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

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

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