LAUSR

2211 Weeds occurring during early crop growth need to be removed because these are known to be most competitive with crops (Knezevic et al., 2002; Norsworthy and Oliviera, 2004; Tursun et al., 2016; Osipitan et al., 2016). Uncontrolled weeds at this early growth stage could cause irreversible and substantial crop yield losses (Knezevic et al., 2002, Adigun et al., 2014). If weeds are controlled at this time, crops can get a head start, achieve canopy closure, and compete effectively with later emerging weeds (Rajcan and Swanton, 2001). Typical early season weed control options include pre-plant, pre-emergence, and early post emergence herbicide applications in no-till cropping systems or mechanical cultivation in tilled systems. Herbicides provide an easy and cost-effective way of controlling weeds in crops and result in increased crop vigor and yield. Conversely, they are also a potential threat to the environment (e.g., pesticides residues in surface and/or groundwater) and in some areas, the development of resistant weed biotypes has reduced the utility of herbicides. In tillage-based cropping systems, mechanical operations such as plowing, harrowing, disking, and cultivating are used. Tillage for weed control has been utilized for a long time (Abdin et al., 2000) as it reduces weed density. At the same time, weed seeds receive a brief exposure to sunlight, due to soil inversion after tillage that can trigger their germination. There are still concerns about the negative impact of tillage on soil health and topsoil erosion (Loaiza Puerta et al., 2018). Cover crops have been documented to improve soil quality and minimize environmental degradation while providing a level of weed suppression in crops (Bachie and McGiffen, 2013; Norsworthy et al., 2007; Petrosino et al., 2015; Teasdale and Mohler, 2000). Cover crops can potentially provide an alternative tactic for control of herbicide-resistant weeds (Price et al., 2016; Wiggins et al., 2016). Reported weed suppression provided by cover crops has not been consistent, as it can range from 0% weed control (Galloway and Weston, 1996) to 98% control (Hayden et al., 2012), perhaps due to environmental, management, or inherent factors (Teasdale, 1996). Cover crops provide weed suppression either through competition (Mirsky et al., 2013), smothering (Hutchinson and McGiffen, 2000), or allelopathic activity (Barnes et al., 1987; Kunz et al., 2016). Cover crops can either be inter-seeded (Abdin et al., 2000; Cover Crop for Early Season Weed Suppression in Crops: Systematic Review and Meta-Analysis