The environemntal conditions at the moment of application determine most of the times the efficacy of post emergence herbicides. This study aimed to evaluate the influence of weather conditions at the moment of application g of different post emergencet herbicides on the control efficacy of Raphanus raphanistrum (Turnip) in the wheat crop. The study was carried out under field conditions at the "Fundação ABC" Experimental Station in Tibagi, Parana, Brazil, during the 2002 season. The crop system was no tillage and the cultivar used was OR1. The experimental design was randomized blocks in a factorial scheme 5 x 4 (five herbicides and four application times), with four replications. The herbicides (g a.i. ha-1) metsulfuron-methyl (3.6), iodosulfuron-methyl (5.0), metribuzin (144.0), 2,4-D amina (1005.0), and 2,4-D ester (400,0) were used. The application times were at 7:00h a.m.; 10:30h a.m.; 1:30h p.m., and 5:45h p.m. Herbicide application was performed when the crop reached full tillering, and turnip infestation of 288 turnip plants m-2 with five to seven leaves. The evaluated characteristics were: effectiveness to control turnip and percentage of crop phytotoxicity at 8, 16, 22, and 32 days after treatment application. The statistical software SAS was used and the results were analyzed by Anova and the F test; the Fishes LSD test, at 5% probability was used to determine the significant differences between means. The results showed interaction among herbicides and application times; metribuzin and iodosulfuron-methyl were the least influenced by the environmental conditions during the application times. Nevertheless, metribuzin was more efficient in controlling turnip but evidence of phytotoxicity was observed that disappeared at 30 DAA. The weather conditions during the different application times affected herbicide performance: metsulfuron-methyl, 2,4D amina, 2,4-D ester showed great differences in weed control, with 7:00h a.m. and 5:45h p.m. application times being worse than 10:30h a.m. and 1:30 p.m. in terms of control. This study showed the importance of weather conditions at the moment of herbicide application during the winter season for the wheat crop.
cereals; weed; application time
