Weed management in onion: A review

Abstract

The bulbous vegetable onion Allium cepa Var. aggregatum L. (2n=16) is the most important species of Allium group and is regarded as the single most important vegetable spices as it forms an indispensable part of many diets, both vegetarian and non-vegetarian. Onion is valued for its bulbs having characteristic odour, flavor and pungency. Onion is regarded as a highly export oriented crop and earns a valuable foreign exchange for the country. Weeds are of great menace as they interfere with production of crop and add to the cost of cultivation. The reduction in crop yield has direct correlation with weed competition. Onion exhibits greater susceptibility to weed competition as compared to other crops due to its inherent characteristics such as their slow growth, small stature, shallow roots and lack of dense foliage. The effective weed control involves identification of weed flora, method of weed control and judicious combination of effective weed control methods. Hand weeding in onion is a common practice in India, but it is a tedious, expensive and time consuming task due to closer spacing and shallow root system. Non-availability of labourers during critical period of crop makes hand weeding difficult leading to heavy yield losses. Spraying of pre-emergence herbicides keeps the crop in weed free conditions during the early stages. At later stage, second flush of weeds will affect the bulb formation. Hand weeding helps to keep the weed population below economic threshold level throughout the crop growth period. Pre-emergence combined with hand weeding may be costly because of the reduced labour availability and higher labour cost. After bulb formation manual or mechanical methods of weed control will damage the bulb. Application of early post emergence may be helpful to reduce damage to the bulb, weed competition and cost of weeding. Hence a brief review was presented to find out the effect of different weed management method in onion.

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AGRICULTURAL RESEARCH COMMUN ICATION CENTRE
www.arccjo urnals.com
*Corresponding author’s e-mail: dhananivetha@gmail.com
1,2Department of Agronomy, TNAU, Coimbatore-6410 03, 3Department of Soil survey, Vellore – 632 002
Agricultural Review, 38 (1 ) 20 17 : 76- 80
Print ISSN:02 53-1 496 / Online ISSN:0976 -0539
Weed management in onion: A review
M. Dhananivetha*, M. Mohammed Amnullah1, P. Murali Arthanari2 and S. Mariappan3
Department of Agronomy,
Agricultural College and Research Institute, Madurai-625 104, India.
Received: 30-06-2016 Accepted: 07-10-2016 DOI:10.18805/ag.v0iOF.7311
ABSTRACT
The bulbous vegetable onion Allium cepa Var. aggregatum L. (2n=16) is the most important species of Allium group and
is regarded as the single most important vegetable spices as it forms an indispensable part of many diets, both vegetarian
and non-vegetarian. Onion is valued for its bulbs having characteristic odour, flavor and pungency. Onion is regarded as a
highly export oriented crop and earns a valuable foreign exchange for the country. Weeds are of great menace as they
interfere with production of crop and add to the cost of cultivation. The r eduction in crop yield has direct correlation with
weed competition. Onion exhibits greater susceptibility to weed competition as compared to other crops due to its inherent
characteristics such as their slow growth, small stature, shallow roots and lack of dense foliage. The effective weed control
involves identification of weed flora, method of weed control and judicious combination of effective weed control methods.
Hand weeding in onion is a common practice in India, but it is a tedious, expensive and time consuming task due to closer
spacing and shallow root system. Non-availability of labourers during critical period of crop makes hand weeding difficult
leading to heavy yield losses. Spraying of pre-emergence herbicides keeps the crop in weed free conditions during the early
stages. At later stage, second flush of weeds will affect the bulb formation. Hand weeding helps to keep the weed population
below economic threshold level throughout the crop growth period. Pre-emergence combined with hand weeding may be
costly because of the reduced labour availability and higher labour cost. After bulb formation man ual or mechanical
methods of weed control will damage the bulb. Application of early post emergence may be helpful to reduce damage to
the bulb, weed competition and cost of weeding. Hence a brief review was presented to find out the effect of different weed
management method in onion.
Key words: Growth, Onion, Weed management, Yield attributes.
