Glyphosate-Resistant Horseweed (Conyza canadensis) in Mississippi

Abstract

Survival of horseweed in several glyphosate-tolerant cotton and soybean fields treated with glyphosate at recommended rates preplant and postemergence was observed in Mississippi and Tennessee in 2001 and 2002. Plants originating from seed collected from fields where horseweed escapes occurred in 2002 were grown in the greenhouse to the 5-leaf, 13- to 15-leaf, and 25- to 30-leaf growth stages and treated with the isopropylamine salt of glyphosate at 0, 0.025, 0.05, 0.1, 0.21, 0.42, 0.84, 1.68, 3.36, 6.72, and 13.44 kg ae/ha to determine if resistance to glyphosate existed in any biotype. All biotypes exhibited an 8- to 12-fold level of resistance to glyphosate when compared with a susceptible biotype. One resistant biotype from Mississippi was two- to fourfold more resistant than other resistant biotypes. Growth stage had little effect on level of glyphosate resistance. The glyphosate rate required to reduce biomass of glyphosate-resistant horseweed by 50% (GR50) increased from 0.14 to 2.2 kg/ha as plant size increased from the 5-leaf to 25- to 30-leaf growth stage. The GR50rate for the susceptible biotype increased from 0.02 to 0.2 kg/ha glyphosate. These results demonstrate that the difficult-to-control biotypes were resistant to glyphosate, that resistant biotypes could survive glyphosate rates of up to 6.72 kg/ha, and that plant size affected both resistant and susceptible biotypes in a similar manner.

Resistência de Conyza canadensis e C. bonariensis ao herbicida glyphosate

“…Atualmente existem sete espécies de plantas daninhas com casos relatados de biótipos resistentes ao glyphosate: Eleusine indica, na Malásia (Tran et al, 1999;Lee & Ngim, 2000); Lolium rigidum , na Austrália e nos Estados Unidos (Powles et al, 1998;Pratley et al, 1999;Simarmata et al, 2003); Plantago lanceolata, na Áf ri ca do Su l (H ea p, 20 04 ); Co ny za bonar iensis , na Áf rica do Sul e Es pan ha (Urbano et al, 2005); Lolium multiflorum, no Brasil, Chile e nos Estados Unidos (Perez & Kogan, 2003;Christoffoleti et al, 2005;PerezJones et al, 2005); Conyza canadensis, nos Estados Unidos e na África do Sul (VanGessel, 2001;Koger et al, 2004;Main et al, 2004) (Heap, 2004).…”

Resposta de biótipos de Euphorbia heterophylla a doses de glyphosate

“…Atualmente, a maioria dos agricultores realiza três aplicações do produto por ciclo da soja (Nohatto, 2010). Dessa forma, o uso contí-nuo e repetido desse produto pode promover a evolução de casos de resistência em diversas espécies daninhas (Koger et al, 2004).…”

Morpho-Physiological Characterization of Glyphosate-Resistant and -Susceptible Horseweed (Conyza canadensis) Biotypes of US Midsouth

“…Seeds of GR and GS horseweed biotypes, collected from field-grown plants in Mississippi (Koger et al 2004), were planted in 12.5 cm by 10 cm by 6 cm plastic trays containing a mixture of field soil (Bosket sandy loam, fine-loamy, mixed, thermic Mollic Hapludalfs) and potting mix (Jiffy Products of America Inc., Batavia, IL, USA) (1:1 by volume). Trays were covered with a plastic wrap and placed in a greenhouse (32˚C/25˚C ± 3˚C day/night temperature; natural light supplemented with light from sodium vapor lamps to provide a 13-h photoperiod).…”

“…Glyphosate-resistant (GR) horseweed biotypes from Mississippi were 8-to 12-fold more resistant to glyphosate than a glyphosate-susceptible (GS) biotype [7]. Koger and Reddy [9] reported 28% reduced translocation of 14C-glyphosate from the treated leaf of a GR biotype from Mississippi compared with a GS biotype.…”