Organic vegetable growers have indicated that weed control is a challenge in organic crop production (Bond and Grundy, 2001; Stopes and Millington, 1991; Walz, 1999); therefore, it has become an important topic of research for organic growers (Radhakrishnan et al., 2002). Poor weed control results in lower vegetable and other agronomic crop yields (Gianessi and Reigner, 2007; Griffith et al., 2006; Peacock and Norton, 1990; Rowland et al., 1999). Synthetic herbicides cannot be used in organic production (Kuepper, 2002), and manual removal and cultivation are labor-intensive (Boyd et al., 2006; Gianessi and Reigner, 2007). A wide range of both synthetic and nonsynthetic broad-spectrum contact chemicals have been approved by the U.S. Department of Agriculture National Organic Program for weed control in organic systems (Kuepper, 2002), including vinegar (Garrett and Beck, 1999; Webber et al., 2005).
Previous studies have evaluated the efficacy of vinegar and other natural products to control weeds in vegetable crop and other agronomic production systems (Boyd et al., 2006; Evans et al., 2009; Radhakrishnan et al., 2002), as well as the effects that natural products have on the desired crop (Bingaman et al., 2000; Evans and Bellinder, 2009; Evans et al., 2011; Moran and Greenberg, 2008; Patton and Weisenberger, 2012). In addition to general weed control, natural controls for weeds at two growth stages were examined by Abouziena et al. (2009), and Brainard et al. (2013) studied the effectiveness of vinegar and clove oil applied at different temperatures, relative humidity, and weed growth stages.
In nonorganic production systems, glyphosate has been widely used as a broad-spectrum compound to control weeds globally (Malik et al., 1989). With conservation tillage systems, glyphosate is commonly applied before planting (Bruff and Shaw, 1992) and has been successful at controlling weeds with some residual control (Buhler and Werling, 1989; Wilson and Worsham, 1988). Several studies have evaluated the effectiveness of glyphosate at controlling weeds in crop production systems (Culpepper, 2006; Griffith et al., 2006; Norris et al., 2001; Shaw and Arnold, 2002), whereas others have compared glyphosate with natural products to control weeds (Abouziena et al., 2008; Patton and Weisenberger, 2012; Young, 2004).
Research of the use of natural products to control weeds before garden establishment with continued control throughout the growing season is limited. Additionally, research comparing the efficacy of weed suppression treatments applied in the fall for a spring garden compared to spring-only weed treatments is lacking. Therefore, to assist home gardeners or commercial farmers considering a transition from conventional to organic production systems, this study was undertaken to compare the effectiveness of three organic weed-control methods and that of glyphosate. Specific objectives of the study included: 1) evaluating the differences between spring and fall treatment applications and a spring-only treatment application; 2) evaluating the number of days after treatment (DAT) to 50% and 100% weed regrowth; and 3) evaluating the number of follow-up treatment applications required throughout the growing season.
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