Weed is a plant that does more harm than good and
has a habit of encroaching crop production. Onions do not
compete well with weeds. They are slow growing and can
suffer from successive flush of weed. They have narrow
upright leaves which do not shade out weeds that emerge in
the row. So, early season weed control is essential for
successful crop production. Hand weeding, a conventional
method of weed control is effective but it is time consuming,
cu m bersom e and un d er ma n y si t u a t i on s becom e
un economical. Manual weedin g is ver y tedious and
expensive laborious method of weed control, even often
damages the crop as well. Numerous herbicides with
high potency and environ mental safet y are becoming
available for effective control of weeds in field crops in
present days. Hence, a brief review is presented on the effect
of weed on crop growth, yield and different weed control
methods.
Effect of weeds on crop growth and yield
Growth components: Singh and Singh (1994) reported that
unweeded onion plots recorded reduced plant height, number
of leaves, which in turn reduced the bulb diameter and bulb
yield due to in creased weed competition. Maximum number
of leaves plant-1 at 90 days after transplanting and at harvest
was observed in oxyfluorfen applied plots due to reduction
in weed population as noticed by Ravinder Singh et al.
(2001). Taller plants, higher bulb diameter and bulb weight
were recorded under weed-free condition, followed by
alachlor 2.0 kg ha-1+ Hand Weeding on 45 days after
transplanting and pendimethalin at 1.5 kg ha-1 followed by
Hand Weeding on 45 DAT (Ved Prakash et al., 2000). Plant
height, number of leaves, fresh and dry weight were found
to be higher under weed free condition and pendimethalin
treated plots as reported by Sharma and Khandwe (2008).
Taller plants, neck thickness and dry matter accumulation
was observed under pendimeth alin applied plots by Patel
et al. (2011).
Yield and yield components : James and Harlen (2010)
reported that uncontrolled weed growth caused 49-86 per
cent reduction in bulb yield compared with the best herbicidal
treatment. The higher onion bulb yield of 38.3 t ha-1 due to
lesser weed population and weed growth from initial crop
growth as compared to weedy check was obtained by Patel

Volume 38 Issue 1 (2017) 77
et al. (2011). Higher fresh bulb weight (135.4 g) was obtained
in the plots where hand weeding was done after every 15
days while lesser fresh bulb weight (65.75 g) was recorded
in control plots where no weeding was done throughout the
season. Bulb diameter, bulb height, bulb volume, bulb weight
and bulb yield were found to be high in weed free plots
followed by pendimethalin (Rahman et al., 2011).
Saini and Walia (2012) confirmed that oxyfluorfen
treated plots recorded higher fresh bulb weight and diameter
of the bulb. Karimi et al. (2012) recorded higher bulb yield
of 15.3 t ha-1 in pendimethalin treated plots while lesser yield
of 4.2 t ha-1 in weedy control plots. Rahman et al. (2012)
reported lower bulb yield of onion in weedy check to the
fact that weeds appeared immediately after sowing and
competed with onion crop until harvest. Higher bulb yield
was recorded under early post emergence application of
quizalofop-ethyl under grass dominated field as recorded
by Dhananivetha et al. (2015).
Method of weed management : Weeds can be controlled
by different weed control methods such as manual, cultural,
chemical, mechanical and biological. Usually farmers do not
remove weeds early enough to prevent major damage due to
this weed competition.
Manual and cultural: Calamai and Martini (1994) reported
that 86 per cent weed control efficiency was with hoeing alone
in onion. Hand weeding on 45 DAP gave more yield due to
minimum crop weed competition for resources (Saraf et al.,
1994). Higher bulb yield was obtained with three Hand Wdeding
(HW) and it was statistically on par with fluchloralin 1.0 kg ha-1
and pendimethalin 1.25 kg ha-1 with one hand weeding for each
(Sharma and Mehta, 1994). Shah et al. (1996) reported that
hand weeding was significantly better in increasing the bulb
diameter, bulb weight, bulb yield and loss of bulb weight when
compared with unweeded control.
Singh et al. (1997) observed higher onion bulb yield
and weed control efficiency in treatment combination of one
HW on 30 DAT + mulching. According to Melander and
Hartvig (1997), hoeing close to the row leaving 5 cm untilled
strip, has the potential of saving labour cost for hand weeding
in non herbicidal growing system of onion. The higher bulb
and weed control efficiency were recorded in the weed free
treatment followed by three HW on 20, 40 and 60 days after
transplanting (Amrutkar et al., 1998).
