1. INTRODUCTION

Water is the most versatile and indispensable component on this

planet earth, holding both biotic and abiotic entities in a complex dynamic

and delicate ecological balance by virtue of its unique capacity of existing in

solid, liquid and gaseous states. The total quantity of water on the earth is

about 13.2 x 109 km3 , 97% of it is marine water, while fresh water is only

2.7%. Of the latter, 90% is either frozen in the north and south poles or very

deep groundwater at a depth of more than 700 m. The amount of

groundwater in the world is estimated to be about 22 million km3 . Thus, they

are not available to man (Abdel Shafy and Aly, 2002). The total amount of

water in the entire world rivers are about 48.000 km 3 , human use less than

4.000 km 3/a, only.

India is a country studded with scenic beauty, comprising of various

landforms criss - crossed by rivers. There are fourteen major rivers in India

that share 83 % of the total drainage basin and contribute 85 % of the total

surface flow Chaudhuri, 1982). India receives an average annual

rainfall equivalent of about 4,000 billion cubic metres (BCM) (Rajvaidya and

Markandey, 2005). This only source of water is unevenly distributed both

spatially as well as temporally. Of the 4,000 BCM of available water from

precipitation, the mean flow in the country's rivers is about 1,900 BCM. Out

of this, only 690 BCM is utilizable. With 177 BCM of live storage created by

the existing major and medium projects and another 75 BCM of storage from

projects under construction, there is still a gap of 440 BCM of water, which is

utilised (Central Water Commission, 1997). Since independence, India has

witnessed an unprecedented increase in population. From a population of

about 343 million in 1947, the population has grown at a rate of 2.04% to

cross the 1,000 million mark in 2000. With increasing number of mouths to

feed, there has been additional pressure on agriculture resulting in increase

in net sown area from 119 million hectares in 1951 to 142 million hectares in

1997; high cropping intensity has also resulted in increased demand for

water resources. Domestic water need in the urban areas has also grown

notably with the current urban population at 4.5 times the population level in

1950s (TERI, 1998). The relationship between water quality and human

activities is extremely complicated. Water is used extensively for domestic,

industrial and agricultural purposes and after use is usually returned in a

degraded state to rivers, lakes, estuaries or oceans. The growth of

population and industry has resulted in an increase, both in the total volume

of sewage and the degree of toxicity of industrial effluents in which the share

of obnoxious matter has markedly increased (Gaitonde, 1995; Murugesan

et al., 2002a) resulting in eutrophication of water bodies and inturn leading to

the invasion of foreign vegetative species.

Most of the rivers have been unmindfully used for the disposal of

domestic and industrial effluents far beyond their assimilative capacities and

have been rendered grossly polluted (Agarwal and Sharma, 1982). They

also estimated that about 80 % of total population in India is deprived of pure

and safe drinking water and revealed that there were 1,53,000 problem

villages in India, which had infected water supply, 90 % of total drinking

water are severely polluted. Ganga is the most polluted river of the world.

Other Indian rivers including Damodhar, Hooghly, Kulu have almost the

same story to reveal.

In Southern India, the perennial river Tamirabarani serves as the

prime source of water for Ambasamudram, Vickramasingapuram,

Cheranmahadevi, Tirunelveli, Sankarankoil, Alankulam and Tenkasi places

like, Sattur and Radhapuram of Thoothukudi district. Rising up of number of

industries and populations, especially in the lower reaches have increased

concern over the water quality of the river.

1.1. Tamirabarani River Basin

Tamirabarani, one of the perennial rivers in Tamil Nadu, originates

from Pothigal hills on the eastern slopes of the Western Chats and drains its

water with the Bay of Bengal at Punnakayal of the Gulf of Mannar. The total

area of the basin is 5969 sq. km out of which the hilly catchment area

comprises of 688 sq. km . The river travels about 120 km through Tirunelveli

and Thoothukudi districts, covering a total area of about 5969 sq. km (Plates

1 D and 1 E). Its historical importance is depicted by the reference of river

Tamirabarani in great Indian epics, Ramayana and Mahabharatha and

various Tamil literatures. An eminent sage and poet Agasthiar is much

associated with this river. Etymologically the term "Tamirabarani" is treated

in different contexts. In Sanskrit "Tamira" means copper or red, "Parna"

