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Review of Literature

Weeds are unwanted and undesirable plants which interfere with the

utilisation of land and water resources. Depending upon place of their

occurrence, weeds can be divided into nine groups:-1.Cropland weeds; 2.

Fallowland weeds; 3. Grassland weeds; 4. Non-cropland weeds; 5. Aquatic

weeds; 6. Forest and woodland weeds; 7. Lawn and garden weeds; 8.

Orchard weeds; 9. Weeds of plantations (Gupta and Lamba, 1978).

The aquatic weeds are those unwanted aquatic plants which grow in water

and complete at least a part of their life cycle in water. Aquatic ecosystems

all around the globe are threatened by the presence of various aquatic weed.

Some of the most common dangerous aquatic weed are (Eichhornia crassipes

[Mart.] Solms), alligator weed, Alternanthera philoxeroides (Mart.), giant

salvinia, Salvinia molesta and water lettuce (Pistia stratiotes L.) (Coetzee et

al., 2011; Ray and Hill, 2013).

Out of about 140 aquatic weeds, Eichhornia crassipes, Ipomoea aquatica,

Typha angustata, Ceratophyllum demersum, Salvinia molesta, Nelumbo

nucifera, Alternanthera philoxeroides, Hydrilla verticillata, Vallisneria spiralis,

Chara sp; Nitelia sp; Potamogeton sp; are of primary concern in India

(Varshney et al., 2008).

2.1- Classification of aquatic weeds:-

Aquatic weeds are generally classified into three groups:-

Floating aquatic weeds

Submerged aquatic weeds

Emergent aquatic weeds

Floating types are often recognised by general public as aquatic weeds. They

are found in the surface of large, deep and shallow depths of water bodies;

deep continuous flowing canals and large ponds, tanks. The roots of most of

the floating plants hang in the water and are not attached to the soil.

Members of this group are purely intermingled with emergent and

submerged plants in water up to 4 feet deep. Eichhornia crassipes is an

example of this category. Free-floating plants, such as duckweed and water

meal are seed-bearing plants which float free on the water's surface. They

never become rooted in the soil, and are propagated by sexual and asexual

means. They can completely cover the surface of a pond. Both are extremely

small. Duckweed is no more than 1/4 inch in diameter and water meal is

even smaller. Both plants are found in nutrient-rich waters. Input of waste

water from sources such as livestock feedlots and septic tank fields should

be eliminated. These types of weed make loss of water through

evapotranspiration (Jayan and Sathyanathan, 2012).

Rooted floating plants include water lily, spatterdock, and water

lotus. Spatterdock is usually the weediest of the three and completely fills in

shallow areas less than 3' or 4' deep. Spatterdock is a massive, difficult to

kill underground rhizome from which new plants sprout. It differs from

water lily in having heart-shaped leaves that come above the surface of the

water and a yellow flower. Water lily has round leaves.

The unwanted plants growing below the water surface are called submerged

aquatic weeds. So, they germinate, grow and reproduce beneath the water

surface. Like the floating aquatic weeds, they can be either free floating

(Ceratophyllum sp.) or anchored to the hydrosoil (Hydrilla verticillata). Their

roots and reproductive organs remain in the soil at the bottom of the water

body. These types of weeds damage the maximum because they are not

visible on the surface.

Emergent (shore or marginal) plants commonly grow in shallow water. They

include cattails, bulrushes, spike rushes, reed canary grass, and other

grass-like perennial plants. Broadleaves include willow trees and creeping

water primrose.

The rooted aquatic weeds extending above the water surface are called

emergent aquatic weeds (e.g. Typha sp.) (Jayan and Sathyanathan, 2012).

2.2- Problems caused by water hyacinth:-

Water hyacinth can cause a variety of problems when its rapid mat like

proliferation covers areas of fresh water. Some of the common problems are

listed below:-

2.2.1. Destruction of biodiversity:-

Today, biological alien invasions pose a major driver of biodiversity loss all

around the globe (Pysek and Richardson, 2010; Vila et al., 2011). Water

hyacinth is challenging the major problem for ecological stability of

freshwater water bodies (Khanna et al., 2011; Gichuki et al., 2012). Out-

competing all other species growing in the vicinity, posing a threat to

aquatic biodiversity (Patel, 2012). Besides suppressing the growth of native

plants and negatively affecting microbes, water hyacinth prevents the

growth and abundance of phytoplankton under large mats, ultimately

affecting fisheries and thus affecting biodiversity (Gichuki et al., 2012;

Villamagna and Murphy, 2010).

2.2.2. Oxygen depletion and reduced water quality:-

Large water hyacinth mats prevent the transfer of oxygen from air to the

water surface, or decrease oxygen production by other plants and algae

(Villamagna and Murphy, 2010). When the plant dies and sinks to the

bottom the decomposing biomass depletes oxygen content in the water body

(EEA, 2012). Dissolved oxygen levels can reach dangerously low

concentrations for fish that are sensitive to such changes. Furthermore, low

dissolved oxygen conditions catalyse the release of phosphorus from the

sediment which in turn accelerates eutrophication and can lead to a

subsequent increase in water hyacinth or algal blooms (Bicudo et al., 2007).

Death and decay of water hyacinth vegetation in large masses deteriorates

water quality and the quantity of potable water, and increases treatment

costs for drinking water (Patel, 2012; Mironga et al., 2011; Ndimele et al.,

2011).

2.2.3. Breeding ground for pests and vectors:-

Floating mats of water hyacinth support organisms that are detrimental to

human health. The ability of its mass of fibrous, free-floating roots and

semi-submerged leaves and stems to decrease water currents increases

breeding habitat for the malaria causing anopheles mosquito as evidenced

in Lake Victoria (Minakawa et al., 2008). Mansonioides mosquitoes, the

vectors of human lymphatic filariasis causing nematode Brugia, breed on

this weed (Chandra et al., 2006; Varshney et al., 2008). Snails serving as

vector for the parasite of Schistosomiasis (Bilharzia) reside in the tangled

weed mat (Borokini and Babalola, 2012). Water hyacinth has also been

implicated in harbouring the causative agent for cholera. For example, from

1994 to 2008, Nyanza Province in Kenya, which borders Lake Victoria

accounted for a larger proportion of cholera cases than expected given its

population size (38.7% of cholera cases versus 15.3% of national

population). Yearly water hyacinth coverage on the Kenyan section of the

lake was positively associated with the number of cholera cases reported in

the Province (Feikin et al., 2010). At the local level increased incidences of

crocodile attacks have been attributed to the heavy infestation of the weed

which provides cover to the reptiles and poisonous snakes (Patel, 2012;

Ndimele et al., 2011).

2.2.4. Blockage of waterways hampering agriculture, fisheries,

recreation and hydropower:-

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

can often clogs waterways due to its rapid reproduction and propagation

rate. The dense mats disrupt socioeconomic and subsistence activities (ship

and boat navigation, restricted access to water for recreation, fisheries, and

tourism) if waterways are blocked or water pipes clogged (Ndimele et al.,

2011; Patel, 2012). The floating mats may limit access to breeding, nursery

and feeding grounds for some economically important fish species

(Villamagna and Murphy, 2010). In Lake Victoria, fish catch rates on the

Kenyan section decreased by 45% because water hyacinth mats blocked

access to fishing grounds, delayed access to markets and increased costs

(effort and materials) of fishing (Kateregga and Sterner, 2009). In the Wouri

River Basin in Cameroon the livelihood of close to 900,000 inhabitants has

been distorted; the entire Abo and Moundja Moussadi creeks have been

rendered impassable by the weed leading to a complete halt in all the

socioeconomic activities with consequent rural exodus (Mujingni, 2012). The

weed has made navigation and fishing an almost impossible task in Nigeria

(Ndimele et al., 2011).

While navigation in the Brahmaputra River in India has been affected by the

weed, it has also blocked irrigation channels and obstructed the flow of

water to crop fields. For example, in West Bengal, it causes an annual loss

of paddy (Patel, 2012) by directly suppressing the crop, inhibiting rice

germination and interfering with harvesting (EEA, 2012). The dense growth

entangles with boat propellers, hampering fishing (Patel, 2012). Water

hyacinth slows water flow by 40 to 95% in irrigation channels (Jones, 2009),

which may cause severe flooding. The communities of Bwene and Bonjo in

the Wouri River Basin in Cameroon regularly suffer from floods during the

rainy season due to blockage of waterways around the villages by the weed

(Mujingni, 2012).

It is estimated that the flow of water in the Nile could be reduced by up to

one tenth due to increased losses from evapotranspiration by water hyacinth

in Lake Victoria (Ndimele et al., 2011). Water loss by the same process and

blocking of turbines on Kafue Gorge in Zambia translates into lost water for

power generation and eventually into lost revenue of about US$15 million

every year for the power company (ZEO, 2008). Many large hydropower

schemes are also suffering the effects of water hyacinth (Shanab et al.,

2010). For example, cleaning intake screens at the Owen Falls hydroelectric

power plant at Jinja in Uganda were calculated to be US$1 million per

annum (Mailu, 2001).

2.2.5. Economic Impacts:-

In Florida, every year millions of dollars have been wasted on water hyacinth

control; finally getting the plant under "maintenance control" has greatly

reduced that expenditure.

2.3-Taxonomy, morphology ecology and habitat of water hyacinth:-

2.3.1-Taxonomy:-

Kingdom- Plantae

Subkingdom- Tracheobionta

Super division- Spermatophyta

Division- Magnoliophyta

Class- Liliopsida

Subclass- Commelinidae

Order- Pontederiales

Family- Pontederiaceae

Genus- Eichhornia

Species- crassipes

2.3.2-Morphology:-

It is a perennial, aquatic plant, anchored in shallow water and free floating

herb perpetuating by means of stolons. Generally it is 100 – 200 mm high

and can extend up to 1 meter when growing in dense mat like proliferation.

