Weed Management Strategies in Chickpea (Cicer arietinum): A Review

India has achieved self-sufficiency in food grain production through increased productivity and Green Revolution, particularly in cereal crops. India is the largest producer as well as consumer of pulses, where production lags behind consumption. The net availability of food grains per capita per day has increased from 144.1 kg year^-1 in 1951 to 179.6 kg year^-1 in 2019 in spite of an increase in population whereas the net availability of pulses has reduced from 25 kg year^-1 in 1961 to 17.5 kg year^-1 in 2019 (Anonymous, 2020). In developing countries, particularly India, where vegetarian populace predominates, pulses are the second most important component of the diet after cereals. Pulses play a significant role in diversifying the traditional cropping systems because of their ability to fit well in the crop rotations. Due to their, ability to fix atmospheric nitrogen, they can produce protein efficiently (Havlin et al., 2014). Chickpea is one of the most important rabi pulse crops in India accounting for 44.50% of the total pulse production from 35.21 per cent of the total pulse area during 2017-18. It also has qualities like low glycaemic index, gluten-free and acts as a functional food (Rao, 2002).
       
Chickpea, being slow in its early growth and short stature, is highly susceptible to weed competition and often considerable yield losses up to 75 per cent (Chaudhary et al., 2005) may occur if weed growth remains unchecked at appropriate time. They compete with the crop for nutrients, space, light, water and carbon dioxide. Thus weed management in chickpea is an important component of plant protection and improving production potential of the crop.
 
Crop-weed competition
 
Losses caused by weeds
 
Chickpea crop is not a competitive crop, especially when weed competition occurs at early stages (Barker, 2017). Yield losses caused by weeds in chickpeas have been estimated at 40 to 87 per cent in India, 41 to 42 per cent in the former Union of Soviet Socialist Republics (USSR) and 23 to 54 per cent in West Asia (Bhan and Kukula, 1987). 
       
However at Indian Institute of Pulses Research, yield losses due to weed in chickpea varied between 29-70 per cent over the years (Anonymous, 2009). Mohammadi et al., (2005) reported that severe infestation of weeds caused reduction in seed yield of about 66.4 and 48.3 per cent throughout the crop growing season of chickpea. However, maximum yield to the extent of 81 to 97 per cent has also been reported by Barker (2017). In addition to this, losses from weeds include extra cost on harvest and reduced crop quality (Miller et al., 2002). Hassan et al., (2007) reported an increase of 12-14 per cent with pre-emergence application of herbicides and 6-23 per cent with post emergence application of herbicides. Bhalla et al., (1998) reported that the herbicidal treatment resulted in 50-54 per cent weed control in chickpea. 
 
Weed flora in chickpea
 
Weeds are major challenge in realizing potential chickpea production. In order to control weeds, detailed knowledge of the weed population is acquired from the field. It is critical to identify weeds during early stages which can be challenging since many species mimic crop plants. Knowledge regarding weed flora of a particular location is the first and foremost step for an effective weed management strategy.
       
The weed species infesting the chickpea fields vary from one location to another depending on the agroclimatic conditions in the country. The field was infested with Chenopodium album, Fumaria parviflora, Spergula arvensis and Lepidium sativa at Ludhiana (Singh et al., 2003). Dewangan et al., (2016) observed that Medicago denticulata, Convolvulus arvensis, Chenopodium album, Melilotus indica and Brachiaria mutica were some of the dominant weed flora in the experimental field at Raipur. Out of these weeds Medicago denticulata was the most dominant followed by Convolvulus arvensis.
       
Among monocots Brachiria mutica, Echinochloa crusgalli L. and Cynodon dactylon L.; Cyperus rotundus among sedges and Amaranthus viridis L., Digera arvensis, Physalis minima, Euphorbia hirta, Parthenium hysterophorus and Alternanthera sessilis among dicots were the prominent weeds at Parbhani, Maharashtra (Gore et al., 2018). At Kanpur, Chenopodium album L., Parthenium hysterophorus, Cynodon dactylon, Asphodelus tenuifolius, Fumaria parviflora Lamk., Anagallis arvensis, Cronopus didymus and Spergula arvensis were some of the weeds that dominated the experimental field (Pooniya et al., 2009). The field at Jodhpur during the rabi season observed the infestation of Chenopodium murale, Chenopodium album and Rumex dentatus. Among these Chenopodium murale was the most dominant weed species (Yadav et al., 2018).
       
