Control of ALS- and EPSPS-Resistant Amaranthus palmeri by Alternative Herbicides Applied in PRE- and POST-Emergence

Abstract

The emergence of resistant biotypes of the Amaranthus palmeri species in cotton production areas of the state of Mato Grosso, Brazil, generated the need for correct identification of this species and information on viable herbicidal tools for their management. Thus, greenhouse experiments were conducted to evaluate the efficacy of alternative herbicides applied to A. palmeri in pre and post emergence. A randomized block design with four replications was used. The efficacy of herbicides applied in pre emergence was evaluate in two experiments, one in a clayey and other in a sandy soil; 9 herbicide treatments (8 with herbicide application and a control without application) were applied on each soil. Subsequently, two experiments with different populations of A. palmeri were conducted, using a 13 x 2 factorial arrangement, to evaluate the efficacy of herbicides applied in post emergence. The factors consisted of 13 herbicide treatments (12 with herbicide application and a control without application) and two weed development stages (2-4 and 6-8 leaves). Pre-emergence application of the flumioxazin, S-metolachlor, isoxaflutole, and trifluralin herbicides controlled the weed satisfactorily in both evaluated soils. The sulfentrazone and metribuzin herbicides were effective in the sandy soil, and diuron was effective in the clayey soil. The clomazone herbicide did not successfully controlled the A. palmeri plants in any of the soils. All post-emergence herbicide treatments were effective for the management of A. palmeri plants, when they were applied at the 2-4 leaf stage.

Recent Discovery of Amaranthus palmeri S. Watson in Italy: Characterization of ALS-Resistant Populations and Sensitivity to Alternative Herbicides

“…Instead, the efficacy of clomazone was weak, with variable responses between the ALS-resistant populations and an incomplete control of the susceptible check. This is in keeping with the results from other studies [29,30] and with the indication that Amaranthus spp. is a "medium susceptible species" reported on the label of most herbicides containing clomazone as single active ingredient.…”

Herbicides reduce the severity and sporulation of Phakopsora pachyrhizi in soybean with triple herbicide resistance

“…The use of dicamba has been increasing because of weed resistance 49 . In Brazil, this increase is also linked to recent reports of the presence of Amaranthus palmeri in some Brazilian states 50 . Therefore, more studies should be carried out using technologies recently launched in the Brazilian market, such as soybean resistant to the herbicide dicamba, analyzing commercial products, active principles, their metabolites and the occurrence of diseases.…”

“…49 In Brazil, this increase is also linked to recent reports of the presence of Amaranthus palmeri in some Brazilian states. 50 Therefore, more studies should be carried out using technologies recently launched in the Brazilian market, such as soybean resistant to the herbicide dicamba, analyzing commercial products, active principles, their metabolites and the occurrence of diseases. It should be noted that the application of dicamba, as well as Gly and 2,4-D, up to R2 in soybeans is very important for clean harvesting, controlling palmer amaranth and horseweed plants, which are problematic in Brazil.…”

Investigating the origins and evolution of a glyphosate‐resistant weed invasion in South America

“…Several agronomic factors have seen Amaranthus palmeri emerge as a major weed of cotton, corn and soybean production systems of the USA over the last 20-30 years (Ward et al, 2013). Many of the same drivers have also been witnessed in South America, coincident with a recent increased incidence of A. palmeri in Argentina (Montoya et al, 2015), Brazil (Gonçalves Netto et al, 2019) and Uruguay (Kaspary et al, 2020). In this study, we have attempted to address an obvious and significant question: has GR A. palmeri recently invaded South American cropping systems from the USA, or does the emergence of GR populations represent a similar phenomenon to that seen in the USA, where a relatively minor weed has risen to prominence with changing agronomic practices, high glyphosate selection pressure and in situ evolution of glyphosate resistance?…”