means a leaf or a tree and the "Verna" means colour. Hence it may be called

as the river of red. Another synonym being, the "river flowing among red

(sandal) trees". Those days the river basin comprised ample number of

sandal trees along the banks of the river, imparting the fragnance to the river

water (Pate, 1916). Peyar, Vellar, Karaiyar, Pambar and Servalar are the

tributaries of Tamirabarani river basin in the Western Ghats. Three important

reservoirs namely, Pabanasam, Servalar and Manimuthar have been

constructed across this river. The following are the important channels of this

river, Kannadian, Palayam, Maruthur, Srivaikundam (Murugesan and

Sukumaran, 1999; Murugesan et al., 2002c). The perennial flow of

Tamirabarani river basin is regulated by Pabanasam and Servalar reservoirs

that impound and regulate its flow to meet out the irrigation demands and to

produce hydroelectric power. Kodaimelagian, Nadiyunni, Kannadian,

Ariyanayagipuram, Palavur, Suthamalli, Maruthur and Srivaikundam are the

eight anicuts endowed with this river basin.

1.2. Pollution due to Industrial Discharge in River Tamirabarani

Pollution of river courses associated with industrial discharge and

refuse from human settlements is a global problem. In India it is reported that

about 70 % of the water in freshwater systems are polluted (Citizens Report,

1982). The chief source of pollution is identified to be sewage constituting 84

- 92 % of the wastewater. Industrial wastewater comprises 8 - 16 %

(Chaudhari, 1982). Tamirabarani river basin on its banks has a number of

industrial units including pulp and paper, textile, state transport corporation

workshops, photographic industries and other small-scale industries. Every

industry draws fresh water and discharges wastewater at some stage or the

other.

The problem that greatly confronts the public is the liquid waste with

inorganic and organic content. The waste liquids from textile mill comprises

mainly of dye stuff, sulphates, sulphide, copper, zinc, lead, phenolics and

wastes from the manufacture of pulp and paper contains sulphides,

/1

chlorides, lignocellulosic wastes, mercaptans, mercury etc. such pollutants

are of much concern to the ecosystems as they do not breakdown, resist to

biodegradation and ar found to enter the animal and human systemsaHi ck,ttj11,.

(Murugesan 1988).

Tamirabarani, mainstream receives the effluent from the major textile

industry, Madura Coats situated on the banks at Vickramasingapuram. It

draws water from the river for the manufacturing process and emptying

effluent and sewage with partial treatment through a channel into the river

(Murugesan and Haniffa, 1992). Oily wastewater from the Tamil Nadu state

transport corporation workshop at Pabanasam adds much more pollution

into river. Another major industry, M/S Sun Paper Mills situated on the banks

at Cheranmahadevi also draws water and generates effluent, a part of which

ultimately reaches the river. In addition there are small-scale industries, large

and medium industries functioning in the river basin. Systematic

observations made at various points of the riverine basin shows that the

effluents are being regularly discharged and cause serious pollution

problems (Kundra etal., 1997; Murugesan and Sukumaran, 1999).

1.3. Exuberance of Aquatic Weeds in River Tamirabarani

The head reach of Tamirabarani river basin is almost devoid of

perennial weeds. However, luxuriance of few exotic weeds like Clerodendron

inflortunnatum, C!erodendron phomidis, Lantana camara and Chromolaena

odorata were scarcely dispersed. The exuberance of weeds was highly

incidenced in places especially where the solid and liquid wastes confluence

with the river. Weeds like Xanthium indicum, Cyperus corymbosus Typha

angustifolia, Parthenium hysterphorus, Prosopis chilensis, Ipomoea carnea,

c

Ipomoea obsura and Eichornia crassipes were found invariably in pools,

ponds, puddles, channels, canals and ditches associated with the river.

Moreover, free floating weeds like Salvinia molesta, P1st/a stratiotes, Lemna

minor, Azolla pinnata, Spirodela polyrchiza were found to be seasonal. Also,

the algae like Microcystis aeruginosa, Sps. of Anabaena, Osdilatoria,

Chiamydomonas, and Pandoriana, Eudorina, Volvox etc. were common.