Singh et al., (2016) reported that Melilotus alba, Chenopodium album,Cynodon dactylon, Phalaris minor and Medicago hispida were the major weeds in rabi season in the experimental field at Varanasi. Khope et al., (2011) revealed that Chenopodium album, Fumaria parviflora and Phalaris minor were the major weed flora in their experimental field at Hisar (Haryana). Convolvulus arvensis, Anagallis arvensis, Melilotus alba, Cronopus didymus and Spergula arvensis were the minor weed species infesting the chickpea field. Merga and Alemu (2019) reported that Solanum nigrum, Medicago polymorpha, Galinsoga parviflora, Commelina benghalensis, Parthenium hysterophorus and Cyperus rotundus were the prominent weeds infesting the chickpea at Haramaya, Ethiopia.
 
Weed threshold
 
An economic threshold for weed control, or the “break-even point” is the level of weed infestation at which the cost of controlling the weeds is equal to the increase in crop value obtained as a result of controlling the weeds. They are often used in the decision-making process for weed management.
       
Knowledge of economic threshold level and growth habits of weeds in chickpea is essential to implement timely, effective and economical weed control treatments. Mohammadi et al., (2005) estimated a 1 per cent reduction in chickpea seed yield for every additional 3.85 g m^-2 of  weed dry weight. The effect of weed density on growth and yield performance in chickpea using dragon spurge (Euphorbia dracunculoides) as a test weed was investigated (Tanveer et al., 2015). Dragon spurge density levels of 5, 10, 15, 20, 25, 30, 35 and 40 plants m^-2 were compared with weed-free plots. Each increment in densities of dragon spurge from 5 to 40 plants m-2 reduced plant height, number of fruits, seeds and dry weight per plant. Chickpea grain yield losses varied between 1 to 63 per cent with dragon spurge density ranging from 5 to 40 plants m^-2. The seed protein content of chickpea was found to be significantly reduced above a weed density of 25 plants m^-2. Thus, dragon spurge should be controlled at densities above 5 plants m^-2 to achieve optimum chickpea yield. Chenopodium album caused 17.8, 18.7, 27.4 and 24.2 per cent reductions in yield at densities of 50, 100,150 and 200 plants m^-2, respectively (Paradkar et al.,1997).
 
Critical period of weed interference
 
There are certain crops that are able to tolerate the interference caused by weeds to certain period of time. After that time period this competition causes decline in yield which cannot be reversed later (Dawson, 1986). The time span or duration growth when crop must be kept free from weeds to prevent losses in the yield due to their interference (Weaver and Tan, 1987; Van Acker et al., 1993) is called critical period of crop weed interference. Most crops are sensitive to weed competition in early stages of crop growth (Ramamoorthy et al., 2004). This period differs for depending upon the time of weed emergence. If weeds emerge early, then the critical period will also be early (Knezevic et al., 2002). Thus, the weed density is an important parameter for determining the critical period for the crops (Martin et al., 2001).
       
The critical period of crop weed competition (CPWC) for a given crop species varies greatly and depends on the density of weed infestation, crop species characteristics, climatic conditions and environment (Knott and Halila, 1986). The CPWC can also differ with differing planting densities (Ahmadvand et al., 2009) and the length of the CPWC can be affected by weed densities and weed emergence time (Knott and Halila, 1986; Mohammadi et al., 2005). The CPWC concept typically assumes that weed emergence, species composition and density are spatially homogenous across an environment (Knezevic et al., 2002). Variability in environment, crop characteristics and other factors results in CPWC estimates specific to a crop only within a given region.
       