Roots of these plants are long, feathery and leaves are shiny dark green in

colour, in rosettes with distinctive erect swollen bladder-like petioles.

Flowers are pale violet or blue, in flowered spikes with each flower

measuring about 50mm in diameter. The upper petal has a prominent dark

blue, yellow centred patch. Fruit consists of capsules with very fine seeds

(Henderson, 2001).

2.3.3-Ecology:-

Water hyacinth generally occurs both in acidic and alkaline water but

maximum growth of the plant found in near neutral water bodies (Gopal,

1987). It may be believed that under optimum conditions one hectare of

water hyacinth plants could absorb the average daily nitrogen and

phosphorus waste production of over 800 people. Water hyacinth causes

disturbances in aquatic systems water flow by slowing it by 40 to 95% in

irrigation channels. Invasive species are widely recognised as one of the

leading causes for the loss of biodiversity and can have significant effects on

resource availability and suppress or enhance the relative abundance of

native species (Didham et al., 2005). A dense mat of water hyacinth reduces

and prevents light penetration of water. Without the presence of light,

phytoplankton and submerged plants cannot photosynthesize and they die.

So, oxygen levels decrease and carbon dioxide level increases, which cause

catastrophic effects on the aquatic fauna (Howard and Harley, 1998). Due to

overgrowth of water hyacinth populations of fishes can be reduced as well as

it eliminates other animals (Gratwicke and Marshall, 2001). Few invaded

ecosystems are free from habitat loss and disturbance, leading to

uncertainty whether dominant invasive species are driving community

change or are passengers along for the environmental ride (MacDougall and

Turkington, 2005).

Water hyacinth creates problems in aquatic systems water flow by slowing it

by 40 to 95% in irrigation channels which cause flooding. This could have a

detrimental effect on the ecology of the system. The dense mats of water

hyacinth causes lower temperatures, pH, bicarbonate alkalinity, dissolved

oxygen level and increase the free carbon dioxide content and nutrient levels

(Jones, 2009).

During periods of strong winds, mats of water hyacinth drift and scour

indigenous vegetation. This in turn destroys both plant and wildlife habitats.

Exotic species (water hyacinth) that invade systems represent a threat to

that ecosystem and could directly modify an ecosystem, causing a cascading

effect for resident biota e.g. space (Crooks, 2002).

2.3.4-Habitat:-

Water hyacinth can be located not only in India but all around the globe in a

variety of different habitats. These include habitats from shallow ponds,

possibly temporary, to large lakes and even fairly fast flowing rivers and

canals (Gopal, 1987). Eichhornia crassipes grows and spread rapidly in

freshwater. It can withstand extremes of nutrient supply, pH level,

temperature, and can even grow in toxic water. It grows well in still or slow-

moving water. Water hyacinth invasion is facilitated by water bodies that are

enriched by agricultural, chemicals, sediments from catchment erosion,

domestic effluents and plant nutrients. Where the plant is situated in

shallow water bodies it does not have to contend with excessive wave action

and varying depths of water. The velocity of water also plays a key role in the

plant‘s habitat. Changes of climatic conditions vary within a system and will

have an effect on the ecology of the plant itself. Water hyacinth can be

located in both natural water and aquatic systems. However, it does not

occur in aquatic systems when an average salinity greater than 15% of sea

water (Jones, 2009).

Water hyacinth is able to remove high levels of nutrients from water, which

then influences the plant‘s growth form e.g. plant established in or near to a

sewage outlet, compared to those plant‘s established in a low nutrient

habitat. The plant grows prolifically in nutrient enriched waters and new

plant populations forms from rooted parent plants. Wind and current assists

to distribute them. Excessively large mats can be formed. The root system,

as well as the above water structures of the plant, forms a habitat for

organisms. However, large mats of water hyacinth are capable of negatively

affecting the original habitat.

The feathery root of water hyacinth provides a suitable habitat and

substrate for some specific plants. In addition, a large variety of

invertebrates are particularly associated with the roots hanging in the water

as they provide a habitat, and may possibly trap them from the water

column. In some cases a few organisms have been reported to be specifically

associated with water hyacinth mats. Water hyacinth mats also provide a

suitable habitat for germination and establishment of the seedlings of a

number of emergent species (Gopal, 1987).

2.4-Growth and reproduction:-

Water hyacinth, growing in ideal situations, has an incredible mechanism to

outgrow any native species occurring in the system. It is capable of

reproduce vegetatively and this is the primary reproductive method of water

hyacinth. This is carried out from the ‗mother‘ plant via stolons. So, stolons

play a significant role for the reproduction and growth of water hyacinth.

During periods of high wind and wave action, plants are able to disperse

and colonize other areas of the system. Gopal (1987) reports that water

hyacinth has the capacity to increase sevenfold in 50 days, that the edge of

mat extends by 60 cm per month, that 2 plants can multiply to 1200 plants

in 120 days, that the surface area increases by an average of 8% per day

and that the surface mat can double every 6.2 days.

Another method of reproduction of water hyacinth is sexual. Which is

reported to be limited (Gopal, 1987). Plants are capable of flowering

throughout the year, should environmental factors be suitable. Penfound et

al. (1948) reported that a water hyacinth ovary may produce up to 500

ovules, but rarely sets more than 50 seeds per capsule. Barrett (1980),

performed trials and concluded that 44.2 seeds per capsule were the

average, with a high seed germination rate of 87.5% on average. Penfound et

al. (1948) further recorded that upwards of 900 capsules have been counted

in an area of one hectare. This equates to 45 million seeds per hectare. Of

interest is the fact that they further suggest that pollination by insects rarely

occurs, but that self-pollination is a common phenomenon during the

wilting stage. Water hyacinth seed can lay dormant for many years, until the

correct climatic conditions arise, when it may then germinate. Seed can

remain dormant for up to 20 years (Gopal, 1987). Very few seeds germinate

on the mat, as they are lost in the detritus build-up, or sink due to being

heavier than water.

2.5- Origin and distribution:-

The first description of water hyacinth was given by the German naturalist

von Martius in 1823 while carrying out floral surveys in Brazil. He named it

Pontederia crassipes. It was later transferred to the genus Eichhornia (in

honour of TAF Eichhora, a Russian Minister of Education) by Kuntz in

1843. Solms included it in the Eichhornia genus. However, a collector by the

name of von Humbolt had already collected specimens from Colombia in

1801, together with the species azurea (Gopal, 1987).

The reason for the worldwide distribution of this weed varies, but generally

it has coincided with the plant‘s ornamental properties or as feed (Ding et

al., 2001). The first record of water hyacinth infestation onto the continent

was for Egypt in the period 1889– 1892, during the regin of Khevede Tawfiq.

It is believed that it has been introduced as an ornamental plant. Water

hyacinth occurs throughout the region of Nile Delta and is believed to

spreading southwards, due to the construction of the Aswan Dam, which

has slowed the river down (Gopal, 1987).

The second record for the continent is for South Africa in 1908 (Stent,

1913). Water hyacinth is believed to have been introduced as an ornamental

aquatic plant for garden ponds and aquaria, due to its attractive flowers

(Ashton et al., 1979). In the case of water hyacinth, a warning of what was

likely to happen, was printed as early as 1913 (Jacot, 1979).

Thirdly, Zimbabwe recorded water hyacinth infestations in 1937. The first

record was from the Mukuvisi River in Harare and the plant only attained its

pest status in the early 1950‘s into the Lake Chivero (Chikwenhere et al.,

1999). In the period 1941 to 1960, a further ten African countries recorded

water hyacinth infestations, namely: Angola (1942), Benin (1942), Burundi

(1957), Congo (1950-1951), the Democratic Republic of Congo (1952),

Ethiopia (1956), Mozambique (1942), Rwanda (1957), Sudan (1954) and

Tanzania (1955).

There appears to be a slump in water hyacinth introductions, in the period

from 1961 to 1980, and this is due to the fact that a further eight countries

are recorded to have water hyacinth infestations but no accurate data are

available to claim when the first recordings were made. However, a further

four African countries, published their first records of water hyacinth

infestations during 1961-1980, namely: Central African Republic (1970),

Malawi (1960‘s), Senegal (1963) and Zambia (1965). Nine African countries

recorded that water hyacinth infestations occurred in the period of 1981 to

2000, namely: Burkina Faso (1989), Cote d‘ Ivoire (1980‘s), Ghana (1984),

Kenya (1982), Niger republic (1987), Nigeria (1982), Togo (1987) and Uganda

(1988). Both intentional introductions (ornamental) and unintentional

introductions (rivers flowing from one country to another) of water hyacinth

have occurred throughout Africa, since the first intentional introduction into

Egypt.

The native range of E. crassipes in South America includes Argentina,

Brazil, Paraguay, Uruguay, Bolivia, Ecuador, Colombia, Chile, Guyana,

Surinam and Venezuela. It has spread to Panama, Nicaragua, Honduras and

El Salvador in Central America (Gopal, 1987). There appears to be several

schools of thought when it comes to the actual point of origin / dispersal of

E. crassipes. In North America, it is believed that it has been introduced in

1884 at the Cotton States Exposition in New Orleans, Louisiana. It is

frequently spread across the south-eastern part of United States to Florida

in 1895 and California in 1904. It is more prolific in the south-eastern

region as well as being recorded in Hawaii (Center et al., 2005).

