MEMO FROM NARA

While I go for my early morning or evening walk, I observe many kinds of plants – big and small all along the way. One of the small categories, about 50 to 100 cm tall green plants with full of tiny white flowers does not escape my eyes. They are in thousands growing happily all along the road and also in plots where no house is constructed so far. Residential colonies are invaded by these plants which are called Parthenium causing diseases like dermatitis and asthma. Along with this, many other unwanted plants grouped as weeds also grow, flower and die. They are the annual plants botanically termed as Parthenium hysterophorus and popularly known as Congress Grass or Carrot Weed. It belongs to the botanical family Asteracae.

It appears that Parthenium is not native to India, but it came with the imported wheat as a mixture, when the US sent wheat to India under PL 480 (Public Law 480 passed 1964 to give food grains to developing countries) in 1956. However, this concept was contradicted by some as not the real story because Parthenium was present in India even in 1951itself. Whatever may be the source of this nasty weed, the tiny seeds spread throughout the country. In general, weeds grow widely in waste lands, fields and field bunds. Controlling them is a stupendous task for weed scientists and farmers. Parthenium is very difficult to eradicate.  So far no single method appears to be satisfactory.

Since the regeneration capacity of this weed is very high, even the mechanical eradication like cutting or slashing did not work. Removal by hand or hoe at the pre-flowering stage is one of the physical methods of eradication recommended. But there are other methods too. Weed killing chemicals are sprayed on the land to kill the weed seeds or on the post-emergence stage of the weeds. One of the potent chemical used was the sodium salt of 2,4–dichlorophenoxy acetic acid popularly called 2,4–D  which acts as a plant hormone at homeopathic dose, whereas at high concentration it kills plants. Such chemicals are grouped as herbicide or weedicide. 

Large-scale usage of herbicides are followed at the US, Australia and many other advanced countries but only limited quantity is being used in developing countries like India. These herbicides are specific for certain plant species. For example, dicot plants are generally susceptible to all herbicides whereas the monocots – the grass family cannot be eradicated by most of them. Fortunately, Parthenium is a dicot plant amenable a variety of herbicides.

In fact, research to find out suitable chemicals for eradicating weeds in cultivated fields as well as in waste land is being extensively carried out in various agricultural universities and research institutes. Even biological control measures and biotechnological techniques are attempted to eradicate Parthenium. In order to control this weed, awareness camps are being conducted regularly in every colony as it has been done in villages for the farmers. Instructions are given to the citizens for effectively controlling Parthenium.

I used to watch carefully the growth behavior of this weed. At the onset of South West Monsoon, the plants emerge from the soil in rosette form by spreading it leaves close to the ground without an elongated stem. Only with the shower of rain, these plants look dark green as if we have applied good amount of nitrogenous fertilizer. I do not know how they got such green foliage. May be they mine the nutrients available in the waste-land. A month afterwards, I used to observe them to put forth elongated stem which grow to the size of about a meter with good number of branches with hundreds of tiny flower buds. This process is technically known as bolting. Once the plants reach such a stage, the pollen from the flowers fly in the air and animals and humans happen to inhale them and end up in irritation of body and develop allergy symptoms. I tried to pull out some of those plants which came up in front of my house. Fortunately I did not get the allergy, when I enquired with the weed specialists; they told me that it will affect only some susceptible people. I was happy that Parthenium is afraid of me.

Once the Parthenium blooms, the seeds – thousands of them are carried by wind and spread all around the place. The seeds settle on the dry soil and stay there, till another rain soaks them. They remain dormant for a long period of time in the dry soil. So it is evident that this weed remains as a menace for human beings. In residential areas, to control this and other weeds, the only way comes to my mind is to construct houses as soon as possible without leaving the plot vacant. No other method is in sight for the time being to get rid of Parthenium around the residential colony.