Mohammadi et al., (2005) estimated a CPWC 17 to 49 days after emergence (DAE) or between the four leaf and beginning of flowering stages, but in a second location the CPWC was between 24 and 48 DAE or between the five leaf and the full flowering stages. In western Iran Mashhadi and Ahmadi (1998) estimated a CPWC  27 to 44 DAE, between the 6 and 14 leaf stage and 205 to 385 growing degree days (GDD). Al-Thahabi et al., (1994) in Jordan estimated 35 to 49 DAE; Masood-Ali (1993) in India estimated 0 to 56 DAE; Ahlawat et al., (1981) in India estimated 28 to 56 DAE and Saxena et al., (1976) in India estimated that hand-weeding’s at 30 and 60 DAE would prevent unacceptable yield loss from weeds. The average of these estimates is 23 to 52 DAE, but the estimates for the lower and upper limit ranged from 0 to 35 and 42 to 60 DAE, respectively (Yenish, 2007).
       
Based on a 5 per cent yield loss threshold, Smitchger (2010) found that the CPWC for the ‘Sierra’ chickpea was 16 to 26 DAE. Alternatively, the CPWC could be expressed as 162 to 256 GDD or the 9 to 13 node stage in terms of crop development. Crop yield, crop biomass and 100 seed weight declined with an increasing duration of weed competition. Singh and Singh (1992) reported that grain yield of chickpea was reduced by 17.1 per cent due to competition with weeds during the first 30 days of sowing. Grain yield was increased when the initial weed-free duration was extended up to 60 days and further increase in the duration of weed-free had no beneficial effect on grain yield.
 
Weed management practices
 
The slow growth habit of chickpea is the reason that the crop is severely infested by the weeds both in the irrigated as well as the dryland areas.
 
Non-chemical control
 
Before the advent of chemical herbicides, cultural practices played vital role in intensifying crop competitiveness against weeds at very low cost. It was an eco-friendly strategy. It attempts to minimize the introduction, establishment and spread of weeds into new areas and check seed set. While, herbicides may be able to control the weeds effectively during the crop growth but time of crop establishment also significantly influences the competitive abilities of the crop. Malik et al., (1988) observed the decline in density of Chenopodium album and increase in Lathyrus aphaca with delay in sowing date from 20^th November to 5^th December.
       
Blessdal (1960) informed that increasing crop densities through manipulation of seed rate and row spacing effectively subdues niches accessible to weeds and diminish the growth of weeds. Whish et al., (2002) while conducting their experiments at New South Wales concluded that the chickpea yields from the crops sown in narrow rows (32 cm) were consistently higher than yields with wide row (64 cm) spacing under weed free conditions. Narrower row spacing considerably advanced the competitive ability of the crop as consequence of earlier canopy closure.
       
Balwan et al., (2014) reported maximum uptake of nitrogen, phosphorus and potash by grain and stover and minimum uptake of nitrogen, phosphorus and potash by weeds, maximum protein content (21.37 per cent) and minimum losses by weeds (11.69 per cent) under hand weeding at 20, 40, 60 DAS. Numan et al., (2017) found two times hand weeding is the most economical and beneficial method for controlling weeds in chickpea and increasing yield and yield components due to maximum nutrient availability for the crop, makes the soil porous for penetration of roots and increases water holding capacity of soil. Singh et al., (2003) found Hoeing at 30 or 60 days after sowing (DAS),was effective in chickpea.
       
Dixit et al., (2014) observed that among different tillage operations, zero-tillage registered significantly lower weed density and weed dry matter, 87.9 number m^-2 and 6.76 g m^-2, respectively. It was lower than the conventional tillage by 19.5 and 14.5 per cent, respectively. Chauhan et al., (2017) at Jabalpur also concluded that bed planting of chickpea was significantly better than the conventional tillage due to better weed management, better root development and favourable soil environment. Post-emergent harrowing is not recommended for weed control as it can spread disease and cause severe crop injury. Intercropping of safflower, linseed and wheat with chickpea exhibited significant suppression of weeds from 43-60 per cent (Anonymous, 2009).
 
