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Reduced-tillage peanut production is increasing due to reduced production costs and increased environmental and economic benefits compared to conventional systems. Experiments were conducted in Alabama and Georgia between 2005 and 2007 to evaluate a strip-tillage system utilizing a high-residue cereal rye cover crop, in comparison to a conventional tillage system. Six weed management schemes were evaluated including a preemergence (PRE) application of pendimethalin alone at 1.12 kg ai/ha or in combination with S-metolachlor at 1.36 kg ai/ha. Both PRE applications were applied alone or followed by (fb) a postemergence (POST) application consisting of a mixture of paraquat at 0.140 kg ai/ha plus bentazon at 0.56 kg ai/ha plus 2,4-DB at 0.224 kg ae/ha. The remaining two treatments consisted of a no-herbicide control and aforementioned POST-only application. In 2005 at the Alabama location, pendimethalin plus metolachlor with or without a POST application controlled all weeds >91% in the strip tillage treatment and controlled tall morningglory, yellow nutsedge, and common bermudagrass >83% in the conventional tillage system. Pendimethalin fb a POST application controlled all weeds > 97%, except large crabgrass (75%) and common bermudagrass (≤ 58%) regardless of tillage system. In 2007, pendimethalin and pendimethalin plus S-metolachlor followed by (fb) a POST application controlled smooth pigweed, tall morningglory, large crabgrass, Florida beggarweed, and sicklepod 70 to 99%, across tillage systems. In 2005 at the Georgia location, large crabgrass control was consistently reduced in strip-tillage compared to conventional tillage regardless of herbicide treatment. In 2006, pendimethalin plus S-metolachlor fb POST controlled common bermudagrass and yellow nutsedge 74 to 99%. Herbicide treatment effect on peanut yield varied with environment. Peanut yield was equivalent or greater by 25% or more in 3 of 4 site years utilizing strip-tillage indicating a yield advantage compared to conventional tillage. Peanut market grade was not affected by any herbicide treatments or tillage methods evaluated. Results show that producers can maintain weed control, equivalent grade and yield in reduced-tillage systems when utilizing a high-residue conservation agriculture system integrated with a PRE plus POST herbicide system.

A field experiment evaluated simulated salvage herbicide application injury and injury timing on cutleaf groundcherry density, biomass, seed production, and crop yield in a peanut system. Treatments included: 1) a non-treated control; 2) hand pruning; 3) diclosulam applied preemergence (PRE) alone at 27 g/ha ; 4) paraquat applied at cracking early postemergence (EPOST) at 140 g/ha followed by bentazon at 560 g/ha late postemergence (POST) alone or mixed with 5) 2,4-DB at 220 g/ha; 6) acifluorfen at 280 g/ha; 7) imazapic at 70 g/ha; or 8) chlorimuron ethyl at 9 g/ha. Hand pruning and POST herbicide treatments were performed at 1-week intervals for four weeks beginning in June of each year. Herbicide treatments do not reflect current peanut herbicide recommendations but were chosen based on likely differential cutleaf groundcherry biomass and subsequent seed production. Diclosulam applied PRE provided season-long cutleaf groundcherry control; imazapic applied POST in combination with bentazon also provided excellent control. Use of bentazon alone or mixed with chlorimuron ethyl, or hand pruning resulted in similar cutleaf groundcherry biomass and subsequent seed production compared to the non-treated control in almost all comparisons. Peanut yield reflected early-season weed interference and late season cutleaf groundcherry control. Highest yields were recorded for diclosulam PRE and POST applications containing 2,4-DB and imazapic with 6040, 5990, and 6430 kg/ha, respectively. When early-season weed control efforts fail to completely control cutleaf groundcherry, it is crucial to have effective late season herbicide options for salvage treatments in order to prevent additions to the seed bank.Nomenclature: Acifluorfen, bentazon, chlorimuron ethyl, diclosulam, imazapic, paraquat, 2,4-DB, cutleaf groundcherry, Physalis angulata (L.) PHYAN, peanut, Arachis hypogaea (L.).

