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.

Cont….

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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 pre-dominant 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 ecosystemDiverse weed flora is observed in moisture stress ecosystems.

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.

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.

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.

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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.

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.)

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

Survey should be conducted in an area twice in a year during both main seasons of kharif and rabi.

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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:

(a) Density m-2 =

Total no. of individuals of sp. A in all the quadrats

Total number of quadrats plotted

(No. of individuals per 50cm x 50cm quadrat should be multiplied by 4 to obtain the density m -2)

(b) Relative density (%) =

Density of species AX 100

Sum density of all species

(c) Frequency % =

Number of quadrats where the species A occurred

X 100Total number of quadrats plotted

(d) Relative Frequency (%) =

Frequency of species A X 100  

Sum Frequency of all species  

(e) Importance Value Index (IVI) = Relative Density + Relative Frequency

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Weed species(Total No.---)

Density m-2 Frequency %

Relative Density (RD) %

Relative Frequency (RF) %

IVI

Grasses1.2.3.4.

Sedges 1.2.3.

Broadleaved species1.2.

Others

Descriptive account of survey in briefTable : Weed flora of (crop) in the district (_____________)

(GPS data for range of latitude, longitude and height above MSL for the district)

(Please note: Only dominant weed species (about 10) should be listed and rest should be included in others, which may be mentioned in text).

The results should be presented in the following way: