Wheat (Triticum spp.), grown over 220 m ha throughout the globe, is the major cereal crop of the world and along with rice forms the backbone of the global food security system. However, in India, it is the second most important cereal crop after rice with an area of 29.1 m ha and annual production of 102.2 mt (Economic Survey 2020). Wheat production in South Asian region had seen multi-fold increase after green revolution, mainly attributed to high yielding varieties (HYVs), use of recommended chemical fertilizers, irrigation infrastructure and improved production technologies. But, during recent past the growth rate of wheat production has started declining (Ray et al. 2013), which is mainly due to several emerging problems like weed infestation, delayed sowing after rice harvest, soil salinity build-up, soil compaction due to puddling in rice and outbreak of various diseases (Choudhary et al. 2018). Among above all the factors, weeds are the major threat for wheat cultivation (Nakka et al. 2019). Numerous weed species have been influencing the productivity of wheat which include mainly Phalaris minor Retz., Chenopodium album L., Avena fatua L., Chenopodium murale L., Circium arvense L., Daucus carota L., Coronopus didymus L., Convolvulus arvensis L., Melilotus alba Lamk., Avena ludoviciana Dur. and Rumex dentatus L. These weeds altogether cause a yield loss of ~ 15–50% to wheat (Jat et al. 2003) and sometimes above 60% if weeds are allowed to grow rampantly (Singh et al. 2015a). Due to weeds, India suffered a loss of wheat produce worth US$ 3376 million, across 18 states during 2003–2014 (Gharde et al. 2018). Although yield penalties due to weeds vary according to relative proportion of weed flora, weed density and period of weed infestation. Apart from yield losses, weeds like R. dentatus and C. arvense make the harvesting and threshing operations difficult, whereas, heavy infestation of P. minor during maturity period leads to severe lodging of wheat crop (Chhokar et al. 2012).

Chemical herbicides have been considered as the effective and economical method to control weeds in the cereals (Singh et al. 2017). However, herbicide usage has many negative effects like excessive and repeated use of same herbicide or herbicides of same mode of action; which led to development of resistance in many weed species across the Indo-Gangetic plains region (IGPR) (Bhowmik et al. 2010; Chhokar and Malik 2002; Malik and Singh 1995), weed flora shift (Chhokar et al. 2014) and carry-over effect on the succeeding crops, resulting in low productivity of the cropping systems (Grey et al. 2012). Herbicides also cause toxicity to crop plants and drift hazards if handled improperly. Herbicide residues can accumulate in plant parts and may enter the food chain (Bai and Ougbourne 2016). Therefore, there is a need to look for alternate weed management options. Ecological approaches of weed management can be a possible non-chemical option for weed management in wheat. Non-chemical/ecological methods of weed control include sowing weed free seeds, adjusting sowing time, cultivation of competitive cultivars, soil solarisation, adoption of scientific crop rotations, adjusting crop geometry, row orientation and seed rate, stale seed-bed technique, laser land levelling, newer tillage and crop establishment methods, proper irrigation scheduling, nutrient management, mechanical weed control methods and straw management. These technologies can also be successfully used for controlling weeds in organic agriculture in various crops including wheat. The present paper aims to identify the effective ecological practices for weed management in wheat crop, especially under rice–wheat cropping system (RWCS) in IGPR in general and western IGPR in particular.

Use of weed free seed

Crop seed contamination with weed seeds is primary mechanism of dispersal of weeds. Both monocot and dicots weed species have a unique capability of producing seeds in large quantities (Kurdyukova 2018). Weeds like P. minor show phenotypic and chronological mimicry with the host crop like wheat and get harvested and threshed with wheat, which results into mixing of P. minor seeds with wheat grains. Seeds of other weeds also get mixed with crop seeds during harvesting and threshing operations. Yadav et al. (2002) collected the seed and grain samples of wheat (each sample of 125 kg) from 5 districts of Haryana state (India) and found ~ 0.2–1.7 million and ~ 15–72 thousand seeds of P. minor in grain samples and seed samples respectively (Table 1). Most of the farmers use a part of the previously harvested grain as seed stock for next season crop sowing as evident by low seed replacement rate of wheat (32.6%) reported by the Seed Division, Department of Agriculture Cooperation, Government of India during 2011. Such practices multiply the weed seed contamination, thus regular replacing of old seed with high quality seed can reduce the weed infestation to a great extent and consequently save a large amount of money by avoiding unnecessary weed control operations and herbicidal sprays for achieving higher wheat yields.

