The objective of this work was to determine the periods of weed interference in sunflower crops. Two experiments were done with the sunflower hybrid Helio 250, one in the summer and the other in the winter. For both experiments, a randomized block design with four repetitions was used and each experimental unit was composed of plants in five lines, 6.0 m in length, spaced 0.7 m apart. In the summer experiment eight periods of cohabitation and weedy plant control were evaluated: 10, 20, 30, 40, 50, 60, 70 and 88 days after emergence (dae). In the winter experiment, the periods were 7, 14, 21, 28, 38, 48, 58 and 82 dae. The dry matter mass, leaf area of sunflower plants, yield, thousand achenes mass and weedy plant dry matter mass were evaluated. The periods prior to interference (PPI), the critical periods of preventing interference (CPPI), and the total periods of preventing interference (TPPI) were estimated. Considering the yield of achenes in the summer, the PPI was 16 dae of the crop, the CPPI was 39 dae and the TPPI lasted 23 days of the crop cycle. In winter, the PPI was 12 dae and the CPPI lasted for 34 dae, resulting in a TPPI of 22 days.
Helianthus annuus L.; competition; yield