Comparable weed control efficiency of 89.8 per
cent could be achieved with manual weeding with that of
pendimethalin at 0.75 kg ha-1 + hand weeding (90.6 per cent)
or Metolachlor 1.25 kg ha-1 + hand weeding (77 per cent) or
oxyfluorfen 0.07 kg ha-1 + hand weeding (74.0 per cent)
(Tewari et al., 1999). Weed management by hoeing gave
higher yield closely followed by the application of oxadiazon
and pendimethalin (Ishwar Singh et al., 2000). Priyadharshini
and Anburani (2004) reported that dry biomass of weeds
was significantly reduced by the application of herbicides
and through hand weeding practices.
Higher weed control was obtained with manual
weeding throughout the crop season (Zubiar et al., 2009).
Maximum bulb size and yield of onion were recorded in
hand weeded plots followed by pendimethalin as compared
to weedy check as noticed by Hussain et al. (2008). Rahman
et al. (2011) reported that hand weeding th roughout the
growing season controlled all weeds and resulted in higher
onion bulb yield.
Chemical: Ranpise and Patil (2001) observed that pre-
emergence application of oxyfluorfen at 0.4 kg ha-1 in onion
recor ded maximum yield (24 2.2 q ha-1) followed by
oxyfluor fen 0.2 kg ha-1 (233.3 q ha-1) as compared to the
lower yield under control (50 q ha-1) due to maximum weed
intensity. Kolhe (2001) indicated th at dr y matter of weeds
wa s si g n i f i can t l y reduced du e to ap p l i ca t i on of
pendimethalin, metalachlor, oxyfluorfen either alone or in
combination with hand weeding at 35 DAP compared to
weedy check in onion. Presen tly herbicides are widely
applied for weed destruction and oxyfluorfen is a very
effective herbicide suitable for weed destruction in onion
and cabbage (Stall and Gilreath, 2002).
Oxyfluorfen, pendimet ha lin and met ri bu zin
significantly reduced the weed population and increased
onion yield to levels comparable to yields of weeded control
in a relay cabbage-onion cropping system (Sanjeev et al.,
2003). Priyadharshini and Anburani (2004) recorded lesser
weed population of 67.90 m-2 with the application of
pendimethalin at 1.0 kg ha-1 with mulching in onion.
Dawale et al. (2009) inferred that quizalofop ethyl
at 40 g ha-1 as post-emergence + one HW and one inter culture
operation on 40-45 DAS (1889 kg ha-1) was effective in
sesame. Sharma and Khandwe (2008) observed lesser weed
population and dry weight of weeds m-2 with pendimethalin
at 1.25 kg ha-1. An increase in the bulb yield of onion by
62.69 per cent with pendimethalin at 2.5 l ha-1 than the
unweeded plots was recorded by Zubiar et al. (2009).
Meena et al. (2009) reported that quizalofop ethyl
at 50 g ha-1 + chlorimuron ethyl at 9 g ha-1 as post emergence
significantly reduced weed density, weed dry weight and
recorded higher seed, straw yield and weed control efficiency
in soybean. Patel et al. (2009) revealed that application of
quizalofop-p-ethyl at 200 g ha-1 on 30 days after sowing was
effective in controlling weeds in groundnut. In onion,
pendimethalin at 1.0 kg ha-1 + hand weeding and oxyfluorfen
at 0.24 kg ha-1 recorded higher weed control efficiency of
80.6 and 73.4 per cent (Patel et al., 2011).
