Germination Performance of Yellow Cosmos: Understanding Its Invasion under Tropical Conditions

To further investigate the recently observed invasion of a new weed in the S o Paulo areas, Brazil, we studied the germination performance and emergence characteristics of Bidens sulphurea. We measured the seed germination under different fixed temperatures (15, 20, 25, 30 and 35°C), photoperiods (18h/6h, 12h/12h, 6h/18h and 0h/24h [light/dark], respectively), light quality (white, blue, yellow, green, red and dark condition); and emergence in two seasons (winter and spring) in different sowing depths (0, 1, 3, 5, 7 and 9 cm). This species has the ability to germinate and emerge above 90% in a range of conditions of light, but it is very sensitive to variations in temperature, and several reductions on its germination and emergence are found bellow 20°C. The emergence of this species is severely controlled by seasonality and could occur up to 9 cm depth in Brazilian spring.