Vol. 9, Issue 12, Part E (2025)

Invasive alien plant species are among the most pressing challenges to global biodiversity, agriculture, forestry, livestock and human health. Weeds, described as unwanted plants since the dawn of civilization, cause 10-80% crop losses depending on management practices, with average losses of 36.5% in Kharif and 22% in Rabi seasons. In India, the economic burden of invasive species has exceeded $127 billion over six decades, with major weeds such as Parthenium hysterophorus, Lantana camara, Eichhornia crassipes, and Salvinia molesta severely impacting ecosystems and productivity. Their success is attributed to rapid growth, prolific reproduction, genetic variability, long seed dormancy, allelopathy, and capacity to adapt across habitats. Invasions are facilitated by ecosystem disturbances, nutrient enrichment, lack of natural enemies, and global trade, typically progressing through introduction, establishment, lag, and expansion phases. These weeds not only displace native flora but also disrupt ecosystem services, degrade soil and water quality, reduce food and fodder security, and increase risks to livestock and human health.
Biological control has emerged as an effective and eco-friendly management approach. Successful examples include Zygogramma bicolorata against Parthenium hysterophorus, Neochetina spp. against water hyacinth, and Cryptobagous salviniae against Salvinia molesta, which have significantly reduced weed populations without complete eradication. Such interventions alleviate economic losses, restore ecological balance, and reduce reliance on herbicides, especially as more than 270 weed species are herbicide-resistant globally. However, despite a century of progress, gaps persist in awareness, policy, and large-scale implementation. To address the ecological and socio-economic threats posed by invasive alien weeds, there is an urgent need for integrated strategies that combine prevention, early detection, biological control, habitat restoration, and strict quarantine measures. This chapter synthesizes the biology, mechanisms, impacts, and management of invasive alien weeds with special reference to India, highlighting the need for coordinated, science-based solutions.