Sequential Herbicide Applications Research Articles

Weed Dynamics and Dry Seeded Rice Productivity in Relation to Sowing Time, Variety and Weed Control in Sub-Tropical and Semi-arid Region of Punjab

A field experiment was conducted at Ludhiana, during kharif 2008 to study effects of sowing time, variety and weed control on weed dynamics and productivity of dry/direct seeded rice. Six sowing dates (dry seeding on 0 (June 5), 7, 14, 21, 28 days after nursery sowing (DANS) and transplanting 28 DANS) in main plots and combinations of two varieties (PR 115 and PAU 201) and two weed control treatments (3 hand hoeings at 20, 40, 60 days and pendimethalin 0.75 kg pre-emergence followed by bispyribac-sodium 0.030 kg/ha as post emergence) in sub plots were evaluated in a split plot design with three replications. Transplanted crop recorded the lower population of all weeds sp and similar in dry seeding on 0 DANS. Population of all weed sp was lower under early sowing of crop on 0, 7 and 14 DANS as compared to delayed sowings. Population of Echinochloa sp, Leptochloa chinensis, Digitaria sanguinalis, Cyperus rotundus and Cyperus iria did not vary among seeding dates; Ammania baccifera and Caesulia axillaris intensity was significantly higher in 21 and 28 DANS as compared to early seeding dates. Weed density did not vary among rice varieties. Sequential application of herbicides effectively controlled Echinochloa sp and D sanguinalis while control of Eragrostis sp and L chinensis was very poor. Herbicides control broad leaf weeds and sedges except Cyperus rotundus. Transplanted crop recorded the highest rice grain yield and was at par to dry seeding 0 DANS but significantly higher than dry seeding on later dates. The grain yield of transplanted crop was 11.9, 22.1, 20.8, 41.7 and 71.4% higher as compared to dry seeding on 0, 7, 14, 21 and 28 DANS, respectively. Rice varieties recorded similar grain yield. Three hand hoeings gave significantly higher grain yield than herbicides. Rice seeding directly on 0, 7 and 14 DANS produced similar grain yield under herbicides and three hand hoeings; further delay in seeding significantly reduced grain yield under herbicides as compared to hand hoeings.

Herbicide Options for Weed Control in Dry-Seeded Aromatic Rice in India

The looming water crisis and shortage of labor during rice transplanting in northwest India have led researchers to develop alternative methods to transition away from puddled transplanted rice. In this context, dry-seeded rice (DSR) is emerging as an efficient production technology to replace puddled transplanted rice. Weeds, however, are the main biological constraints to its success. A study comprising 12 treatments was conducted to evaluate the efficacy of PRE (pendimethalin and pyrazosulfuron) and POST herbicides (bispyribac, penoxsulam, and azimsulfuron) applied either alone or in a sequence for weed control in dry-seeded fine rice cv. ‘Punjab Mehak 1’. Results indicated that the single application of pendimethalin (750 g ai ha−1) PRE, pyrazosulfuron (15 g ai ha−1) PRE, bispyribac-sodium (25 g ai ha−1) POST, penoxsulam (25 g ai ha−1) POST, and azimsulfuron (20 g ai ha−1) POST reduced total weed biomass by 75, 68, 73, 70, and 72%, respectively, compared with the nontreated control at flowering stage of the crop. Azimsulfuron POST and pyrazosulfuron PRE proved effective against purple nutsedge and crowfootgrass, respectively. Chinese sprangletop, large crabgrass, and junglerice were effectively controlled with pendimethalin PRE. POST application of bispyribac-sodium and penoxsulam provided effective control of rice flatsedge. Compared to the nontreated control, grain yield following the single application of pendimethalin PRE, pyrazosulfuron PRE, bispyribac-sodium POST, penoxsulam POST, and azimsulfuron POST increased by 149, 119, 138, 124, and 144%, respectively. The sequential application of herbicides proved better than single applications. The lowest weed biomass was observed with the sequential application of pendimethalin PRE followed by azimsulfuron POST, and rice yielded 228% more than the nontreated control following this treatment. The results of this study are important for farmers growing DSR in making decisions regarding the application of POST herbicides, according to existing weed flora in the field.