Allelopathy
 
Allelopathy involves the synthesis and release of bioactive chemical compounds that affect the growth and development of neighbouring plants. Putnam (1988) described six classes of allelochemicals from different plants. They have the capability of damaging the normal growth of weeds by affecting their metabolic pathways (Weston and Duke, 2003).
       
Allelopathy is a chemical (biochemical) relationship among plants (Rice, 1984). At the same time, mulching is a recent and effective non-chemical weed control method (Ramakrishna et al., 1992). Regar et al., (2010) reported that straw mulching resulted in better grain yield and significantly enhanced water use efficiency in different chickpea cultivars. Khan et al., (2018) found better weed control using Eucalyptus leaf mulch, crop or weed straw mulch, Asphodelus tenuifolius mulch, Cyperus rotundus extract and Sorghum halepense extract.
 
Chemical control
 
Herbicides are the most effective weed control tools. In all of these considerations, there are opportunities to reduce the risks associated with herbicide use.
       
Sesharee et al., (1996) revealed that fluchloralin was more effective than pre-emergence alachlor or isoproturon in Andhra Pradesh. In recent years, it has been demonstrated that the application of two or more chemicals at the same time provides control of different weed species.
       
Lyon and Wilson (2005) at Sidney, US observed that pre-plant incorporation of Ethalfluralin @0.84 kg ha^-1 and pre-emergence application of Pendimethalin @1.12 kg ha^-1 were not significantly different from each other and hand weeding maintained total weed densities 4 weeks after emergence. Further study revealed that herbicides containing Sulfentrazone @0.11 kg ha^-1 or in combination that is Sulfentrazone + Dimethenamid-P @0.11 + 0.72 kg ha^-1, Sulfentrazone + Pendimethalin @0.11 + 1.12 kg ha^-1 and Sulfentrazone + Imazethapyr @0.11 + 0.026 kg ha^-1 also provided good and consistent weed control in both irrigated as well as dryland areas. Metachlor 83% + Pendimethalin 13% @2230 ml ha^-1 shpwed promising results in controlling weeds (Abbas et al., 2016).
       
 
Kachhadiya et al., (2009) revealed that significantly lower dry weight of weeds was recorded with pre-emergence Oxyfluorfen @0.12 kg ha^-1 + 1 Hand-weeding + 1 Inter-cultivation at 30-35 DAS and also with pre-emergence Fluchloralin @0.675 kg ha^-1 + post-emergence Imazethapyr @0.05 kg ha^-1. These treatments also exhibited significantly higher weed control efficiency and higher herbicide efficiency index. However, Yadav et al., (2019) observed that sequential application of pre-emergence Pendimethalin @0.60 kg ha^-1 + post-emergence Imazethapyr @60 g ha^-1 at 20 DAS recorded significantly higher yield and was at par with pre-emergence Pendimethalin @0.60 kg ha^-1 + post-emergence Imazethapyr @40 g ha^-1. Pendimethalin @0.75-1.5 kg ha^-1 as pre-emergence and Quizalofop-p-ethyl @40-100 g ha^-1 as post emergence was found effective (Pedde, 2016; Dixit and Varshney, 2009). Malik et al., (2001) found post-emergent Fluizfop butyl @0.75 kg ha^-1 effective in controlling weeds.
       
Dubey et al., (2018) observed the toxic effect of post emergence Oxyfluorfen @200 g ha^-1 fb Clodinafop @60 g ha^-1 at 35 DAS on the formation of root nodules whereas Pendimethalin @1 kg ha^-1 fb post-emergence Clodinafop @60 g ha^-1 effectively controlled grassy as well as the broad-leaf weeds. The pre-emergence Pendimethalin @1 kg ha^-1 fb post-emergence Clodinafop @60 g ha^-1 or Quizalofop @60 g ha^-1 were the most effective treatment with respect to weed control efficiency, grain and straw yield of chickpea. Khope et al., (2011) recorded higher chickpea yield with Quizalofop @50 g ha^-1 at 30 DAS. On comparing the different doses of Quizalofop i.e. 40 g ha^-1 and 50 g ha^-1 at 20 and 30 DAS with Imazethapyr i.e. 25 g ha^-1 and 40 g ha^-1 at 20 and 30 DAS, Quizalofop recorded highest grain yield except for Quizalofop @40 g ha^-1 at 20 DAS. The performance of Chlorimuron-ethyl was not effective to control weeds due to its severe phyto-toxicity which resulted in mortality of the chickpea.
       
