Field experiments were conducted in 2004 and 2005 at Clemson, SC, and in 2004 at Clinton, NC, to quantify Palmer amaranth and large crabgrass growth and interference with plasticulture-grown bell pepper over multiple environments and develop models which can be used on a regional basis to effectively time removal of these weeds. Experiments at both locations consisted of an early and a late spring planting, with the crop and weeds planted alone and in combination. Daily maximum and minimum air temperatures were used to calculate growing degree days (GDD, base 10 C) accumulated following bell pepper transplanting and weed emergence. Linear and nonlinear empirical models were used to describe ht, canopy width, and biomass production as a function of accumulated GDD. Palmer amaranth reduced bell pepper fruit set as early as 6 wk after transplanting (WATP) (648 GDD), whereas large crabgrass did not significantly reduce fruit set until 8 WATP (864 GDD). Using the developed models and assuming Palmer amaranth and large crabgrass emergence on the day of bell pepper transplanting, Palmer amaranth was predicted to be the same ht as bell pepper at 287 GDD (20 cm tall) and large crabgrass the same ht as bell pepper at 580 GDD (34 cm tall).

Summary Experiments were conducted to compare growth characteristics, biomass production and glucosinolate content of seven autumn‐planted glucosinolate‐producing cover crops that were terminated the following spring. The control of Digitaria sanguinalis and Amaranthus palmeri following cover crop incorporation into soil was characterised and fruit yields of bell pepper transplanted into cover crop‐amended soil were determined. Differences in glucosinolate concentration and composition were noted between cover crop roots and shoots and among cover crops. Total biomass production by cover crops ranged from 103 g m−2 for garden cress to 894 g m−2 for Indian mustard (F‐E75), but cover crop biomass was not correlated with D. sanguinalis and A. palmeri control. D. sanguinalis and A. palmeri control in bell pepper varied by cover crop. D. sanguinalis control by cover crops ranged from 38% to 79%, and A. palmeri control was 23% to 48% at 4 weeks after transplanting (WATP) bell pepper in 2004. D. sanguinalis control was positively correlated with total glucosinolate production, but A. palmeri control was not. D. sanguinalis control in 2005 ranged from 0% to 38% at 2 WATP. In the absence of weeds, cover crops did not negatively affect fruit yields which were often higher than in the absence of a cover crop. Glucosinolate‐producing cover crops are not a stand‐alone weed management strategy, but some will provide early season control of D. sanguinalis and A. palmeri without having a negative effect on transplanted bell pepper.

Field experiments were conducted near Blackville, SC, and Tifton, GA, in 2004 and 2005, to evaluate the effect of wild radish and rye cover crops on weed control and sweet corn yield when used in conjunction with lower-than-recommended herbicide rates. Cover crop treatments included wild radish, rye, and no cover crop, alone and in conjunction with half and full rates of atrazine (0.84 and 1.68 kg ai ha−1) plusS-metolachlor (0.44 and 0.87 kg ai ha−1) applied before sweet corn emergence. Florida pusley, large crabgrass, spreading dayflower, ivyleaf morningglory, and wild radish infested the test sites. Wild radish and rye cover crops without herbicides reduced total weed density by 35 and 50%, respectively, at 4 wk after planting (WAP). Wild radish in conjunction with the full rate of atrazine plusS-metolachlor controlled Florida pusley, large crabgrass, and ivyleaf morningglory better than rye or no cover crop treated with a full herbicide rate in 2004 at Blackville. In 2005, at Blackville, weed control in sweet corn following wild radish cover crop plots alone was not different from that following rye. Wild radish or rye in conjunction with a half or full rate of atrazine andS-metolachlor controlled > 95% Florida pusley, wild radish, and large crabgrass in sweet corn at Tifton during both years. Ten glucosinolates, potential allelopathic compounds, were identified in wild radish, including glucoiberin, progoitrin, glucoraphanin, glucoraphenin, glucosinalbin, gluconapin, glucotropaeolin, glucoerucin, glucobrassicin, and gluconasturtin. Sweet corn yields at Blackville and Tifton following wild radish or rye cover crops were similar between the half and full rates of atrazine plusS-metolachlor. Sweet corn in wild radish or rye cover crop plots without herbicides produced less-marketable ears than herbicide-treated plots, indicating that a combination of cover crops and herbicides are required to optimize yields and to obtain desirable weed control.