Confirmation and Management of Common Ragweed (Ambrosia artemisiifolia) Resistant to Diclosulam

Selection for biotypes of common ragweed expressing resistance to acetolactate synthase (ALS)–inhibiting herbicides has increased in North Carolina and surrounding states. Research was conducted in North Carolina to confirm common ragweed resistance to diclosulam and to compare herbicide programs designed to control ALS-resistant common ragweed in corn, cotton, peanut, and soybean. In greenhouse experiments, 50% inhibition values following POST application of diclosulam for mortality of plants, visual estimates for percentage of control, and percentage of reduction in plant fresh weight were 557- to 653-fold higher for the suspected ALS-resistant biotype compared with a suspected ALS-susceptible biotype. Herbicides with different modes of action, including atrazine, dicamba, and glyphosate in corn; fomesafen, glyphosate, MSMA, and prometryn in cotton; bentazon, flumioxazin, and lactofen in peanut; and flumioxazin, glyphosate, and lactofen in soybean controlled common ragweed more effectively than programs relying on cloransulam-methyl (soybean), diclosulam (peanut), thifensulfuron (corn), and trifloxysulfuron (cotton), which typically control nonresistant common ragweed populations. Applying tank-mix or sequential applications of herbicides with different modes of action was effective in controlling ALS-resistant common ragweed in all crops.

Sequential Postemergence Applications for the Control of Khakiweed in Bermudagrass Turf

Khakiweed (Alternanthera pungens Kunth) response to single and sequential herbicide applications was evaluated during the summer of 2009 and 2010 in Texas. No bermudagrass phytotoxicity was observed throughout the length of each trial regardless of herbicide treatment. Carfentrazone at 0.034 kg a.i./ha, metsulfuron + carfentrazone at 0.021 + 0.034 kg a.i./ha, and trifloxysulfuron + carfentrazone at 0.018 + 0.034 kg a.i./ha exhibited 74% to 85% khakiweed control 2 weeks after initial treatment (WAIT) regardless of application regime. Control with carfentrazone (0.017 kg a.i./ha) was only 63% to 65% 2 WAIT regardless of application regime. Metsulfuron and trifloxysulfuron treatments exhibited 54% or less khakiweed control 2 WAIT regardless of rate. Six weeks later (8 WAIT), sequential applications of metsulfuron exhibited 98% control regardless of rate, whereas control with single applications was 79% to 87%. Sequential applications of trifloxysulfuron exhibited 86% to 88% khakiweed control 8 WAIT regardless of rate, whereas single applications exhibited 47% or less control. Carfentrazone treatments exhibited 5% or less control regardless of rate or sequential application 8 WAIT. Tank-mixing metsulfuron or trifloxysulfuron with carfentrazone did not improve control 8 WAIT compared with either sulfonylurea herbicide applied alone. Although initial khakiweed injury was observed in all treatments, effective long-term control was difficult to achieve. Excellent control (95% to 97%) was exhibited by sequential metsulfuron applications 12 WAIT regardless of rate. Sequential applications of trifloxysulfuron (0.018 or 0.028 kg a.i./ha) and single applications of metsulfuron at 0.042 kg a.i./ha exhibited moderate khakiweed control (75% to 80%) 12 WAIT. All other treatments exhibited 57% or less khakiweed control 12 WAIT. Efficacy of sequential metsulfuron applications is a strong incentive for its adoption over trifloxysulfuron applications for the control of khakiweed in bermudagrass turf.