Table 1 Presence of Phalaris minor seeds in the wheat grain and seed samples in Haryana, India.
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Time of sowing

Crop sown at optimum time always gives them competitive advantage over the weeds. Wheat sown in the last week of October generally experiences less infestation of P. minor as the prevailing temperature during this period is not favourable for its germination in western IGPR (Chhokar and Malik 1999). Modern rice cultivars like ‘Pusa Basmati-1509’ matures in 120 days duration thereby, gives opportunity to sow wheat crop timely in rice–wheat cropping system (Singh et al. 2014). However on the other hand, Singh et al. (1995) reported that infestation of A. ludoviciana is prominent in the early sown wheat crop. They observed that the density of wild oat at 60 days after sowing was 97, 27 and 9 plants/m2 in November 10, 30 and December 30 sown wheat, respectively. Ibrahim et al. (1986) also found that dry matter accumulation (m−2) by broad leaved weeds and narrow leaved weeds reduced from 33.3 to 11.4 g and 48.3 to 7.7 g, respectively, when the wheat sowing was delayed from October 21 to November 30, whereas the yield increased from 2.7 to 4.6 t ha−1. Therefore, sowing time should be tinkered as per the intensity and target weed species in particular region.

Competitive cultivars

Crop varieties vary in growth habits which is mainly responsible for different weed competing ability (Choudhary et al. 2015). During past few decades high yielding dwarf wheat and rice varieties have become quite popular among farmers but many of these varieties lack the weed suppressing ability. Varieties with quick growing habit swiftly cover the ground and disfavor the growth of weeds early in the season, reducing the efforts required for controlling weeds at later crop stages. Weed-suppressive crop varieties have larger specific leaf area, uniformly distributed leaves along plant height, wider plants per unit biomass and their width and plant height get increased when shaded (Colbach et al. 2019).

Blackshaw (1994) found that yield reduction in wheat in western USA due to Bromus tectorum, an annual winter season grassy weed, was 14–30% higher in semi-dwarf varieties as compared to the tall growing varieties. Similarly, in India, Yaduraju and Ahuja (1997) observed that wheat variety C-306, which is a tall statured cultivar, has caused a significant decrease in dry matter accumulation (DMA) and plant height of P. minor, as compared with HD-2329 and Kundan cultivars. High weed suppressing ability of cultivar C-306 was attributed to its tall stature and quick growth. Chauhan et al. (2001) found that wheat varieties WH-542 and WH-157 are less competitive than HD-2687 and PBW-343. Whereas, Walia and Singh (2005) reported less DMA by P. minor in wheat varieties PBW-343, WH-283, PBW-373 and Raj-3765 as compared to varieties WH-157, WH-896 and WH-512 (Fig. 1).

Fig. 1
figure 1

Source: Modified from Walia and Singh (2005)

Effect of wheat varieties on dry matter accumulation (DMA) of Phalaris minor in herbicide untreated crop.

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Hossain et al. (2010) compared the competitiveness of eight different wheat varieties against various weed species, and ranked those varieties for their weed suppressing ability. ‘Prodip’ cultivar was the most competitive and ranked first while ‘Bijoy’ was least competitive. Yenish and Young (2004) compared tall and dwarf winter wheat cultivars for their competing ability against jointed goat grass (Aegilops cylindrica) and found that tall wheat varieties are superior to dwarf wheat varieties in suppressing the grass. Different species of wheat also differ in weed competing potential and Triticum aestivum is more suitable in curbing weeds as compared with durum wheat. Among different wheat varieties throughout the world, varieties of South America and Eastern Europe are more competitive against weeds than Indian, Mediterranean and Australian varieties (Lemerle et al. 1996). There is no doubt that dwarf wheat varieties have high yield potential as compared to tall varieties, but in high weed infestation fields tall varieties should be preferred over dwarf ones, owing to their better weed suppressing capability. Thus, selection of cultivars should be location specific depending upon weed dynamics is important for effective weed management.

