Seed survival and periodicity of seedling emergence of some important weeds in south Benin.
Of the weed seeds sampled in S. Benin, >1% of Brachiaria deflexa, Digitaria horizontalis and Rottboellia cochinchinensis seeds survived 2 years' storage in soil (3 and 10 cm deep), while 7% of Tridax procumbens seed remained viable under the same conditions. Preventing seed shed of these species was regarded as an important contribution to their control. Grasses and broadleaved weeds showed periodicity of seedling emergence, with a peak of emergence at the onset of the monsoon season. Grass emergence was promoted by cultivation during this period. Mariscus alternifolius emergence peaked in the middle of the rainy season. Grasses such as B. deflexa had sufficient time to produce seeds before the first weeding and consequently could build up large populations, even with a relatively short period of seed survival in the soil.