and corn in Nebraska, with emergence beginning in March (Kaur et al, 2016). Studies have shown that giant ragweed is very competitive in field crops even with low densities (Ganie et al, 2016; Harrison et al, 2001). In the more recent history, widespread adoption of glyphosate-tolerant (GT) crops and repeated use of glyphosate for both burndown and post-emergence weed control (Regnier et al, 2016) resulted in many glyphosate resistant species, including giant ragweed (Kaur et al, 2014; Heap & Duke, 2018). Giant ragweed control using herbicides with multiple modes of action would reduce risk of weed resistance. Nebraska to determine the level of glyphosate resistance in a suspected glyphosate-resistant (GR) giant ragweed population and to evaluate alternative herbicides for pre-plant, pre-emergence (PRE) and post-emergence (POST) herbicides in corn and soybeans for GR giant ragweed control
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