Amaranthuscontrol in cotton can be difficult with the loss of glyphosate efficacy, especially in conservation-tillage cropping systems. Research was conduction from 2006 to 2008 at EV Smith Research Center, Shorter, AL, to determine the level of glyphosate-susceptibleAmaranthuscontrol provided by four initial tillage and herbicide treatments, including 1) moldboard plowing followed by a single-pass disking and field cultivation plus pendimethalin at 1.2 kg ai ha−1preplant incorporation (PPI), 2) two-pass disking followed by field cultivation plus pendimethalin at 1.2 kg ha−1PPI, 3) no tillage including an application of pendimethalin at 1.2 kg ha−1PRE, or 4) no tillage without pendimethalin in 2006. No further tillage practices or pendimethalin applications were utilized after study initiation. Initial tillage operations, including inversion with disking or disking twice, resulted inAmaranthusdensity of ≤ 4 plants m−2and 47 to 82% control, whereas no-tillage treatments had ≥ 4 plants m−2and 14 to 62% control. Subsequent applications of PRE herbicides included fluometuron at 1.68 kg ai ha−1or prometryn at 1.12 kg ai ha−1and provided 53 to 98% and 55 to 93% control, respectively, and reducedAmaranthusdensity compared to no PRE herbicide to < 2 plants m−2, regardless of tillage treatment. A POST application of glyphosate at 1.0 kg ae ha−1improved control in conjunction with almost all treatments in each year. Results indicate that a one-time tillage operation followed by a return to reduced tillage may aid in the reduction ofAmaranthusdensity when used with PRE-applied herbicides; however, this system will likely not provide adequate control when high population densities of glyphosate-resistantAmaranthusare present, thus highlighting the need for a highly efficacious POST herbicide system.

The increased adoption of conservation tillage in vegetable production requires more information on the role of various cover crops in weed control, tomato quality, and yield. Three conservation-tillage systems utilizing crimson clover, turnip, and cereal rye as winter cover crops were compared to a conventional black polythene mulch system, with or without herbicide, for weed control and tomato yield. All cover crops were flattened with a mechanical roller/crimper prior to chemical desiccation. Herbicide treatments included a PRE application of S-metolachlor (1.87 kg a.i. ha−1) either alone, or followed by an early POST metribuzin (0.56 kg a.i. ha−1) application followed by a late POST application of clethodim (0.28 kg a.i. ha−1). Except for spotted spurge and tall morningglory only the main effect of herbicide treatments and cover crops affected weed control. For the majority of the weeds, no significant differences in weed control were observed with rye residue and plastic mulch treatments; however, turnip and crimson clover residue failed to control most weeds. Rye residue provided 86% large crabgrass, 80% goosegrass and 84% Broadleaf signalgrass control. Yellow nutsedge was controlled 65% by plastic mulch and only 60% by Rye residue. Pokeweed was controlled 80% by plastic mulch treatment. S-metola‐ chlor applied PRE was sufficient in controlling leafy spurge and tall morningglory in plastic mulch and rye residue plots. Yield was less following either crimson clover or turnip cover crops compared to rye or the polythene mulch system. Application of herbicides resulted in better yields compared to the no-herbicide treatments. Economic analysis indicated that there was no significant difference between using a rye cover crop or plastic under any of the alternative herbicide treatment regimes in 2005. This research demonstrates the possibility of growing tomato in conservation tillage systems using high residue cover crops and herbicides to maintain season long weed control.

The increased adoption of conservation tillage and organic weed control practices in vegetable production requires more information on the role of various cover crops in integrated weed control, tomato quality, and yield. Two conservation-till‐ age systems utilizing crimson clover and cereal rye as winter cover crops were com‐ pared to a conventional black polythene mulch system, with or without organic weed management options, for weed control, tomato yield, and profitability. All cover crops were terminated with a mechanical roller/crimper prior to planting. Or‐ ganic weed control treatments included: 1) flaming utilizing a one burner hand torch, 2) PRE application of corn gluten, 3) PRE application of corn gluten followed by flaming, or 4) intermittent hand weeding as needed. A non-treated control and a standard herbicide program were included for comparison. The herbicide program consisting of a PRE application of S-metolachlor (1.87 kg a.i./ha) followed by an ear‐ ly POST metribuzin (0.56 kg a.i. /ha) application followed by a late POST applica‐ tion of clethodim (0.28 kg a.i./ha). In general, high-residue clover and cereal rye cover crops provided substantial suppression of Palmer amaranth, large crabgrass, and yellow nutsedge. Across systems, minimum input in high-residue systems pro‐ vided the highest net returns above variable costs compared to organic herbicide treatments that are costly and provide marginal benefit.

