Eco biological adaptability of blood grass (Isachne miliacea) proliferation in wetland rice ecosystems

Blood grass (Isachne miliacea Roth ex Roem. & Schult.), locally known as valari, changalipullu, naringa or vanchi, is a major constraint in the wetland rice ecosystems of Kerala. It occurs across cultivated fields, fallows, bunds and irrigation channels, although its vigour diminishes under continuous flooding. Weed biology assessments revealed it as a perennial, prostrate grass with year-round growth and flowering, with peak activity during the monsoon. Propagation occurs via seeds and rooted stem fragments, which establish within 2–6 and 3–8 days, respectively, in puddled soils. Seedlings initiated branching at 11–24 days, coinciding with early crop growth and intensifying competition. Flowering commenced within 28–42 days and seeds matured and shattered by 60–75 days, resulting in steady replenishment of the soil seedbank. Mechanical land preparation accelerated vegetative spread, with plants forming around 8 rooted nodes capable of establishing independently. Dense mat formation within 3 weeks impeded identification of individual plants and rendered manual or mechanical weeding highly difficult. Freshly shed seeds germinated readily; viability declined to 79.7 % by 6 months and reached zero by 10 months. The requirement for direct sunlight during germination enhances establishment under high-temperature environments, while tolerance to elevated iron concentrations and prolonged soil moisture contributes to its persistence and widespread occurrence. Heavy-metal uptake followed the order Fe > Mn > Zn > Cu > Cr > Cd > Pb, with maximum iron uptake (0.65 kg ha-1), highlighting the capacity of the weed to thrive in acidic lateritic and iron-toxic wetland environments.