North American weed spotted in India, could be major threat to agriculture and forests in future

If the initial hints are anything to believe, the farmlands and forests in India have a brand new invasive threat from a rarely reported foreign plant species native to North America. A recent research correspondence published in the Current Science journal claims to report the plant for the first time from India and argues that the plant can have tremendous invasive potential.

Western ragweed (Ambrosia psilostachya)
Image courtesy: Krzysztof Ziarnek Kenraiz (Wikimedia commons)

 According to the researchers, the plant is presently reported from farm lands in the M. Bevinahalli village in Turuvekere taluk of Karnataka. On close examination and surveying the literature, the researchers were able to identify the new plant as Ambrosia psilostachya. Though the plant resembles its close relative Ambrosia artemisiifolia which is found in India, it is actually different, says the correspondence. 

Its Indian variety, Ambrosia artemisiifolia, was the only member of the genus hitherto reported from India. According to the correspondence, the new weed is native to North America and is known as perennial rag weed or western ragweed in North America.

New invasive plant threat in India

The research note warns that the weed has tremendous capacity to spread very rapidly and is known to cause allergic reactions in Humans. “If the weed is not controlled now, it may create a difficult to control situation once it proliferates from the location of present report”’ says the correspondence. 

According to the correspondence, the weed has not only invaded finger millet, mulberry, coconut and areca nut cultivation  but has also conquered the cattle pastures which have affected animal husbandry of these villages. The correspondence also notes that the plant has seriously affected local flora, by replacing local grass varieties, thus decreasing fodder availability. 

The plant is capable of spreading to large areas through extensive vegetative reproduction through underground rhizome like roots and stolon (part of the plant which makes new plant).  Though the plant has been present in some villages in Karnataka for the last 15 to 20 years, it is not yet clear what restricts it from spreading to other places.

 According to the researchers, since the plant does not have parts which supports seed dispersal through wind, the plant has not yet started spreading to other places. It is also not clearly known at this point if all the seeds produced by the plant are viable or if they exhibit any type of dormancy.

Though, there are not many issues reported about this plant expect its rapid invasion of farm lands in Karnataka Villages, reports from other countries indicate that the plant can cause allergic diseases in humans. “The species is said to be responsible for causing severe allergenic diseases in human beings in the United States”, says the correspondence.

The North American Connection

The plant is actually native to North America and the way in which it has reached Indian farmlands is still unknown. Though some speculates that the seeds could have been brought to India by migratory birds that use the seeds and other parts the plant for making nests, the connection is yet to be scientifically proved.

Though contaminated food grains are a usual way in which invasive plants reach farther places -as in the case of Lantana, a notorious weed in Indian forest- that may not be the reason for the spread of the present weed. “The introduction of the species through contaminated food grain may not be possible, as the weed is localized only in these villages in Karnataka”, says the paper.

The plant has already spread to parts of South America, Europe, New Caledonia, Japan, Taiwan and Australia. The researchers do not rule out the chances that the seeds reaching India from either of these places.

Weed control measures

 The presence of root buds, horizontally running rhizomes and dense root ramification makes the plant difficult to manage and eradicate. Periodical manual removal, shallow plowing before passing cultivator in farms has been recommended as a control measure. According to the note, if repeated control measures are taken, the weed can be controlled in 4 to 5 years from the country with its present restricted proliferation.

 M. T. Sanjay  and T. V. Ramachandra Prasad from the Directorate of Weed Science Research Centre, University of Agricultural Sciences, Bangalore, R. A. Sharma from Directorate of Weed Science Research, Indian Council of Agricultural Research, Jabalpur and R. R. RAO, from Bangalore co-authored the correspondence.

Read more on IBT's coverage on invasive species in India.