Evaluation of different dosage of Oxyfluorfen herbicide on weeds control and growth characteristics of black-eyed Susan (Rudbeckia hirta L.)

In order to investigate the response of Black-eyed Susan to different dosages of herbicide and comparing it with hand weeding treatment, an experiment was conducted with 6 treatments based on randomized complete block design (RCBD) in three replications during 2018-2019 in Agricultural Sciences and Natural Resources University of Khuzestan. The treatments included different dosages of Oxyfluorfen herbicide (0, 0.5, 1, 1.5 and 2 L ha-1) and a weed free treatment in the entire period (hand weeding). Herbicide application was done as a postemergence herbicide on the transplanted seedlings after complete establishment (4-6 leaves). The results indicated that different dosages of herbicides led to severe plant burns and regrowth occurred after two weeks of herbicide application. In the no application of herbicide treatment (weed interference), the lowest characteristics of height (33 cm), plant dry weight (154 g m-2), number of flowers (27 number m-2) and flower dry weight (20 g m-2) were observed. The highest height (74 cm), plant dry weight (1117 g m-2), number of flowers (276 number m-2), and flower dry weight (395 g m-2) were recorded in hand weeding treatment. Among different dosages of herbicide, applications of 1 and 1.5 L ha-1 led to an increase in the number of flowers (201 and 196 number m-2) and the dry weight of flowers (287 and 281 g m-2), and no significant difference was observed between these two treatments. The total dry weight of weeds decreased with the increased herbicide dosage, and in 2 L ha-1 of herbicide, the lowest dry weight was 22 g m-2 and the highest dry weight was in 195 g m-2 in weedy treatment (no application of herbicide). There was no statistically significant difference in the dry weight of weeds between the three-herbicide dosages 1, 1.5 and 2 L ha-1. Fitting the logistic equation to the data of the total dry weight of weeds showed that the dosage required to reduce the total dry weight of weeds by 50% was estimated as 0.448 L ha-1. Although due to the application of herbicide, intense burning of plants and reduction in regrowth of black-eyed Susan plants was observed, according to labor costs, the application of 1.5 L ha-1 of herbicide can be recommended to control weeds in the urban green space in the condition of highly weed contamination.