These invasive species produce undesirable odour and taste in the

impounded water and makes it unhygienic (Abraham and Samuel, 1999).

However, the exuberance of water hyacinth has been highly noticed

throughout the course of the river Tamirabarani (Murugesan, 2001;

Murugesan et al., 2002b).

The rapid colonization and distribution of aquatic weed Ipomoea

carnea have reflected the abundance of sewage pollution in places like

Ambasamudram, Veeravanallur, Cheranmahadevi, Melapalayam, Tirunelveli

Town and Sindupoondural. Pandey (1973) reported that encroachment of

aquatic weeds due to adverse pollution along the course of river has

changed the water flow and it's current. The luxuriant growth of invading

aquatic weeds in the main stream could however be attributed to the

domestication, industrialization and clearance of riparian vegetation along

the course of riverbanks. On the zone affected by the organic enrichment

there has been an increase in the total biomass of the benthic fauna due to

good supply of waste, where the effects are severe, pollution can lead to the

elimination of fish population from long reaches of the stream (Murugesan

and Sukumaran, 1999).

IN

1.4. Causes for Weed Proliferation

The abundance of weeds in this river ecosystem could be attributed to

the following reasons.

1. Clearance of riparian vegetation along the bank for

domestication or industrialization.

2. Invasion of exotic weeds.

3. Eutrophication of riverine ecosystem.

4. Reduced water flow due to construction of dams.

5. Lack of controlling measures of weeds.

Aquatic weeds are generally characterized by a rapid vegetative

growth and the ability to regenerate by asexual means, by fragmentation

(production of new plants from small plant segments) or vegetative

hibernation organs (tubers and turions). The factors, however, which

contribute to their rapid development, are often connected with the normal

pattern of succession. Some of the most troublesome aquatic weeds are

essentially primary colonizers of aquatic ecosystems. If control measures are

not carried out and factors like nutrient content of the water, light,

temperature, or water movement do not bring about a limiting effect on plant

growth, shallow waters will eventually be filled up with vegetation. This will

lead to swamp formation and, ultimately, transformation into a terrestrial

habitat.

From an ecological point of view the floating aquatics are pioneer

plants because they occupy water surface and spread essentially in two

dimensions. The growth rates are usually high. The large growth rates are

IVA

obtained through clonal growth. The clone itself is usually long-lived and the

individual ramets are mostly short-lived. The spread is from one or more

inoculation points and it spreads with a closed front (Cook, 1990). The

causes for the extensive growth of aquatic weeds, are discharge of domestic

sewage and agricultural drainage water containing nutrients like nitrates and

phosphates. Both nitrogen and phosphorus occur in small amounts in

natural waters, but their concentrations get greatly increased by activities of

man. As much as 80 % of nitrogen and 75 % of phosphorus added to

surface waters originate from the discharge of domestic sewage. It is

estimated that upto 70 % of this comes from thethe use of household

detergents. Continuous addition of nitrates and phosphates enrich the water

body and accelerate the proliferation of aquatic weeds. Although aquatic

weeds are found to infest pristine waters, their proliferation rate is enhanced

in waters rich in nutrients.

1.5. Water Hyacinth - Morphology and Growth Pattern

One of the major problems in freshwater bodies of the tropics and sub

- tropics is the floating aquatic weed water hyacinth, Eichhornia crassipes.

Another species, Eichhornia azurea, is found in shallow waters and is

rooted. The centre of origin of Eichhornia crassipes is believed to be

Amazonia, Brazil, with natural spread throughout Brazil and to other Central

and South American countries (Barett and Forno, 1982). Plants continued to

spread around USA and eventually around the world. Many of these plants

were disposed of or spread into ponds and waterways where they rapidly

established and continued to expand their range. The spread of water

hyacinth has been spectacular and disastrous. Particularly extensive

infestations developed in the Southern USA, Mexico, Panama, much of

IN

Africa, the Indian sub-continent, Southeast Asia. Australia and the Pacific.