Water hyacinth has more prolific since its introduction into Louisiana,

spread to Alabama, Arkansas, Arizona, California, Colorado, Florida,

Georgia, Hawaii, Kentucky, Louisiana, Missouri, Mississippi, North Carolina,

New York, Oregon, South Carolina, Tennesse, Texas, Virginia and

Washington, (USDA–NRCS, www.USDA.gov), in other words, it covers

approximately 50% of the States in the U.S.A.

Towards the end of the 19th Century, it was introduced into Asia via Japan

and Indonesia (Ueki et al., 1975) where it naturalized in rice fields in

Indonesia (Backer, 1951), and grown as an ornamental plant in the

Botanical Gardens. In Asia, water hyacinth is spread over freshwater

wetlands of the Mekong Delta, especially in standing water (MWBP/RSCP,

2006).

In India, this plant had made its entry into Bengal before 1900 and today it

has spread to all types of water bodies throughout the country and is

believed to occupy over 2, 00,000 ha of water surface. In the state of Tamil

Nadu (India), the Veeranum lake and its distributaries form the major

irrigation source that covers a large proportion of the rice tract of the state

with an area of 18,000 ha. Presently, this lake and its distributaries have

been infested with E. crassipes (Gnanavel and Kathiresan, 2007). It has

been found in the Sundarbans mangrove forest of Bangladesh (Biswas et al.,

2007) and caused a serious problem for wetlands of the Kaziranga National

Park, India. Deepor Beel, a freshwater lake formed by the Brahmaputra river

is also infested with water hyacinth (Patel, 2012). The lake is considered one

of the large and important riverine wetlands in the Brahmaputra valley of

lower Assam, India. In Haryana (India), it is the most troublesome aquatic

weed distributed all over the state except north west and south west

Haryana.

It has also established in Taiwan and China, as early as 1901 as a good

fodder plant (Ding et al., 2001).

It was first noticed in Australia in Brisbane, Sydney and Grafton in the

1890‘s and has since spread to all mainland states and territories. In

Australia it was introduced as an aquarium plant. It has in addition spread

to Papua New Guinea, where it was first recorded from dredge ponds in old

gold fields of Bulolo in 1962 (Harley et al., 1996).

Holm et al. (1977) recorded that both New Zealand and Bangladesh also

have suffered water hyacinth infestations. Burton (2005) records that many

islands in the Pacific Ocean also have weed infestations. Europe has also

been affected by water hyacinth, where it was introduced as an ornamental

plant in Portugal. The first record of it was made in 1939. First documented

records for Spain are for 1989 (Tellez et al., 2008). Gates (2000) and Harper

(2000) reported that water hyacinth has also been observed in the wild in

Britain. Water hyacinth was originally introduced outside of its home range,

due to the lack of understanding of the plant invasive properties and the

immense ecological negative impacts that it would have on fresh water

ecosystems. Africa has particularly been affected by the introduction and

spread of water hyacinth, because of lack of naturally occurring potential

fungal biocontrol agents. Most published reports conclude that water

hyacinth infestation in eastern, southern and central Africa was first

recorded in Zimbabwe in 1937 (Mujingni, 2012). It colonized water bodies,

such as the Incomati River in Mozambique in 1946, the Zambezi River and

other important rivers in Ethiopia in 1956. In the late 1950s, rivers in

Rwanda and Burundi were colonised by water hyacinth while the infestation

were recorded in the rivers Sigi and Pangani during the year 1955 and 1959.

After that it was colonised Kafue river in Zambia in the 1960s, the Shire

River in Malawi in 1968 and Lake Naivasha in Kenya in 1986 (Mironga et al.,

2012). The plant was also recorded from Lakes Kyoga in Uganda in 1988-89,

Victoria in 1989–1990, Malawi/Nyasa in 1996 and Tanganyika in 1997.

Lake Victoria in Africa country is the second largest freshwater lake in the

world and currently supports approximately 30 million people and

infestation due to water hyacinth in the lake has been a serious problem,

generating public outcry (World Agro Forestry Centre, 2006; Kateregga and

Sterner, 2007; Gichuki et al., 2012). It was estimated that the weed was

continuously growing at 3 hectares (12 acres) per day on the lake (Ayodo

and Jagero, 2012).

Water hyacinth has also spread continuously in West Africa. It was first

recorded in Cameroon between the year 1997 and 2000 (Forpah, 2009).

In Nigeria it has spread into all river bodies (Borokini and Babalola, 2012). It

occurs all over the Nile Delta in Egypt and is believed to be occupy

southwards, due to the construction of the Aswan Dam which has slowed

down the river flow (Dagno et al., 2007).

Infestation of water hyacinth was also recorded in Ethiopia which has also

been manifested on a large scale in many water bodies of the Gambella area,

Lake Ellen in the Rift Valley and Lake Tana (Fessehaie, 2012).

In Europe, water hyacinth is established in the Azores (France), Corsica

(Italy), and also recorded from Belgium, the Czech Republic, Hungary, the

Netherlands and Romania (EEA, 2012). It is a major threat in Spain and

Portugal (DellaGreca et al., 2009).

The invasion of rivers, dams and lakes throughout Africa by introduced

aquatic vegetation represents one of the largest threats to the socioeconomic

development of the continent (Cilliers et al., 2003). Mali has been

particularly affected by the introduction and spread of this dangerous

aquatic weed and the weed causes a serious problem for the country (Dagno

et al., 2011, 2012). Water hyacinth will be able to infest most of the

continent and the fact that it does not occur in all countries in Africa is

more due to it not having being recorded or not having spread there, rather

than it not being able to establish (Wise et al., 2007).

In southern part of China water hyacinth has caused economic, social and

environmental problems (Choo et al., 2006).

In Mexico, more than 40,000 hectares of reservoirs, lakes, canals and drains

are infested with this weed (Jimeonez and Balandra, 2007).

In California, USA, this weed has caused severe ecological impacts in the

Sacramento- San Joaquin River Delta (Khanna et al., 2011).

2.6-Management of water hyacinth:-

Aquatic weed control measures may be preventive, manual, mechanical,

ecological, biological, chemical and through their utilization. In preventive

weed management, quarantines are legislative tool that may be used to

mitigate the effects of weeds. Preventive weed programmes usually require

community action through the enactment and enforcement of appropriate

laws and regulations. Existing methods for control of water hyacinth often

been insufficient to contain the aggressive propagation of the weed and

viability of its seeds (Gichuki et al., 2012).

2.6.1-Chemical control:-

Chemical control, i.e. control of weeds by using chemical pesticides

(herbicides or weedicides), is most expensive method and requires a high

load of manpower, chemicals and mechanical equipment. But the advantage

of chemical control is that it is quick and effective. However, the direct and

indirect impacts of the herbicides on the environment are enough to invite

caution in their use. The rapid kill of large mats of weed adds a huge

quantity of organic matter to the water body. The detritus formed after

chemical control cannot be removed and its decay releases large amounts of

nutrients. These results in rapid degradation of water quality, development

of algal blooms and other changes associated with eutrophication. More

often, the organic matter creates anoxic conditions in shallow water bodies

resulting in large-scale death of fish and other aquatic organisms. Most

chemicals are broad-spectrum in action and often not confined in their

action to the target organisms alone but affect other organisms also in and

around the water body. If residues are excessive the water will be unsuitable

for human consumption or irrigation (Aneja, 2009).

Among the chemicals recommended to control water hyacinth are 2, 4-

dichlorophenoxy acetic acid (2,4-D) Paraquat, Diquat, Glyphosate and

Amitrole are most effective and are widespread in use. Plants sprayed with

2, 4-D exhibit twisting, curling and elongation of leaves within 24 hrs.

(Villamagna and Murphy, 2010). The herbicide biodegrades rapidly and lasts

for about a week. The U.S. Federal Food, Drug and Cosmetic Act established

a tolerance level of 1 mg/kg2, 4-D in fish and shellfish and 0.1 mg/l in

potable water. N-(phosphonomethyl) glycine (glyphosate) is reported to kill

the plant within 14 days at a concentration of 2 kg/ha. Glyphosate acts

slowly but may prove better than 2, 4-D and other chemicals. It has the

advantage of low toxicity to fish and rapid biodegradation in soil and water

(Gopal, 1987). However, the cost of application may be prohibitive in some

countries (Labrada, 1996). Harley (1994) reviewed the negative effect on

biocontrol agents by the chemical herbicides. If not applied carefully and

selectively, they can nullify the effect of biocontrol agents by disrupting or

eliminating local populations of parasitoids and predators. When a large

population of water hyacinth is killed within a short period, a large

population of natural enemies especially arthropods may die of starvation.

He stated that any surviving adults and immature stages might not be able

to migrate to chemically untreated populations of the weed and face adverse

physical conditions in the drying of the weed. The normal cyclic increase in

arthropod population will be upset and the biocontrol pressure on

subsequently emerging host populations will be disrupted (Bateman, 2001).

These kill aquatic organisms directly; however, they can cause

developmental abnormalities and diseases in animals and humans

(Varshney et al., 2008). Use of chemical herbicides leads to environmental

pollution besides causing its own inherent ill effects (Babu et al., 2003;

Aneja, 2014).

2.6.2-Mechanical/physical control:-

The control of weeds by using tools is known as mechanical control (Patel,

2012). Some techniques to control weeds by using tools are: (A.) Netting, (B.)

Barriers (C.) Chaining (D.) Water weed cutters. Mechanical control involves

pulling out the plants by hand and by employing boats, rakes and booms to

help in the collection and transport of the plants to the land in cases of large

and deeper water-bodies, and is practiced in many developing countries.

Another method is to construct floating barriers, which help in

accumulating the weed in a certain part of the water body to also prevent it

from reaching other water bodies. Under water weed cutters are employed at

Kota (Rajasthan) to clear Chamble canals from aquatic weeds (Varshney et

al., 2008).

