**7. Effect of pre-emergence herbicides on weed control in maize**

When herbicides apply immediately or 1–4 days after maize seeds sowing, and it can be also mixed with soil during sowing, but it must be applied before weed seed emergence, are known as pre-emergence herbicides. Earlier findings [55] showed that pendimethalin can be applied as pre-emergence to get maximum weed control efficiency and crop selectivity by decreasing the weed population and increased the maize grain yield over the weedy check field [56]. Thus, Mekky et al. [57] reported that when pre-emergence herbicides were applied immediately after seed sowing or pre-emergence, weed control efficiency was the maximum and also increased the maize yield.

A field experiment in the clay loam soils of Guntur, Andhra Pradesh (India), with zero tillage maize found that atrazine 1.5 kg ha<sup>−</sup><sup>1</sup> applied at pre-emergence followed by (*fb*) manual hand weeding (HW) at 30 DAS recorded the tallest plant and the maximum dry-weight over un-weeded check at all stages of crop growth [30]. Scientist [26] reported that when maize was grown under zero till condition with pre-emergence herbicides atrazine at 1.0 kg ha<sup>−</sup><sup>1</sup> and topramezone 0.030 kg ha<sup>−</sup><sup>1</sup> in combination of two hand weeding at 20 and 40 DAS was produced significantly higher plant height, dry matter production of maize.

*Maize - Production and Use*

*T. portulacastrum*, and *D. arvensis* [37].

**4. The critical period of crop-weed competition**

crop growth stages, the yield losses may occur 30–100% [47, 48].

ranth (*Amaranthus palmeri* S. Wats) plants per meter row length.

**5. Weed control in zero-till maize by chemical measures**

in a maize crop were *Chenopodium album, Asclepias syriaca, Ambrosia artemisiifolia, Physalis heterophylla* and *Polygonum rensylvanicum* and the most common grasses were *Elymus repens and Setaria pumila* [35]*.* In another studies conducted on sandy loam soils at Hyderabad, India [26, 36], revealed that among the major weeds in maize field *E. colona* (grasses), *E. crus-galli, Paspalum distichum, C. rotundus* (sedges)*, Ageratum conyzoides* and *T. portulacastrum, Sonchus oleraceus, Acalypha indica, Eclipta alba and Parthenium hysterophorus* (broad-leaved) were the predominant weeds. A 3 years field survey in Andhra Pradesh of India also confirmed that most dominant weed species in maize field were *E. colona*, followed by *P. repens*,

The critical crop growth stages considers as the most vulnerable period for cropweed competition, during which crop must be weed free in order to prevent yield losses. Earlier studies observed [38–40] that the critical period of weed control in maize ranges from 7 to 56 days after seedling emergence. Other studies also reported [41–46], the critical period usually corresponds for maize up to 8–10 leaf stages. Wider canopy spacing and slow-growing nature of the maize crop should control weeds in first till 21–28 days after sowing for free from crop-weed competition and it was also suggested that if the weeds are not control within the critical

Weed species, densities, and their interactions influence maize yield loss [49, 50]. Weed plants compete with maize for their essential growth resources like water, nutrients, space etc. which ultimately reduce the yield up to 65% when weeds control measure was not performed at critical crop growth stages [46]. While, some problematic weeds species as they are similar in nature and life cycle of maize are difficult to control. Massinga et al., [51] reported that the yield reduction in maize could be 91% by competition if more than eight ama-

In maize production, weed management is considered as an important agronomic measure for attaining the potential yield. To minimize the maize yield loss due to weed competition, farmers are practicing several methods for controlling the weeds are available such as mechanical, cultural, biological and chemical control methods. The cultural methods are very expensive and time consuming so, farmers have to move towards other alternative methods of weed control [10]. Furthermore, due to the increasing cost and non-availability of labour for manual weeding during peak and critical maize growth stages significantly influence the maize yield. The role of herbicides is not only control the weeds timely and effectively, but also offer a great scope for minimizing the cost of production [10]. The chemical control method is quick, more effective, time and labour saving method than others [13]. However, it is important to use a broad-spectrum herbicide program including preand post-emergence herbicides for season-long effective weed control and to avoid shifts towards problematic weed species [32] or evolution of herbicide-resistant weed biotypes. On the other hand, it is decisive to select the appropriate weedicide depending upon the weed flora exist in a given field. In addition, the precise dose, methods, weed growth stage, timings, soil moisture and application techniques should be followed. A number of herbicides have been evaluated in sequential

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Recently, a study conducted in a clay loam and sandy loam soils of Bangladesh as a weed management strategy in pre-emergence and post emergence combinations and results showed that the even application of both Pendimethalin and atrazine separately reduces the weed biomass, weed population at 30 days after seeding which further provided better crop yield [58]. In another study clay soils of Rajendranagar (Telangana, India) was found that the highest crop dry matter was recorded with two times HW (at 20 and 40 DAS), which was at par with pre-emergence atrazine at 1.0 kg ha<sup>−</sup><sup>1</sup> + paraquat 0.60 kg ha<sup>−</sup><sup>1</sup> , followed by oxyfluorfen 0.150 kg ha<sup>−</sup><sup>1</sup> + paraquat 0.60 kg ha<sup>−</sup><sup>1</sup> [59]. The sequential application of pre-emergence followed (fb) protected spray of non-selective herbicide (Atrazine as pre-emergence at 1.25 kg ha<sup>−</sup><sup>1</sup> *fb* Paraquat 0.6 kg ha<sup>−</sup><sup>1</sup> at 3 weeks after sowing (WAS) or Pendimethalin as pre-emergence at 1.5 kg ha<sup>−</sup><sup>1</sup> *fb* Paraquat 0.6 kg ha<sup>−</sup><sup>1</sup> at 3 WAS) produced the significantly higher yield than weedy check [60]. An experiment was conducted with application of atrazine or glyphosate herbicide alone and tank mix application of selective (atrazine) and non-selective (glyphosate) herbicides and found that the grain yield was 170 and 70% more when atrazine + glyphosate (5.25 kg ha<sup>−</sup><sup>1</sup> ) were applied as tank mixture than weedy check and sole application of atrazine or glyphosate, respectively [26]. Similar to previous study, a field research in the sandy clay loam soils of Kampasagar (Telangana, India) reported that when atrazine 1.25 kg ha<sup>−</sup><sup>1</sup> + paraquat 0.75 kg ha<sup>−</sup><sup>1</sup> were applied as a pre-emergence in tank mixture produced the significantly maximum grains cob<sup>−</sup><sup>1</sup> , cob diameter and 100 grain weight than other herbicides [61]. Similar grain yields were recorded when applied atrazine alone as pre-emergence 1.25 kg ha<sup>−</sup><sup>1</sup> (6.7 kg ha<sup>−</sup><sup>1</sup> ) and atrazine 1.25 kg ha<sup>−</sup><sup>1</sup> + glyphosate 0.5 kg ha<sup>−</sup><sup>1</sup> (7.0 kg ha<sup>−</sup><sup>1</sup> ) as tank mixture of pre-emergence.