Weed Control, Environmental Impact and Profitability of Weed Management Strategies in Glyphosate-Resistant Corn

Eleven field trials were conducted over a three-year period (2006-2008) at three locations in southwestern Ontario, Canada to evaluate the effect of various weed management strategies in glyphosate-tolerant corn on weed control, crop injury, corn yield, environmental impact and profit margin. No visible injury resulted from the herbicide treatments evaluated. Overall, the effect of all factors assessed were location specific. By 56 days after treatment, depending on location, glyphosate applied at the 7 - 8 leaf stage (LPOST), preemergence (PRE) herbicides followed by (fb) glyphosate LPOST and sequential glyphosate applications (EPOST (3 - 4 leaf stage) followed by LPOST) provided more consistent control of annual broadleaf weeds and annual grasses compared to glyphosate applied alone EPOST. Weed control at 56 days after treatment was lower when glyphosate was applied alone LPOST compared to sequential applications of glyphosate or PRE herbicides fb glyphosate. There were no differences in corn yield among the sequential programs evaluated; however, a yield benefit was found when a sequential program was used compared to glyphosate applied alone LPOST. Among the sequential programs the lowest environmental impact was isoxaflutole/atrazine fb glyphosate. The lowest profit margins were associated with atrazine, S-metolachlor/atrazine/benoxacor, dicamba/atrazine and glyphosate LPOST treatments compared to all other treatments. Overall, profit margins tended to be somewhat higher for treatments that included glyphosate applications. Based on these results, the most efficacious and profitable weed management program in corn was a sequential application of glyphosate; however, isoxaflutole/atrazine fb glyphosate was the treatment with the lowest environmental risk while also adding glyphosate stewardship benefits.

Control of Rattail Fescue (Vulpia Myuros) in Winter Wheat

Rattail fescue, a winter annual grass weed, has been increasing in Pacific Northwest (PNW) dryland cereal producing areas. Although rattail fescue is not a new weed species in the PNW, its incidence is expanding rapidly in circumstances where soil disturbances are minimized such as in direct seed systems. Options for effective rattail fescue control in winter wheat cropping systems have not been adequately investigated and need to be developed. Rattail fescue control with herbicide treatments was investigated in imidazolinone-resistant winter wheat using imazamox and other herbicides. Across multiple sites and two growing seasons, crop injury from herbicide treatments was minor to negligible with some exceptions. Treatments containing imazamox or mesosulfuron produced minor, transient winter wheat crop injury at some locations in some years. With the exception of flufenacet applied preemergence (PRE), control of rattail fescue in wheat was variable with single herbicide applications, but improved with sequential herbicide treatments. Rattail fescue biomass was greatly reduced by several treatments especially those containing flufenacet or from sequential herbicide application. Crop yield varied among sites due to growing season precipitation, and in some cases from rattail fescue control or herbicide related crop injury.Nomenclature: diuron, flufenacet, imazamox, mesosulfuron, pendimethalin, sulfosulfuron, rattail fescue, Vulpia myuros (L.) K.C. Gmel. VLPMY, winter wheat, Triticum aestivum L. ‘ClearFirst’®

History and Management of Herbicide-resistant Barnyardgrass (Echinochloa Crus-galli) in Arkansas Rice

