Sanjeev K. Bangarwa

Evaluation of Cereal and Brassicaceae Cover Crops in Conservation-Tillage, Enhanced, Glyphosate-Resistant Cotton

Abstract Research was conducted for 2 yr at Marianna, AR, to determine whether the fall-planted cover crops rye, wheat, turnip, and a blend of brown and white mustard (Caliente) would aid weed management programs in conservation-tilled, enhanced, glyphosate-resistant cotton. Wheat and rye easily were established both years and turnip and mustard blend stands were better in the second year. The cover crops alone were more suppressive of Palmer amaranth, pitted morningglory, and goosegrass in 2007 than in 2008. Rye was generally superior to wheat in suppressing the three evaluated weeds. Once herbicides were applied, there were seldom differences among cover crops for a particular herbicide program as a result of the highly efficacious herbicide programs. Cotton yields were not affected by wheat, rye, or the mustard blend, but yields were lowest in plots that followed turnip both years, possibly because of allelopathy. Integration of cover crops, especially cereals, into conservation-tilled, glyphosate-resistant cotton aided early-season weed management and could reduce the selection of glyphosate for herbicide resistance. Nomenclature: Goosegrass, Eleusine indica (L.) Gaertn. ELEIN; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; brown mustard, Brassica juncea (L.) Czern.; cotton, Gossypium hirsutum L; rye, Secale cereale L.; turnip, Brassica rapa L., wheat, Triticum aestivum L.; white mustard, Sinapis alba L

Glucosinolate and Isothiocyanate Production from Brassicaceae Cover Crops in a Plasticulture Production System

Brassicaceae cover crops are gaining attention as potential biofumigants for soil pest suppression because of their ability to release biologically active isothiocyanates (ITCs) and other compounds from hydrolysis of glucosinolates (GSLs). However, biofumigation potential of a Brassicaceae is related to its GSL and ITC profile and GSL to ITC conversion efficiency. Field and laboratory experiments were conducted to evaluate the biofumigation potential of seven Brassicaceae cover crops for weed control in plasticulture tomato and bell pepper. GSL concentration and composition varied among cover crops and between roots and shoots of each cover crop. Similar GSLs were produced in both years by roots or shoots of each cover crop, but GSL concentrations were variable between years. Total GSLs contributed to the soil by incorporation of Brassicaceae cover crop tissues were estimated between 47 to 452 nmol g−1 soil. Highest ITC concentration was detected in soil at 3 h after cover crop incorporation, and concentration decreased at later timings. GSL to ITC conversion efficiency ranged from 1 to 39%, with variation among cover crops and between years. No injury was observed in tomato and bell pepper transplanted 1 wk after cover crop incorporation, indicating the tolerance of tomato and pepper to ITCs released by the cover crops. Early-season yellow nutsedge control from Brassicaceae cover crops was ≤ 53% at 2 wk after transplanting and declined to ≤ 18% later in the season. This research demonstrates that Brassicaceae cover crops have marginal potential for early-season weed control and cannot be used as a weed control practice in commercial tomato and bell pepper production. Nomenclature: Yellow nutsedge, Cyperus esculentus L. CYPES; bell pepper, Capsicum annuum L. ‘Heritage’; tomato, Lycopersicon esculentum Mill. ‘Amelia’