Physical control has obvious limitations of scale and re-infestation by

remnant plant fragments and seeds (Harley, 1994).

The methods present very little environmental hazards and provide room for

plant utilization. They are useful methods for reducing small infestations

and for maintaining canals. But the physical, manual and mechanical

removal are costly as wages per working day and machine running and

maintenance costs are prohibitively high. Management of water hyacinth in

China through mechanical means were estimated to amount around 1

billion EUR annually (EEA, 2012). In Europe, it is estimated that

approximately costs to remove 2, 00,000 tonnes of the plant along 75 km in

the Guadiana river basin on the Portuguese-Spanish border amounted to

EUR 14,680,000 between 2005 and 2008 (EEA, 2012). Mechanical

management of the weed in Mali cost around US$ 80,000–100,000 per year

(Dagno et al., 2007). In Uganda estimated cost around US$ 3-5 million per

year (Mailu, 2001). While mechanical removal has been effective up to a

considerable extent, the infestations soon return because of shredded bunch

of the weed are carried by waves to other unaffected areas where they

establish and start proliferating (Shanab et al., 2010). The major limitations

are:-

Provides temporary relief from water hyacinth and other aquatic

weeds.

Physical removal by machines often induces their dissemination to

new sites.

Repeated physical removal depletes the water body of its nutrients,

reducing growth and planktons.

It is dependent on human labour, work efficiency under water weed

cutters or harvesters.

2.6.3-Biological control:-

The term biological control refers to regulating the excessive growth of an

organism by means of its natural enemies (Gopal and Sharma, 1981).

Pieterse (1990) defined biological control of aquatic weeds as ‗activities

aimed at decreasing the population of an aquatic weed to acceptable levels

by means of a living organism or virus‘.

These days, plant pathogenic fungi are one of the most suitable biocontrol

agent alternatives to chemical herbicides but several ecological parameter

are associated with them as most disease causing pathogenic fungi required

suitable environmental conditions such as temperature, humidity, dew

requirement for disease incidence and severity (Auld and Morin, 1995; Ray

and Hill, 2013). To control these problems attention is going on the

secondary metabolites produced by the disease causing pathogens (Ray and

Hill, 2013). Pathogenic microorganisms have been a successful source of

phytotoxins with the potential to control weed (Vurro, 2007). A toxin

bostrycin and de-oxybostrycin has been isolated from Alternaria eichhorniae

that concerned leaf necrosis and chlorosis on water hyacinth (Charudattan

and Rao, 1982; Maity and Samaddar, 1977). Metabolites of Alternaria

alternata of water hyacinth have shown phytotoxicity against the weed

(Babu et al., 2003). Ray and Hill (2013) suggested that for better control of

aquatic weeds with the help of secondary metabolites, more studies are

required to be undertaken to develop potential mycoherbicides.

In general there are three approaches for control of aquatic weeds:

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

a few species;

The use of non-selective organisms i.e. organisms which attack all (or

nearly all) weed species present and;

The use of competitive plants species i.e. plants which compete with a

weed species for one or more critical growth factors (Aneja, 1999).

2.6.3.1-Control by means of arthropods:-

Research in biological control of water hyacinth by means of arthropods

began in 1961. The control agents by means of arthropods have been

introduced in many countries worldwide (Harley and Forno, 1990). For

examples, at Lake Chivero (Zimbabwe), Lake Victoria (Kenya), Louisiana

(USA), Mexico, Papua New Guinea and Benin, two South American weevil

beetles (Neochetina eichhorniae and Neochetina bruchi) and two water

hyacinth moth species (Niphograpta albiguttalis and Xubida infusella) have

been recorded for control of water hyacinth (Williams et al., 2007; Venter et

al., 2012; Gichuki et al., 2012; Dagno et al., 2012). Researchers have also

identified a tiny insect, Megamelus scutellaris, from South America which is

highly host-specific to water hyacinth and does not pose a threat to native or

economically and ecologically important species (Coetzee et al., 2009).

The weevils reduce water hyacinth infestation by decreasing plant size,

vegetative reproduction, flower and seed production. They also contribute in

the transfer and ingress of deleterious microorganisms associated with the

weevils (both fungi and bacteria) (Venter et al., 2012).

Arthropod control agents such as Neochetina eichhorniae and N. bruchi

(Coleoptera: Curculionidae), the moths Niphograptha (=Sameodes)

albiguttalis, Acigona infusella and Arzema densa (Lepidoptera: Pyralidae) and

the mite Orthogallum terebrantis (Acarina: Galumnidae) have been found to

control water hyacinth in its native habitats (Center et al., 1982, 1988).

According to Gopal (1987), the Neochetina weevils have attained the highest

levels of control among all the agents so far released.

2.6.3.2-Biological control of aquatic weeds with plant pathogens.

Attempts have been made in several countries to use pathogens for water

hyacinth control. For instance the use of Cercospora sp. in Rodmanii

Reservoir (USA) and in South Africa (Waterhouse, 1994). However, it is

worth noted that plant pathogens exert a limiting pressure on target water

hyacinth populations but seldom eliminate it (Freeman et al., 1974). A

susceptible host, a virulent pathogen and favourable environmental

conditions are essential components for plant disease to occur

(Charudattan, 1986). Several important factors apparently limit the

development of natural epidermics of plant pathogens of weeds. These

factors may include host heterogeneity, a narrow range of temperature or

moisture conditions conducive to infection, poor survival of inoculum from

season to season, and limiting dispersal mechanisms (Charudattan et al.,

1990).

According to Charudattan (1986), the dew or moisture requirements needed

to establish infection are a major concern. In most cases 12 hrs. of moisture

appear sufficient to establish infection at an incidence high enough to

establish control. Post inoculation/incubation temperatures are critical to

establishment of the disease by affecting the latent period (Charudattan,

1988). Successful biological control agents require relatively short moisture

periods and have relatively wide temperature latitude for rapid disease

development. The relative survival of the biological control agents appears to

depend on the amount of inoculum and specialized structures possessed by

each pathogen. Pathogens that have specialized fruiting structures such as

teliospores, oospores, ascospores, or sclerotia may be expected to survive

with relative success (Charudattan, 1988).

2.7-Biological weed control strategies

Tactics to control weeds with plant pathogens fall into three categories:-

2.7.1-The classical or inoculative strategy.

2.7.2-The mycoherbicidal or inundative strategy.

2.7.3-The integrated control

2.7.1-The classical or inoculative strategy.

In the classical strategy, a fungus is simply introduced or released into a

weed population to establish, in time, an epiphytotic requiring no further

manipulation. In a severe epidemic, the weed is killed or stressed such that

its population is reduced to economically acceptable levels. Pathogens with a

low level of virulence are frequent, may co-exist stable with their host

pathogens with intermediate pathogenicity, and are good candidates for the

classical strategy, maintaining a stable interaction and efficiency. The

probability of extinction of a pathogen increases when pathogenicity is

greater than a critical value at the intermediate range. The pathogens used

in this strategy are generally rusts and other fungi capable of self-

dissemination through air borne spores (Andres et al., 1976; Emge and

Kingsolver, 1977; Templeton and Smith, 1977; Vonzon and Scheepens,

1979; Batra, 1981; Quimby, 1982; Aneja, 2014). For example, introduction

of Puccinia chondrillina from Mediterranean (South Europe) for the control

of Chondrilla Juncea (Skeleton weed) in Australia (Cullen, 1978), Puccinia

abrupta var. partheniicola has been evaluated for biocontrol of Parthenium

hysterophorus and has shown potential to control it in Mexico (Evans,

1987; Hassan, 1988; Aneja and Mehrotra, 1996). Some of the successful

examples for the control of weeds using classical approach are given in the

table 2.1.

Table-2.1:- Successful examples of control of weeds through classical

approach:-

Weed

Bio-agent Kind of bioagent

Reporting Country

Chondrilla juncea Puccina chondrillina Plant

pathogen

Australia

Cyperus rotundus

Bactra verutana Shoot boring

moth

India,

Pakistan, USA

Eupatorum riparium

Entyloma compositarum Plant pathogen

USA

Hydrilla verticillata

Hydrellia pakistanae Shoot fly USA

Orobanche cernua

Sclerotinia sp. Plant pathogen

USA

Parthenium hysterophorus

Puccinia abrupta var. partheniicola

Plant pathogen

Mexico

Parthenium hysterophorus

i) Zygogramma bicolorata ii) Epiblema strenuana

Leaf eating beetle, Stem

Mexico Australia

iii) Conotrachels sp. galling

insect, Stem galling insect

Australia

Rumex spp.

i) Uromyces rumicis ii) Gastrophysa viridula

Plant

pathogen Beetle

USA

USA

Tribulus terrestris

Microlarinus lareynii and M. lypriformis

Pod weevil USA

2.7.2- The Mycoherbicide Concept

A third approach – the manipulated mycoherbicide strategy – has been used

by Sands and Miller (1993). In this strategy, lethal broad host-range

pathogens are genetically modified to permit their safe release. Either they

are rendered host-specific or they are given a chemical dependency that

prevents their spread or long term survival. The genetic-manipulative

approach offers numerous and diverse scenarios for biocontrol of weeds and

may open the door to large-scale corporate development and perhaps also to

larger-scale public development.

In 1974, Danial and coworkers first introduced the mycoherbicide concept.

They demonstrated that endemic fungal pathogens might be rendered

completely destructive to its weed host by applying a massive dose of

inoculum at a particularly susceptible stage of weed growth. Since this

initial definition of the concept, the term mycoherbicide has been redefined.

