Sensibilidade de crotalaria (Crotalaria juncea), girassol (Helianthus annuus) e feijão de porco (Canavalia ensiformis) ao herbicida tiafenacil

Abstract

The residual effect of herbicides, known as carryover, is a critical issue in modern agriculture, especially in systems that use green manure crops. This study aimed to evaluate the sensitivity of three green manure species—Crotalaria juncea, sunflower (Helianthus annuus), and jack bean (Canavalia ensiformis)—to the herbicide tiafenacil, a protoporphyrinogen oxidase (PPO) inhibitor, with respect to plant establishment and early development. The experiment was conducted in a greenhouse using a completely randomized design, with the application of nine herbicide doses (0, 15, 25, 50, 75, 100, 125, 150, and 200 g ha⁻¹) and four replications; the recommended commercial dose ranges from 70 to 100 g a.i. ha⁻¹, depending on the use. Seedling emergence, visual phytotoxicity, plant height, and shoot and root dry biomass were evaluated. The results demonstrated that the residual effect of tiafenacil was species- and dose-dependent, indicating high susceptibility of the evaluated species. Crotalaria juncea and Helianthus annuus showed high sensitivity to the herbicide, with pronounced reductions in growth and biomass, reaching 100% phytotoxicity and complete plant death at doses equal to or greater than 150 g ha⁻¹. Canavalia ensiformis was also susceptible to the residual effect of tiafenacil, exhibiting marked phytotoxicity symptoms and reduced development, although with less uniform responses across the evaluated doses. It is concluded that the application of tiafenacil, even at doses close to those commercially recommended, may compromise the establishment of green manure crops in succession systems, thus requiring caution in management practices and in the interval between herbicide application and the planting of these species.