Rupareliya et al., (2018) revealed that pre-emergence Oxyfluorfen @0.18 kg ha^-1fb pre-mix of Imazamox + Imazethapyr @0.03 kg ha^-1 as post-emergence at 40 DAS recorded lowest dry weight of weeds (83 kg ha^-1) and weed index (6.63%). Besides, highest weed control (92.23%) and herbicide efficiency (6.11) was obtained with the application of Imazamox + Imazethapyr @0.03 kg ha^-1. Kumar et al., (2020) concluded that application of pre-emergence Pendimethalin @1 kg ha^-1 + post-emergence Quizalofop @60 g ha^-1 recorded lowest nutrient depletion by weeds, highest nutrient uptake by crop and highest crop yield followed by pre-emergence Pendimethalin @1 kg ha^-1 + post-emergence Imazethapyr @40 g ha^-1.
       
Dewangan et al., (2016) revealed that with the use of tank-mix pre-emergence application of Oxyfluorfen + Metribuzin @125 + 350 g ha^-1 there was a notable increase in the yield (73.10%), over the control. While Metribuzin @250 g ha^-1 at 20 DAS and Oxyfluorfen @125 g ha^-1 at 12 DAS showed phytotoxic effects on chickpea plant.
       
Kantar et al., (1999) revealed that Terbutryne + Fluazifop-P-butyl @125 g ha^-1 + 100 g ha^-1 was the most effective herbicide followed by pre-emergence Imazethapyr @20g ha^-1 and pre-emergence Linuron + Propyzamide @200g ha^-1 + 50 g ha^-1. These herbicides were able to control Cirsium arvensis, Chenopodium album, Amaranthus retroflexus and Equisetum arvense effectively.
       
Balyan et al., (1987) found application of fluchloralin and pendimethalin alone at 1.0 and 1.5 kg ha^-1, respectively and combination of fluchloralin + pendimethalin and fluchloralin + metribuzin at higher rates produced better growth and reproductive characters of crop than their combinations at lower rates. Metribuzin @0.5 kg ha^-1 also produced significantly better growth and yield of chickpea as compared to the weedy check.
 
Integrated weed management
 
Weed management, a system approach, not only minimizes the invasion of weeds in aggressive forms but also gives a competitive advantage to the crop plants. As Indian agriculture is moving towards intensive agriculture from subsistence farming, dependency on the use of herbicides for weed control is increasing. Due to indiscriminate use of herbicides, the problems like poor quality produce, deteriorating human and animal health and of herbicide resistance may arise. At such times, Integrated Weed Management (IWM) is the only alternative that combines all the weed control methods to keep the weed population well below the economic threshold level (ETL) and also improves the pulse production.
       
Singh et al., (2003) found application of pendimethalin and isoproturon pre- or post-emergence and application of pendimethalin pre-emergence in combination with hoeing 45 DAS were effective in C. arietinum.
       
Rathod et al., (2017) concluded from the two years study that pre-emergence application of pendimethalin 0.75 kg ha^-1 + HW at 25-30 DAS was the best option for controlling weeds. Further, application of imazethapyr 30 g ha^-1 at 10 DAS was found effective for the control of weeds and resulted in higher grain yields and net returns. Merga and Alemu (2019) found that S-metolachlor 1.0 kg ha^-1 supplemented with hand weeding 5 weeks after emergence (WAE) recorded lowest total number of weeds (21.78 m^-2) following the weed free. Pendimethalin @ 0.75 kg/ha fb one hand weeding at 45 days after sowing was found effective (Chandrakar et al., 2015).
       