In the inundative (or mycoherbicidal) strategy, usually large doses of

inundative indigenous fungal pathogen are applied to specific weed-infested

field to infect or kill susceptible weeds (Daniel et al., 1974; Templeton et al.,

1979). Pathogens with high levels of virulence may exist in nature in low

frequencies due to high extinction rates and are suitable for mycoherbicide

strategy (Yang and TeBeest, 1992). On the other hand, pathogens with a low

level of virulence are frequent, may co-exist stable with their host pathogens

with intermediate pathogenicity, and are good candidates for the classical

strategy, maintaining a stable interaction and efficiency. The probability of

extinction of a pathogen increases when pathogenicity is greater than a

critical value at the intermediate range.

Mycoherbicides are simply plant pathogenic fungi developed and used in the

inundative strategy to control weeds the way chemical herbicides are used

(TeBeest and Templeton, 1985). They are highly specific disease-inducing

fungi which are isolated from weeds, cultivated in fermentation tanks and

sprayed on fields to control biologically a specific weed without harm to the

crop or any non-target species in the Environment (Templeton et al., 1988).

Where an agent that occurs as a pest in its native range is cultured, mass-

produced, registered, marketed and applied inundatively like chemical

pesticides comes in the inundative strategies (Aneja, 1999). Mycoherbicides

are developed from fungal pathogens that normally incite diseases at

endemic levels in specific weed population and the fungal pathogens are

applied in the form of spray that uniformly kill or suppress weed growth

(Daniel et al., 1974; Templeton and Smith, 1977; Collaway et al., 1985,

1987). So, fungal based formulations used to control weeds are called

mycoherbicides (Aneja, 2008; Aneja, 2014).

There are several advantages of mycoherbicides over the chemical

herbicides. Some of these are as follows:

• Fungi used as mycoherbicides are easy to isolate, mass produce,

identify, grow and manipulate.

• They are inherently less harmful than conventional pesticides.

• Effective in very small quantities and often decompose very quickly.

• They are non-toxic to humans, domestic animals and plants.

• They are economically feasible, safe and non- pathogenic to non-target

organisms.

• When used as a component of IPM programmes, mycoherbicides can

greatly decrease the use of conventional herbicides, while crop yields

remain high.

Initiation of field surveys

Discovery of a plant disease from

local environment

Isolation and identification of

the pathogen

Histopathological studies

and diseases development

Proving of Koch‘s postulates

Production of spores/inoculum for

small scale experiments Host-specificity

tests

Technology for mass

production of inoculum

Toxicity tests for

animal safety

Preliminary screening trials for biocontrol

potential in laboratory and green house

Technology for drying and

formulation of dry spore

Ecological

and

Use of formulation epidemiological

studies

Small scale field tests on local

experiment station

Performance test across geographic areas

including on farms in cooperation

with growers (10 acres)

Registration of product

Approved

Whole-field commercial scale operation

Approved

Delivered into commercial practice

Figure- 2.1. Protocol for the development of a fungal biocontrol agent

into a mycoherbicide (Adapted from Aneja, 1999).

2.7.3.-Status of mycoherbicides

Several recent reviews have provided an overview on various bioherbicides

projects being conducted around the globe (Charudattan, 2001; Bailey et al.,

2010; Ash, 2010; Aneja, 2009). Fifteen bioherbicides have been registered in

various countries with several other microbial candidates in various stages

of evaluation and development. In addition to these commercialized

products, Charudattan (2001) who compiled a comprehensive list of

bioherbicide products worldwide also listed over. 50 examples of pathogens-

weed combinations which have been reported as having potential as

bioherbicides. A further search of the literature using the ISI Web of Science

(http://apps isiknowledge.com) database has revealed 509 papers published

which mentioned bioherbicides or mycoherbicides since 1987 clearly

indicating the plethora of articles on ―potential bioherbicides‖. Perhaps until

an agent is commercialized it should be called a biological control agent and

the term bioherbicide or mycoherbicide should be reserved for the

formulated, marketed and commercialized product.

Essentially the discovery and development of bioherbicides has been

undertaken by plant pathologists, weed scientists or entomologists and

begins with the observation of naturally occurring diseased plants. The early

stages of the investigation follow traditional plant pathology techniques

including the application of Koch‘s postulates and other standard

techniques (Aneja, 2003). At this stage high concentration of single or mixed

inoculum are used to increase the likelihood of plant motility. Following the

isolation of a likely candidate, the research programme often includes

culture purification, host range testing, laboratory scale fermentation and

preliminary formulation. A number of reviews have offered reasons why

bioherbicides developed in this way have not been successful (Auld and

Morin, 1995; Gupta et al., 1998; Aneja, 1999, 2009; Hallett, 2005; Weston,

1999).

Out of the several bioherbicides developed around the globe, a few of them

are commercially available (eg. DeVine, Stumpout, Chontrol, Ecoclear,

Mycotech, Sarritor). The others are unavailable due to lack of continued

commercial lacking, high cost of mass production, and resistance in some

weed biotypes (eg. Dr Biosedge), low sales or regulatory concerns and lack of

funding for infrastructure, personal and patenty of the product; close

collaboration between non-industrial and industrial sectors for

commercialized. One BCA, C. gloeosporioides f.sp. aeschynomene has been

registered (previously Collego) as of March 2006 under the commercial name

LockDown for use in rice in the three states of USA; Arkansas, Lousiana and

Mississippi (Yandoc et al., 2006).

2.8- Integrated approach:-

For several aquatic weeds such as Salvinia and Azolla, the use of single

insect as biocontrol agent has been sufficient to effective control but novel

strategies are required for the control of some of the other dangerous

aquatic weeds such as water hyacinth (Coetzee et al., 2011). Integrated

management of weeds is a novel approach for minimizing weed impact (Ray

and Hill, 2013). Tactics to control weeds with integrated approach fall into

two categories.

2.8.1-Combination of pathogens & insects

2.8.2-Combination of two or more fungi

2.8.1- Mixture of pathogens & insects:-

In this method, the use of plant pathogen is combined with compatible

insects. The combined effect of plant pathogens and insects for the biological

control of weeds has been suggested a form of integrated control

(Charudattan, 1986; Smith, 1982). The biological control of the water

hyacinth is a good example where the leaf spot fungus, Cercospora rodmanii,

shortly to be commercialized as a mycoherbicide, is likely to be used to

control the weed in Florida, in combination with arthropod parasites and

herbicides and 99% control has been seen (Freeman and Charudattan,

1984). Singh (1992) studied integrated control of water hyacinth using

insect or fungal pathogens, using the organisms in various combinations i.e.

WH+AE (Water hyacinth +Alternaria eichhorniae), WH+NE (Water hyacinth

+Neochetina eichhorniae), and WH+AE+NE. Recently good biological control

with insects have been seen with Neochetina eichhorniae and N. bruchii.

There is proof that combinations of treatments can be more effective for

controlling several weeds than individual treatments in any biological

control programme (Ray and Hill, 2012; Ray et al., 2008 a). Several

scientists worked on integrated control of weeds with pathogenic fungi and

insects (Crowson, 1984; Paine et al., 1997; Guadalupe et al., 1999). Several

insect biocontrol agents have also played a key role in spread of phyto-

pathogens of a specific weed (Caesar et al., 2002; Caesar, 2003a, b, 2004;

Caesar, 2011).

2.8.2- Mixture of two or more fungi:-

Through integrated approach method, the fungal suspension containing

spores of mixtures of fungi are tested on leaf surface of water hyacinth. So,

the pathogens when applied with a mixture of fungi caused better

penetration to leaves than applied singly. The combination of two or more

fungi given the maximum control of the weed in comparison of individual

pathogen (Singh et al., 2012). Combined treatment using two or more

pathogens have also resulted in causing larger lesion diameters on water

hyacinth in comparison of pathogens tested singly (Ray et al., 2008 b).

Several scientists suggested that several isolates of single pathogen or

several species of pathogens each having slightly different environmental

requirements could be mixed for biocontrol formulation to ensure that at

least one could be faced the optimal environmental window (Templeton and

Heiny, 1989; Ray and Hill, 2013). Hasan and Ayers (1990) reported that

interaction between the biotroph and necrotroph occurs at the infection site

of biotrophs, where infection by one pathogen makes the host more

susceptible to secondary infection. The synergistic relationship of two

pathogens can provide biological and economical feasibility by the use of the

mixtures of two or more fungi for effective control of one or more weeds. Den

Breeyen (1998) while conducting similar study reported greater lesion

diameters on water hyacinth when using combination of pathogens than

lesion diameter using individual pathogens.

2.9. Control of weeds through mycoherbicide formulations:-

Now days, Herbicides are used in the production of almost 100% of major

crops throughout the world. Biological weed control with plant pathogenic

fungi used as mycoherbicides offers successful biocontrol of weeds. But

there are several biological and environmental limitations for any successful

biological control programme. Recent advances in adjuvant formulation and

delivery system have been used by scientists to control these limitations

(Boyette et al., 1996). Formulation is the blending of an active ingredient,

such as fungal spores with an adjuvant. Currently, Sodium alginate and

other adjuvants were used to prepare pelletized formulations with fungal

biocontrol agents for control of different weeds (Walker et al., 1983).

A total of 17 mycoherbicides have been registered, of these, 8 registered in

USA, 4 in Canada, 2 in South Africa and 1 each in Netherland, Japan and

China (Table-2.2) (Aneja 2009; Dagno et al., 2012; Aneja, 2014), as

discussed below.

Table- 2.2: Examples of commercial bioherbicides and type of

formulation used.