Conservation agriculture (CA) practices are threatened by glyphosate-resistant Palmer amaranth. Integrated control practices including PRE herbicides and high-residue CA systems can decreaseAmaranthusemergence. Field experiments were conducted from autumn 2006 through crop harvest in 2009 at two sites in Alabama to evaluate the effect of integrated weed management practices onAmaranthuspopulation density and biomass, cotton yield, and economics in glyphosate-resistant cotton. Horizontal strips included four CA systems with three cereal rye cover crop seeding dates and a winter fallow (WF) CA system compared to a conventional tillage (CT) system. Additionally, vertical strips of four herbicide regimes consisted of: broadcast, banded, or no PRE applications ofS-metolachlor (1.12 kg ai ha−1) followed by (fb) glyphosate (1.12 kg ae ha−1) applied POST fb layby applications of diuron (1.12 kg ai ha−1) plus MSMA (2.24 kg ai ha−1) or the LAYBY application alone. Early-seasonAmaranthusdensity was reduced in high-residue CA in comparison to the CA WF systems in 2 of 3 yr.Amaranthusdensities in herbicide treatments that included a broadcast PRE application were lower at three of five sampling dates compared to banding early-season PRE applications; however, the differences were not significant during the late season and cotton yields were not affected by PRE placement. High-residue conservation tillage yields were 577 to 899 kg ha−1more than CT, except at one site in 1 yr when CT treatment yields were higher. CA utilizing high-residue cover crops increased net returns over CT by $100 ha−1or more 2 out of 3 yr at both locations. High-residue cover crop integration into a CA system reducedAmaranthusdensity and increased yield over WF systems; the inclusion of a broadcast PRE application can increase early-seasonAmaranthuscontrol and might provide additional control when glyphosate-resistantAmaranthuspopulations are present.

White lupin is of increasing interest in the southeastern United States (US) as a winter legume cover crop or as mid-winter forage for ruminants. White lupins are poor weed competitors during early establishment, making effective weed control necessary; however, only three herbicides are currently registered for use in lupin. An experiment was conducted at two Alabama sites in 2007 and 2008 to evaluate herbicide efficacy provided by ten preemergence (PRE) and nine postemergence (POST) herbicides as well as lupin injury and yield. Overall, PRE applied herbicides, particularly imazethapyr, linuron, and flumioxazin, caused less crop injury than POST herbicides while providing ≥ 86% control of annual bluegrass, corn spurry, heartwing sorrel, henbit, and lesser swinecress six weeks after application. Grass-active herbicides, fluazifop and sethoxydim, provided greater than 95% of annual bluegrass control without causing unrecoverable lupin dam‐ age. Imazethapyr applied POST controlled shepherd’s purse (96% to 98%), cutleaf evening-primrose (81% to 96%), and wild radish (71% to 99%) without lupin injury. POST- directed spray applications of glyphosate and flumioxazin provided good weed control of corn spurry (80% to 98%) and winter vetch (71% to 95%) but caused significant crop injury due to drift. In general, grain yields were only reduced with the use of chlorimuron, diclosulam, glyphosate, and thifensulfuron. This research suggests there are several herbicides not currently registered that could be beneficial for use in US lupin production.

