The weed plant, Parthenium hysterophorus L., does not need an introduction about it, because it can be seen everywhere in our country. It is also known as Congress grass and also as Carrot weed. Earlier it was introduced to India in seed form as a contaminant of food grains imported from Mexico and it was reported in Pune (Maharashtra) in 1956 for the first time. Within a decade it spread so vigorously in the plains of India that it became a problematic weed posing problem of its extermination.
How does it spread so fast ?
A portentous fact about Parthenium is that a single plant can produce 620 million pollen grains and about 15,000-25,000 seeds. The seeds are fluffy, very small in size and light in weight easily dispersed by wind, water or through various human activities. And also it has the capacity to regrow from the cut or broken parts.
The allelopathic effect, coupled with the absence of natural enemies like insects and diseases, is responsible for its rapid spread in its introduced ranges. Growth inhibitors like lactones and phenols are released from this plant into the soil through leaching, exudation of roots and decay of residues. These growth inhibitors suppress the growth and the yield of native plants.
Why Parthenium is a dangerous weed ?
The pollen grains of the weed are allergic causing bronchitis, asthma, rhinitis, conjunctivitis, hay fever, sinusitis, common cold, pain in neck and even depression in human beings. The common allergens found in congress grass are parthenin, coronopilin, tetraneuris and ambrosin. Frequent contact with the weed causes dermatitis, eczema and gangrene. This weed is harmful and even fatal to the livestock population. As a weed of agricultural crops, this weed has marked effect on growth and yield of the crops.
Is there a way to control it ?
• Uprooting of Parthenium – should be done before flowering
• Chemical control is an effective method to control Parthenium in the areas where its natural enemies are absent.
• Controlling through Mexican beetle (Zygogramma bicolorata)
• Planting of Cassia tora, Cassia sericea and Tagetes spp., reduce the infestation
• Composting of Parthenium plants parts before flowering can also be done for better utilization.
• Can be effectively managed by Integrated Weed Management
Parthenium offers a big challenge to all attempts of control because of its high regeneration capacity, production of large amount of seeds, high seed germinability and extreme adaptability to a wide range of ecosystems. Parthenium grows luxuriantly in wastelands and vacant lands, flood plains, scrub/shrublands, urban areas, overgrazed pastures and along roadsides and railway track.
In non- cropped areas, we can manage the Parthenium easily by using Common salt. 1 kg of Common salt is mixed in 4 L of water and sprayed on the Parthenium plants which causes them to dry in one or two days. Foliar application of salt solution results in rapid absorption and translocation so that faster effect is noticed i.e rapid leaf discoloration or chlorosis leading to decrement of photosynthesis in parthenium weed and rapid oxidation of the photo assimilate reserved in the leaves and stem of this weed.
Let us all take some small but coordinated steps to eradicate this weed.
The Author L Mohanapriya is an agriculture student.