CULTURAL AND CHEMICAL CONTROL OF Conyza spp. IN CORN INTERCROPPED WITH Urochloa ruziziensis

Abstract

Integrated weed management practices to control fleabane (Conyza spp.) have been essential in integrated crop production systems, such as corn (Zea mays) associated with Congo signal grass (Uruchloa ruziziensis). The objectives of these studies were to evaluate the efficacy of Congo signal grass covering on fleabane suppression and to evaluate different chemical control options to control fleabane during the production of Congo signal grass. The first experiment was conducted after the corn harvest integrated with Congo signal grass by evaluating fleabane infestation and its correlation with the biomass of the grass. The second experiment consisted in herbicides applied in mixture, in a factorial arrangement 3x7: 2,4-D (1,209 g ha-1 a.e.), [halauxifen-methyl + 2,4-D] (5.76 + 780 g ha-1 a.i.), and dicamba (960 g ha-1 a.i.) composing the first factor; and metsulfuron-methyl (2.4 g ha-1 a.i.), chlorimuron-ehtyl (20 g ha-1 a.i.), diclosulam (25.2 g ha-1 a.i.), saflufenacil (35 g ha-1 a.i.), bentazon (576 g ha-1 a.i.), atrazine (1,000 g ha-1 a.i.), and untreated control composing the second factor. Corn cultivated in the second season integrated with Congo sinal grass reduced 80, 60, and 96% of fleabane emergence, growth, and biomass, respectively, during the off-season period. All chemical treatments provided >80% control on fleabane up to 8 cm tall, except for 2,4-D isolated. For plants with 8-16 cm tall, all mixtures were efficient (>85% control), while in plants taller than 16 cm, 100% control was observed for treatments composed by saflufenacil in mixture with all auxins herbicides. The selective treatments for Congo signal grass were 2,4-D and dicamba isolated and the associations with bentazon.