Soil solarization

Cultivated soils are full of weed seeds as every year weed plants shed huge quantum of seeds. Weed seeds possess variable dormancy which helps them to germinate repeatedly over several years. Even if we are able to fully control the weeds for numerous years, the seed bank having variable dormancy will contribute to continuous appearance of weeds over the years (Rana et al. 2014b). Therefore, any technique which can destroy weed seed bank can act as very powerful tool for controlling weeds. Soil solarization is one such technique which can reduce the weed seed bank. Soil solarization is not a new technique; rather it is an age-old practice widely followed by ancient Indian farmers for restricting the growth of various harmful biological agents in soil as well as plants (Raghaven 1964). In soil solarization, whole field is covered with transparent plastic sheet during hot summer months. Covering of soil with plastic sheets increases the soil temperature to a level where it has a lethal effect on underlying weed seeds, spores of various pathogenic microorganisms and pupae and eggs of insects. Soil temperature in different layers increases by ~ 12–15 °C under soil solarized plots (Abd-Elgawad et al. 2019). Egley (1983) reported a soil temperature of 40–50 °C during soil solarization, and this temperature may reach above 60 °C in upper soil layers during full sunlight conditions. The major reasons for this rise in soil temperature under plastic sheet are greenhouse effect and restriction of evaporative cooling (Avissar et al. 1986).

Increase in soil temperature is more in soils which are irrigated before laying plastic sheets as compared to the non-irrigated soils because in irrigated soils a thin layer of water is formed underside the plastic sheet, which allows the incoming short-wave radiations to pass through it but blocks the outgoing long-wave radiations. This thin water layer also keeps the plastic sheet adhered to the ground, whereas in non-irrigated soils, without such water layer formation plastic sheet does not stick with the soil, making it prone to damage due to high speed winds (Arora and Yaduraju 1998). In soil solarization two major mechanisms govern the weed control, first, the weed seeds present near the soil surface are directly killed due to higher temperature in upper soil layer and second, the weed seeds present in relatively deeper layers are not subjected to very high temperature that will be able to kill the weed seeds but the temperature in deeper soil layers reaches up to an extent that the dormancy of those seeds gets broken, resulting into their germination. But due to small size and lesser stored energy in the weed seeds, the germinated seedlings fail to emerge and die within the soil (Rana et al. 2014a).

Arora and Yaduraju (1998) reported a reduction in germination of A. fatua up to 85 and 78% in top 5 and 15 cm soil depths, respectively. The same trend was also shown by P. minor seeds, but seeds of Melilotus indica remained unaffected by high temperature during soil solarization, attributed to their hard seed coat. Das and Yaduraju (2008) also reported decrease in overall weed population in wheat owing to soil solarization. Another major broad leaved weed of wheat i.e. R. dentatus is also very susceptible to soil solarization (Patel et al. 2005). Besides controlling weeds, soil solarization also increases the available nitrogen (Arora and Yaduraju 1998) and organic matter content of the soil (Khan et al. 2012). Therefore, soil solarization can act as an effective non-chemical method for controlling weeds in wheat but its suitability is limited to tropical and sub-tropical regions only, where temperature remains higher during summer months.

Crop rotation

Periodical rotation of crops of different life cycles, growth habits and requiring different management practices offers several advantages as compared to growing the same crop year after year. Several weeds are favored by growing same crop repeatedly, and mostly crop associated weeds (weeds which have similar climatic requirement, growth habits and life cycle to the crop) are most benefitted due to monoculture (Rana et al. 2018). Crop rotation interrupts the growth and development of weeds which are associated with a particular crop by changing the micro-climate of the field and the crop management practices. Stacked rotation is an emerging concept in the field of crop rotation. In stacked crop rotation one crop is grown for more than one year and after that some other crop is grown for the same number of years and this cycle continues. Stacked crop rotation is more effective than alternating crops each year in terms of weed control (Garrison et al. 2014). There are several weeds which exhibit phenotypic mimicry with crop plants like P. minor and A. fatua with wheat, Echinochloa colonum and Echinochloa crus-galli with rice. These weeds are difficult to control through hand weeding and various mechanical methods, but can be easily distinguished in the field of crop plants other than wheat and rice and can be controlled by hand weeding. Monoculture of wheat favors the infestation of P. minor which is the major concern for sustaining wheat productivity under rice–wheat cropping system (RWCS). Mono-cropping promotes the buildup of the weed-seed bank, which can be reduced to a manageable level if wheat is substituted with some other crops for 2–3 years. Altering wheat in RWCS by some other rabi crops like mustard, chickpea, lentil, sugarcane, sugar beet, fenugreek, cauliflower and cabbage might provide successful control of weeds associated with wheat (Brar 2002; Om et al. 2004). Growing fodder crops like oat and berseem instead of wheat for 2–3 years offers a wide spectrum weed control as weed plants get mowed during cutting of fodder crops. Fodder crops are cut 2–3 times in a single cropping season and weeds are also cut along with fodder crops and thereby minimize their seed production, subsequently a major portion of weed seed bank gets exhausted (Choudhary et al. 2018).

