- In 2019, researchers projected that Assam would remain highly vulnerable to parthenium even as its suitable habitat shrank across much of India, a threat now increasingly visible on the ground.
- Fragmented eradication efforts, without a standardised protocol for removing and disposing of the weed, may be inadvertently aiding its further dispersal.
- Accounts of allergic reactions point to the need for further state-specific research on parthenium exposure, alongside greater clinical awareness and preparedness.
On a June morning in 2025, 24-year-old Niharika Deka of Kaliabor in Nagaon district, Assam, took the family’s cattle out to graze, filling in for her mother. By evening, an intense itch had developed around her eyelids and lips. Her mother had similar allergic reactions on her hands.
Several doctors’ consultations and treatments followed. Doctors initially suspected a cosmetic trigger. “The symptoms eased with medication, but the itch would flare up the moment I stepped into the fields or sometimes even outside the house. We kept shuttling between doctors,” Deka said.
The picture became clearer when other villagers and students began reporting similar rashes and allergic episodes on exposed skin. Suspicion narrowed to a small, white-flowering wild plant that had recently begun proliferating across the locality. When its conspicuous flowering subsided after August, the allergies eased too. When the flowers returned in the summer of 2026, so did the itching. Deka said the repeated flare-ups have left dark patches around her eyelids and mouth, with similar discolouration on her mother’s hands. “It looks awful, and we don’t know if it’ll fade. I’m of marriageable age, and my parents are worried,” she said.
About 150 km away, in Raja Mayong in Morigaon district, farmer Mahesh Nath is grappling with the same weed on his one-acre plot, where he grows vegetables and grains for a living. “It outpaces everything else,” he said. Around 2021, parthenium covered nearly 70% of his plot. During floods, Nath and his wife uprooted the plants when the soil loosened, allowing the water to carry them away. Since then, they have learned to pull out the saplings and spray herbicides soon after ploughing. He estimates the weed now covers around 20-30% of the plot. “With constant maintenance, we have managed to control much of it. But often after working in the field, our bodies itch and rashes appear,” he said. The uprooted plants, he added, are usually thrown on vacant land or along riverbanks away from the cultivated field.
Native to tropical and subtropical America, Parthenium hysterophorus, commonly known as congress grass or carrot grass, arrived in India in the 1950s and had aggressively invaded an estimated 35 million hectares across the country by 2017. Like most weeds, its rapid growth and prolific seed production allow it to colonise agricultural land, pastures, roadsides and natural ecosystems. Exposure is also associated with human health problems, including contact dermatitis and allergic rhinitis.
An old presence, expanding
Parthenium is not new to Assam. An earlier survey conducted between 2009 and 2011 along 12 selected national highways in the Northeast, including four in Assam, found the weed at all sampled sites. Assam’s overall infestation was classified as medium relative to other Indian states such as Andhra Pradesh, Karnataka, Maharashtra and Uttar Pradesh (where it was ranked as ‘high’), but it showed high vulnerability within the northeastern corridor. Density peaked between June and August, and the researchers noted that habitat disturbance associated with construction and vehicular movement could aid its establishment and spread.
A 2019 study mapped the potential spread of parthenium across India and identified three major invasion hotspots — the Northeast, the Western Himalaya and parts of Peninsular India. Modelling climatic suitability under then-current conditions, the researchers found that almost the entire state of Assam, alongside the other northeastern states, was vulnerable to its invasion. While suitable habitat for parthenium was projected to shrink across much of India under a warming climate, by as much as 40% nationally by 2070 under the high-emissions scenario, the Northeast and parts of the southern Western Himalaya were exceptions, where suitable habitat was projected to persist. Just years later, accounts from farmers, residents and researchers across Assam suggest that this vulnerability is becoming increasingly visible on the ground.
Residents across Assam have shared accounts of the weed overrunning roadsides and unused land, along with reports of skin rashes and calls for removal. Research has also recorded parthenium among invasive plants in protected landscapes including Kaziranga, Manas, Orang, Pobitora and Amchang. People have reported flowering in different months, suggesting that growth may extend beyond the most conspicuous seasonal bloom.
Milon Jyoti Konwar, Principal Investigator of the All India Coordinated Research Project on Weed Management at Assam Agricultural University (AAU), said the shift is increasingly apparent. “We cannot deny the presence of parthenium in Assam for decades now. However, from secluded patches it has proliferated on a significant scale in the past two to three years,” he said.
