Ways to weed parthenium out
Parthenium, a notorious weed, first sneaked into the country along with wheat grains imported from the us in the early 1950s. It has become a widespread menace ever since. The plant is a rapid coloniser and differs from other weeds in its remarkable adaptability to all kinds of soils and climatic conditions. During its initial years in India, parthenium flowered between February to April in the western part of India and between August to October in eastern India. However, its excellent adaptive qualities have ensured that today the plant completes its life cycle within a very short period and flowers 3-4 times in a year. Moreover, it can also proliferate vegetatively, if need be. Since it is an exotic plant, parthenium does not have natural enemies such as pests, pathogenic fungi, bacteria and viruses. Also, herbivores do not eat this weed and this helps its unhindered growth.
After taking root, parthenium out-competes other vegetations in its vicinity; its seed leachates even inhibit germination of other weed plants. There is thus no room for any plant biodiversity in a parthenium-infested area. Moreover, its luxuriant growth sucks out even the last drop of juice from the soil, rendering it totally infertile.
During a flowering season parthenium produces more than 600 million pollens per plant. These can cause diseases such as asthma, respiratory tract infection, rhinitis, conjunctivitis, hay fever, acute dermatitis and other debilitating allergies. However, it must be noted that only people allergic to parthenium suffer its ill-effects. But such numbers are not very large.
Next to impossible Uprooting parthenium is almost next to impossible, though scientific measures can check its spread to great extent. Recent researches suggest that the proliferation of the weed can be checked best through measures at the local level. The most widespread method used in the country today is manual extirpation. While this is economical, it exposes a person to health hazards associated with bodily contact with the weed.
Another alternative is the use of chemicals. This is a broad-spectrum controlling procedure. Weedicides such as atrazine, metribuzin, monuron, neburon, oxadiazon, simazine, terbutryn have been found effective in controlling parthanium. Herbicides such as dicamba, glyphosate and picloram have also yielded good results. Perhaps the most economical chemical control method is spraying brine salt (15 per cent common salt) solution to dry out the plants and burning them thereafter. However, this method is not always advisable: biomass burning in large amount may generate biogenic gases, which cause serious pollution. Moreover, this method is not suited for densely populated areas.
Biological methods have also been used to curb parthenium-spread. Research has shown that wasteland shrubs, ca ssia serecia and cassia tora, inhibit germination of the weed's seeds. Plant extracts or leachates of marigold have also been found to inhibit germination of parthenium seeds. The introduction of the Mexican beetle (Zygogramma bicolorata) satisfactorily curbed parthenium growth in fields of Central and southern America. However, recently it has been found that this beetle feeds on other plants such as sunflower, xanthium and cocklebur. Moreover, its efficacy in Indian conditions has not yet been proved.
But parthenium is not always a menace. It has some potential uses as well: to make green manure or vermicompost, as an efficient binding agent to check soil erosion and as a raw material for biogas generation. Parthenium pollen is also being used these days in the manufacture of pesticides.
Managing parthenium calls for proper planning; awareness about this weed should be raised among the general public. Government, voluntary organisations and panchayats should join hands in this endeavour.
Dipanjan Ghosh is at the Centre of Advanced Study, department of botany, Calcutta University