Arkansas has been the leading state in rice production in the United States for many years. Barnyardgrass is the dominant weed in Arkansas rice. Propanil was the first highly effective herbicide for weed control in rice and has been used in Arkansas since 1959 as the primary herbicide for rice weed control. By 1989, its continual use led to the development of propanil-resistant barnyardgrass, which had spread to 16 of the 38 rice-producing counties in Arkansas by 1992. Arkansas rice growers are dependent on herbicides for the control of weeds in this drill-seeded crop. The residual herbicides thiobencarb, molinate, and pendimethalin mixed with propanil applied early postemergence improved control of propanilresistant barnyardgrass. But it was quinclorac, introduced in 1992, that became the real replacement treatment for propanil-resistant barnyardgrass. Then in 1999, a barnyardgrass biotype with resistance to both quinclorac and propanil was confirmed in Craighead County, Arkansas. Additionally, problems with quinclorac drift to other crops, especially tomato, led to restrictions on application of quinclorac in Arkansas by 1994. Fortunately, alternative herbicides for barnyardgrass control were developed, and clomazone was introduced in 2000. Clomazone is currently the standard herbicide for annual grasses in rice, including barnyardgrass. Herbicides recently developed for rice allow a broad range of options for a resistance management program, based on rotational and sequential herbicide applications. These include fenoxaprop and cyhalofop (both acetyl-CoA carboxylase [ACCase] inhibitors), bispyribac and penoxsulam (acetolactate synthase [ALS] inhibitors), and imazethapyr and imazamox (also ALS inhibitors for imidazolinone-resistant rice). From a global standpoint, there is considerable evidence that barnyardgrass has the propensity to develop resistance to most of these herbicide groups. Therefore, efforts to manage and monitor for herbicide resistance in this species need to be diligently continued. Research on nonchemical options is in progress utilizing weed-suppressive rice breeding lines to control barnyardgrass. Nomenclature: 2,6-bis[(4,6-dimethoxy-2-pyrimidinyl)oxy]benzoic acid, proposed common name bispyribac-sodium; clomazone; cyhalofop; fenoxaprop; imazamox; imazethapyr; molinate; pendimethalin; {2-(2,2-difluoroethoxy)-6(trifluoromethyl-N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyrimidin-2-yl))benzenesulfonamide}, proposed common name penoxsulam; propanil; quinclorac; thiobencarb; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; rice, Oryza sativa L.; tomato, Solanum lycopersicum L.

Management Strategies for Herbicide-resistant Weed Populations in Australian Dryland Crop Production Systems

In most world crop-production areas, the evolution of herbicide-resistant weeds is becoming a major issue. This problem has become most severe across the Australian dryland crop-production region, where herbicide-resistant weed populations are threatening crop-production profitability and sustainability across 20 million ha. Widespread herbicide resistance has forced changes in agronomic and herbicide practices. This problem is particularly evident in Western Australia, where the frequency and distribution of herbicide-resistant weed populations appear to be greater than anywhere else in the world. Judicious use of herbicide mixtures and rotations can reduce the selection pressure for evolved resistance to any one specific herbicide. Additionally, agronomic practices, such as the double knockdown (preseeding sequential application of nonselective herbicides), increased seeding rates, and targeting of weed seed production to prevent seedbank inputs, are needed to reduce the selection pressure on all herbicides by reducing in-crop weed populations. However, these techniques are not without problems or limitations, and their weed control efficacy is inferior to that of most in-crop selective herbicides. The adoption by Australian farmers of the current limited technology is clear evidence of the value placed on the use of these alternate crop weed-control practices. The continued evolution of herbicide resistance more than justifies continuing research and development efforts to produce integrated strategies and smarter herbicide use so as to achieve sustainable weed management.

Control Strategies for Common Dandelion (Taraxacum officinale) in No-Tillage Cropping Systems

Common dandelion has developed into a troublesome agronomic weed for no-tillage corn and soybean producers in Michigan and throughout the north central region of the United States. Field experiments were conducted on established populations of common dandelion in 2001 to 2002 and 2002 to 2003 to evaluate the effect of preplant and sequential herbicide applications on established populations of common dandelion. Preplant treatments of glyphosate or 2,4-D ester were applied early fall, late fall, early spring, and late spring. For both glyphosate and 2,4-D ester, the fall applications were more effective than the spring applications. Glyphosate at 840 gae/ha was more effective than 2,4-D ester at 1,120 gae/ha at each application timing. A single application of glyphosate or 2,4-D ester applied either in the fall or spring did not provide season-long control of common dandelion. Sequential treatments of glyphosate following preplant applications of either glyphosate or 2,4-D ester provided season-long control of common dandelion.

Management of Amaranthus rudis S. in glyphosate-resistant corn ( Zea mays L.) and soybean ( Glycine max L. Merr.)