Water hyacinth infestation has been a menace choking river systems to a

greater extent in Africa and Asia (Mshigeni et al., 2002). The explosive

growth rate of the weed is to a large extent due to eutrophication in water

bodies. In addition, the absence of natural enemies of the plant contributes

to the rapid growth of this weed. The problems are very severe especially in

countries where human activities and livelihood are intimately tied to public

water resources.

Water hyacinth is a monocotyledon belonging to the Pontederiaceae

family. Plants are sturdy and robust, varying in height from a few inches to

50 inches and form a bushy mass of fibrous roots 6 to 24 inches long

(Harley, 1990). Perennial rhizomes 1 to 10 inches long are surmounted by a

rosette of broad, glossy, dark-green petioled leaves, which are generally

emersed. The plant will also root on the margins of lakes and swampy areas.

The inflorescence consisting from 2 to 38 flowers is borne on a spike above

the leaves. Individually flowers are about an inch-and-a-half in diameter, the

lavender perianth having six lobes, with the banner petal displaying a yellow

spot surrounded by a purple-blue border (Parsonsand Cuthbertson, 1992).

As the individual flowers wilt the spike twists and bends over; when the

mature fruit capsule splits, the seeds are cast into the surrounding mat of

hyacinths or into the water, where they sink to the bottom. A stand of

medium sized water hyacinths can produce as high as 45 million seeds per

acre, but because relatively few of the seeds have the requisite conditions

for germination only about 5 % normally produce seedlings. Seeds have

been reported as remaining viable for 5 - 20 twenty years (Mathews et al.

1977). Viability seems to be unaffected by storage in wet or dry conditions.

Seeds kept in wet conditions may germinate sooner than those kept dry

though the percentage of seed germination does not appear different

between the two conditions. Buried seeds do riot germinate (Wright and

Purcell, 1995). High light intensity and alternating high and low temperatures

(5 - 400C) favour germination (Gopal, 1987). The vegetative reproduction is

asexual and takes place at a rapid rate under preferential conditions

(Herfjord etal., 1994). In vegetative reproduction daughter plants are being

produced by stolons, which grow laterally below the water surface from the

central rhizome, and interconnected plants forming enormous mats of

vegetation. The growth form of the shoot system is sympodial, with ramets

produced from lateral meristems (Watson, 1984). This fast multiplying weed

can produce 3000 offsprings in 50 days and can double its biomass in 10-12

days (Naseema et aL, 2004). The average water content of the water

hyacinth is about 94 percent and approximately 1 1 wet tons are required to

produce 1 dry ton containing 5% moisture (Mazjid, 1992).

Habitat

E. crassipes grows in shallow temporary ponds, wetland and

marshes, sluggish flowing waters and large lakes, reservoirs and rivers.

Optimum growth of water hyacinth occurs in eutrophic, still or slow - moving

freshwater with a pH of 7 and abundant nitrogen, phosphorus and potassium

(Reddy et al., 1991). Plants can however tolerate a wide range of growth

conditions and climate extremes, allowing the weed to infest countries

across a wide range of latitudes and climates.

Good growth can continue at temperatures ranging from 22 0C to 350C

and plants survive frosting (Wright and Purcell, 1995). Although prolonged

1 (1

cold weather may kill plants, the seeds remain viable (Ukei and Oki, 1979).

Plants can infest pristine, relatively low nutrient waterways (Hitchcock et al.,

1949) and can survive for several months in low--moisture substrates. They

can tolerate acidic water but cannot survive in salt or brackish water

(Penfound and Earle, 1948).

1.6. Problems Caused by Water Hyacinth in Waterways

(a) Impediments to flow in open channels

Water hyacinth can grow so densely that a human being can walk on

it. When it takes hold in rivers and canals it can become so dense that it

forms an herbivorous barrage and can cause dangerous flooding (Joffe and

Cooke, 1997).

(b) Blockage of intakes

Water hyacinth has high growth rate and causes physical obstruction

of waterways, hydropower, water abstraction units etc., which has serious

consequences (Masifwa et al., 2001)

(c) Micro-habitat for a variety of disease vectors

Water hyacinth is known to cause environmental problems by

encouraging breeding mosquitoes (Charudattan, 1996; Honmura and

Miyauchi, 1998). The diseases associated with the presence of water

hyacinth weeds in tropical developing countries are among those that cause

the major public health problems: malaria, schistosomiasis and lymphatic

filariasis. Some species of mosquito larvae thrive on the environment

created by the presence of aquatic weeds, while the link between

schistosomiasis (bilharzia) and aquatic weed presence is well known.

