Surinder Sud: Deadly Parthenium is back

FARM VIEW

But the Mexican beetle has finally been cleared as an environmentally safe bio-agent to control it.

Parthenium, one of the world's seven most devastating and hazardous weeds, which had played havoc in India in the 1970s, has again become a formidable menace almost throughout the country.

Entering India along with imported foodgrains in the mid-1950s, it had established itself quickly and spread so rapidly as to necessitate a nation-wide Parthenium eradication campaign in the 1970s. There is a danger of a similar situation arising again if it is allowed to proliferate unabated.

More worrisome are its health hazards for humans and animals as its contact can cause skin allergies and its ingestion by animals can lead to their mortality.

Technically called Parthenium hysterophorus, this wild plant has acquired various local names. The most common of these names is "congress grass", presumably because of its white flowers, similar to the white cap worn by many Congress party leaders.

Besides, it was deemed as difficult to remove as the Congress party rule in the country seemed till the 1970s. It is also called gajar ghas and gajar buti because of its resemblance with the carrot plant.

The weed, now occupying even non-crop areas like wastelands, pastures, open forests, orchards, municipal gardens and along road and rail lines, spreads through the plant's seed that can easily be transported through wind, water and animal, and human activity.

The plant proliferates exceedingly fast because it starts bearing seed in a month and a single plant can produce up to 25,000 seeds.

The control of this weed through manual uprooting or even chemical weedicides is unworkable for various reasons. For one, it is difficult to employ so much manpower to uproot the plants from such a vast area. The allergic reaction that it produces on sensitive individuals is another hurdle.

Besides, there is also the danger that mature seeds will drop off during hand-pulling and infest more areas. The use of chemicals, on the other hand, is impractical because of the needed scale of operation and cost involved. Moreover, it can also create environmental problems.

However, the Jabalpur-based National Research Centre for Weed Science (NRCWS) has come up with a biological control method that seems practical, economically affordable and environmentally safe.

The Centre has also discovered some gainful uses of the residues of this plant. The biological control agent for Parthenium is a beetle (an insect called Zygogramma bicolorata).

It feeds on this plant, especially the growing portions, curbing its growth and seed-bearing. The defoliated plants gradually die.

Indeed, though the effectiveness of the Mexican beetle in controlling Parthenium was ascertained long ago, its widespread deployment has been held back because of the controversy over its effect on other crops.

Some reports indicated that this beetle could also feed on and destroy sunflower, an important commercial oilseed crop. But a fact-finding committee appointed by the Indian Council of Agricultural Research (ICAR) in November 1992 has finally cleared the Mexican beetle as an environmentally safe bio-agent for the control of Parthenium.

The field studies sponsored by this committee indicated no evidence of this beetle damaging any commercially important crop. The ban on its widespread use has consequently been lifted.

In other countries, several other species of insects and some rust disease pathogens have also been used to check Parthenium. These include Epiblema strenuana (a Mexican moth) and Listronotus setosipennis (a stem-boring weevil from Argentina) among others. But these bio-agents have yet to be tried out under Indian conditions.

According to NRCWS director N T Yaduraju, an effective control of this weed can be achieved by releasing about 500 to 1,000 Zygogramma beetles at a spot.

They multiply quite fast. Once they have destroyed the weed in the area where they are released, they migrate to adjacent regions in search of this plant.

The NRCWS is breeding these beetles and is distributing them free of cost so that it can get established over a larger area. It is sending them even through couriers to those who ask for them.

It has also discovered that this plant can be composted and converted into nutrient-rich manure. Besides, its stems can be used for making plyboards.

The Dehradun-based Forest Research Institute has discovered that the stem contains fibre which is strong and can perhaps be put to some useful application.