Establishment of the Baseline of Sourgrass (Digitaria insularis) Biotypes with Multiple Resistance and Selectivity and Efficacy in the Santa Fé System

• Grant number: 25/07259-7
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2025
• End date: June 30, 2026
• Field of knowledge: Agronomical Sciences - Agronomy - Crop Science
• Principal Investigator: Rafael Munhoz Pedroso
• Grantee: Ana Luiza Magri Ramos
• Host Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil

Abstract

The presence of weeds in agricultural fields imposes direct and indirect consequences onto the desired crop species, with reduced yields as the main subsequent effect. In this context, sourgrass is a weed capable of causing maize yield losses of up to 22% due to its quick dissemination, competitiveness and resistance to commonly-used herbicides such as glyphosate and graminicides. It is, thus, crucial to understand how populations of this weed vary through time as well as seeking for effective control options. Establishing a base-line level of tolerance to herbicides is key to evaluate the selection pressure exerted by these products onto weed populations, allowing for proper monitoring of changes in sourgrass susceptibility to herbicides through time. This, in turn, allows for proper understanding of herbicide resistance evolution and for the adoption of weed management strategies. Furthermore, it is important to include control alternatives into an integrated weed management approach to reduce herbicide resistance selection pressure. Taking into account the relevance of crop residues and straw for weed control, especially from a direct sowing system standpoint, it is noteworthy to mention the feasibility of the maize-forage species consortium, known as Santa Fe system. This system allows growers not only to harvest maize but also high-quality forage that can be used as straw or silage. However, the overall difficulty for properly managing sourgrass in such systems hinders many growers from benefiting from this system. Given the aforementioned, two trials will be carried out. The first experiment will be conducted in a greenhouse located at the University of Sao Paulo campus (ESALQ/USP) and will aim at evaluating the effects of different rates of tolpyralate, quinclorac, and tiafenacil herbicides for the control of two sourgrass biotypes. Focus will be establishing a base-line to uncover susceptibility of these biotypes to the herbicides mentioned. The second trial will be conducted in the field and will evaluate sourgrass control efficacy achieved by applications of nicosulfuron, atrazine, s-metolachlor, clomazone, mesotrione, tiafenacil, and tolpyralte in a Santa fe system settings employing maize as the crop and Urochloa ruziziensis as the forage species. (AU)