Intensive selection pressure from repeated use of propanil and quinclorac led to the evolution of herbicide-resistant barnyardgrass biotypes. Twenty-two composite field samples were tested for level of resistance in 2002 and 2003, and field studies were conducted at the Rice Research and Extension Center, Stuttgart, AR, in 2002 and 2003 to evaluate alternative rice herbicides to control propanil-resistant (PR) and quinclorac-resistant (QR) barnyardgrass. Of the 22 composite samples, four were PR (30 to 40% control); four had a mixed population of PR, QR, and susceptible (S) barnyardgrass; and two had multiple resistance to propanil and quinclorac (P/QR), with control from propanil of 15 to 30% and control from quinclorac of 5 to 10%. ‘Wells’ rice was used where conventional herbicide programs were evaluated, and Clearfield rice ‘CL-161’ (imidazolinone-resistant) was used for herbicide programs involving imazethapyr. All PR and QR barnyardgrass were controlled > 90% by alternative herbicides, including all preemergence (PRE) and delayed preemergence (DPRE) treatments. By 56 d after emergence (DAE), cyhalofop or fenoxaprop applied to two- to three-leaf barnyardgrass (early postemergence [EPOST]), followed by (fb) a preflood application, controlled barnyardgrass > 93%. Pendimethalin controlled PR barnyardgrass 21 DAE, but not all season long. In contrast, imazethapyr in Clearfield rice controlled all grass weeds 100% all season long. Midpostemergence (MPOST) bispyribac application at the four- to five-leaf stage also provided season-long control of all barnyardgrass biotypes (> 88%, 56 DAE). Rice yields ranged from 5,300 to 5,700 kg ha−1in conventional weed-control treatments and from 2,800 to 5,000 kg ha−1in imazethapyr-treated plots. Nontreated plots yielded 1,500 kg ha−1.

. 2015. Weed control and crop tolerance of micro-encapsulated acetochlor applied sequentially in glyphosate-resistant soybean. Can. J. Plant Sci. 95: 973Á981. Acetochlor, an acetamide herbicide, has been used for many years for weed control in several crops, including soybean. Micro-encapsulated acetochlor has been recently registered for preplant (PP), pre-emergence (PRE), and post-emergence (POST) application in soybean in the United States. Information is not available regarding the sequential application of acetochlor for weed control and soybean tolerance. The objectives of this research were to determine the effect of application timing of micro-encapsulated acetochlor applied in tank-mixture with glyphosate in single or sequential applications for weed control in glyphosateresistant soybean, and to determine its impact on soybean injury and yields. Field experiments were conducted at Clay Center, Nebraska, in 2012, and at Waverly, Nebraska, in 2013. Acetochlor tank-mixed with glyphosate applied alone PP, PRE, or tank-mixed with flumioxazin, fomesafen, or sulfentrazone plus chlorimuron provided 99% control of common waterhemp, green foxtail, and velvetleaf at 15 d after planting (DAP); however, control declined to 540% at 100 DAP. Acetochlor tank-mixed with glyphosate applied PRE followed by early POST (V2 to V3 stage of soybean) or late POST (V4 to V5 stage) resulted in ]90% control of common waterhemp and green foxtail, reduced weed density to 52 plants m (2 and biomass to 512 g m , and resulted in soybean yields 3775 kg ha (1 . The sequential applications of glyphosate plus acetochlor applied PP followed by early POST or late POST resulted in equivalent weed control to the best herbicide combinations included in this study and soybean yield equivalent to the weed free control. Injury to soybean was B10% in each of the treatments evaluated. Micro-encapsulated acetochlor can be a good option for soybean growers for controlling grasses and small-seeded broadleaf weeds if applied in a PRE followed by POST herbicide program in tankmixture with herbicides of other modes of action. , avec pour re´sultat un rendement du soja supe´rieur a`3 775 kg par hectare. Les applications se´quentielles de glyphosate et d'ace´tochlor avant les semis, puis au de´but ou a`la fin de la leve´e assurent une lutte e´quivalente aux meilleures combinaisons d'herbicides examine´es dans le cadre de l'e´tude et de´bouchent sur un rendement en soja e´quivalent a`celui de la parcelle te´moin de´sherbe´e. Les traitements e´value´s causent moins de dix pour cent de dommages au soja. Les microcapsules d'ace´tochlor Abbreviations: AMATA, common waterhemp, Amaranthus rudis Sauer; ABUTH, green foxtail, Setaria viridis (L.) P. Beauv; DAP, days after planting; DBP, days before planting; POST, postemergence application; PP, preplant application; PRE, pre-emergence application; SETVI, velvetleaf, Abutilon theophrasti Medik Can. J. Plant Sci. (2015) 95: 973Á981