EFICÁCIA DO HERBICIDA CLETHODIM NO CONTROLE DO CAPIM-AMARGOSO (Digitaria insularis)

Abstract

Sourgrass (Digitaria insularis) is one of the weed species with the greatest agronomic impact in Brazil, mainly due to its capacity for perennialization, vigorous regrowth, and accumulation of reserves in rhizomes, characteristics that make chemical control difficult. Among the available herbicides, clethodim, an ACCase inhibitor, is widely used for the management of this species; however, its efficacy may be reduced by environmental, operational, and chemical factors that interfere with herbicide absorption, translocation, and stability. Therefore, the objective of this study was to evaluate the main factors that compromise clethodim performance in the desiccation of mature D. insularis plants during the soybean pre-sowing period. Four experiments were conducted at the Staphyt experimental station in Formosa, Goiás, Brazil, evaluating: (i) application timing; (ii) the effect of spray solution storage time of clethodim, applied alone or in mixture with auxinic herbicides; (iii) the interaction between clethodim and auxinic herbicides combined with the effect of mechanical mowing performed after application; and (iv) the comparative performance of commercial formulations subjected to mowing at different intervals after application. Weed control was visually assessed at 7, 14, 21, 28, and 35 days after application, and data were analyzed using linear mixed models in R software. Application timing significantly influenced clethodim performance. Applications performed at 4:00 p.m. resulted in greater control efficiency, whereas applications at 4:00 a.m. resulted in lower efficacy, highlighting the negative effect of environmental conditions such as lower temperatures, dew presence, and variations in relative humidity. Spray solution storage for up to 72 hours showed variable effects among products, but clethodim and halauxifen-methyl demonstrated greater stability, whereas triclopyr-butotyl and 2,4-D showed a gradual reduction in control. The association of clethodim with auxinic herbicides resulted in antagonism, particularly when followed by immediate mowing, which reduced herbicide absorption due to rapid removal of foliar tissue. Intervals of 2 to 4 hours between application and mowing mitigated this effect, allowing greater translocation and improved control. Among the formulations evaluated, 2,4-D and triclopyr-butotyl showed lower performance, whereas halauxifen-methyl stood out for its higher efficiency when mixed with clethodim. Among the commercial clethodim formulations, Grasidim and Cletodim CCAB 240 EC® showed superior performance when associated with delayed mowing. It is concluded that clethodim efficacy is influenced by application timing, being reduced when applied under less favorable environmental conditions, by antagonistic interactions with auxinic herbicides, by prolonged spray solution storage when associated with certain auxins, and by differences in performance among the evaluated formulations. Optimizing these factors is essential to maximize control of perennial sourgrass during pre-sowing desiccation.