GAB-2015v6n3 - page 5

Genomics and Applied Biology 2015, Vol. 6, No. 3, 1-14
http://gab.biopublisher.ca
2
Chenopodium album, Rumex dentatus, Ageratum
conyzoides, Convolvulus arvensis, Cynodon dactylon,
Oxalis corniculata, Malva parviflora, Malvastrum
coromandelianum, Trifolium resupinatum, Euphorbia
prostarta and Phalaris minor were found to be the
most prevalent weed species in turmeric at Kasur
district of Pakistan. Cyperus rotundus, Cynodon
dactylon, Eleusine aegyptiacum and Euphorbia hirta
were the dominant weed species in turmeric at Punjab
(Manhas et al., 2011).
Ratnam et al. (2012) observed that grasses like
Echinochloa colona (L.), Dinebra retroflexa (L.),
Cynodon dactylon (L.), and Panicum repens (L.),
sedges like Cyperus rotundus (L.), and broad leaved
weeds like Phyllanthus niruri (L.), Celosia argentea
(L.), Chrozophora rotteleri (L.), Cleome viscose (L.),
Parthenium hysterophorus (4%), Abutilon indicum (L.),
Digera arvensis (L.), Trianthema portulacastrum (L.),
Euphorbia hirta (L.), Corchorus acutangulus (L.),
Portulaca oleracea (L.), Acalypha indica (L.), Eclipta
alba (L.) and Commelina bengalensis (L.) dominated
in turmeric at Guntur, Andhra Pradesh.
According to Suresh Kumar et al. (2014),
Echinochloa colona, Digitaria sanguinalis , Panicum
dichotomiflorum, Commelina bengalensis, Cyperus
iria, Ageratum conyzoides, Polygonum sp., Physallis
minima, Eragrotis spp and Aeschynomene indica were
the predominant weeds in turmeric field of Himachal
Pradesh.
Crop-Weed Competition
The degree of crop-weed competition is determined
by the weed species and their density, duration of
infestation, associated crops in the field, growth habit
of crop plants and environmental conditions. Weeds
that grow with crop depleted considerable amount of
costly fertilizer, limited moisture, light and space,
thereby leading to poor growth and development of
crops resulting in lower yields.
Critical period of crop-weed competition
Establishing the critical period of competition is the
most essential to develop effective and economical
weed control measures.
The critical period of weed competition is an important
consideration in the development of alternative weed
management strategies (Swanton and Weise, 1991).
The critical period indicates the appropriate timing for
weed management and it assists in understanding the
impact of weed density on the crop (Hall et al., 1992) .
Knezevic et al. (2002)described the critical period of
weed competition as a window in the crop growth cycle
in which weeds must be controlled to prevent
unacceptable yield losses. Weed competition
throughout the crop period, on an average caused 82.2
per cent reduction in bulb yield. According to Hossian
et al. (2008), for higher yield of turmeric the weeds
need to be removed during 70 to 160 days after
planting, indicating that it needs a longer period of
weed free condition than other crops.
Effect of competition on growth and yield
components
Reduction in crop yield has a direct correlation with
competition in drought situation and weeds thrive
better than crop plants, when left uncontrolled. Weeds
can grow taller than crop plants and suppress the
growth.
Many workers have emphasized that the effect of
weeds on growth and yield components ultimately
decide the yield. The reduction may occur as a result of
competition between the crop and weed for nutrients,
space, light and water (Klingman, 1961).
Growth components: The plant growth parameters in
onion such as height, leaves plant -1, fresh and dry
weight of plants were measured significantly higher
under weed free situation. Manjunath et al. (1989)
found that weeds affected plant height, leaf area index
(LAI), leaf area duration (LAD), net assimilation rate
(NAR) and crop growth rate (CGR) of onion.
According to Singh and Singh (1994), plant height
and number of leaves increased significantly with
treatments which were kept weed free till harvest due
to least crop weed competition for nutrients, moisture,
space and sunlight between crop and weeds in onion.
Similarly, Verma and Singh (1997) observed that plant
height, leaves plant-1, fresh and dry weight of plant
were significantly higher under weed free condition in
onion. In onion, Dandge and Satao (1999) found that