Malik and Singh (1995) reported higher resistance development in P. minor against isoproturon under RWCS as compared to rice–sunflower/vegetables/clover/pigeon pea. P. minor infestation remained higher in wheat grown after rice (Om et al. 2004) therefore, replacing rice with some other crop can also reduce the P. minor menace. However, replacing rice or wheat with some other crop on a large scale is not feasible as both are the major food crops. Small size of land holdings in India (~ 0.14 ha) also disfavors the adoption of the appropriate crop rotations. Some other negative factors like marketing and risk of crop failure are also associated with alternate crops. But intensification of RWCS by inclusion of short-duration vegetable crops like potato or vegetable pea can help in controlling weeds like P. minor without use of any herbicide (Chhokar et al. 2008). In addition to weed control, these crops also enhance the overall system productivity (Bana et al. 2015).

Crop geometry, row orientation and seed rate

Plant spacing and seed rate are two important factors which determine the plant density and affect the crop growth and yield. For reaping good harvest seed rate and row spacing should be optimum. Besides influencing crop growth and yield, these two factors also affect the weed population. Increasing the planting density increases the competitiveness of crops against weeds but one should be aware of intra-specific competition between the crop plants as well. Higher planting density decreases the spaces available for weed plants to grow. Higher seed rate and narrow spacing between crop plants facilitate early ground cover by crop plants and deprive the weeds from sunlight which is the basic requirement for proper growth. In a field study, decreasing the row to row spacing of wheat from 20 and 18 cm to 16 cm decreased the biomass of narrow-leaved weeds by 19.5 and 17.2%, and broad-leaved weeds by 20.7 and 19.9% respectively (Table 2), but grain yield was higher with 18 cm spacing (Devi et al. 2017).

Table 2 Effect of row spacing on weed biomass and grain yield in wheat
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There is significant reduction in P. minor, M. indica and Rumex acetosella densities by increasing wheat seed rate from 120 to 150 kg/ha (NATP Report 2001). There was a significant improvement in wheat yield with ~ 15% reduction in total DMA by different weed species in wheat after reducing the row spacing from 22.5 to 15 cm (Brar 2002). Likewise, the tiller density of wheat increased, by increasing wheat seed rate from 100 to 150 kg/ha and number of productive tillers and grains per spike decreased by increasing the seed rate, but overall, there was an increase in yield of wheat by ~ 7–8% (Duary and Yaduraju 2006). At low density of P. minor, increase in wheat yield by increasing seed rate from 100 to 150 kg/ha was only 4–5% but at higher densities of P. minor, wheat yield increase were up to 16% (Duary and Yaduraju 2006). Criss-cross sowing is a popular technique of wheat sowing. It helps in control of weeds and results into higher yield as compared to conventional line sowing method. Chhokar et al. (2017) reported 2.4% higher yield in criss-cross sown wheat as compared to the line sown wheat. Hussain et al. (2017) found that weed density and weed biomass at the time of wheat harvest was lower by ~ 18.4 and ~ 23.4%, respectively, in criss-cross sown wheat as compared to line sown wheat when 100 kg ha−1 seed rate was used. Criss-cross sowing of wheat at a spacing of 22.5 cm can control the weeds equal to the unidirectional sowing at 15 cm, but yield is 5% higher in criss-cross sown wheat (Mongia et al. 2005). In addition to crop geometry and seed rate, orientation of crop rows is also an effective weed management tool which is not well explored. Crop orientation decides the amount of solar radiations intercepted by a plant. Borger et al. (2010) reported reduced weed biomass and increased grain yield in east–west oriented wheat crop as compared to north–south oriented one.

Stale seed bed technique

In this weed management approach, the seed-bed is prepared for sowing of wheat crop, but before sowing of crop, light irrigation is applied which stimulates the germination of weed seeds present in upper soil surface and these germinated seeds can be controlled through a light tillage operation or hand-weeding or by a heavy planker. After the control of weeds, the wheat is then sown, having less weed infestation. Thus, stale seed-bed technique reduces the weed seed bank in upper soil layers drastically (Johnson and Mullinix 2000). Rasmussen (2004) also reported a decrease in weed seed bank by stale seed-bed technique in winter wheat. Although it is very effective weed control method but a good management skill is required for planning of these operations timely, otherwise sowing of wheat gets delayed.