Although the statistical link is not well defined between the presence of

aquatic weeds and malaria and schistosomiasis., it can be shown that the

brughian type of filariasis (which is responsible for a minor share of

lymphatic filariasis in South Asia) is entirely linked to the presence of water

hyacinth (Bos, 1996).

(d) Water loss due to evapo-transpi ration

Various studies have been carried out to ascertain the relationship

between aquatic plants and the rate of evapotranspiration compared with

evaporation from an open-surfaced water body. Saelthun (1994) suggests

that the rate of water loss due to evapotranspiration can be as much as 1.8

times that of evaporation from the same surface but free of plants. Gopal

and Sharma (1981) have estimated that the average loss of water due to

evapo transpiration by water hyacinth is 3.5 times greater than from the free

water surface. Of the about 8 lakh hectare of fresh water available in India

for pisciculture, about 40 % is rendered unsuitable for fish production by

E. crassipes and S. molesta (Abassi et al., 1988). FACTS (2003) document

that water loss in water body infested with water hyacinth is 4 times higher

than open water. In India water hyacinth reduces the volume of available

freshwater by increasing losses through evapotranspiration (upto 9.84%

reduction reported). It impedes the flow of water in irrigation systems

(40-90% reduction reported) (Jayanth, 2000).

(e) Problems related to fishing

Water hyacinth poses several problems for the fisherman. Access to

sites becomes difficult when weed infestation is present, loss of fishing

equipment often results when nets or lines become tangled in the root

systems of the weed and the result of these problems is more often than not

a reduction in catch and subsequent loss of livelihood. In areas where

fishermen eke a meagre living from their trade, this presents serious socio-

economic problems (De Groote and Neuenschwander, 2003). Fishermen on

Lake Victoria have also noted that, in areas where there is much water

hyacinth infestation, the water is 'still and warm and the fish disappear'. They

also report that crocodiles and snakes have become more prevalent.

(f) Reduction of biodiversity

Where water hyacinth is prolific, other aquatic plants have difficulty in

surviving. This causes an imbalance in the aquatic micro-ecosystem and

often means that a range of fauna that relies on a diversity of plant life for its

existence will become extinct. The weed forms a permanent floating fringe

replacing, Pistia stratiotes at the highly productive wetlands, altering food

web and affecting biological diversity (Masifwa et al., 2001). Diversity of fish

stocks is often affected with some benefiting and others suffering from the

proliferation of water hyacinth. To date, some of the species like Protopterus

aethiopius, C/anus ganiepinus and Mormyrus species have disappeared in

catches (Ogari, 2002). People often report of localised water quality

deterioration. This is of considerable concern where people use water for

domestic purposes.

1.7. Methods of Water Hyacinth Control

Attempts to control the weed by conventional methods mainly by

mechanical or manual removal and chemical herbicides are providing only

temporary, but costly solutions. Constant removal of water hyacinth by

manual and mechanical methods from the water bodies weakens

productivity. Moreover, the use of chemical herbicides is often prohibited

because people and livestock often depend heavily on these water

resources. The chemicals, which are nearer to the natural constituents of the

chemical ingredients of the ecosystem either in them or in their degradation

products, should be preferred. The only logical, long-term and sustainable

solution is to employ an approach to water hyacinth management in which

biological control agents play the central role. Biological control (pest or

weed suppression in a gradual and long-lasting manner), especially by using

insects has been highly successful in reducing water hyacinth infestations in

the Southern United states and several other countries.

Physical Control

The time-honoured method of aquatic weed control is that of manual

labour hand pulling, raking, cutting and other techniques. A range of hand-

held tools is used in Europe for weed control. They include sickles, grass

hooker, rakes, forks and chain knives, most of which are used in rivers,

canals and drainage channels. Implements used in tropical regions are

similar but the diversity of techniques is greater, including devices for

cleaning lakes, such as floating blooms, rope or nets used for removing free

floating weeds (Philipose, 1968; Ramachandran, 1963). Manual techniques

are an important means of weed control in countries where labour is readily

available and cheap, but success is variable due to such factors as the

extent of weed removed. In India 50 % of manual treatments of water

hyacinth achieved partial success. Short - term control of water hyacinth by

hand - picking seedlings has been effected.

