Unraveling the influence of environmental factors on fireweed (Senecio madagascariensis) germination and its management implications

Fireweed (Senecio madagascariensis Poir.) has invaded and colonized numerous habitats in the coastal areas of southeastern Australia and is a major weed in cultivated lands as well as in poorly grassed, neglected, and highly grazed pastures. To examine the seed germination ecology of two populations (Felton and Gatton) of S. madagascariensis, experiments were conducted in the laboratory and screenhouse. The germination of both populations increased as the alternating temperatures increased from the coolest temperatures (15/5 C) to warmer temperatures (25/15 C). However, the highest temperature regime (35/25 C) resulted in the lowest germination rates. The Gatton population exhibited greater tolerance to higher temperatures, resulting in significantly higher germination (2.4 times) than the Felton population at the highest alternating temperature of 35/25 C. Compared to the Felton population, the Gatton population demonstrated higher tolerance to salt and water stress. In comparison to alternating light and dark periods (12 h each) (97-98%), the germination of both populations of S. madagascariensis was significantly reduced under complete darkness (24 h) (33-39%). A screenhouse seed burial depth experiment revealed similar emergence of S. madagascariensis seedlings between the populations. The maximum emergence (60%) was observed for seeds placed at the soil surface, followed by a dramatic decline in seedling emergence with an increase in depth. No seedlings emerged from a burial depth of 4 cm. With the addition of wheat crop residue to the soil surface at rates comparable to 4 to 8 Mg ha-1, seedling emergence of S. madagascariensis decreased significantly. Information acquired from this study could be utilized to manage and develop effective weed management strategies for controlling S. madagascariensis in different agroecological conditions.