Purple Nutsedge (Cyperus rotundus) Management in an Organic Production System

Abstract Research was initiated in March 2005 to test various integrated purple nutsedge management strategies over two growing seasons in an organic production system in which bell pepper was grown as a fall crop. Main plots consisted of integrated purple nutsedge management strategies from mid-March through July 2005 and 2006. The main-plot factors were (1) green polyethylene film, (2) clear polyethylene film, (3) turnip followed by (fb) green polyethylene film, (4) turnip fb clear polyethylene film, (5) tillage every 3 wk, and (6) fallow. Subplots consisted of hand-weeding, mulching with wheat straw, and no weeding following bell pepper transplanting in early August. Purple nutsedge tuber density was determined in March, August, and November each year. Viable tubers were categorized into three sizes: small (0.1 to 0.25 g), medium (0.26 to 0.50 g), and large (> 0.50 g). The initial tuber density averaged 500 small, 300 medium, and 110 large tubers m−2 in mid-March 2005 (910 total tubers m−2). Total tuber density increased to > 5,400 tubers m−2 in fallow, nonweeded plots by November 2006. Yearly tuber density remained relatively constant over the 2 yr when the fallow period was fb hand-weeding in the bell pepper crop. Density of large and medium tubers in the season-long management systems remained stable, whereas small tubers were prone to depletion over time. Frequent tillage or use of a polyethylene film with or without turnip resulted in a lower density of large tubers in November 2006 relative to fallow treatments, regardless of management intensity in bell pepper. The density of large tubers after 2 yr was similar among treatments involving frequent tillage or use of a polyethylene film with or without turnip, regardless of subplot treatment; this was also observed for medium tubers, but not for small tubers. All hand-weeded plots had comparable densities of small tubers, ranging from 25 to 194 viable tubers m−2. Intensive management involving frequent tillage or use of a translucent polyethylene film with or without turnip fb hand-weeding was not effective in eradicating purple nutsedge over two growing seasons. Purple nutsedge management costs calculated for each main-plot treatment revealed that use of a translucent polyethylene film alone was at least 4.5-fold more costly than frequent tillage. This research demonstrates that season-long management is essential to prevent purple nutsedge proliferation over time. Nomenclature: Purple nutsedge, Cyperus rotundus L. CYPRO; bell pepper, Capsicum annum L. ‘Heritage’; turnip, Brassica rapa L. ‘Seventop’.

Evaluation of Legume Cover Crops and Weed Control Programs in Conservation-Tillage, Enhanced Glyphosate-Resistant Cotton

Abstract Research was conducted at Marianna, AR, for 2 yr to determine whether hairy vetch and Austrian winter pea cover crops would aid weed management programs in conservation-tilled, enhanced glyphosate-resistant cotton. Both cover crops were easily established and produced rapid growth in early spring, with biomass production of 435 to 491 g m−2 by Austrian winter pea and 415 to 438 g m−2 by hairy vetch. The effect of cover crops on weed control was short-lived in both years, with herbicide programs being the major determinant of weed control and seed-cotton yield. Averaged over cover crops, seed-cotton yields when the initial in-crop glyphosate application was delayed to the four-node cotton stage were up to 710 kg ha−1 less than in a PRE herbicide program. In 1 of 2 yr, seed-cotton yields were greater in PRE-treated plots compared with a program where initial weed management was delayed to the one-leaf stage of cotton. As a result of rapid decay of hairy vetch and Austrian winter pea biomass following cotton planting and the lack of adequate Palmer amaranth, pitted morningglory, and goosegrass control in the absence of herbicides, it appears there may be minimal weed management benefits from the use of hairy vetch and Austrian winter pea in Midsouth cotton production. Nomenclature: Goosegrass, Eleusine indica (L.) Gaertn. ELEIN; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; Austrian winter pea, Pisum sativum L. ssp. arvense (L.) Poir.; cotton, Gossypium hirsutum L.; hairy vetch, Vicia villosa Roth.

Allyl Isothiocyanate: A Methyl Bromide Replacement in Polyethylene-Mulched Bell Pepper

