Germination and emergence of common beggar's-tick (Bidens alba) seeds at two different stages of afterripening as affected by environmental factors

Experiments were conducted to determine the effect of various environmental factors and burial depth on germination and seedling emergence of common beggar's-tick [Bidens alba (L.) DC.] seeds at two different stages of afterripening. Mature B. alba seeds were stored at 4 C for 3 to 5 mo (new seed lot) and 13 to 15 mo (old seed lot) until experiment initiation. Germination exponentially decreased with increasing moisture stress. Germination rate decreased from 87 ± 2.9% to 13 ± 6.1% as osmotic potential decreased from 0 to -0.5 MPa and was completely inhibited at osmotic potentials below -0.83 MPa. A large portion of the new seeds tested positively photoblastic, but seeds that had afterripened for 1 additional year were partially desensitized to the light requirement. New and old seeds still germinated to a greater percentage in the presence of light than under continuous dark at temperatures ranging from 15 to 35 C. Both new and old seeds germinated over a range of temperatures from 5 to 35 C, but the optimum temperatures for germination was 15 to 30 C in the presence of light. Regardless of seed lot, seedling emergence was the greatest when seeds were sown at the soil surface. Seedling emergence was abruptly reduced when burial depth was 1 cm or greater. Based on these results, we conclude that shallow cultivation could effectively suppress this population of B. alba from emerging when incorporated into an integrated control strategy. The information obtained in this research identifies some important factors that facilitate the widespread presence of B. alba in Florida and may contribute to weed management programs.