With the objective to study the control of Brachiaria decumbens and Panicum maximum by herbicide S-metolachlor as influenced by the time interval between the herbicide application the occurrence of rain and the amount of sugarcane straw on the soil, two experiments were conducted in pots under greenhouse conditions. In the first, the factors were the amount of sugarcane straw left on the soil surface (0, 3, 6, 10, or 15 ton. ha-1) and the S-metolachlor applied at doses of 0, 0.96, 1.44, 1.92, or 2.40 kg ha-1. In the second, the factors were the amount of sugarcane straw left on the soil surface (0 or 10 ton. ha-1), the interval of time elapsed between the application of S-metolachlor and simulated rain, which took place 1 day before and 0, 4, 8, 12, 16, or 20 days after the application. The herbicide doses were not affected by the amounts of straw left on the soil surface. When straw was not left on the soil surface, the control of the weeds by the herbicide was not influenced by the time interval up to 20 days after herbicide application. With 10 ton. ha-1 of straw, the control exerted by S-metolachlor was equally efficient whether it rained up to 12 days after the herbicide application. P. maximum was controlled even when the rain fell one day before the herbicide application.
signal grass; buffalo grass; crop residues; herbicide leaching
