जलकुंभी: कृषि के लिए एक गंभीर खतरा

Water hyacinth (Eichhornia crassipes) is a free floating perennial aquatic plant, native to South America.  Water hyacinth is a popular water garden plant because of the beauty of its large, purple to violet flowers and its interesting floating vegetation. Many plant nurseries and big box stores sell it as an ornamental pond plant.

Later it was seen that the plant is basically a very aggressive invader which can form thick mats on water surface. Gradually, it is known that among the aquatic plants, water hyacinth is the worst aquatic plant in the world.

It becomes a fierce competition with other micro flora and fauna in the aquatic ecosystem for light, space, nutrients and water. Now, water hyacinth is the most predominant, persistent and troublesome weed in India.

Water hyacinth (Eichhornia crassipes) is a perennial aquatic macrophyte belongs to the family Pontederiaceae and its name Eichhornia was derived from well known Prussian politician J.A. F. Eichhornia. 

Identification of Water hyacinth

Following are the points by which it is possible to identify the plant.

1. A mass of fine roots hang in the water underneath the plant.
2. The leaf stalk is thick and spongy and helps to keep the plant buoyant.
3. They are floating plants with round to oval; shiny green leaves up to ten inches in diameter, although smaller leaves are common.
4. Leaves are held upright so they act like sails.
5. The flowers are large (2-3 inches) and attractive. They are blue-purple or lilac-coloured with a yellow spot.

Similarity of Water hyacinth with other plants

Water hyacinth is often confused with a native floating plant, Frog’s bit. When not in bloom, water hyacinth may be mistaken for Frog’s bit (Limnobium spongia).  Another tropical floating leaved nursery plant, called water lettuce (Pistia stratiotes), may be mistaken for water hyacinth.

However, water lettuce does not have showy flowers and has large ribbed leaves. Water lettuce is much less cold-tolerant than water hyacinth.

Water hyacinth is one of the fastest growing plant

The growth rate of water hyacinth is among the highest of any known plant. Water hyacinth reproduces primarily by way of runners or stolons, which eventually form daughter plants. Each plant can produce thousands of seeds each year, and these seeds can remain viable for more than 28 years. Some water hyacinths were found to grow upto 2 to 5 meters a day in some sites in south-east Asia. The common water hyacinths (Eichhornia crassipes) are vigorous growers known to double their population in two weeks.                                                                                                  

Water hyacinth is wealth or weed? 

Water hyacinth is a plant with many advantages firstly because it can be used for many purposes, and other hand it’s a most invasive weed that can destroy precious aquatic ecosystem within a short time.

Uses of Water hyacinth:-

1. Green parts and inflorescence used as vegetable.
2. Used as animal feed especially as pig feed, fish feed (especially for gold fish).
3. Used for mushroom production.
4. Used in hydroponics (soilless agriculture).
5. Used for compost and vermicompost making.
6. It is used as green manure.
7. Ashes to fertilize the field.
8. Flowers used for treating the skin of horses.
9. Dry water hyacinth is used as fuel.
10. May be used in biogas production.
11. The plant has a high capacity for the uptake of heavy metals which could be make it suitable for the bio-cleaning of industrial waste water.
12. It removes cyanide which is environmentally beneficial.
13. It removes arsenic from arsenic contaminated drinking water and keeps water clean.
14. Water hyacinths can be cultivated for waste water treatment.
15. It can remove pesticides from contaminated water.
16. A means of removing radioactive contaminants from nuclear power plant waste water.
17. Used to make furniture, hand bag, rope, basket, mat, carpet, soap, paper etc.
18. Used in mulching.
19. Providing an alternative source of biomass
20. In charcoal briquetting, water hyacinth is used.
21. Leaf extract has been shown to exhibit phytotoxicity against another invasive weed Mimosa pigra.
22. Water hyacinth is a popular water garden plant (as an ornamental plant) because, of the beauty of its large, purple to violet flowers and its interesting floating vegetation.

Disadvantages of water hyacinth:-

1. It creates dense mats of biomass on water surface which are reducing light to submerged vegetation, can cause oxygen depletions and fish kills.
2. It causes imbalance in the aquatic micro-ecosystem. It is now considered a serious threat to biodiversity.
3. Diversity of fish stocks is often affected from proliferation of water hyacinth.
4. It causes significant increase in water loss due to evapo-transpiration.
5. It causes practical problems for marine transportation, in hydro-power and irrigation schemes.
6. Blockage of canals and rivers causing flooding.
7. Micro-habitat for a variety of disease vectors.
8. It is also becoming a serious menace in flooded rice fields, considerably reducing the yield.
9. Water hyacinth is often problematic in man-made-ponds if uncontrolled.
10. Alter animal communities by blocking access to the water.
11. Eliminate plants on those animals depend on for shelter and nesting.
12. Reduces fishing opportunities.
13. Decaying plants make water unfit for drinking by humans, livestock and wildlife.
14. Tremendous losses annually in fish and paddy production in India.
15. Destroying natural wetlands.
16. Changing the temperature, PH and oxygen levels of water.
17. Reducing gas exchange at the water surface.
18. Restricting recreational use of waterways.
19. Reducing aesthetic values of waterways.
20. Destroying fences, roads and other infrastructure when large floating rafts become mobile during flood events.
21. Destroying pastures and crops when large floating rafts settle over paddocks after flood events.

