A field trial was conducted in Londrina/PR in 1991/92 to verify the influence on timing of application of atrazine alone and in mixtures with alachlor or vegetable oil. The treatments were arranged in randomized block design with four reaplications. Herbicide treatments were applied with CO2 pressurized knapsac, nozzle fan 110.03, with 300 l/ha, at the rate: atrazine 2.400, alachlor + atrazine (1.820 + 1.820) and atrazine + crop oil (2.400 + 1.800) g/ha a.i., applied on October 12, 1991 at 4, 6, 8, 10, a.m. and 12, 2, 4, 6, 8, 10, p.m. The relative humidity (RH) at 4:00 a.m., 2:00 and 10:00 p.m were 68, 35 and 65%, respectively. Brachiaria plantaginea at 1 to 5 leaf stage and Amaranthus hybridus, Euphorbia heterophylla, Bidens pilosa, Emilia sonchifolia and Sida rhombifolia at 2 to 6 leaf stage were used. The control of B. plantaginea was influenced by the time of application. Alachlor + atrazine and atrazine + vegetable oil, provided more than 90% of control during 4:00 to 8:00 a.m. When the RH was 35 % there was a decrease on the control of about 80 to 60% from 10:00 a.m. to 6:00 p.m. Atrazine + surfactant showed 40% of control at all the timing of application. For broadleaves there was no influence of the timing of application because the herbicides always provided 100% control. The mixture of atrazine with alachlor or vegetable oil increased the control of B. plantaginea.
Application; relative humidity; weeds; herbicides