S. No.

Target weed Fungus Product name

Year of registrat

ion

Formulation type

Liquid formulations

1. Persimmon (Diospyros virginiana) trees in rangelands

Acremonium diospyri

Acremonium diospyri

1960 Conidial suspension

2. Dodder (Cuscuta chinesis and C. australis) in soybeans

Colletotrichum gloeosporioides f. sp. cuscutae

Lubao

1963

Conidial suspension

3. Milkweed vine (Morrenia odorata)

Phytophthora palmivora (P. citrophthora)

DeVineR

1981 Liquid spores

suspension

4. Yellow nutsedge (Cyperus esculentus)

Puccinia canaliculata

Dr. Biosedge

1987 Emulsified suspension

5. Turf grass (Poa annua) in golf

Cylindrobasidium leave

StumpoutT

M 1997 Liquid (oil)

suspension

courses, Acacia

sp.

6. Woody plants

Blackberry weed (Prunus serotina)

Chondrostereum purpureum

BioChonTM 1997 Mycelial

suspension in water

7. Hakea gummosis & H. sericea in

native vegetation

Colletotrichum acutatum

Hakatak 1999 Conidial suspension

8. Deciduous tree

species


MycotechTM

Paste

2004 Paste

9. Alder, aspen and

other hardwoods


ChontrolTM

(EcoclearTM) 2004 Spray

emulsion & paste

10. Dodder species Alternaria destruens

SmolderR 2008 Conidial suspension

11. Soda apple (Solanum viarum)

Tobacco mild green mosaic virus

SolvinixTM 2009 Foliar spray suspension

Solid formulations

1. Northern joint-

vetch (Aeschynomene virginica)

Colletotrichum gloeosporioides f.sp.

aeschynomene

CollegoTM

LockDownTM

1982 Wettable

powder

2. Sickle-pod and

coffee senna (Cassia spp.)

Alternaria cassiae

CasstTM 1983 Solid

3. Water hyacinth (Eichhornia crassipes)

Cercospora rodmanii

ABG-5003

1984 Wettable powder

4. Velvet leaf

(Abutilon theophrastus)

Colletotrichum coccodes

VelgoR 1987 Wettable

powder

5. Round-leaved mallow (Malva pussila)

Colletotrichum gloeosporioides f.sp. malvae

BioMalR 1992 Mallet wettable

powder

6. Hakea gummosis

& H. sericea in native vegetation

Colletotrichum acutatum

Hakatak 1999 Granular

(dry conidia)

7. Dyers woad (Isastis tinctoria)

in farms, rangeland, waste areas & roadsides

Puccinia thlaspeos

Woad Warrior

2002 Powder

8. Dandelion (Taraxacum officinale) in lawns/turf

Sclerotinia minor Sarritor 2007 Granular

2.10- Registered mycoherbicides against water hyacinth:-

Formerely, two mycoherbicides have been developed to control Eichhornia

crassipes. One of the best known example was Cercospora rodmanii

registered by the United States named as ABG-5003. This product was

developed by Abbott laboratories (Freeman and Charudattan, 1984). Second

developed mycoherbicide is known as HYAKILLTM which contains

formulation of fungus Sclerotinia sclerotiorum. HYAKILLTM was submitted

to the European Patent Office in 2003 (De Jong and De Voogd, 2003) but

this product had not been commercialized because of a disadvantage that it

was not host specific.

2.10.1. ABG-5003

ABG-5003 is the formulation of the fungus Cercospora rodmanii, (Fig-2.2) for

controlling water hyacinth. This fungus was first isolated in 1973 by

Conway from diseased water hyacinth plants found in the Rodman reservoir,

Florida, USA. The experimental formulation of ABG-5003 was developed in

1984 by Abbott laboratories which consisted mycelium and spores and

applied as wettable powder, however, this formulation was not found to be

very efficient when applied in natural conditions. The notable advantage of

this fungus is that it is compatible with various chemical herbicides and

insects for controlling water hyacinth (Conway et al., 1978; Charudattan,

2001).

Figure-2.2. (A) Infected water hyacinth plants with Cercospora

rodmanii; (B) Colony on an agar medium (C) Conidia and conidiophores.

A B C

2.11. Limitations/constraints in development of bioherbicides:

Bioherbicides or mycoherbicides serves an important role as a

complimentary component in successful integrated management strategies

for control of weeds (Hoagland et al., 2007), and a good replacement for

chemical herbicides and other weed management strategies (Singh et al.,

2006). Phytopathogenic microorganisms or microbial phytotoxins are very

useful for biological weed control programme applied in similar ways to

conventional herbicides (Goeden, 1999; Boyetchko et al., 2002; Boyetchko

and Peng, 2004). But the challenges that have limited the advancement of

bioherbicide or mycoherbicide have been categorized into four constraints:-

Environment constraints

Biological constraints

Technological constraints

Commercial limitations

(Boyetehko and Peng, 2004)

2.11.1. Environmental limitations:-

Environmental factors such as temperature, free moisture play a key role for

formulation and performance of a bioherbicides or mycoherbicides. In the

application of bioherbicides, environmental conditions overcome in the

phyllosphere of plants are frequently hostile for biological control agents

(Kenerley and Andrews, 1990; Andrews, 1992). A requirement for more than

12 h of dew period for causing infection by a pathogen has been reported by

many scientists for several potential bioherbicides (Boyette & Walker, 1985;

Wymore et al., 1988; Morin et al., 1990; Makowski, 1993) and this may limit

the biocontrol efficacy of the bioherbicide in the greenhouse as well as in the

field.

Environmental factors that limit the distribution of biocontrol agents in

nature are numerous and poorly known. Biological control agents are more

sensitive to relative humidity and temperature (Kempenaar & Scheepens,

1999). Wheeler and Center (2001) have suggested that the possible abiotic

limiting factors reduce the fly activity of the small-weak flies of Hydrellia

pakistanae (Diptera: Ephydridae).

2.11.2. Biological limitations:-

It is desirable for a bioherbicide or mycoherbicide to act relatively quick

response and have sufficient efficacy to control weeds. Unfortunately, many

of the weed pathogens discovered may provide only partial control of only

one weed species, even under ideal conditions (Charudattan, 2005).

Host specificity is related to the basic biology of the pathogen and to host

variability (Gabriel, 1991; Leonard, 1982). Biological constraints including

host variability and resistance, as well (Auld et al., 2003).

2.11.3. Technological-commercial limitations:-

Various technology based limitations have been identified that could prevent

the global use of bioherbicides or mycoherbicides. Pathogenically strains,

method of formulation and the interaction among two parameters

significantly influence the shelf life of the formulations at room temperature

(Altman et al., 1990; Hebbar et al., 1998). The most challenging aspect of

formulating bioherbicides is to overcome the dew requirement that exists for

several of them.

Now days, various invert and vegetable oil emulsion formulations have been

used to eliminate or reduced the free moisture requirements and increased

biocontrol efficacy (Boyette et al., 1999). Attempts to overcome this

limitation also have included developing granular pre-emergence

formulations (Watson and Wymore, 1990). Some application constraints also

are expected to arise upon the commercial release of potential bioherbicides

(Greaves et al., 1999). Aerosol sprayers perform experimental bioherbicide

applications in the laboratory or glasshouse. These sprayers apply sufficient

inoculum suspension to induce run-off from the target at rates between

1000 and 3000 L ha-1. Modern field spray application practices, on the

contrary, aim to reduce the application volume to the minimum reliable

volume, usually <250 L ha-1 and never exceeding 500 L ha-1, with droplet

spectrums markedly different from that produced by aerosol (Ghosheh,

2005).

2.12-Potential fungal pathogens of water hyacinth:-

Field surveys by several researchers from different country of the world

demonstrated that Water hyacinth is susceptible to several virulent

pathogens worldwide, of these the majority are fungi which induce leaf

spots, leaf blotches and foliar blights symptoms. Review of literature reveals

that a number of pathogenic fungi have been recorded on water hyacinth.

Some disease causing and virulent pathogens of water hyacinth of

worldwide importance and have potential to be developed as mycoherbicide

are given in the table-2.3.

Table-2.3- Some disease causing and virulent pathogens of water

hyacinth of worldwide importance:-

S.no. Fungal pathogen Reported

from

Year References

1. Fusarium sp. India 1932 Agharkar and

Banerjee (1932)

2. Fusarium equiseti India 1942 Banerjee (1942)

3. Cercospora piaropi Australia,

India, Sri

Lanka, USA

1954 Thirumalachar and

Govindu (1954)

4. Marasmiellus inoderma India 1965 Nagraj (1965)

5. Cephalosporium

eichhorniae

(Acremonium zonatum)

Australia,

India,

Pakistan, USA

1966 Sukapure and

Thirumalachar

(1966)

6. Cylindrocladium

scoparium var.

brasiliensis

India 1969 Reddy (1969)

7. Helminthosporium

bicolour

India 1970 Rao (1970)

8. Alternaria eichhorniae India,

Pakistan,

Egypt

1970 Nag Raj and

Ponnappa (1970 b)

9. Myrothecium roridum India, Sri

Lanka

1970 Ponnappa (1970)

10. Fusarium rossum USA 1972 Rintz & Freeman

(1972)

11. Cercospora rodmanii India, Florida,

USA

1974 Freeman and

Charudattan

(1974)

12. Curvularia lunata India 1974 Chandra (1974)

13. Uredo eichhorniae Argentina,

Brazil,

Pakistan, USA

1975 Charudattan and

Conway ( 1975)

14. Fusarium solani Australia,

India

1983 Jamil et al.(1983)

15. Septofusidium

elegantulum

Sri Lanka 1983 Hettiarachachi et

al. (1983)

16. Bipolaris oryzae Dominican

Republic

1984 Charudattan

(1984)

17. Rhizoctonia solani India, Panama

USA

1987 Srivastava and

Verma (1987)