Laser land-leveling

Laser land leveling is a novel resource conservation technology which reduces the irrigation duration in wheat by 20–25% and can increase the wheat grain yield by 6–9% in rice–wheat rotation (Aryal et al. 2015). Laser leveling is also useful in reducing the weed population and cost of weeding by ~ 10% (Hussain et al. 2020). Labour required for weeding operation reduces up to 75% owing to precise levelling of the field (Rickman 2002). In uneven fields germination of crops is less and ungerminated patches in the field become conducive for weed growth. Whereas, in laser levelled fields, uniform moisture distribution promotes even crop stand and growth, resulting in lower weed menace (Jat et al. 2006).

Tillage management

Tillage is the physical manipulation of soil, to form a good seed-bed for optimum germination of crops. Tillage influenced the physical (bulk density, soil moisture, temperature and aggregation), chemical (pH and cation exchange capacity) and biological (microbial population and organic matter) properties of soil (Busari and Salako 2013; Stanek-Tarkowska et al. 2018). Tillage also has a role in distribution of weed seeds in soil profile (Clements et al. 1996). Tillage methods adopted for rice cultivation also influence the vertical distribution of rabi season weeds. Due to puddling, numbers of R. dentatus seeds in upper soil layers were found to be more as compared to P. minor seeds. This can be attributed to low seed density of R. dentatus (16.2 kg/hectolitre) than P. minor (61.3 kg/hectolitre) (Chhokar et al. 2007a). Infestation of broad-leaved weed like C. arvense, C. arvensis, Malva parviflora and R. dentatus increases (Catizone et al. 1990; Chhokar et al. 2007b; Koch and Hess 1980), whereas P. minor population remains low under zero tillage (ZT) wheat as compared to conventional tillage (Usman et al. 2012). Lower infestation of P. minor under ZT wheat is attributed to higher soil strength in furrow slice of soil (top 15 cm) under ZT as compared to conventional tillage (Chhokar et al. 2007a). Therefore, due to adoption of ZT in wheat, the weed flora is shifted from narrow-leaved to broad-leaved weeds. But broad-leaved weeds can be easily distinguished from wheat plants and their mechanical control is possible, whereas it is very hard to control narrow-leaved weeds especially P. minor and A. fatua due to their phenotypic similarity with wheat plants. If weeds are effectively controlled for initial few years in ZT wheat and are not allowed to set seeds, weed seed bank is significantly reduced as the ZT soil is not disturbed and movement of weed seed from lower soil layer towards upper layer is drastically restricted. Besides weed control, the ZT in wheat also reduce the operational cost by ~ 25% and fuel cost by ~ 90% and permit timely sowing of wheat after rice, cotton or pigeon pea harvest (Chauhan et al. 2003; Sharma et al. 2002).

Soil moisture management

Soil moisture is a critical factor which governs the germination and growth of crop as well as weed plants. Wheat is able to germinate in slightly drier soils but germination of weeds like P. minor and R. dentatus is discouraged in dry soils (Kumar et al. 2013). Singh and Singh (2004) found that pre-sowing irrigation reduced total weed density from 45 to 32 plants m−2, weed dry matter accumulation from 63 to 43 g m−2 and increased the wheat grain yield by 12% as compared to the post-sown irrigation. So, managing the soil moisture in such a way that it favors the wheat germination and disfavor the germination of weeds might be an affective ecological technique for controlling weeds in wheat. Sowing of bold-seeded crops at a slightly deeper moist layer, where upper surface is dry can give an initial advantage to crop plants over weeds (Liebman and Mohler 2001).

Nutrient management

Optimum nutrient application is necessary for higher crop yield (Bana et al. 2016). Both crop and weed plants compete for limited amount of nutrients present in the soil. Amount, method and time of fertilizer application are major factors which affect the crop-weed competition. Singh et al. (2015b) found that increasing nitrogen (N) application rate from 120 to 160 kg/ha reduces the total weed density and biomass in wheat (Table 3). Basal application of 50% nitrogen, and then two-split applications of 25% each at crown root initiation (CRI) and flowering stage resulted into lesser weed population and biomass in wheat as compared to 33.3% N, each as basal, at CRI and flowering (Singh et al. 2015b). Therefore, amount, time and method of fertilizer application should be managed properly to give a competitive edge to wheat crop over weeds. Sub surface application of nitrogenous fertilizers disfavors the growth of weeds, whereas, broadcasting encourages weed growth (Blackshaw et al. 2004). Weed growth was also influenced by type of nutrient; nitrogen favors the growth of grassy weeds, whereas, growth of broad leaved weeds were enhanced by phosphatic fertilizers (Chhokar et al. 2012). Seeds of many weed species do not lose their viability even after passing through animal alimentary canal (Pleasant and Schiather 1994; Rahimi et al. 2016), therefore, whenever farm yard manure (FYM) has to be applied it should be well decomposed.

