Efforts to control parthenium growth in and around Bangalore city started by
programme for parthenium elimination (PROPEL) in 1986-88. Initially, a few kilograms
of Cassia sericea (CS) seeds were procured from Dharwad and sown in vacant
sites and waste lands in some parts of Bangalore city, through
voluntary organisations and individuals. In the subsequent years, the
quantity of C. sericea seed obtained increased to quintals and sowing was done in
larger areas excluding vacant sites. Because, the sites were either used for construction
or dumped with debris, thereby coming in the way of establishment of C.
sericea. From the year 1988-89, release of a beetle, Zygogramma
bicolorata was integrated with the sowing of C. sericea. In some places like
Hebbal railway station, Arnruthahalli cross road (Bellary road), Jakkasandra and
Sarakki layout, the method has proved successful. In some areas like Indira Nagar,
the results have been discouraging. In highways like Bellary road, Tumkur
road, Bannerghatta road, the method proved to be partially successful. For the first time,
an intensive sowing of C. sericea was taken upduring 1990, from May to July on most of the
highways.
A survey conducted in the mid-August during 1990 and 1991 on the
establishment of C. sericea, beetle activity and the stand of parthenium could
reveal the following:
Cassia sericea has established well by 1991 in 90% of the
places, where it had shown partial establishment in the previous year, viz.,
Hebbal railway station, Arnrutahalli cross road and parts of Bellary Road.
The growth of C. sericea during 1990 was not as vigorous as in the previous years because
of a prolonged drought.
From among the areas sown during 1990, very early sown (May)
places have shown good establishment of CS although the growth in terms of plant
height is not normal in some places. In places where intermittent rains were received,
establishment and growth of CS were very satisfactory, both during 1990 and 1991.
This plant species could spread on its own and extended its area in 1:5 proportion.
In places where the soil was very porous and rains were scanty,
both germination and establishment were far from satisfactory during 1990.
But, in patches where there were ravines, open drains and depressions, the establishment
was better and these plants multiplied in 1:10 proportion by 1991.
Sowing was also done in some places where the soil is very compact
and trampled daily by passers-by. Although the C. sericea germinated in these places,
establishment was poor for the want of proper soil conditions, even parthenium did
not establish itself normally in such situations. Hence it was felt unnecessary to takeup
any operation in future.
The above areas were observed closely to find out the reasons for good,
moderate and poor germination and establishment of C. sericea in different
locations.
Successful establishment of C. sericea in
some places mentioned above may be attributed to early sowings, followed
by enough rains for good germination, growth and root formation before the
commencement of long drought spell. To some extent, the moisture retention capacity of the
soil and low land situations have also contributed to its successful growth.
Non-establishment of C. sericea in some places may be attributed to
late sowings (July), which might have led to a situation wherein seeds germinated up
to two leaf stage (with one or two rains) followed by long drought spell (4 to 5 weeks)
leading to death of seedlings. Probably leaving no seeds behind for germination
after the revival of rains following the drought spell.
Partial establishment of C. sericea in some places is either due to
some intermittent rains during the drought spell or due to high moisture content in
soil itself due to high water holding capacity or seepage from the neighbourhood drains,
ponds etc.
In places, where sowing was not followed by early rains, the
entire process of germination and growth of C. sericea had commenced only
after the revival of rains in the month of August (second rains) and germination and
growth was very satisfactory. The CS plants growing from second rains, however,
could not put up normal growth and produce as many seeds as growing from the beginning of
the season (June- July). Still, there was enough pods (fruit formation) to multiply
the plant population in a small proportion for the next year.
In places, where the beetle, Z. bicolorata have been released,
defoliation has taken place and the results are clearly visible even to a layman.
The insects however did not move to western side from places where they were
released, but they moved to some extent to the eastern side. None to 50 numbers of beetles
were counted per plant, wherever beetle activity was observed. Considerable
reduction in parthenium seed formation could be seen because of the beetle activity. But
this was limited only to the rainy season i.e., from July to November. Parthenium
started reappearing again wherever it was controlled by insects but not so wherever
it was controlled by C. sericea and other botanical agents.
An analysis of the situation
The long drought spell during 1990 was a big handicap for the establishment of
Cassia sericea and also for the multiplication of the beetle. Despite this unusually
prolonged drought, successful establishment of C. sericea and spread of beetle in some
places indicated the potentiality of the method in controlling parthenium growth. The
prolonged drought intervals are not very common though intervals are not uncommon. The
effect of partial and sparse establishment of C. sericea in some places may lead to some
disappointment for not showing the expected results. Because C. sericea leachate, that was
expected to accumulate in soil to suppress germination and growth of parthenium was
inadequate. Wherever the C. sericea had germinated, but remained without further
growth due to stunting in the initial stage could not contribute enough leachate to
suppress parthenium.
Follow up action
In some areas, where the seedlings dry up due to drought, the entire process of
sowing has to be repeated next year. In areas, where C. sericea has established partially,
supplementary sowings in the coming year will help quick establishment of C. sericea. In
areas where C. sericea has established with normal growth, there is no need for
fresh sowings. Some corrections needed in the next sowing:
Highly compact and overtrampled soils like play ground, should not be
selected for sowing C. sericea because neither parthenium nor C. sericea can grow
there. The areas likely to be disturbed for construction, roads etc., may also be avoided.
Spacing between rows which is 3" - 8" should be reduced to 2" while sowing
Cassia sericea.
Thick sowing should be avoided. Only 'I,th of the present
quantity of seeds per unit area should be sown i.e., 6-8 kg seeds are enough for
planting one acre. This wilt help to cover more area with the same quantity of seed,
besides avoiding inter-plant competition and- aiding better growth of the young
plants.
As far as possible, early sowings and even dry sowings may be taken up (April to
June) so that C. sericea plants could grow strong enough to withstand any drought
intervals.
For better results, the parthenium plants are to be uprooted before sowing Cassia
sericea.
Conclusion
The integrated approach being adopted at present has high potential to control
parthenium in the targeted area, as evidenced by success seen to the extent of 60 to 80
per cent in various districts especially in northern Karnataka and southern Maharashtra.
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