18. Alternaria alternata Australia,

India,

Pakistan

1988,

1989

Aneja et al.(1988);

Aneja and Singh

(1989)

19. Fusarium

chlamydosporum

India 1990 Aneja et al.(1990)

20. Epicoccum nigrum India 1990 Aneja et al.(1990)

21. Phoma sorghina India, Sudan 1990 Aneja et al.(1990)

22. Bipolaris sorokiniana India 1992 Aneja and Srinivas

(1992)

23. Myrothecium advena India 2004 Praveena and

Naseema (2004)

24. Drechslera hawaiiensis Egypt 2004 EL-Morsy (2004)

25. Ulocladium atrum Egypt 2004 EL-Morsy (2004)

26. Fusarium pallidoroseum India 2007 Praveena et al.

(2007)

27. Collectotrichum sp. China 2008 Ding et al. (2008)

28. Alternaria jacinthicola Mali 2011 Dagno et al.(2011)

29. Cadophora malorum Mali 2011 Dagno et al.(2011)

30. Alternaria geophila Ethiopia,

Germany

2012 Tegene et al. (2012)

31. Ascochyta chartarum Ethiopia,

Germany


32. Cochliobolus carbonum Ethiopia,

Germany


33. Pythium ultimum Ethiopia,

Germany

2012 Tegene et al.

(2012)

34. Stemphylium vesicarum Ethiopia,

Germany


A total of 18 fungal pathogens have been recorded on water hyacinth from

Kurukshetra, India as given in table 2.4. Out of these, Cercospora rodmanii,

Alternaria eichhorniae, Fusarium chlamydosporum and Alternaria alternata

have been evaluated to their biocontrol potential in India.

Table-2.4- Fungal pathogens of water hyacinth recorded from India

S.no. Fungal pathogen Symptoms Year References

1. Fusarium sp. Leaf decay 1932 Agharkar and Banerjee (1932)

2. Fusarium equiseti Leaf spot 1942 Banerjee (1942)

3. Cercospora piaropi Leaf spots

and leaf

necrosis

1954 Thirumalachar and

Govindu (1954)

4. Marasmiellus

inoderma

Foliar blight 1965 Nagraj (1965)

5. Cephalosporium

eichhorniae

(Acremonium

zonatum)

Stem and

root rot

1966 Sukapure and

Thirumalachar(1966)

6. Cylindrocladium scoparium var. brasiliensis

Leaf spot 1969 Reddy (1969)

7. Helminthosporium

bicolour

Leaf spot 1970 Rao (1970)

8. Alternaria

eichhorniae

Leaf spot and

severe leaf

blight

1970 Nag Raj and Ponnappa

(1970 b)

9. Myrothecium roridum Leaf spot 1970 Ponnappa (1970)

10. Cercospora rodmanii Leaf spot 1974 Freeman and Charudattan

(1974)

11. Curvularia lunata Leaf spot 1974 Chandra (1974)

12. Fusarium solani Raddish

brown leaf

spot

1983 Jamil et al. (1983)

13. Rhizoctonia solani Foliar blight 1987 Srivastava and Verma

(1987)

14. Alternaria alternata Leaf spot 1988

,

1989

Aneja et al. (1988); Aneja

and Singh (1989); Babu et

al. (2003)

15. Fusarium chlamydosporum

Leaf spot 1990 Aneja et al.(1990)

16. Epicoccum nigrum Leaf spot 1990 Aneja et al.(1990)

17. Phoma sorghina Leaf spot 1990 Aneja et al.(1990)

18. Bipolaris sorokiniana Leaf spot 1992 Aneja and Srinivas (1992)

l2.12.1-Development of Alternaria eichhorniae as a biocontrol agent of

water hyacinth-

Alternaria eichhorniae, was firstly reported on water hyacinth from India by

Nagraj and Ponappa in 1970. The fungus was later discovered on water

hyacinth in Australia, Bangladesh, Indonesia, and South Africa. It causes

discrete or blotchy necrotic leaf spots with dark centres and brownish black

margins, often with a thin yellow halo surrounding the spots resulting in

severe leaf blights. A. eichhorniae is being worked out in Egypt for

controlling water hyacinth (Shabana et al., 1995 a).

The pathogen produces a diffusible, bright red colouration in certain

nutrient media. This colouration is due to the production of reddish

pigments which have been identified as bostrycin and deoxy-bostrycin

(Badur-Ud- Din, 1978; Charudattan and Rao, 1982). Pellet and powder

formulation of the fungus have been tested in greenhouse trials in Egypt.

The vegetable oil emulsions formulation of A. eichhorniae has a great

potential in controlling water hyacinth (Shabana and Mohamed, 2005). So,

this fungus has a potential to be developed as a biocontrol agent as it is

having the desirable characteristics required by the fungus to be developed

as a mycoherbicide.

Table-2.5: Steps in the development of Alternaria eichhorniae Nag Raj

and Ponnappa as a potential biocontrol agent of water hyacinth

Steps Year References

Discovery of the disease and

identification of the pathogen and first

reported as potential biocontrol agent

for water hyacinth

1970 Nag Raj and Ponappa

(1970 a, b)

Recorded from Indonesia 1977 Mangoendihardjo et al.

(1977)

Recorded from Bangladesh 1978 Badur-ud-Din (1978)

Recorded from Thailand 1978 Rakvidhyasastra et al.

(1978)

Reported from Hyderabad 1983 Jamil et al. (1983)

Recorded from Egypt 1987 Shabana et al. (1995)

Discovery of the disease from

Derabassi (Punjab) and Kurukshetra

(Haryana) and identification of the

pathogen

1988-

89

Aneja and Srinivas

(1992)

Evaluation of the pathogen for

biocontrol potential in the laboratory

and field conditions at Kurukshetra

1988-

1990

Aneja and Srinivas

(1992)

Evaluation of pathogen for its

biocontrol efficacy in Egypt

1995-

1996

Shabana et al.(1995 a)

Evaluation of the alginate

formulations of Ae5 for weed control

efficacy

1996 Shabana et al. (1997)

The use of oil emulsions for improving

the efficacy of A. eichhorniae as a

mycoherbicide

2005 Shabana (2005)

2.12.2-Development of Alternaria alternata as a biocontrol agent of

water hyacinth-

Alternaria alternata is a type of cosmopolitan fungus and has been isolated

from almost all habitats (EL-Morsy, 2004). The fungus has been described

as a pathogen of water hyacinth firstly in Bangladesh (Bardur- Ud- Din,

1978) then in Australia (Galbraith and Hayward, 1984), Egypt (Elwakil et

al., 1989; Shabana et al., 1995; El-Morsy, 2004), and India (Aneja et al.,

1988; Aneja and Singh, 1989; Babu et al., 2003). This fungal species

induces spots and lesions mainly on leaves and less severely on stolons and

finally leads to complete death of the plant (Babu et al., 2003; El-Morsy,

2004). During pathogenicity, when applied to 7 days old mycelial culture

disc to the leaves surface, disease started as small necrotic spots and

developed into a leaf blight that entirely covered the whole leaf. This

pathogen has been evaluated for its biocontrol potential against water

hyacinth by several researchers around the globe and has shown the

presence of all the desirable features of a potential mycoherbicide such as

conidial production on simple agar media, biocontrol efficacy, host

specificity and non- toxicity to human beings and hence the possibility for

its development as a commercial mycoherbicide in the near future (Babu et

al., 2003; El-Morsy, 2004).

Table-2.6: Steps in the development of Alternaria alternata as a

potential biocontrol agent against water hyacinth (Eichhornia

crassipes)

Sr.

No.


1. First description of Alternaria alternata

as a pathogen of water hyacinth

1978 Bardur-ud-Din

(1978)

2. Isolation of the pathogen from disease

water hyacinth leaves from India

1988

Aneja et al. (1988)

3. Identification of the pathogen as

Alternaria alternata and description of

the pathogen i.e. leaf spot of

Eichhornia crassipes caused by

Alternaria alternata in India

1989

Aneja and Singh

(1989)

4. Testing of the pathogenicity of the

isolated pathogen on fresh water

hyacinth leaves in India

1989

Aneja and Singh

(1989)

5. Biocontrol potential of Alternaria

alternata to water hyacinth in India

1989

Aneja and Singh

(1989)

6. Test of efficacy of the isolated

pathogen to use as biocontrol agent of

water hyacinth In India

1989 Aneja and Singh

(1989)

7. Host range of Alternaria alternata—a

potential fungal biocontrol agents for

water hyacinth in India

2002 Babu et al. (2002)

8. Bioassay of the potentiality of

Alternaria alternata (Fr.) keissler as a

bioherbicide to control water hyacinth

and other aquatic weeds In India

2003 Babu et al.(2003)

9. Solid substrate for production of

Alternaria alternata conidia: a

2004 Babu et al. (2004)

potential mycoherbicide for the control

of Eichhornia crassipes (water

hyacinth) in India

10. Deleterious effect of herbicides on

water hyacinth biocontrol agents

Neochetina bruchi and Alternaria

alternata

2008 Ray et al. (2008 a)

11. Integrated approach for the

management of water hyacinth

(Eichhornia crassipes)

2012 Singh et al. (2012)

2.12.3-Development of Fusarium chlamydosporum as a biocontrol

agent of water hyacinth:-

Fusarium chlamydosporum a new host records on water hyacinth from India.

Macroconidia are curved, sickle shaped hyaline fusoid with a narrowly

rounded to pointed apex and marked foot cell. The infection of water

hyacinth leaves one month post inoculation with F. chlamydosporum ranged

between 25-54 percent. In covered pits, infection was lower than the

uncovered pits. Results revealed that large sized leaves exhibited more

infection than the small and medium sized leaves. This pathogen has a

potential to be developed as a future mycoherbicides (Aneja et al., 1990).

