Soil Seedbank Persistence of Parthenium hysterophorus L.

Parthenium hysterophorus L. is highly invasive across many countries, impacting agriculture, human and animal health and the environment. Despite a widespread invasive range, the persistence of P. hysterophorus seeds (achenes) in the soil profile has been identified as a gap in current knowledge. A long-term seed persistence field trial was under-taken, where packets of P. hysterophorus seeds were buried, retrieved periodically over 10 years and the viability assessed. Time, burial depth and soil type (clay or loam) significantly influenced seed viability. Overall viability was <5% after 5 years, and <0.2% of viable seed was recovered after 7 to 10 years. The decline was faster in seeds at 0 cm (on the soil surface) and buried at 20 cm and slower in seeds buried at 2.5 cm and 10 cm. At most retrieval times viability was higher in seeds retrieved from clay soil plots than from loam soil plots. Pasture cover (present or excluded) did not significantly influence the viability of seeds. Data from controlled ageing laboratory experiments indicated persistent seeds and complemented the field trial data. Based on the weight of 1000 seeds, less than 20 mm of rainfall could incorporate 50% of seeds into three soil types. Parthenium hysterophorus develops a persistent seed bank when incorporated into the soil and infestations will require longer-term control even if seed input is prevented.