IWAI

Manual clearance may be inefficient as it can leave 10 % or more of

the weed untouched. It has been recorded that the improvement of flow in

an Indian irrigation canal following manual clearance was consistently poorer

than that produced by mechanical cutting. Regrowth to nuisance density

tends to be rapid and more than one removal per season is usually required

(Fourie, 2002). The removed plants can be allowed to dry or can be utilized

for other purposes, such as making pulp and papers, utilizing for compost -

making etc. They have also been used in preparation of animal feed. Crude

protein of high nutritive value has also been extracted from water hyacinth.

Manual control is a preliminary measure for chemical control. Manual

harvesting is not economically feasible, as it requires 600 - 900 man - hours

per hectare. Reproliferation of weeds within short period is also experienced.

So this method has proved unsatisfactory and uneconomical.

Mechanical control involves the use of mechanical harvesters. Many

mechanical devices have been developed for removing water hyacinth from

water. These are weed-harvesting machines that pull out the weed out of the

aquatic systems (Ramey, 1982). They are usually mounted on floating

platforms and consist of belts, cutters, forks etc. to remove the weed from

the water. A 100 ha infestation of water hyacinth grows by 5 ha per day and

in this case a mechanical harvester would be required to remove at least

8 - 10 ha per day if significant progress is to be made. Harvesting is very

costly. It is a slow and time-consuming process and in inaccessible areas, it

is difficult to operate.

1

Chemical Control

An effective herbicide cannot be an ideal herbicide so far its effect on

the life in the ecosystem is concerned. The longer the herbicide remains

active in the ecosystem the more effective it is for weed control. However,

since most such herbicides are unnatural chemicals, they are considered as

pollutants in the ecosystem and have some chronic adverse effects upon the

animal organisms of the aquatic habitat and human health also may be

affected by direct and indirect exposure or ingestion. The indiscriminate use

of chemicals has given rise to problems like development of resistance to

weedicides, emergence of new weed problems and environmental problems.

The scope of minimizing their adverse effects lies in their judicious and safe

application. It would involve need-based application.

Various herbicides have been employed in water hyacinth control.

Glyphosate is a herbicide specific in controlling water hyacinth (Baird et al.,

1983; Gopal, 1987). Kill of water hyacinth is gradual and takes up to four

weeks for foliage destruction. 2 - 4 - D amine has also been used for water

hyacinth control (Behawi and Mohamed, 1984; Gopal, 1987), but now

prohibited due to its toxic effects on fish and other aquatic organisms. It is

commonly used at the rates of 2 - 4 kg / ha but more effective if applied in

two separate applications at half the rates. Another herbicide, Diquat that is

a non-selective contact herbicide, has also been used. It causes rapid kill,

but poilLiLes the water. 2 - 4 kg / ha of herbicide is generally required for

causing effective destruction (Okuma and Chikura, 1985; Chikura, 1986).

Terbutryn and ametryn used to control water hyacinth also cause

rapid kill of the weed (Langeland et al., 1983). Severe depletion of dissolved

oxygen of the water takes place resulting in fish mortalities. Mammalian

toxicities are low but both compounds are persistent for several months in

the environment. An application rate of 3 kg / ha of ametryn has shown to

give about 90 % kill of water hyacinth in Sudan and an application rate of

1 kg / ha of terbutryn has affected 100 % kill of water hyacinth in Nigeria.

Other herbicides such as aminotriazol and sulphonylureas have also proved

effective. Application of 40 g I ha of sulphonylureas showed good effect on

water hyacinth. Use of chemical herbicides leads to environmental pollution

besides causing its own inherent ill effects (Barretc et al., 2000).