Konwar said Assam’s lower temperatures and higher moisture availability are conducive to its growth. A single plant can produce around 15,000-25,000 lightweight seeds. “More worryingly, parthenium has also entered paddy fields in certain pockets. We are often called to places reporting the plant in areas where it wasn’t previously found, seeking awareness and advice on eradication. Majuli is a recent example. The impact on crops may not be significant yet, but eventually this is going to become a concern,” he added.
Remove early, dispose right
Chiranjeev Bezbaruah, Assistant Professor in the Department of Botany at Kaliabor College, has been spreading awareness after residents approached the college seeking help. “The problem had escalated in the district since around 2024,” he said. Their field survey found the plant largely in scattered patches along riverbanks and unused land. But sand extracted from such areas for road construction and land-filling, he said, carries the seeds elsewhere, while vehicle movement aids further dispersal. Several residents Mongabay-India spoke to in Nagaon and Morigaon similarly pointed to sand transportation or land-filling near their properties as a possible trigger for new infestations.
Another problem is misidentification. People mistake parthenium for Gypsophila (Baby’s breath), using the white flowers in decorations, bouquets and hair ornamentation. Vegetable vendors have also been seen lining baskets with the plant during transport, potentially carrying its seeds further. When Mongabay-India spoke to these vendors, many said that they had no idea what the plant was, that it was wild and abundant, so they felt that it could be used as a lining instead of banana leaves. They added that sometimes their hands itched, but they never gave it much thought.
The spread has prompted increasingly localised responses. Residents have approached district authorities, while students and youth groups in Nagaon and Morigaon have organised awareness programmes and removal drives. Forest personnel have undertaken similar efforts around Pobitora Wildlife Sanctuary. But volunteers and forest guards working without adequate protective gear have also reported allergic reactions after exposure.
Bezbaruah’s team experimented locally with a generic herbicide solution containing acetic acid and sodium chloride, but he said treating individual patches cannot match the scale of infestation. Konwar similarly recommended removing the plant at the vegetative stage, before flowering and seed set. He also pointed to competitive vegetation as one management option: “In Assam, one possibility is planting Senna tora. Although it is itself a weed, we have observed that it can suppress the growth of parthenium.”
No dedicated process for removal, disposal
Despite parthenium having been established in India for decades, no publicly available national Standard Operating Procedure (SOP) specifically governs its removal and disposal, nor is there an Assam-specific protocol. Instead, guidance remains scattered across institutional advisories, awareness campaigns and research literature. For over a decade, ICAR institutes have observed Parthenium Awareness Week from August 16 to 22, promoting awareness and management practices such as uprooting the weed before flowering and composting the removed biomass, alongside mechanical, chemical and biological control measures.
But as parthenium invades new spaces, reaching even home gardens, and shows signs of persisting through much of the year in Assam, the need for aggressive public awareness and clear, stringent norms for its removal and disposal is increasingly being felt. Flowering plants uprooted during local drives are transported in open vehicles or dumped on riverbanks and vacant land, allowing seeds to disperse again. A 2014 academic review concluded that no single method is adequate for controlling parthenium and that management requires an integrated approach, including biological control.
Konwar said AAU has been working with district administrations on awareness drives, but isolated removal is unlikely to contain a plant with such reproductive capacity. “Unless sustained, integrated management is undertaken across the state, the plant will continue to rejuvenate,” he said.
Health evidence is also lacking. Although residents are increasingly suffering allergic reactions to the weed, no formal state-specific study has yet established parthenium as the confirmed cause of these cases. Dr. Phani Pathak, the Joint Director of Health Services, Nagaon, told Mongabay-India that without a sufficient number of confirmed cases directly attributing symptoms to parthenium, the issue has not formally come to the department’s notice. State-level studies would be needed to establish that connection, he said.
Wildlife biologist Nilutpal Mahanta, affiliated with The We Foundation India said, “Assam has had many invasive species such as water hyacinth and lantana for decades, but we have rarely seen this level of concern among citizens. This could be linked to increasing health problems, particularly skin and respiratory issues, seen in humans, cattle and wildlife.”
“Without adequate awareness of parthenium-related health issues, including among healthcare providers and veterinarians, treatment often appears to be on a trial-and-error basis until individual cases trace the problem to the weed,” Mahanta added. “We urgently need large-scale government and mass-media intervention, from public awareness and safe management of the weed to awareness about its health impacts on people and cattle and timely treatment. Field officials of the concerned departments should be adequately informed,” he said.
Banner image: Vegetable vendors use Parthenium leaves to line vegetable baskets. Image by Barasha Das.
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