Field studies were established at two locations in Missouri to determine Amaranthus rudius (common waterhemp) control by single or multiple pre-emergence and/or postemergence herbicide strategies in glyphosate-resistant corn and soybean. The corn study assessed five herbicide strategies: pre-emergence alone; mid-postemergence alone; early postemergence followed by mid-postemergence; pre-emergence followed by mid-postemergence without glyphosate; and pre-emergence followed by glyphosate mid-postemergence. The soybean study assessed four herbicide strategies: mid-postemergence alone; early postemergence followed by mid-postemergence; pre-emergence followed by glyphosate mid-postemergence; and pre-emergence followed by mid-postemergence without glyphosate. In corn, pre-emergence herbicides suppressed A. rudius growth and development 7–34 days longer, compared to the untreated control. The strategies with single herbicide applications provided 21–99% control of A. rudius, while the multiple application strategies provided 84–100% control of A. rudius. In soybean, the presence of pre-emergence herbicides suppressed A. rudius emergence and growth for 7–31 days, compared to treatments with no herbicide application. A single herbicide application provided 69–100% control of A. rudius, and the multiple application strategies were more consistent with 77–100% control. Effective season-long management of A. rudius in glyphosate-resistant corn and soybean should include sequential herbicide applications.

Interação entre sistemas de manejo e de controle de plantas daninhas em pós-emergência afetando o desenvolvimento e a produtividade da soja

Este trabalho teve por objetivo avaliar a interação entre sistemas de manejo e de controle de plantas daninhas em pós-emergência na cultura da soja, cv. BRS 154, em plantio direto em áreas com expressiva cobertura vegetal. Foram avaliados 13 tratamentos, compostos por um esquema fatorial (3x4)+1. Os fatores eram constituídos por três sistemas de manejo (dessecação imediatamente antes da semeadura, dessecação 10 dias antes da semeadura e dessecação antecipada, sendo esta composta por duas aplicações de manejo, a primeira 24 dias antes da semeadura e a segunda na data da semeadura), quatro formas de controle das plantas daninhas após a emergência da cultura (nenhum controle, capina manual das parcelas, aplicação única e aplicação seqüencial de herbicidas) e um tratamento adicional, constituído por uma testemunha absoluta (sem manejo e sem controle em pós-emergência). Embora a dessecação nos diferentes sistemas de manejo tenha sido eficiente, a antecipação da dessecação no manejo antecipado favoreceu a emergência e o desenvolvimento inicial da soja, proporcionando maiores ganhos de produtividade, nas condições de infestação apresentadas. O sistema de manejo afetou também o fluxo de emergência das plantas daninhas após a emergência da soja, com menos reinfestações no sistema de manejo antecipado, em função do controle dos fluxos iniciais proporcionado pela segunda aplicação deste sistema de manejo. O manejo realizado na data da semeadura e dez dias antes prejudicou o desenvolvimento da soja, resultando em menor produtividade. O manejo antecipado, quando comparado aos demais sistemas, proporcionou maior produtividade da soja.

Efeito de diferentes formulações de glifosate no manejo de plantas daninhas na cultura do cafeeiro

An study was carried out in a commercial one-year-old coffee crop following undercutting, aiming to evaluate the efficiency of different glyphosate salts, that is, potassic, isopropylamine and diamonium in managing weeds in coffee tree crop. The treatments consisted of 10 different managements corresponding to three sequential applications of herbicides, that could be performed with or without the same products. The control efficiency of the weed species were verified at 15, 30, 41, 58, 75, 84, 116 and 140 days after beginning the management (DAM). The management with sequential application of 720 g.ha-1 ac.eq. of potassic salt glyphosate and diamonium salt glyphosate, as well as the management with diuron and paraquat (150 + 300 g.ha-1 a.i., respectively, with added Agral 0.1% v/v) at the third application or at the second and third applications, with the second application performed at 41 days after the first application, and the third one at 54 days after the second application, were all efficient in controlling Brachiaria plantaginea and Bidens pilosa, but inefficient in controlling Euphorbia heterophylla and Commelina diffusa. The management with 720 g.ha-1 ac.eq. of isopropylamine salt glyphosate at the first application, and latter at the second and third ones with the tank mixture of 720 g.ha-1 ac.eq. of isopropylamine salt glyphosate + 30 g.ha-1 a.i. of carfentrazone-ethyl, showed to be effective in controlling Brachiaria plantaginea and Bidens pilosa from 7 to 140 DAM and the Commelina diffusa from 58 to 140 DAM. However, Euphorbia heterophylla were moderately controlled over this period.