Biological Control

Increasing global awareness of environmental hazards caused by

insecticide usage has generated a renewed interest in biological control

techniques and paved way for emergence and acceptance of novel concepts

in this area. Biological control of weeds has been fuelled up as an

environmentally benign but potentially effective method of weed control

(Mohan Babu et al., 2002, Mohan Babu et al., 2003). The use of natural

enemies has strong emotional appeal, as it is environmentally safe and

non-polluting (Charudattan, 2001). Although the utilization of natural

enemies has long been developed, the science of weed biology and its

relationship to environmental ecology and host parasite interaction has not

been developed and exploited fully. Biological control is the best alternative

method of weed control as it is eco - friendly and economically feasible.

Biological control offers a longer term, cheaper and less resource-intensive

solution compared to herbicidal treatment, but the effectiveness of this

approach relies on aspects of herbicidal and biological control (Wyk, 2002).

Biological control of aquatic weeds can be defined as activities aimed at

17

decreasing the population of an aquatic weed to acceptable level by means

of living organisms. In general, there are three approaches for the biological

control of aquatic weeds:

1. The use of selective organisms, i.e., organisms that attack one

or only a few species.

2. The use of non-selective organisms, i.e., organisms that attack

all weed species present.

3. The use of competitive plant species, i.e., plants that compete

with a weed species for one or more critical growth factors.

When selective organisms are used two main methods can be

distinguished as follows

1. Classical biological control- this implies the introduction of a

biological control agent for the control of an unwanted exotic plant. In

general, this is an organism, which attacks the weed in its native range but

does not occur in the region where the plant has been introduced. Most

biological control agents are introduced from the native range of weed,

where they are considered to be coevolved 'natural enemies'. This is

classical biological control (Ehler, 2000).

2. Inundative biological control- this implies an increase in the

numbers of biological control agents, which occurs already in the area. It can

be carried out throughout the season, or can be timed in order to increase

effectiveness during certain periods

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1.8. Potential Biocontrol Agents

Water Hyacinth Weevils

Two species of weevils such as Neochetina bruchi Hustache

(Plate 1B) and Neochetina eichhorniae Warner (Plate 1A) and a mite,

Orthogalumna terebrantis Waliwork (Plate 1C) are common bio-control

agents of water hyacinth. The two Neochetina species are the most widely

distributed and proved to be the most successful (Julien et al., 1999). The

taxanomic position of these weevils and mite are given below.

Neochetina bruchi

Phylum

Class

Order

Family

Genus

Species

- Arthropoda

- Insecta

- Coleoptera

- Curculionidae

- Neochetina

- bruchi Hustache

Neochetina eichhorniae

Phylum

Class

Order

Family

Genus

Species

- Arthropoda

- Insecta

- Coleoptera

- Curculionidae

- Neochetina

- eichhorniae Warner

Me

Neochetina bruchi and Neochetina eichhorniae are weevils generally

thrive in the water hyacinth plants and hence they are called water hyacinth

weevils. The adults of N bruchi and N. eichhorniae can usually be

distinguished by the colour and pattern of the scales covering the elytra

(fore wings). N. bruchi ranges in colour from uniform tan or brown with no

distinct markings to brown with broad, crescent-shaped or chevron-like tan

band across the elytra N. eichhorniae lack the tan band and is usually gray

mottled with brown (Jayanth, 1987). Both species have two short, shiny, dark

lines on the elytra on either side of the mid-line.

Damage

The damage caused by N. bruchi and N. eichhorniae are similar.

Adult feeding scars, when numerous, debilitate the plant by removing

extensive proportions of epidermal tissue thus increasing water loss and

exposing the plant to attack by pathogens. Extensive feeding around the

petiole girdles the petiole and kills the lamina (Plate 3A). Larval tunneling in

the lower petiole and crown, damages tissues and buds, initially preventing

flowering (Julien, 2001). As damage increases, plant growth rate is reduced

and production of new leaves and new stolons is reduced. Decline in plant

size occurs. Prolonged damage to the plant tissues results in rotting of the

lower petioles, water logging of the crown and gradual sinking of the plant.

Water hyacinth mite

Orthogalumna terebrantis

Phylum - Arthropoda

Class - Arachnida

sill

Order - Acarina

Family - Galumnidae

Genus - Orthogalumna

Species - terebrantis Wallwork

The adults of the water hyacinth mite are tiny, brownish-black

coloured and tear-drop shaped, measuring 0.43 x 0.26 mm (Jayanth, 1987;

Julien, 2001). The eggs are laid in the lower surface of the central tender

leaves of water hyacinth.

