This work investigated the potentials of the thermal and chemical treatments in seeds of Brachiaria brizantha cv. Piatã, which have been described as efficient strategies to overcome the physical dormancy of seeds, in the reduction of smut (Ustilago operta). Samples of seeds were immersed in sulfuric acid for 0 to 10 min, or in hot water (27 to 60 ºC) for 5 or 10 min. The effects of the treatments in the number of remaining teliospores of U. operta and in the germination of treated seed have been evaluated. A decrease of inoculum was observed as the time of chemical scarification of seeds was increased. The reduction on the number of teliospores was superior with 10 min of chemotherapy. In general, the exposition to H2SO4 did not result in a decrease of the germinative power of the seeds. The results of the thermotherapy were not as evident as those observed for the chemotherapy. Reductions on the number of teliospores or on the overcoming of the physical dormancy were less apparent, maybe, because the seeds were not immersed in hot water during enough time. In parallel, the efficiency of the application of fungicides on the aerial part of the plants for the control of the smut incidence was verified. The fungicides tested were as follow: 1 - methylic tiofanato + chlorothalonil; 2 - mancozeb; 3 - tebuconazole; 4 - triadimenol; 5 - azoxystrobin + cyproconazole; 6 - pyraclostrobin + epoxyconazole; 7 - trifloxystrobin + cyproconazole; 8 - carboxin + thiram; 9 - methylic tiofanato + flutriafol; 10 - carbendazin, and 11 - difenoconazole. Although the smut incidence observed in the experimental area was low (maximum of 15%), a differentiation among the fungicides was possible. The tebuconazole, pyraclostrobin + epoxyconazole and trifloxystrobin + cyproconazole were the most promising fungicides.
Ustilago operta; seed treatment; chemical control; braquiaria grass
