Bell pepper is an important fresh-market vegetable crop in the southern United States [U.S. Department of Agriculture (USDA), 2008]. Weeds are the major limiting factor in bell pepper production, competing for resources and harboring harmful crop pests (Frank et al., 1988). Purple nutsedge, yellow nutsedge, palmer amaranth, and large crabgrass are among the major weed problems in vegetable-growing areas of the southern United States (Webster, 2002). Methyl bromide, a preplant soil fumigant, has been widely used under polyethylene mulch for effective weed control in vegetable production, including bell pepper (Duniway, 2002). However, because of its ozone-depleting potential, methyl bromide is being phased out from the U.S. agricultural industry (U.S. Environmental Protection Agency, 2008). The loss of methyl bromide may complicate weed management in bell pepper, thereby negatively impacting production. Therefore, an effective alternative of methyl bromide is urgently needed. A number of potential methyl bromide alternatives are available in vegetable production. However, no single alternative is a stand-alone replacement for methyl bromide (Noling, 2002). Thus, research efforts are needed to develop an integrated weed management program by combining two or more alternatives that can provide effective weed control in bell pepper.
One potential nonchemical tactic is the inclusion of cover crops belonging to the mustard family (Brassicaceae) in bell pepper production systems. The weed suppressiveness of plants of the mustard family is attributed to rapid early-season biomass accumulation and groundcover, thereby physically suppressing seed germination and growth of new weed seedlings (Beckie et al., 2008; Eberlein et al., 1998). Additionally, maceration of mustard family plant tissue releases a number of allelopathic compounds, including isothiocyanates (Fahay et al., 2001). Isothiocyanates are biologically active compounds that prevent or delay weed emergence (Brown and Morra, 1995; Haramoto and Gallandt, 2005; Vaughn and Boydston, 1997). Thus, growing mustard family cover crops before a commercial crop may reduce early-season weed competition. Norsworthy and Meehan (2005) found that the competitiveness of bell pepper can be increased over yellow nutsedge by amending soil with wild radish (Raphanus raphanistrum). Likewise, soil amended with rapeseed (Brassica napus) reduced weed density and biomass up to 85% and 96%, respectively, in the following potato (Solanum tuberosum) crop (Boydston and Hang, 1995). ‘Caliente’ mustard has the capacity to produce a high amount of glucosinolates, the precursor of isothiocyanates, which makes it a promising cover crop for weed suppression (Norsworthy et al., 2005).
Chemical weed control options in pepper include pre-emergence (PRE) and post-emergence (POST) herbicides. Registered PRE residual herbicides for in-row weed control include bensulide, trifluralin, clomazone, napropamide, and oxyfluorfen (Smith and Daugovish, 2008; Stall, 2007). Although these herbicides are effective against many annual grasses and certain broadleaf weeds, control of purple nutsedge, yellow nutsedge, and palmer amaranth is marginal. Other factors that limit the use of these herbicides include rotation restrictions, moisture requirement for herbicide activation, and the required interval between application and transplanting. Registered POST herbicide options for in-row weed control include only graminicides such as sethoxydim and clethodim (Stall, 2007). Thus, it would be beneficial to evaluate other herbicides that may provide effective control of purple nutsedge, yellow nutsedge, and palmer amaranth without injuring bell pepper.
S-metolachlor is a chloroacetamide herbicide that has been granted third-party registration for pre- and post-transplant weed control in bell pepper (Culpepper, 2003; Stall, 2007). In polyethylene-mulched bell pepper, the pretransplant application includes a nonincorporated spray of S-metolachlor on preformed beds before laying plastic mulch. The post-transplant application is PD in bell pepper row middles between the parallel mulch rows. S-metolachlor provides effective control of annual grasses, palmer amaranth, and yellow nutsedge, but inconsistent control of purple nutsedge (Clewis et al., 2008; Obrigawitch et al., 1980; Syngenta Crop Protection, 2007a). Halosulfuron, a sulfonylurea herbicide, provides excellent soil and foliar control of purple nutsedge and yellow nutsedge (Grichar et al., 2003; Umeda and Towers, 2006). However, its use is restricted only to row middles, and herbicide contact with plastic should be avoided (Gowan Co., 2007). Trifloxysulfuron, another sulfonylurea herbicide, provides effective control of many weed species, including purple nutsedge, yellow nutsedge, palmer amaranth, and large crabgrass (Clewis et al., 2008; Culpepper and Stall 2003; Hudetz et al., 2000; Syngenta Crop Protection, 2007b). At present, trifloxysulfuron is not labeled for use in U.S. bell pepper production.
Because of weed control efficacy, these herbicides may serve as a viable weed management option in bell pepper. However, sensitivity of bell pepper may limit the use of full rates of these herbicides. Unfortunately, adequate weed control using low rates is doubtful (Sullivan and Bouw 1997). Thus, herbicides may need to be supplemented with other weed control strategies to obtain acceptable weed control without causing crop injury. Malik et al. (2008) suggested that herbicide rates be reduced in sweet corn (Zea mays) when using a spring-grown, mustard family cover crop. The objective of this research was to evaluate weed control and bell pepper response to a ‘Caliente’ mustard with and without PRE and PD herbicides at reduced (1/2×) and full (1×) application rates in a polyethylene-mulched production system.
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