The accidentally introduced weed Pa.rtheaium
hysterophorus L., popularly known as Congress grass or carrot weed in
India, is an erect, herbaceous annual plant belonging to family Asteracae
(Compositae). It is popularly believed to have entered the Indian soil sometime
during 1956 along with wheat sent by USA under PL-480 (Public Law 480 passed
in 1954 to give food. grains to developing countries). This belief was put
forth by R. S. Rao (1956) based on the observations of Prof. Paranjape, a
retired horticulturist who encountered this weed for the first time in
1951 at Pune. But the presence of herbarium specimens of D. Brandis (1888) at
Forest Research Institute, Dehradun reveals that the views of Dr. Rao are unfounded
and the species in question had already entered India prior to his
publication. Probably, it had taken more time to get acclimatized and started
invading newer areas only in the mid fiftees. It is not only a pernicious weed of
immense crop damaging potential, but also poses a serious threat to human beings and
livestock leading to socio-psycho economic problems. It is known to cause
contact irritant dermatitis with itchy lesions over the face, neck and dorsal sides
of hands and legs. Besides contact dermatitis, many people suffer from asthma,
nasal-dermal and naso- bronchial types of diseases. It also causes several other
problems like blockage of common pathways and orchards and reduces the aesthetic
values of parks, gardens and residential colonies. Mostly, it is a weed of fallow
and wastelands, but its intrusion into the agricultural domain in Orissa is
alarming as productivity is going to be adversely affected.
Probing biological pollutant, highly successful in distribution. No species of the
past or the present century can ever match with this. The reasons for its
fast spread are: (l)High germination ability throughout the year, (2) Large seed
production ability, (3) High survival rate, (4) Extreme adaptability in a wide range
of habitats. (5) Easy dispersal of seeds. The word Parthenium is derived from the
Latin word 'parthenice', suggesting medicinal uses. The origin of this
obnoxious weed is traced to the Caribbean but its adverse effects are felt
largely in African, Australian and Asian countries. In India, it is rated as the
"worst weed" of the last century. Though it spread fast in U.P.,
Karnataka, Maharashtra, Tamil Nadu, Andhra Pradesh, West Bengal, Madhya Pradesh,
Gujarat, and Bihar, its invasion into Orissa was delayed. Its occurrence in Orissa
was observed for the first time by this author during November 1977 (Brahmarn &
Saxena,J. Bombay Nat. Hist. Soc. 81:509, 1984) from Bhubaneswar and it might possibly have
entered through parcels unloaded from Kolkata and Mumbai.
Features
It is an annual plant with a deep, tap-root and an erect much - branched stem. It
grows to a height of 1-2 m with lobed leaves. The flowers are creamy white, borne in
profusion at the tips of the stems. Clusters of male and female florets are
grouped as 5-lobed, 4-8 mm diam. heads. Seeds are small, 1-2 mm across, flattened,
triangular, dark brown to black with two thin white spoon-shaped appendages.
In congenial conditions, parthenium can complete its life cycle in four weeks. A
single plant can produce 10,000 to 15,000 viable seeds that occupy roadsides, tank bunds,
fence lines, waste lands, agricultural fields etc.
Control Measures
From the day it was perceived as a menace, efforts are being made to control the weed by
different methods. But so far, no single method appears to be satisfactory, as each
method suffers from one or more limitations, such as high cost, impracticability,
environmental safety, tem and Mechanical Eradication It is observed that cutting or
slashing of paithenium enhances its regeneration. So uprooting manually is the
finest option. During the rainy season, the soil remains wet and hence manual
or mechanical removal can be done before the onset of flowering with people's
participation. This operation should be started before blooming as uprooting after
fruit setting will be a sheer waste of time and money. As manual removal is not cost
effective, it can be advocated only in limited situations. If it becomes imperative to use
labour, they should be equipped with protective measures including ascertaining
their parthenium sensitiveness.
Limitation: Manual methods are very expensive and cannot be employed everywhere. It is
feasible only in high value crops. The relief from this method is temporary and needs to
be repeated. Mechanical removal with the help of tractor, plough, etc., is possible only
up to a certain extent and only in open fields.
Biological Measures
During the last few years much emphasis has been laid on controlling parthenium through
various biological agents like insects, pathogens and by creating competition that
result in 'survival of the fittest'.
Creating Competition
In the recent past, this approach gained momentum to do away with unwanted plants.
Experimentally, it was found that Cassia species can control parthenium.
C.sericea(C.uniflora), a non-nitrogen fixing leguminous herb, colonises more aggressively
without giving scope for Parthenium to manifest. Cassia can be encouraged either
from wild source or by introducing it in targeted areas.
Limitation
In this approach, two apprehensions are imminent. For planting C. sericea in areas of
parthenium dominance, the parthenium needs to be removed physically or mechanically
in the beginning. Secondly, another weed (Cassia) has to be grown to remove the unwanted
weed. There is no guarantee that the introduced weed would not become dangerous to field
crops and orchards in later years.