Table 3 Effect of nitrogen scheduling on total weed density and biomass, and wheat yield
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Mechanical weed control

It includes the removal of weed plants through hand-weeding or use of machinery. It is very effective weed control method if properly exercised. In addition to weed control it also aerates the soil. But it requires a lot of energy, time and cost. Along with these requirements, mechanical weed control is very difficult in wheat as weeds like P. minor and A. fatua look like the wheat plants. Wheel hand hoe with slight modification to match the inter-row spacing can be used to control weeds in wheat grown on light soils, but it is not suitable for heavy soils where wheat is grown after rice harvest. Before tillering, mechanical weed control through spring-tyne harrow was satisfactory in organically grown wheat (Graziani et al. 2012; Rasmussen and Svenningsen 1995). Line-sown flat-bed and furrow irrigated raised bed system (FIRBS) of wheat cultivation are quite suitable for mechanical control of weeds through wheel hoe. Along with possibility of mechanical weeding, weed population remains inherently low in FIRBS system as compared with conventional method (Mollah et al. 2009).

Straw management

Rice residues management particularly in combine-harvested fields is a serious issue for farmers of IGPR who practice RWCS. Burning rice residues for making field ready for sowing of wheat is environmentally unsound practice followed by large number of farmers (Rana et al. 2014b). Moreover, burning of rice residues also facilitates germination of P. minor, as after rice harvesting humidity and soil moisture is high and atmospheric temperature is low (20–25 °C in Oct–Nov months). These conditions prevent the soil temperature during straw burning to reach a level that can prove lethal for P. minor seeds. Germination of P. minor increases by ~ 31% and ~ 82% by burning of rice residues @ 6 t/ha and 12 t/ha, respectively as compared to no burning (Chhokar et al. 2009).

In a field study, the total biomass of three important weed species i.e. P. minor, R. dentatus and Medicago denticulata, reduced in ZT wheat by 28 and 40% through retention of 5 and 7.5 t/ha rice residues, respectively, as compared to no rice residues. Bana et al. (2020) also observed less weed infestation in direct seeded rice due to residue retention in rice–wheat rotation. ZT wheat with 7 t/ha residues recorded ~ 10% less total weed biomass as compared to conventional tilled wheat (Chhokar et al. 2009).

Future prospects

Rice–wheat cropping system covers around 18 mha worldwide, where an alternative strategy for weed management is needed to overcome excessive herbicidal use problem, particularly in wheat. Though, various ecological approaches discussed in the present review have the potential to overcome weed menace in wheat, but still farmers are largely dependent on herbicidal weed management. Poor productivity of weed competitive cultivars, long duration Basmati varieties delaying wheat planting, non-availability of information on long-term effect of new tillage and crop establishment techniques on weed dynamics and yield stability, less information on newer scientific advancement like use of allelopathy for weed control, nano-technology, and biological weed control are biggest bottlenecks in adoption of ecological weed management approaches. Therefore, future research should focus on developing high yielding weed suppressing wheat cultivars (Worthington and Reberg-Horton 2013), short-duration rice varieties (Akhter et al. 2019), long-term studies for better understanding of weed dynamics under new tillage and crop establishment techniques (Bana et al. 2020), use of allelopathy in weed management (Jabran 2017), nano-technology (Balah and Pudake 2019) and biological weed control (Schwarzländer et al. 2018) in wheat. Moreover, majority of ecological approaches have been studied in isolation. Combined studies on ecological weed management approaches can be done for developing integrated weed management strategy.

Conclusion

To overcome the emerging threats of excessive herbicide uses and to face the herbicide resistance development problems, there is an urgent need to explore the alternative ways/methods of weed management especially for wheat. Various ecological approaches have the potential to effectively and efficiently manage the weed problem in wheat, but there are several bottlenecks in their adoption. Therefore, these ecological approaches of weed management need further in-depth research, location specific farming system based fine-tuning and refinement including suitable adjustment with modern agronomic advancements. In addition, the researchers should focus on interaction of diverse ecological approaches and their environmental impacts vis-à-vis conventional weed management practices in wheat under rice–wheat cropping system in Indo-Gangetic Plains.