(Published on the occasion of ‘Parthenium Awareness Week’ from August 16 to 22)
Sontara Kalita &
Milon Jyoti Konwar
Parthenium hysterophorus is commonly known as the ‘congress grass’ is an annual herbaceous weed, which has spread like wild fire in almost every State of India. This weed is known for its invasiveness, and potential to spread besides its adverse economic and environmental impacts. Its large and persistent soil seed bank, fast germination rate and ability to undergo dormancy make it well adapted to semi-arid environments.
The concept of ‘One year seeding, seven years weeding’ is true for Parthenium as it produces about 5,000-10,000 seeds per plant, which are viable even at immature stage. In dry summer months, Parthenium appears in a rosette form while during the rainy season, it grows up to 90 cm height, with profuse flowering and green foliage. It flowers throughout the year. Earlier Parthenium was restricted to only fallow and wasteland but now it has also spread to cultivable land.
Till the 1990s, its impact was not known on crops. But now, it has been identified as a major cause for the loss of crop production not only during the rainy season but also in the rabi season. At present it is one of the most troublesome and obnoxious weed of wasteland, forest, pasture, agricultural land and cause nuisance to mankind. Chemically, parthenin is the toxic substance present in the weed. It is the causative factor for many problems in humans namely dermatitis, skin irritation, nausea, giddiness and respiratory problems like bronchitis and asthma, eye irritation and sinusitis. It also causes acute toxicity in cattle; and milk becomes bitter in taste due to the presence of parthenin. If it is present in animal diet, it causes dermatitis with pronounced skin lesions and a significant amount (10–50%) of P. hysterophorus in the diet can kill cattle and buffalo. In India, P. hysterophorus causes a yield decline up to 40% in agricultural crops and due to the invasive capacity and allelopathic effects, it inhibits the germination and growth of other plants.
Control of Parthenium has been tried by various methods but no single management option has been found adequate to manage it. Hence, there is a need to integrate various management options. Manual uprooting of Parthenium before flowering and seed-setting is the most effective option; but it is not cost-effective due to its continuous germination in fields. In infested cultivated land, normal crop can be rotated with marigold during rains. Exploitation of allelopathy and competition through cultivation of competitive plant species such as Cassia sericea, Abutilon indicum and Cassia tora in non-cropped areas preoccupied by Parthenium has shown encouraging results.
Another important aspect of Parthenium management is its use in a beneficial way in crop production and other human activities. Attempts should be made to use Parthenium for bio-pesticides, biogas generation and green manuring. Parthenium plants before the flowering stage can be a good option to be used as mulch especially in the dry land areas.
Recent researches have identified several potential herbicides for control of Parthenium in the cropped and the non-cropped situations. Timing of chemical weed control is critical and these should be applied when the plants are small and have not produced seeds. In the non-cropped areas, spraying of 15 per cent common cooking salt solution, application of 2,4-D esters 1.0-1.5 kg / ha along with wetting agent, glyphosate 1.0-1.5 kg/ ha before the flowering stage can effectively control this weed. Whereas, in the cropped areas pre-emergence herbicides such as simazine/atrazine can be used in maize, sorghum and sugarcane (0.5-1.5 kg / ha), pendimethalin in almost all cereals, pulses and oilseeds (0.75-1.5 kg / ha) and metribuzinin soybean, potato and sugarcane (0.5-1.0 kg / ha) are the most suitable selective herbicides for its control.
Zygogramma bicolorata, a leaf-eating beetle is a potential bio-control agent which controls the Parthenium weed by feeding on its foliage. Recently a rust pathogen Puccinnia abrupta var.parthenicola was identified, which is also capable of controlling this weed. Some other insects which can be used against this weed are Bucculatrix parthenica (leaf-mining moth), Smicronyx lutulentus (seed-feeding weevil) and Listronotusseto sipennis.
Mass awareness about these weeds among all the section of people of society is of utmost importance. The government should also take initiatives of Parthenium-eradication awareness programmes on a mass scale to acquaint the public about its horrible effect on mankind, animals, biodiversity and crop production. Keeping in view the high reproductive potential and survival ability of Parthenium, possible integration of various methods including biological-based management options should be taken into consideration for its viable solution.
(The writers are from Assam Agriculture University, Jorhat)
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