Abstract Methyl bromide has been a key fumigant for broad-spectrum weed control in polyethylene-mulched bell pepper. However, the ozone-depleting nature of methyl bromide has led to its scheduled phaseout from U.S. agriculture. Thus, an effective alternative to methyl bromide is needed. Field trials were conducted in 2007 and 2009 to evaluate the crop response and weed control efficacy of allyl isothiocyanate (ITC) in polyethylene-mulched bell pepper. The experiment included various combinations of two mulch types (low density polyethylene [LDPE] and virtually impermeable film [VIF] mulch) and six rates of allyl isothiocyanate (0, 15, 75, 150, 750, 1,500 kg ha−1). Additionally, a standard treatment of methyl bromide/chloropicrin (67 ∶ 33%) at 390 kg ha−1 under LDPE mulch was included for comparison. Bell pepper injury was < 3% in all treatments, except 11% injury at 1,500 kg ha−1 allyl isothiocyanate under VIF mulch at 2 wk after transplanting (WATP). VIF mulch did not provide additional weed control and marketable pepper yield over LDPE mulch. Allyl isothiocyanate at 932 (± 127) kg ha−1 controlled yellow nutsedge (90%), Palmer amaranth (97%), and large crabgrass (92%) through 6 WATP and maintained the marketable yield equivalent to methyl bromide treatment. This research demonstrates that allyl ITC under an LDPE mulch can serve as a potential alternative to methyl bromide for weed control in polyethylene-mulched bell pepper. Nomenclature: Allyl isothiocyanate; methyl bromide; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; yellow nutsedge, Cyperus esculentus L. CYPES; bell pepper, Capsicum annuum L. ‘Heritage’

Integration of a Brassicaceae Cover Crop with Herbicides in Plasticulture Tomato

Abstract Weeds are a major constraint in tomato production, especially in the absence of methyl bromide. Field trials were conducted in 2006 and 2007 to evaluate the integrated use of a mustard ‘Caliente’ (a blend of brown and white mustard) cover crop with one-half and full rate PRE/POST herbicides for weed control and crop response in polyethylene-mulched tomato. Caliente was flail mowed and incorporated into the soil prior to forming beds. PRE herbicides were applied under polyethylene mulch, and POST herbicides were sprayed over the top of tomato. Full rates for S-metolachlor, halosulfuron, and trifloxysulfuron were 1,600, 27, and 7.9 g ai/ha, respectively. Caliente had no effect on weed control or tomato injury and yield. Except for large crabgrass control and tomato injury and yield, only the main effect of herbicide selection and application rate affected these parameters. Tomato injury was minimal (< 6%) from PRE- and POST-applied herbicides. S-metolachlor applied PRE provided 66% purple nutsedge, 67% yellow nutsedge, and 77% Palmer amaranth control at 4 wk after transplanting (WATP). S-metolachlor–treated plots at the full rate produced the highest marketable fruit yield among herbicide treatments, with jumbo fruit yield equivalent to the hand-weeded treatment. Trifloxysulfuron was the best POST-applied herbicide based on marketable yield and weed control. POST-applied trifloxysulfuron provided 41% purple nutsedge, 58% yellow nutsedge, and 55% Palmer amaranth control at 8 to 9 WATP. Halosulfuron applied PRE controlled purple and yellow nutsedge 70 and 78%, respectively, at 4 WATP, and POST-applied halosulfuron controlled purple nutsedge 74% and yellow nutsedge 78% at 8 to 9 WATP. Halosulfuron applied either PRE or POST failed to control Palmer amaranth and large crabgrass. Greater weed control and marketable tomato yield were achieved with full rates of herbicides. This research demonstrates no additional advantage of Caliente mustard when used with herbicides in tomato. None of the PRE or POST herbicides applied alone were sufficient to maintain season-long, broad-spectrum weed control and optimum marketable yield in tomato. Therefore, integration of PRE and POST herbicides at full rates is suggested. Nomenclature: Halosulfuron; S-metolachlor; trifloxysulfuron; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; purple nutsedge, Cyperus rotundus L. CYPRO; yellow nutsedge, Cyperus esculentus L. CYPES; brown mustard, Brassica juncea L.; tomato, Lycopersicon esculentum Mill. ‘Amelia’; white mustard, Sinapis alba L.