Remedy
Since the as been found o reduce the prevalence of parthenium, it needs to be popularized
in residential areas - not just to control the weed, but also to enhance their aesthetic
appeal.
By insect feeding -
Insects are known to have host-specificity. By introducing suitable insects, the weed
menace can also be checked to a larger extent. In the wild, many insects have been
reported on parthenium but none of the indigenous insects was found to be host -
specific. Only one insect i.e. cerembycid borer (Oberea sp.) was found infesting
parthenium but its preference was only 30 °/o. Having failed with indigenous
insects, three known exotic insect species were imported and introduced locally on a
trial basis.Of these, only one i.e. chrysomelid beetle Zygogramma bicolorata - imported
from Mexico showed positive results in Indian environment and controlled the weed
successfully.
Limitation
But this experiment was abandoned as this beetle was found to feed also on sunflower and
xanthium. The seed feeding weevil - Smicronyx lutulentus- did not survive in spite
of the best efforts.
Even if one were to ignore its propensity to feed on sunflower, this Mexican weed may not
be very effective to control Parthenium because this beetle is able to produce its
population only during July to September. On the contrary, parthenium is able to germinate
throughout the year. Therefore, only those insects that are active during most
part of the year should be preferred to manage parthenium. Identifying the insects
in their native land and introducing them in our area will be an essential component
of future strategy.
More concerted efforts are needed to screen and identify the indigenous insects
which can control this weed.
By pathogens -
Efforts were also taken to control this weed by introducing pathogens - especially,
fungal taxa. In fact, Fusarium pallidoroseum and Sclerotium rolfsii were found to infest
leaves, stems, seeds and roots of parthenium.
Limitation
But this effort was also dispensed with because of fear that the fast expand their
host range.
CHEMICAL METHODS
Chemical control has supremacy over other control measures on the score of quick
relief,
time saving and cost effectiveness. Research on chemical control of parthenium was
tried with promising results during the seventies and eighties. Bromacil,
Diuron, Terbacil @ 1.5 kg per ha were found to be effective as herbicides. Diquat
0.5 kg per ha in 500 lit. spray effectively controlled parthenium at all growth
stages. Spraying of 2 kg of2,4-D sodium salt or 2 lit. of MCPA in 400 lit. of water
controlled the growth of parthenium seedlings. Likewise, MSMA @ 4 lit. in 400 lit. of
water was able to control fully grown parthenium.
During summer and winter, the population of parthenium remains low in comparison to the
rainy season and, therefore, spraying of glyphosate will be of much use. Before monsoon,
preemergent herbicide like atrazine, metribuzin or bromacil @ 2,2.3 and 1.5 kg per ha can
be applied in the dominant patches. With the onset of monsoon, emerged seedlings of
sufficient height can be controlled by spraying of glyphosate @ I % solution. This
application should be made at any cost before blooming.
A review of the work done so far reveals that only a meager amount of work seems to
have been carried out on the pathogen-parthenium relationship. More concerted
research in this direction is necessary to develop mycoherbicides for effective
management. Integration of bioherbicides with reduced rate of chemical herbicides can
successfully improve the activity of mycoherbicides on this weed. Native pathogens should
be explored for effective results in place of exotics.
.
Limitations
The use of herbicides, in my view, is not an effective solution as the effect
is always a temporary one and repeated operations will not be cost effective. Since
parthenium can survive well in wastelands, the common man will think twice before
investing his hard earned money. Moreover, plants suppressed by chemicals have been
observed to regenerate after remaining dormant for a
nly kill existing population at the given sites but cannot prevent the entry of the seeds
from neighbouring places. Because of the continuous seed production ability of parthenium
throughout the year, reinvasion of the once controlled area can hardly be
checked, unless the seed source itself is controlled.
Remedy
The biology and ecology of parthenium should be studied before advocating the use
of herbicides because parthenium is a hardy weed and may soon develop resistance
against them. It germinates throughout the year. Hence application of pre and post -
emergent herbicide, in sequence, may give effective control of parthenium.
Development of persistent and cheaper herbicides having less residual effects is
imperative. The most sensitive growth stage of parthenium should be identified for
effective management. It is now reasonably clear that there is no single, foolproof method
of controlling parthenium. Every method suffers from some limitation or the other. Hence,
there is an urgent need for an integrated approach by trying out more than one
option to root out this dangerous weed from the face of the earth.
Of course, finding out some useful features in the weed is the surest guarantee for wiping
it out in course of time. The insecticidal nematode and herbicidal properties and oxalic
acid and biogas producing abilities of parthenium are well known. But there is
urgent need for research to find out more such properties, which would make sound economic
sense for the people to go after this so far pernicious weed.
(Courtesy : 22-24 / Community Forestry
/ Volume2 / Issue 3 / February 2003.)
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