José Iran Cardoso da Silva

Efeito de herbicidas sobre plantas de Brachiaria plantaginea submetidas a estresse hídrico

This work aimed to evaluate the efficiency in controlling ACCase inhibiting- herbicides applied in post-emergence on Brachiaria plantaginea, submitted to different soil water contents. The study was carried out under greenhouse conditions. The experiment was arranged in a completely randomized block design with four replications, consisting of a 9 x 4 factorial, with the combination of three water management systems (-0.03, -0.07 and -1.5 MPa) and three herbicides (fluazifop-p-butyl, haloxyfop-methyl and sethoxydim + oil Assist) and four doses of these herbicides (100, 50, 25 and 0% of the recommended dose). Herbicide was applyed at two vegetative stages of the plants, 4-6 leaves and 2-3 tillers. The visual assessments of plant toxicity were performed at 3, 7 and 14 days after application, with the dry matter of the plants being determined at the end of the experiment. Control efficiency was lower in the plants grown at soil water potential of -1.5 MPa (water management 8%), regardless of the herbicide used at the two stages of implementation, with the exception of the herbicide haloxyfop-methyl applied at the 2-3 tillers. No differences were found between the control applications with 100 and 50% of the recommended herbicide doses on plants at the 4-6 leaf stage, regardless of type of water management.

Seletividade de herbicidas em variedades de cana-de-açúcar

The objective of this experiment was to evaluate the selectivity of the herbicide topramezone applied alone, and in a mixture with tebuthiuron. The herbicides were applied after sprouting on ten sugarcane varieties on condition of first crop. The treatments were: topramezone + Dash® (70 g ha-1 + 0.25% v/v); topramezone + tebuthiuron + Dash® (70 + 1.000 g ha-1+ 0.25% v/v); topramezone + tebuthiuron + Dash® (100 + 1.000 g ha-1 + 0.25% v/v), ametryn + tebuthiuron (1.500 + 1.000 g ha-1), applied 30 days after planting, and a control without herbicides. During the experiment, all plots remained free from the interference of weeds by hoeing. Herbicides were applied when the plants had reached the two to four leaf stages. Treatments were arranged in a randomized complete block design in split- plot, with four replications for each treatment, with the varieties in the plots and the herbicides in the subplots. Ten varieties were utilized in this study: SP 83 2847, SP 80 3280, RB 85 5453, SP 80 1842, SP 89 1115, RB 86 7515, PO 8862, RB 85 5156, SP 80 1816, and SP 81 3250. Visual phyto-toxicity evaluations were taken 7, 14, 28, and 35 days after application. At the end of the study, technological parameters such as pol, fiber, and brix, and productive parameters, such as stalk weight, and sugar production, were determined. The formulation of topramezone alone followed by its mixtures with tebuthiuron initially provided severe visual injury to the sugarcane plants; however, the plants of all varieties tested had a total visual injury recovery 35 days after herbicide application. The mixture with tebuthiuron reduced the symptoms of injuries caused by topramezone. The mixture of ametryn + tebuthiuron showed the least severe phytotoxic action against the plants, regardless of the variety studied. None of herbicides tested showed negative effects on the technological or productive components of the studied varieties. The herbicides utilized on the ten varieties of sugarcane can, therefore, be considered selective.