Weed Management in a Furrow-Irrigated Imidazolinone-Resistant Hybrid Rice Production System

Abstract Research was conducted in 2007 and 2008 to evaluate weed-control options in an imazethapyr-resistant rice production system. Raised beds were formed, and imidazolinone-resistant hybrid rice ‘CL 730’ was drill-seeded on beds. Five herbicide programs applied up to the four- to six-leaf stage of rice were evaluated with and without additional “as-needed” herbicide at later stages. All the herbicide combinations and as-needed herbicides tested in this research were labeled for rice, and only minor transient injury (< 5%) was initially observed. Weeds emerged throughout the growing season, and as-needed herbicides were applied after the four- to six-leaf stage of rice to control these late-emerging weeds and weeds not effectively controlled with earlier applications, primarily Palmer amaranth. Most of the Palmer amaranth at this site was insensitive to imazethapyr (possibly acetolactate synthase resistant). Therefore, application of as-needed herbicides with different modes of action, such as 2,4-D, were used to improve Palmer amaranth control. Rice yields were often numerically higher in plots that received additional herbicide after the six-leaf stage of rice, but yields were not significantly improved. Nomenclature: Imazethapyr; 2,4-D; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; rice, Oryza sativa L. ‘CL 730’ ORYSA

Yellow Nutsedge Interference in Polyethylene-Mulched Bell Pepper as Influenced by Turnip Soil Amendment

Abstract Methyl bromide has been widely used as a broad-spectrum fumigant for weed control in polyethylene-mulched bell pepper. However, because of environmental hazards, the phase-out of methyl bromide requires development of alternative weed management strategies. Brassicaceae plants produce glucosinolates which are hydrolyzed to toxic isothiocyanates following tissue decomposition, and therefore can be used as a cultural strategy. Field experiments were conducted in 2007 and 2009 to study the influence of soil amendment (‘Seventop’ turnip cover crop vs. fallow) and the effect of initially planted yellow nutsedge tuber density (0, 50, and 100 tubers m−2) on the interference of yellow nutsedge in raised-bed polyethylene-mulched bell pepper. Total glucosinolate production by the turnip cover crop was 12,635 and 22,845 µmol m−2 in 2007 and 2009, respectively, and was mainly contributed by shoots. In general, soil amendment with the turnip cover crop was neither effective in reducing yellow nutsedge growth and tuber production nor in improving bell pepper growth and yield compared to fallow plots at any initial tuber density. Averaged over cover crops, increasing initial tuber density from 50 to 100 tubers m−2 increased yellow nutsedge shoot density, shoot dry weight, and tuber production ≥ 1.4 times. However, increased tuber density had minimal impact on yellow nutsedge height and canopy width. Compared to weed-free plots, interference of yellow nutsedge reduced bell pepper dry weight and marketable yield ≥ 42 and ≥ 47%, respectively. However, bell pepper dry weight and yield reduction from 50 and 100 tubers m−2 were not different. Light was the major resource for which yellow nutsedge competed with bell pepper. Yellow nutsedge shoots grown from initially planted 50 and 100 tubers m−2 caused up to 48 and 67% light interception in bell pepper, respectively. It is concluded that yellow nutsedge interference from initial densities of 50 and 100 tubers m−2 are equally effective in reducing bell pepper yield and that soil biofumigation with turnip is not a viable management option for yellow nutsedge at these densities. Nomenclature: Yellow nutsedge, Cyperus esculentus L. CYPES; bell pepper, Capsicum annuum L. ‘Heritage’; turnip, Brassica rapa L. ‘Seventop’.

Purple Nutsedge Control with Allyl Isothiocyanate under Virtually Impermeable Film Mulch

