Transcript 4.weed flora and Distribution

WEED FLORA AND DISTRIBUTION
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Weed flora is the common weed vegetation that occurs in the field
which includes all the species of grasses, sedges and broad
leaved weeds.
The distribution of each species varies
according to the ecosystem of cultivation
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Dominant weed flora
Lowland ecosystem
Rice fields can be colonized by terrestrial, semi aquatic or aquatic plants
and have wide variations of weed plants from country to country and with
the different types of rice culture have been reported; they range from
more than 1800 species in South and South East Asia to about 30 species
in Eastern Europe.
Weed survey study indicated that in South and South Asia, 65 species
are found in deep water rice, 194 species in dry seeded rice, 559 species
in transplanted rice, 558 species in upland rice and 180 species in wet
seeded rice.
In transplanted rice ecosystem, Echinochloa species, Ischaemum
rugosum, Caesulia axillaris, Commelina spp., Cyperus spp. and
Fimbristylis miliacea are dominant weeds in India. In wetlands of
Coimbatore, the major weed species are Echinochloa species, Paspalum
distichum (L)., Cyperus difformis, Marsilea minuta (L) and Eclipta
prostrata. Species of Poaceae family are more common, with more than
80 species reported as weeds of rice.
Species in Cyperaceae family rank next in abundance with more than 50
species reported as weeds of rice.
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Cont….
The major weeds of rice ecosystem under Coimbatore condition were
E. crus-galli (22.0 %), E. colona (23.5 %) in grasses, Cyperus
difformis (21.3 %) and Cyperus iria (21.0 %) in sedges, Marsilea
quadrifoliata (5.8 %) and other broad leaved weeds
(6.4 %) in rabi season. In general broad leaved weeds are predominant weed flora accounting for 43.2 per cent of total weed flora
followed by grasses (29.8%) and sedges (26.9%) in transplanted rice.
Garden land ecosystem
The weed flora differ widely in the varied environmental and soil
conditions. In Coimbatore, Trianthema portulacastrum (L.), Amaranthus
viridis (L.), Parthenium hysterophorus (L.), Echinochloa sp. and Cyperus
sp. were dominant weeds in gardenland ecosystem.
Cyperus rotundus (40.03 per cent), Portulaca oleraceae (17.77 per cent),
Cynodon dactylon (13.70 per cent), Echinochloa columum (10.00 per
cent), Convolvulus arvensis (9.25 per cent), Digeria arvensis (3.70 per
cent), Euphorbia hirta (1.85 per cent), Cressia cretica (1.85 per cent) and
Corchorus depressus (1.85 per cent) were the major weeds in winter
season.
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Dry land ecosystem
Diverse weed flora is observed in moisture stress
ecosystems.
Predominant weeds are Andropogan contortus, Cynodon dactylon,
Panicum sp, Achyranthus aspera, Amaranthus viridis, Borreria
hispida, Celosia argentia, Leucas aspera, Ocimum canum,
Oldenlandia
umbellata,
Phyllanthus
niruri,
Phyllanthus
maderaspatensis, Euphorbia hirta, Boerhaavia diffusa, Cynotis
cuculatta Digera arvensis and Cyperus rotundus.
In red soil dominated ecosystems, Amaranthus viridis, Boerhaavia
diffusa, Cleome viscosa, Commelina benghalensis, Digera
arvensis, Cynodon dactylon, Panicum repens, Cyperus rotundus,
Phyllanthus niruri and Phyllanthus maderaspatensis were found
to dominate the weed flora.
Whereas, Acalypha indica, Digera arvensis,
Cyperus
rotundus,
Phyllanthus
maderaspatensis and Tridax procumbens are
the dominant weeds in black soils under
rainfed conditions of Tamil Nadu.
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PROTOCOL FOR WEED SURVEY / SURVEILLANCE
Each State or area of jurisdiction of SAU should be divided into its districts
and/or agro-climatic zones in five parts and route should be fixed for each
part for weed survey / surveillance.
Survey should be conducted in an
area twice in a year during both main
seasons of kharif and rabi.
Stoppage should be made at 10 km each for
survey and the survey spot should not be near any
building or permanent structure. One should walk
50-100 m deep in the field for survey
The minimum area under a particular crop should be
one acre or more for recording observations on weeds
and quadrat of 50 cm x 50 cm should be placed
randomly at least at four spots in a field moving
diagonally. (The size of the quadrat should be bigger
according to the canopy size of the crop.)
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At each field the GPS data for longitude, latitude and height above MSL
should be recorded.
Information from the farmer should be collected on following:
 Crop rotation for last three years.
Herbicide/ weed control method used for last three years.
His experience with applied herbicide/ weed control measure.
The observations on weeds should be recorded on:
Individual count of all weeds from each quadrat.
Record of any new weed encountered.
Climate data should be taken from nearest weather station for the
month in which survey is conducted and mean data for temperature,
RH, rainfall and sunshine hours should be reported. Along with
ambient CO2 concentration should also be recorded.
The each spot fixed through GPS should be surveyed again after 5
years to monitor dynamics in weed flora, if any.
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Route of survey :
A →B →C→ D (Name of village or city)
Work out the following from the weed count data:
Total no. of individuals of sp. A in all the quadrats
(a)
Density
m-2
=
Total number of quadrats plotted
(No. of individuals per 50cm x 50cm quadrat should be multiplied by 4 to obtain the density m-2)
Density
(b)
Relative density (%)
=
of
species
X 100
A
Sum density of all species
Number of quadrats where the species A occurred
(c)
Frequency %
=
X 100
Total number of quadrats plotted
Frequency
of
species A X 100
(d)
Relative Frequency (%)
=
Sum Frequency of
all species
(e) Importance Value Index (IVI) = Relative Density + Relative Frequency
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The results should be presented in the following way:
Descriptive account of survey in brief
Table : Weed flora of (crop) in the district (_____________)
(GPS data for range of latitude, longitude and height above MSL for
the district)
Weed species
(Total No.---)
Density m2
Frequency %
Relative Density Relative Frequency
IVI
(RD) %
(RF) %
Grasses
1.
2.
3.
4.
Sedges
1.
2.
3.
Broadleaved
species
1.
2.
Others
(Please note: Only dominant weed species (about 10) should be
listed and rest should be included in others, which may be
mentioned in text).
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