Management / control of Water hyacinth: -

There are four commonly used control efforts used to suppress water hyacinth infestations. These are  Physical, cultural, biological and  chemical control.

However, no one control is better than the other because each has its own constraints. The choice of control is dependent on the specific conditions of  affected location such as the extent of water hyacinth infestation, regional climate, and proximity to human and wildlife.

1. Physical control:-

Physical control is performed by land based machines such as bucket cranes, draglines, or broom or by water based machinery such as aquatic weed harvester, dredges or vegetation shredder. Mechanical remover is seen as the best short term solution to the proliferation of the plant.

Disadvantage with mechanical harvesting is that it can lead to further fragmentation of water hyacinths by spinning cutters of the plant harvesting machinery. The fragments of water hyacinth that are left behind in the water can easily reproduce asexually and cause another infestation.

The practice of mechanical harvesting is not effective in large scale infestations of the water hyacinth, because this aquatic invasive species grow much more rapidly than it can be eliminated. 

Harvesting and removal of plant material is labour intensive and expensive. A less expensive method is the use of floating barriers that can contain the weed in a small area. Dredges, which drag plants into river banks, are effective if the material is allowed to dry and then burned.

2. Cultural control: -

(i) Nutrient run-off into infested water ways should be minimized. (ii)Drainage or reduction of water levels can also reduce the area of water hyacinth plants. (iii)Salty water is to be introduced to infested water ways.

3.  Biological control:-

Because of E. crassipes invasiveness, several biological agents have been released to control it:-

4. Chemical control:-

The use of chemical herbicides is only used in case of severe infiltration of water hyacinth. The chemical regulation of water hyacinth can be done using common herbicides such as 2, 4-D, Glyphosate and Diquat. The herbicides are sprayed on the water hyacinth leaves and leads to direct changes to the physiology of the plant.

2,4-D: The use of herbicide known as 2,4-D leads to the death of water hyacinth through inhibition of cell growth of new tissue and cellular apoptosis. It can take almost  a two week period before mats of water hyacinth are destroyed with 2,4-D.

Glyphosate:- For the herbicide glyphosate, it has low toxicity than the other herbicides, therefore, it takes longer for the water hyacinth mats to be destroyed about three weeks. The symptoms include steady wilting of the plants and a yellow discolouration of the plant leaves that eventually leads to plant decay.

Diquat:- The herbicide known as diquat is a liquid bromide salt that can rapidly penetrate the leaves of the water hyacinth and lead to immediate inactivity of plant cells and cellular process.

Natural control of Water hyacinth: -

Water hyacinth leaves are killed by frost and salt water. Water hyacinth do not grow when the average salinity is greater than 15 percent that of sea water. In brackish water, its leaves show epinasty and chlorosis and eventually die.

Conclusion:-

As an agrarian country, our main concern is to produce more food and other agricultural products to feed the ever-increasing population  of our country as well as providing basic amenities to them.

In the way of that whatever the hurdles will come, it is necessary to remove (solve) that. Water hyacinth which was brought in our country as ornamental plant, now it becomes a problematic weed in crop field, especially it is becoming a serious menace in flooded rice fields, considering reducing the yield.

It competes with other micro flora and fauna in the aquatic ecosystem especially a hurdle in fish production, major constraint in canal, pond and river water irrigation as well as reduces the quality of irrigation water, though the water hyacinth has the several disadvantages out of agricultural activities also.

The primary objective of water hyacinth management is to maintain the stability of an ecosystem. To do this job satisfactorily, the major eco-friendly approaches are mechanical control, application of anti-transpirant materials, proper use of allelopathy potential and biological control that ranged from partial to highly successful.

The best method of controlling water hyacinth is to prevent it from being introduced into a freshwater system. This can be done by educating the people about the problems. 

Author

Hiralal Jana

Department of Agricultural Extension, College of Agriculture,

Bidhan Chandra Krishi Viswavidyalaya, Agricultural Farm-713101; Burdwan, West Bengal, India;

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