Effects of rainfall on weed control in soil with two moisture levels, after herbicide applied in postemergence

摘要

Two experiments were conducted on a greenhouse, at Fitotecnia Department at University Federal of Viçosa, Viçosa-MG, intending to evaluate simulated rain influence after herbicides application, on the control of Brachiaria plantaginea and Bidens pilosa on corn (Zea mays) crop, on soil with two moisture levels. Nicosulfuron on two formulations (SC and WDG) and the mixtures nicosulfuron+atrazine and atrazine+oil were applied, with 0, 15, 30, 60 and 120 minutes intervals between herbicide application and a 30 mm simulated rain occurrence. Estimated parameters were fresh biomass, dry biomass and plants height. After seedlings emergence two experiments were undertaken; on the first one soil moisture level was kept near to field capacity (41.3%), and on the other one seedlings were submitted to water stress (24.7% of soil moisture). Nicosulfuron efficiency on B. plantaginea control was greater when rain absence rain interval was increased until to 30 minutes after herbicide application, for plants grown on soil with high moisture content. On soil with low moisture content control efficiency was very poor, even when rain occurred 120 minutes after herbicide application. Bidens pilosa control with nicosulfuron SC or WDG was poor, even on humid soil. The mixture nicosulfuron+atrazine resulted on B. plantaginea control similar to that when nicosulfuron was applied alone, and excellent control of B. pilosa, on both soil moisture conditions. Atrazine+oil was inefficient for B. plantaginea control and highly efficient for B. pilosa control, independent of soil moisture and of time interval for simulated rain occurrence after herbicide application.