Weed management in Roundup Ready® corn and soybean in Southern Brazil: survey of consultants’ perception

Abstract

Background:The presence of weeds in Roundup Ready ® (RR) soybean and corn crops compromises yield. Management practices recommended by the consultants and adopted by producers directly interfere in the occurrence of these species. Objective: To survey management practices used in RR soybean and corn fields in the Rio Grande do Sul. Methods: Data were gathered via the application of questionnaires during the 2018/19 growing season to consultants working with RR soybean and corn cropping in Rio Grande do Sul state. There were 112 responses, covering about 72 municipalities in the state. Results: Technical consultants highlighted Conyza spp. and Lolium multiflorum as the most common weed species and classified resistance to herbicides and advanced stages of weeds at the time of herbicide application as the primary causes of low weed control efficacy. They observed an increase in resistance evolution and a two to three-fold increase in the use of herbicides in glyphosate-tolerant crops. Using a mixture of herbicides was the main recommendation for the management of weeds that escape control, while in areas with proven resistance, crop rotation was the main recommendation. Conclusions: Crop rotation and herbicide mixtures are the most recommended management practices, with herbicide resistance and advanced stage of development listed as the main reasons for the difficulties of weed control.

Selectivity and efficacy of herbicides applied on barley for weed control

“…Percentage values of weed control greater than 80% were, for a period, considered effective to be recommended when applying herbicides when they infested the crops (SBCPD 1995). However, ryegrass is a very competitive weed with proven resistance to several mechanisms of action such as ALS-inhibiting herbicides (Mariani et al 2015), ACCase (Kaundun et al 2013), EPSPS (Roman et al 2004, Holkem et al 2022, and more recently Very Long-Chain Fatty Acid Synthesis inhibitors (VLCFA) (Brunton et al 2019, Dücker et al 2019. Therefore, for the herbicide to be recommended for the management of a particular weed, it must have a control greater than 80% (Roman et al 2004, Vargas et al 2013, Mariani et al 2015.…”