Kaushik et al., (2014) observed that post-emergence Imazethapyr @75 g ha^-1 + Hand weeding at 50 DAS recorded lowest no. of weeds/m² to the tune of about 2.91 which was followed by integrated use of pre-emergence Pendimethalin @0.75 g ha^-1 + Hand weeding at 25 DAS with 3.19 weeds/m². Highest Net return of Rs 24,648/ha was also achieved through the integrated use of Pendimethalin fb Hand weeding 25 DAS. In contrast, the highest number of weeds/m² were recorded with the pre-emergence Alachlor @2 kg ha^-1 with 5.34 weeds at 60 DAS.
       
Tiwari et al., (2019) in their field trials concluded that the integrated treatments performed significantly superior to alone application of herbicides. Amongst treatments, pre-emergence Pendimethalin @1 kg ha^-1 fb post-emergence Imazethapyr @50 g ha^-1 at 20 DAS fb manual weeding at 40 DAS recorded highest weed control efficiency (69.5 and 71.4 per cent, 60 and 90 DAS respectively) and lowest weed index of 6.7. Pre-emergence Pendimethalin @1 kg ha^-1 fb post-emergence Imazethapyr @50 g ha^-1 at 20 DAS fb manual weeding at 40 DAS recorded the lowest weed density at 30, 60 and 90 DAS with the corresponding value of 7.7, 6.6 and 5.8, respectively which was tailgated by pre-emergence Pendimethalin @1 kg ha^-1 fb post-emergence Imazethapyr @50 g ha^-1 at 20 DAS.
 
It was also revealed the integration of pre-emergence Pendimethalin @0.5 kg ha^-1 fb Hand weeding at 45 DAS resulted in dry matter accumulation to the tune of about 1.80 q ha^-1 which was followed by integration of pre-plant Trifluralin @0.5 kg ha^-1 fb Hand weeding at 45 DAS resulting in 2.33 q ha^-1 dry matter accumulation. Hence, the integrated treatments performed better than the alone applications of Pendimethalin @0.75 and 1 kg ha^-1 and Trifluralin @0.75, 1 and 1.25 kg ha^-1 (Singh et al., 2008). 

In regards to agriculture, weeds are still the major constraint to crop production. Agricultural practices have evolved over time and scientific community concluded that single method is insufficient to control this problem and integrated approach is the future of weed control. During the recent years, the concept of precision agriculture has hugely increased and it has not yet ceased. The use of herbicides when required is being stressed in order to reduce the carry over effects of herbicide. Keeping this in view, the use of post-emergence herbicides is being advocated. The influence of other agricultural practices like irrigation and nutrient management on the weed emergence has not been discussed due to insufficient research. This may be attributed to the fact that pulses are generally grown in the semi-arid (dryland areas) of the country. Genetically enhanced crops, like soybean, with resistance to broad-spectrum post-emergence herbicides such as glyphosate, have been developed through genetic engineering. Similar trends can also be the future of Chickpea and other pulse crops where mechanisation is a serious constraint to the production. 

Pulses due to their readiness to adapt to a wide range of edaphic and climatic conditions constitute a crucial segment of climate-change mitigation and adaptation strategy. The poor productivity of chickpea can be attributed to stress by weeds and insect-pests. Weeds are the most serious problem and if unchecked, can cause 20-90 per cent yield losses in different pulse crops (Pooniya et al., 2015). Weeds compete with the crops for resources like light, water, space, nutrition etc. thereby reducing the crop yield. They act as alternate host sheltering pests and diseases. Das (2008) reported that Lambsquarters (Chenopodium album L.) acts as an alternate host for greasy cut-worm (Agrotis ipsilon) in chickpea. Besides, the weeds are able to reduce the crop growth due to their allelopathic affect. Weeds like Chenopodium album L. and Matricaria chamomilla L. reduced the chickpea germination by 20 and 22.5 per cent respectively (Kadioglu et al., 2005). Pulses are precisely diverse agricultural share and profoundly impacted by weed stress. Hence, there is dreadful need to shift towards newer herbicide application for better weed control. However, with the modern concept of precision farming, the practice of post-emergence herbicide is being advocated. In the present setting, endeavours have been made to include the post-emergence herbicides that hold promise.