2.12.4-Development of Cercospora rodmanii as a biocontrol agent of

water hyacinth:-

Cercospora rodmanii is the potential fungus which had been developed as a

mycoherbicide in USA for controlling water hyacinth. It was first isolated in

1973 by Conway, from diseased water hyacinth plants found in the Rodman

reservoir, Florida, USA. The experimental formulation of the fungus was

developed in 1984 by Abbott laboratories and named it as ABG- 5003, which

consists fragment of mycelial spores applied as wettable powder. Increased

disease intensities and faster epidemic development rates of leaf spot caused

by C. rodmanii occurred on water hyacinth after one application of

inoculums. Although biocontrol potential of the fungus was good but

efficacy was less as it was required for a desirable fungus to be

commercialized due to the restrictive environment requirement by the

fungus but later on some scientists discovered that the fungus has been

compatible with combination of various chemical herbicides and insects for

controlling water hyacinth (Conway et al., 1979; Charudattan, 2001).

Table-2.7: Steps in the development of Cercospora rodmanii as a

potential biocontrol agent against water hyacinth (Eichhornia

crassipes)


Discovery of the disease from the

Rodman Reservoir, florida, U.S.A

1973 Conway et al. (1974)

Identification and description of the

pathogen

1975 Conway (1976),

Conway and Cullen

(1978)

Preliminary greenhouse and field test of

efficacy

1973-

1976

Conway et al. (1979)

Host range testing in the greenhouse

and the field

1973-

1977

Conway and Freeman

(1977)

Advanced field studies in florida and

Louisiana

1973-

1976

Conway and Freeman

(1976), Freeman et al.

(1982)

A Cercospora rodmanii use patent

obtained

1978 Conway et al.(1978)

Industrial production of C. rodmanii as

wettable powder formulation, ABG-5003

(Abbott Lab.)

1978 Charudattan (1991),

Charudattan et al.,

(1985), Conway et al.

(1978), Freeman and

Charudattan (1984)

An EPA experiment use permit obtained

1979

Freeman and

Charudattan (1984)

Successful large- scale aerial

application of Abbott formulation

1980 Theriot (1981,1982)

EUP studies continued 1980 Freeman and

Charudattan (1984)

Molecular identification of two strains of

Cercospora rodmanii isolated from water

hyacinth present in Yuriria lagoon, and

Guanajuato

2011 Calderon et al. (2011)

2.12.5-Development of Phoma sorghina as a biocontrol agent of water

hyacinth:-

Phoma sorghina is a cosmopolitan fungus belonging to the genus Phoma

(Pleosporales) (Aveskamp et al., 2008). P. sorghina was firstly reported from

Sudan (Abdel-Rahim, 1984) & later from India (Aneja et al., 1990). It caused

small brown lesions of irregular outline on leaves of water hyacinth plants.

Colonies on water hyacinth dextrose agar medium are extremely variable,

usually with a fluffy to dence aerial mycelium which is generally grey green

to olivaceous to darker. Pycnidia globose, papillate, hard and carbonous

black. Conidia unicellular, hyaline ellipsoid and it bears botryoid

chlamydospore. This pathogen is considered to be ubiquitous, weakly

pathogenic to water hyacinth, hence it should not be pursued further as

biocontrol agent.

2.12.6-Development of Bipolaris sorokiniana as a biocontrol agent of

water hyacinth:-

Bipolaris sorokiniana on Eichhornia crassipes is being reported for the first

time from India (Charudattan, 1990; Aneja and Srinivas, 1992). It caused

dark coloured leaf spot disease on water hyacinth. Petiole is often most

affected then leaves. Conidiophores solitary, brown, with five to six

transverse septa. Conidia straight, fusiform to broadly ellipsoidal, dark

brown, smooth three to five pseudoseptate. Though, it has been reported on

several graminaceous (Wheat, barley, rice, rye), non- graminaceous (bean,

pea) hosts and on pteridophyte. Hence, this pathogen has not being

evaluated for biocontrol of water hyacinth.

2.12.7-Development of Epicoccum nigrum as a biocontrol agent of

water hyacinth:-

Epicoccum nigrum is also a new record from India on leaves of water

hyacinth. It is a type of widespread fungus which produces

coloured pigments. The pathogen has been reported earlier by Conway et al.

(1974) from Florida, U.S.A and later from Australia in 1984 by Galbraith

and Hayward. This fungus causes leaf spots or lesions leading to compact

zonation‘s starting from tip of the leaf and spreading backwards. Petioles are

also affected. The conidia are solitary, muriform or pyriform with rough

opaque wall.

2.12.8-Development of Curvularia lunata as a biocontrol agent of water

hyacinth:-

Curvularia lunata causes light brown or yellowish-cream coloured, spots

rounded or elliptical in shape leading to compact zonation‘s starting from tip

of the leaf and spreading backwards. Large leaves comparatively showing

more infection than small leaves, Petioles are also affected. Conidiophores

are straight or flexuous often geniculate and brown. Conidia solitary, simple

or curved shaped with 2-4 transverse septa, pale olive or brown in colour.

The teleomorphic state of the species Curvularia lunata is Cochliobolus

lunatus (Fam. Pleosporaceae, Ord. Pleosporales, Cla. Loculoascomycetes,

Phy. Ascomycota).

2.12.9-Development of Cylindrocladium scoparium var. brasiliensis as

a biocontrol agent of water hyacinth:-

This fungus was first described by A.P. Morgan in 1892 and has been

reported as a plant pathogen on plants in 66 genera of 31 families from

many places in the world. This pathogen produced irregular light brown

spots on leaves which subsequently changed into cinnamon- brown colour.

Hyphae are hyaline and septate, older hyphae forming hyaline ovoid

intercalary chlamydospores, conidiophores and conidia are also hyaline,

closely septate. This pathogen is known to occur in Rajasthan (India)

(Reddy, 1969).

2.12.10-Development of Cephalosporium eichhorniae (Acremonium

zonatum) as a biocontrol agent of water hyacinth:-

Cephalosporium eichhorniae (Acremonium zonatum) was reported as a

pathogen on water hyacinth from Pakistan, India and Louisiana, USA

(Padwick, 1946; Sukapure and Thirumalachar, 1966; Rintz, 1973). The

fungus caused necrotic type small zonate leaf spot characterised by

spreading lesions, mostly occurs on the upper surface. On the lower surface,

the area under the spot may have a sparse, spreading layer of white fungal

mycelial growth. Each spot may be small (2 mm diameter) to large (> 3 cm

diameter). On the basis of extensive studies, Rintz had concluded that the

fungus is restricted to the leaves and petioles but its progress is not rapid. It

does not seem capable of killing the plant nor seriously hindering its prolific

growth. Nonetheless, studies that followed, including limited field tests

demonstrated no control because of the slow spread of the disease.

2.12.11-Development of Fusarium solani as a biocontrol agent of water

hyacinth:-

This pathogen was first reported on water hyacinth by Jamil et al. (1983),

from Hyderabad, India and later on by Galbraith and Hayward in 1984 from

Australia. The infected leaves show reddish brown spots. In addition, it

caused chlorosis and damages the epidermal layer causing yellowing of

petioles and leaves. It produced two types of conidia i.e. micro and macro

conidia. The micro conidia are hyaline, single celled abundantly produced

from elongated conidiogenous cells. Macro conidia are sickle shaped 4-5

septate. It is a seed borne pathogen commonly considered as a contaminant.

Colonies are woolly to cottony with creamish to whitish aerial mycelium

bears long monophialides, and microconidia.

2.12.12-Development of Rhizoctonia solani as a biocontrol agent of

water hyacinth:-

Rhizoctonia solani causes blight disease on water hyacinth. It is noticeable

as irregular, brown, necrotic blotches bordered by dark margins on the

lamina. Severely infected lamina and entire plants may be blighted and

killed. In the necrotic area, appearance of sclerotia was seen with naked

eyes. When young colonies on PDA colourless, which rapidly becomes

yellowish brown to brown with age. Cells of the hyphae 5-10 µm wide and

up to 250 µm long. Sclerotia globose, up to 4mm in diameter, brown to dark

brown. The rhizoctonia disease on water hyacinth is known to occur in

Taiwan, India, USA, Panama (Srivastava and Verma, 1987).

Rhizoctonia solani forms perfect state which belongs to Thanatephorus

cucumeris, a member of basidiomycetes. It produced a highly modified

sexual state with a globose metabasidium having swollen protosterigmata

without adventitious septa named as Aquathanatephorus pendulus (Tu and

Kimbrough, 1978).

2.12.13-Development of Cercospora piaropi as a biocontrol agent of

water hyacinth-

Cercospora piaropi was described as a pathogen on water hyacinth from USA

in 1914 (Tharp, 1917). It causes leaf spot disease on water hyacinth. Leaf

spots ovate, greyish in colour. Conidiophores are epiphyllous, bright brown,

multiseptate and tapering toward the tip. This pathogen was later reported

on water hyacinth from India (Thirumalachar and Govindu, 1954; Nag raj,

1965; Jamil et al., 1983).

2.12.14-Development of Myrothecium roridum as biocontrol agent of

water hyacinth:-

Myrothecium roridum causes a leaf spot disease on water hyacinth. It was

described from Bangalore; India (Ponappa, 1970). The disease is

characterized by tear drop shaped necrotic spots, with long necrotic streaks.

Sporodochia in culture are sessile up to 1.5 mm in diameter. Unicellular

cylindrical conidia with rounded ends, colourless to pale olive, green to

black in mass. But further research reveals that this pathogen was not host

specific so it cannot be used for biocontrol potential.

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