Estudo de resistência múltipla em biótipo de azevém

Abstract

Ryegrass (Lolium multiflorum Lam.) is a grass species considered a weed in winter crops in southern Brazil, and its management represents a major challenge in intensive agricultural systems. This study aimed to evaluate the response of ryegrass biotypes to four herbicides with different mechanisms of action, in order to understand the sensitivity pattern and support control strategies. The experiment was conducted in a greenhouse, in a completely randomized design with four replications, in a 3 x 7 factorial scheme. The first factor consisted of three ryegrass biotypes (Lolium multiflorum Lam.), one susceptible (S) and two resistant (RC and RG) originating from the same population previously identified with multiple resistance to glyphosate and clodinafop-propargyl. The second factor consisted of seven doses of each herbicide (0; 0,125x; 0,25x; 0,5x; 1x; 2x and 4x the recommended dose). The efficiency of the herbicides glyphosate (EPSPS inhibitor) and three ACCase inhibitors (clodinafop-propargyl, clethodim, and pinoxaden) was determined. Visual control assessments were performed 7, 14, and 21 days after application, and the results were fitted using non-linear regression models. The susceptible biotype was completely controlled with the use of doses close to the recommended dose, while resistant biotypes generally maintained low levels of control even at high doses, characterizing multiple resistance to ACCase and EPSPS mechanisms. Among the herbicides evaluated, pinoxaden showed slightly superior performance against the RG biotype, indicating variation in sensitivity within the same chemical class. The results confirm the occurrence of multiple resistance in (L. multiflorum) and reinforce the importance of management strategies that integrate different mechanisms of action and sustainable cultural practices.