Chaitanya et al. (2012) stated that pre-emergence
application of pendimethalin at 1.0 kg a.i.ha-1 along with
post emergence application of quizalofop ethyl at 50 g
a.i.ha-1 on 25 DAS recorded lower weed growth and higher

78 AGRICULTURAL REVIEWS
yield of kharif groundnut. Pre-emergence application of
oxyfluorfen (23.5per cent EC) at 200 g ha-1 recorded lesser
weed density and dry weight in onion (Sathya Priya et al.,
2013). Early post emergence application of quizalofop-ethyl
at 75 g ha-1 recorded lower weed density and dry weight
which resulted in increased yield of onion under grass
dominated field conditions (Dhananivetha et al. 2015a)
Me chani cal: Yadav an d Pon d (2007) reported that
mechanical weed control not only uproot the weeds between
the crop rows but also keep the soil surface loose, ensuring
better soil aeration and water intake capacity. Weed
morphology and stage of growth would influence the
selection and efficacy of weeding implement. It is found that
the physical damage by burial to one cm depth is effective
for controlling weeds followed by cutting at the soil surface
as noticed by Rajakumar (2008). Gore et al. (2010) reported
that cycle hoe weeder produced significantly higher gr ain
yield and found to be effective in controlling grass as well
as broad leaved weeds (69 and 44per cent) and (63 and 67per
cent) at 30 and 60 DAS in soybean.
Gowsalya et al. (2010) observed that effective and
economical weed management in rainfed pigeonpea was
obtain ed eit h er b y pr e-em e r g en ce applica t io n of
pendimethalin at 0.75 kg ha-1 on 3 DAS followed by one
weeding with oleo weeder on 45 DAS or pre-emergence
application of pendimethalin at 0.75 kg ha-1 on 3 DAS
followed by one weeding with wheel hoe weeder on 45 DAS.
According to Sathya Pr iya et al. (2013) pre-emergence
application of pendimethalin at 0.75 kg ha-1 + Rotary weeding
on 45 DAS recorded lower gross and net returns.
Economics of weed management: Nandal and Ravinder
Singh (2002) observed higher net return when oxyfluorfen
at 0.25 kg ha-1 was supplemented with hand weeding at
40 DAT ( 60,196 ha-1) followed by oxyfluorfen at 0.75 kg
ha-1 ( 54,978 ha-1) and pendimethalin at 1.00 kg ha-1 plus
hand weeding at 40 DAT ( 51,162 ha-1) and net loss of
2,624 ha-1 where weeds were not controlled under weedy
check in on ion.
According to Mondal et al. (2005) higher net
mon etary retur ns were obta ined with pre-emergence
application of oxyfluorfen at 100 g ha-1 supplemented
with one hand weeding on 25 DAT ( 33,650 ha-1 )
followed by fluchloralin at 750 g ha-1
+ hand weeding
( 31,983 ha-1), pendimethalin at 750 g ha-1
+ hand weeding
( 31,450 ha-1) and oxyfluorfen at 200 g ha-1 ( 31,400 ha-1).
Ther e was net loss of 3,900 ha-1 under weedy check.
Pre-emergence application of pendimethalin at 1.00 kg
ha-1 supplemented with one hand weeding in onion gave
the higher net return of 51,296 ha-1 with maximum
benefit cost ratio of 8.77 (Channappagoudar and Biradar,
2007).
Economic analysis by Patel et al. (2011) revealed
that higher net profit ( 2,69,422 ha-1) in onion crop was
obtained with application of pendimethalin at 1.0 kg ha-1 +
HW on 40 DAT with the B:C ratio of 7.85 followed by
oxyfluorfen at 1.0 kg ha-1 + HW on 40 DAT ( 2,51,910 ha-1)
an d weed free control. In onion high er net retur n
( 1,85,600) with B:C ratio of 7.63 was registered with the
application of oxyfluorfen (Saini and Walia, 2012).
CONCLUSION
From th e above poin t s of view, it could be
concluded that onion among vegetables has very poor
comp etitive abi lity wit h weed s due to its in h erent
characteristics such as shallow root system, narrow leaf and
less area. Among various causes of low productivity of onion
in India, the weed infestation is a serious problem. The
conventional method of weed control is effective but due to
labour scarcity and high cost of human labour weeding
during the critical stage of the crop is a pr oblem. As an
alternate chemical method of weed control can be adopted.
Numerous herbicides with varying mode of action are
available in the market with wide spectrum of weed control.
Hence, selection of method of weed control should be based
on the nature of the crop and mode of action of the herbicide
that should control weeds effectively and increase the yield
of the crop.
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