Confirmation, Control, and Physiology of Glyphosate-Resistant Giant Ragweed (Ambrosia trifida) in Arkansas

Abstract

Glyphosate-resistant giant ragweed in Arkansas was reported in 2005. A study was conducted to (1) confirm and characterize the glyphosate resistance in giant ragweed, (2) determine if reduced absorption or translocation is the mechanism of glyphosate resistance in giant ragweed, and (3) evaluate the efficacy of nine POST-applied soybean herbicides to control glyphosate-resistant and -susceptible giant ragweed. Based on the rate required to kill 50% of plants (LD50 values), resistant giant ragweed biotypes from Greene and Jefferson counties were 2.3- to 7.2-fold less sensitive to glyphosate compared to susceptible biotypes. Glyphosate absorption and translocation for glyphosate-resistant and -susceptible biotypes was similar at 24 and 72 h after treatment. Thus, differential absorption or translocation is not a mechanism of glyphosate resistance in this resistant giant ragweed biotype. Control of resistant giant ragweed biotypes with glyphosate at a labeled field application rate of 840 g ha−1 was only 60% or less compared to complete control of a susceptible giant ragweed biotype. However, bentazon, carfentrazone, cloransulam, and fomesafen controlled both biotypes more than 95%.

Glyphosate-Resistant Giant Ragweed (<i>Ambrosia trifida</i> L.): 2,4-D Dose Response and Control with Postemergence Herbicides in Soybean

“…Glyphosate plus acifluorfen provided 35% to 65% control and was equivalent to glyphosate applied alone at L1 and L2. This is in contrast to the findings of Norsworthy et al [16] who reported 76% to 87% control of glyphosate resistant giant ragweed with acifluorfen applied at 420 g a.i ha -1 . Similarly applying fomesafen with glyphosate either as a tank mix or a premix gave only 69% control ( Table 4).…”

“…Glyphosate plus fomesafen, bentazon and thifensulfuron provided less than 65% control and were equivalent to glyphosate applied alone across all locations. This is in contrast to the findings of Norsworthy et al [16] who reported 100% control of glyphosate resistant giant ragweed with fomesafen applied alone at 263 g a.i. ha -1 or bentazon applied alone at 840 g a.i.…”

“…Surprisingly, glyphosate plus cloransulam-methyl provided 56% to 74% control 4 WAA opposite to what was observed before with this herbicide combination providing 88% to 92% control [13]. Cloransulam-methyl POST is espe- [16]. Glyphosate plus acifluorfen provided 35% to 65% control and was equivalent to glyphosate applied alone at L1 and L2.…”

Glyphosate-Resistant Weed Control and Soybean Injury in Response to Different PPO-Inhibiting Herbicides

“…However, for 20-cm giant ragweed, lower shoot biomass reduction (< 85%) was observed compared to the visual control at 21 DAT (Table 4). Previous researchers also reported variation in the control of different giant ragweed accessions with aciflourfen, fomesafen, and lactofen (Norsworthy et al, 2011;Tylor et al, 2002). Note.…”

Control of Glyphosate-Resistant Giant Ragweed (&lt;i&gt;Ambrosia trifida&lt;/i&gt; L.) with 2,4-D Followed by Pre-Emergence or Post-Emergence Herbicides in Glyphosate-Resistant Soybean (&lt;i&gt;Glycine max&lt;/i&gt; L.)

“…Several PRE and POST herbicides and their combinations have been evaluated for control of giant ragweed in soybean before commercialization of herbicide-resistant crops [25]- [27]. Prior to evolution of glyphosate-resistant giant ragweed, most no-till soybean growers were applying glyphosate before planting to control the existing population followed by an early-POST application for control of newly emerged giant ragweed plants.…”