Weeds, or unwanted plants competing with crops and native vegetation, have long challenged agricultural and natural ecosystems. Weeds not only compete for sunlight, nutrients and moisture with desirable plants, but also serve as hosts for harmful insects and pathogens. Globally, weeds account for around 34 per cent of the total losses in crop production, often exceeding those caused by pests and diseases. According to a report by the Indian Council of Agricultural Research (ICAR), weeds are responsible for one-third of crop losses, costing over ₹1 lakh crore annually to the country.

Exotic weed species

The fast spread of exotic weed species can jeopardise food security, biodiversity, and environmental sustainability.

The impact of invasive weeds extends beyond agriculture. For example, parthenium hysterophorus, popularly called carrot or ‘congress grass’, produces allelopathic chemicals that inhibit the growth of surrounding biota. Parthenium is a serious health hazard, as it causes skin and respiratory allergies in humans and animals.

Similarly, an ornamental plant of Mexican origin, lantana camara, has invaded India’s entire ecosystem — forests, grasslands, and farm-bunds. It is one of the ten worst invasive species in the world. The infiltration of this weed poses a severe threat to biodiversity, disrupting the balance of ecosystems and leading to the decline of native flora, consequently affecting food-chain and shelter of herbivores and pollinator insects.

The Western Ghats, a biodiversity hotspot, has been severely impacted by invasive weeds. Lantana invasion has intensified fire risks, with dense thickets burning more intensely than native vegetation, leading to more frequent wildfires.

Similarly, native to South America, prosopis juliflora, locally known as vilayati babul, has become among the world’s 100 most invasive species.

Controlling the spread of weeds is all the more important for India as it is looking to increase area under technologies like direct-seeded rice production that needs less water but is more susceptible to weed pressure. The ICAR has initiated several steps to control weeds, including alien species. The country-wide network of ICAR institutes and Agricultural Universities are also working to develop technologies for the weed management. The examples include soil solarisation, conservation agriculture, climate-smart agronomy and recently developed first-ever non-GM herbicide-tolerant rice varieties, Pusa Basmati 1979 and Pusa Basmati 1985. The gravity of the problem requires the following comprehensive strategies.

First, research, public awareness initiatives, and coordinated efforts at local, national, and global levels are vital to control invasive weeds. Collaboration among State agricultural, forest, and animal husbandry departments, ICAR institutes, and agricultural universities is crucial for awareness campaigns, research, and developing effective weed management technologies.

Second, identify hotspots and implement large-scale plantation drives, focusing on fast-growing species like cassia tora, Malabar Neem and Ailanthus excelsa.

Third, promote alternative uses of these species into biochar production, energy generation, mulching, agro-based industries, and soil-water conservation.

Fourth, the recent nationwide campaign, ‘Ek Ped Maa Ke Naam’, has heightened awareness and participation in tree-plantation. Such appeals to the masses can significantly contribute to tackling weed menace as well.

Fifth, establish dedicated programmes aimed at managing and ultimately eradicating invasive weeds with minimum use of agro-chemicals.

Sixth, global initiatives like the International Plant Protection Convention and the Convention on Biological Diversity provide frameworks for countries to work together on invasive species management.

The writers are Senior Scientists with ICAR, New Delhi. Views are personal

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