Abstract Nutsedge control is challenging in commercial vegetable production in the absence of methyl bromide, and therefore, an effective alternative is needed. This study investigated allyl isothiocyanate (ITC) as a methyl bromide alternative for purple nutsedge control under polyethylene-mulch. Greenhouse experiments were conducted to compare the retention of allyl ITC in treated soil (3,000 nmol g−1) under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches. Field experiments were conducted to evaluate the effectiveness of allyl ITC (6 rates: 0, 15, 75, 150, 750, 1500 kg ai ha−1) under VIF mulch against purple nutsedge. Additionally, a standard treatment of methyl bromide+chloropicrin (67 : 33%) at 390 kg ai ha−1 under LDPE mulch was included for comparison. In the greenhouse experiment, the predicted half-life of allyl ITC under LDPE and VIF mulch was 0.15 and 0.59 d, respectively. In the field experiment, it was predicted that allyl ITC at 1,240 and 1,097 kg ha−1 under VIF mulch is required to control purple nutsedge shoot and tubers equivalent to methyl bromide + chloropicrin at 4 wk after treatment (WAT). It is concluded that allyl ITC under VIF mulch would need to be applied at 2.8 to 3.2 times the standard treatment of methyl bromide + chloropicrin under LDPE mulch for commercially acceptable purple nutsedge control. Nomenclature: Allyl isothiocyanate; purple nutsedge; Cyperus rotundus L. CYPRO. Resumen El control de Cyperus rotundus es un reto en la producción comercial de vegetales en ausencia de methyl bromide, y por esto se necesita una alternativa efectiva. Este estudio investigó el uso de allyl isothiocyanate (ITC) como alternativa al methyl bromide para el control de C. rotundus bajo cobertura de polyethylene. Se realizaron experimentos de invernadero para comparar la retención de allyl ITC en suelos tratados (3,000 nmol g−1) bajo coberturas de polyethylene de baja densidad (LDPE) y de láminas virtualmente impermeables (VIF). Se realizaron experimentos de campo para evaluar la efectividad contra C. rotundus de allyl ITC (6 dosis: 0, 15, 75, 150, 1500 kg ai ha−1) bajo cobertura VIF. Adicionalmente, se incluyó un tratamiento estándar de methyl bromide + chloropicrin (67:33%) a 390 kg ai ha−1 bajo cobertura LDPE para fines de comparación. En el experimento de invernadero, la vida media predicha de allyl ITC bajo coberturas de LDPE y VIF fue 0.15 y 0.59 d, respectivamente. En el experimento de campo, se predijo que se requiere allyl ITC a 1,240 y 1,097 kg ha−1 bajo cobertura VIF para controlar la parte aérea y los tubérculos de C. rotundus a niveles equivalentes a methyl bromide + chloropicrin a 4 semanas después del tratamiento (WAT). Se concluyó que allyl ITC bajo cobertura VIF debería ser aplicado de 2.8 a 3.2 veces el tratamiento estándar de methyl bromide + chloropicrin bajo cobertura LDPE para controlar C. rotundus a niveles comercialmente aceptables.

Allyl Isothiocyanate as a Methyl Bromide Alternative for Weed Management in Polyethylene-Mulched Tomato

Abstract Methyl bromide has been widely used for weed control in polyethylene-mulched tomato production. With the phaseout of methyl bromide in the United States, an effective alternative is needed. Field experiments were conducted in 2007 and 2009 to determine if allyl isothiocyanate (ITC) would provide substantive weed control in tomato along with crop tolerance under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulch. Treatment factors included two mulch types (LDPE and VIF) and six rates of allyl ITC (0, 15, 75, 150, 750, 1,500 kg ha−1). A standard treatment of methyl bromide ∶ chloropicrin (67 ∶ 33%) at 390 kg ha−1 under LDPE mulch was also established. Allyl ITC was broadcast applied and incorporated in soil before forming raised beds and laying plastic mulch. Tomatoes were transplanted 3 wk after applying allyl ITC or methyl bromide treatments. Tomato injury was ≤ 8% in all treatments at 2 wk after transplanting (WATP). Allyl ITC at 913 (± 191) kg ha−1 was required to control yellow nutsedge, Palmer amaranth, and large crabgrass equivalent to methyl bromide at 6 WATP and maintain marketable tomato yield equivalent to methyl bromide treatment. VIF mulch was not effective in increasing weed control or improving the marketable yield of tomato over LDPE mulch. This research demonstrates that allyl ITC under an LDPE mulch can have a practical application for weed control in polyethylene-mulched tomato in the absence of methyl bromide. Nomenclature: Allyl isothiocyanate; methyl bromide; large crabgrass, Digitaria sanguinalis (L) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; yellow nutsedge, Cyperus esculentus L. CYPES; tomato, Lycopersicon esculentum Mill. ‘Amelia’.