Previous research has indicated that conservation tillage is a viable option for suc‐ cessful peanut production; however, interactions between cover crop residues and peanut growth are not fully understood. Additional information is needed about the effects of varying levels of cover crop biomass on peanut growth and develop‐ ment. Level of cover crop residue may also affect the preemergence herbicide activi‐ ty through interception and efficacy of weed suppression. The objectives of this peanut research were to determine if varying amounts of cover crop biomass would affect peanut growth, herbicide interception, or weed control. This research also aimed to determine if cover crop management practices (rolling or standing cover) would affect herbicide interception rates. The study consisted of a rye (Secale cereale L.) cover crop planted at three different dates as well as a fallow treatment at two locations: Dawson, GA, and Headland, AL. Pendimethalin was applied PRE at 1 kg ai/ha across the entire area just prior to planting of the Georgia 03-L peanut variety. Soil samples were collected at three different dates after planting for high-pressure liquid chromatography (HPLC) analysis to determine pendimethalin levels. Peanut yields differed only between location regardless of cover crop residue level with the Headland, Alabama, site averaging 4,272 kg/ha and the Dawson, Georgia, site aver‐ aging 2,247 kg/ha. Pendimethalin extraction from soil samples indicated no differ‐ ence in herbicide recovery between winter fallow systems compared to treatments with cover crops. Weed control ratings taken at 21 and 45 days after planting (DAP) showed greater weed suppression for cover crop systems for an extended period of time when higher levels of cover crop biomass are present. Results of this experi‐ ment indicate the inclusion of cover crops in a conservation-tilled peanut system can be a successful alternative to winter fallow systems without reducing peanut yield or herbicide efficacy.

Sustainable agriculture requires the use of multiple, integrated weed management practi‐ ces to ensure long-term viability. A number of cultural, mechanical, and chemical weed control options can be utilized in a production system to reduce weed interference and safeguard crop yield. The dependence on one single weed control strategy may result in short-term success; however, long-term use can lead to multiple setbacks including poor soil health, reduced crop production, and increasing herbicide resistance. In turn, employing multiple weed control tactics simultaneously may prove difficult without previous knowl‐ edge as to how best to implement an integrated weed management system. To that end, this chapter is dedicated to illustrating successful herbicide use in conjunction with cover crops and their residues, practices proven not only to suppress weed germination and growth, but also to reduce soil erosion and water runoff and build soil organic matter and thus subse‐ qent productivity.

There has long been observed an inhibitive response by plant species to certain neighboring plants. The Greek philosopher and botanist, Theophrastus, noted this effect from cabbage as early as 300 BC (Willis 1985). Since that time, others have documented similar plant interactions. In 1937, Austrian botanist, Hans Molisch, described this phenomenon as allelopathy, which he determined to be the result of biochemical interactions between plants (Molisch 1937; Putnam and Duke 1978). When first described, allelopathy referred to both deleterious and beneficial interactions between species; since that time, however, allelopathy has been applied to only adverse plant interactions, rather than to both. First described by a Roman scholar during the first century, black walnut (Juglans nigra L.) has long served as the common example of allelopathic effects with its ability to inhibit growth of surrounding plants either through decaying leaves or nuts or from the tree itself (Weir et al. 2004). Researchers have continued to examine allelopathy and the mechanism for biochemical inhibition, which was initially scrutinized by many since differentiation between this effect and plant competition remained uncertain (Weir et al. 2004). Subsequent bioassays involving specific chemical compounds extracted from plants have confirmed that certain species do, in fact, produce biochemicals that can inhibit plant germination and growth in the absence of resource competition (Einhellig 1994a).

The use of smother crops or cover crop residue to suppress weed growth in agriculture is not a recent innovation; yet, only recently have smother, or cover crops, received considerable attention. The need to develop increasingly integrated pest management and sustainable food production systems has encouraged a greater interest to thoroughly evaluate effective utilization of cover crops in agricultural systems. In addition to providing a measure of weed control through physical obstruction and/or biochemical suppression, cover crops provide numerous environmental benefits that can promote long-term viability of farm lands (Jordan et al. 1999; Phatak et al. 2002; Yenish et al. 1996). Implementation of cover crops can reduce soil erosion, reduce runoff and improve water availability, improve soil structure, enhance soil organic matter, and increase diversity of soil biota (Bugg and Dutcher 1989; Reeves 1994; Wang et al. 2002a). These soil improvements, along with weed suppression capabilities, have made cover crops ideally suited for use in current and future sustainable agronomic systems.