Plant residues of a fall/winter coverage crop can influence weed infestation of the subsequent summer crops. This research was carried out to evaluate the effects of mulch from several sorghum (Sorghum bicolor) hybrids plus the herbicide imazamox on the control of the subsequent weed infestation of soybean crop (Glycine max cv. 'Conquista'). The experiment was carried out in the 2000/2001 crop year in Uberlândia, MG. Four types of mulch were used, three from sorghum hybrid residues (Sara, DKB 860 and Ambar) and one without residues (no previous winter crop). Twenty-four days after the application of imazamox, the control of the species Leonotis nepetifolia, Aternanthera tenella, Amaranthus hibridus, A. retroflexus, A. spinosus, Ipomoea grandifolia, Commelina benghalensis, and Nicandra physaloides was more effective with the use of Sara or Ambar mulch without the herbicide, with 40 and 41% of control, respectively. When associated to 15 g ha-1 of imazamox, Ambar mulch resulted in better efficiency, with 76% of control. DKB 860 combined with 30 g ha-1 of imazamox was the most efficient treatment, providing 85% of weed control. Without soil coverage, 62.5% of control was achieved with 30 g ha¹ of imazamox and 47.5% with 15 g ha-1. The results indicated wide control variability in relation to the sorghum hybrid used and possibility of imazamox dose reduction when associated to sorghum residues.
Sorghum bicolor; Glycine max; allelopathy; no-till system