Damage

The nymphs of the mite, Orthogalumna terebrantis form galleries

between the parallel veins of the laminae from which adults emerge

(Plate 3B). High population of the mite causes leaf discoloration and

desiccation (Julien, 2001).

Grass carp

Ctenopharyngodon idella

Phylum

Class

Order

Family

Genus

Species

- Chordata

- Pisces

- Cypriniformes

- Cyprinidae

- Ctenopharyngodon

- ide/Ia Valenciennes

A number of herbivorous fish have been recommended for controlling

various aquatic weeds and have also been tried for water hyacinth (Reichert

and Trede, 1977). Of these species, the Chinese grass carp,

Ctenopharyngodon ide/Ia is the most promising species (Sutton and

Blackburn, 1971). According to Van Der Zweerde (1990), often a

combination of grass carp with other control agents, i.e. an integrated control

method is the best way to tackle the weed problem. An additional advantage

is that the grass carp provides a source of protein, which could be of special

importance in developing countries. The grass carp will not be useful for all

aquatic plant problems, rather it offers the potential to effectively and

economically manage certain of them. It is the most promising biological

agent for many submerged plant problems (Sutton and Vandiver, 2000).

Grass carp is a slender fish with a nearly round cross section and a

broad head. The body is silver coloured at the belly, shading into golden-

brown to dark brown at the back. The scales have dark edges, which marks

the pattern clearly. The pharyngeal teeth are heavy, sawed and in fish longer

than 30 cm, have a broadened surface, which makes them suitable for

grinding hard plant material. Grass carp are highly tolerant to adverse

limnetic conditions such as low oxygen, high salinity and chemical hazards

(Chiffon and Muoneke, 1992).

Pond Snail

Pila globosa

Phylum - Mollusca

Class - Gastropoda

Genus - Pila

Species - globosa Swainson

They are voracious, relatively generalist feeders on aquatic plants

((Plate 3C); this is partly the reason for their reported success in controlling

weed species (Perara and Walls, 1996). In some areas of the world, Marisacornuarietis has been deliberately introduced in attempts to control aquatic

plant nuisances, notably water hyacinth and hydrilla (Simberloff and Stiling,

1996). P1/a globosa has been found to control Salvinia in paddy fields

(Thomas, 1975).

Grasshopper

Gesonula punctifrons

Phylum -

Class -

Order -

Family -

Genus -

Species -

Arthropoda

Insecta

Acrididae

Oxyinae

Geson u/a

punctifrons Stal.

The insect has been reported from India. It is most common in Mysore

and occurs in Andhra Pradesh, Tamilnadu, Kerala, Assam, Rajasthan and

Delhi (Sankaran et a/., 1966). The nymphs and adults feed on leaves and

superficial tissues of petioles. Oviposition is done in water hyacinth,

Monchoria vagina/is and co/ocasia sp. It causes considerable damage to

water hyacinth. It has also been recorded from Indonesia.

1A - Orthogalumna terebrantis

lB - Neochetina bruchi

NEW-

Jlmbt1C-Neochetina eichhorniae

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1E River Tamirabarani

1.9 Objectives of the Study

1. To study the water quality of river Tamirabarani and to investigate the

influence of nitrate and phosphate on water hyacinth abundance.

2. To survey the existence and distribution of all types of aquatic weeds

in the river Tamirabarani.

3. To investigate the influence of nutrients on the growth of water

hyacinth.

4. To study the life cycle, biology and morphology of water hyacinth

weevils.

5. To investigate the efficiencies of weevil, mite, snail, fish and

grasshopper in controlling water hyacinth growth in laboratory

experiments.

6. To investigate the efficiencies of weevil, mite and fish as biocontrol

agents in controlling water hyacinth growth in field trials.

7. To analyze the water quality of experimental and control ponds.

8. To estimate the economic losses due to the spread of water hyacinth

and to evaluate the cost economics of various control strategies like

mechanical, chemical and biological control of water hyacinth.