The Response of Potted Orchids to Sequential Postemergence Herbicide Applications in Hawaii

Two experiment were conducted in 1999 and 2000 to determine the response of orchid cultivars, grown as potted plants, to postemergence herbicides. In a film covered commercial nursery in Pahoa, four orchid cultivars were exposed to five sequential herbicide applications. The cultivars used were: Emma White (Dendrobium), Wildcat Blood Ruby, Volcano Queen (both Oncidiums), and SuFun Beauty (Vanda). The herbicides evaluated in this experiment were diuron and clopyralid applied at the anticipated (1×), 2×, and 4× use rate. Spray applications were made directly to crop foliage using a spray to wet application. The first application was applied on 11 Nov. 1999 with sequential applications made at 20-, 208-, 73-, and 69-day intervals for a total of five sprays. Orchid dry weight accumulation was not significantly reduced and all cultivars responded in a similar way. “Emma White” was the only cultivar to express abnormal growth to clopyralid in the form of J-shaped flower spikes and deformed flowers. The other three cultivars did not show any noticeable injury in response to any of the spray applications. A follow up experiment was conducted on the dry leeward coast of Oahu in a commercial saran house. Diuron was the only herbicide evaluated at one and four times the anticipated labeled use rate. The first application was made on 27 Apr. 2000 with sequential applications made at 50-, 21-, 70-, and 66-day intervals for a total of five sprays. The orchids selected for this experiment included nine Dendrobiums and one Vanda. Treatments were made directly to plant foliage using a spray to wet application. Whole plant dry weight accumulation of the 10 cultivars responded in a similar way and no herbicide treatment reduced dry weight accumulation in comparison to untreated plants.

Integration of cover crops with postemergence herbicides in no-till corn and soybean

The integration of cover crops with selected postemergence herbicides was evaluated on the basis of weed control and grain yields in no-till soybean and corn. Soybean was planted into wheat residue, whereas corn was planted into hairy vetch residue. Full, half, and quarter rates and sequential herbicide applications were made. The wheat cover crop did not increase weed suppression but increased soybean grain yields. Half rates of thifensulfuron plus quizalofop-P as single or split applications were as effective as full rates in reducing weed weight in soybean. Soybean grain yields were similar in the half- and full-rate treatments in 1994, but yield was highest in the full-rate treatment in 1995. The hairy vetch cover crop did not increase weed suppression but lowered corn stands and grain yields in 1995 and enhanced corn grain yields in 1996. Full, half, and quarter rates (1996 only) of nicosulfuron plus primisulfuron were equally effective in reducing weed weight. Corn grain yields were similar at all herbicide rates in 1995 but were inversely related to herbicide rate in 1996. Split herbicide applications did not improve weed suppression over single applications of the same herbicide rate in either crop. Results indicate that cover crops can improve crop productivity and reduced rates of environmentally benign herbicides can minimize the herbicide requirements in no-till corn and soybean.

GENE FLOW IN COMMERCIAL FIELDS OF HERBICIDE‐RESISTANT CANOLA (BRASSICA NAPUS)

Multiple herbicide resistance to glyphosate, glufosinate, bromoxynil, or imidazolinone in volunteer plants of canola (Brassica napus) has been attributed to pollen flow among cultivars with different resistance traits. A study was conducted in Saskatchewan, Canada, in 1999 and 2000 to assess gene flow in space and time in adjacent commercial fields of glyphosate‐ and glufosinate‐resistant canola, including (1) estimation of gene flow with distance; (2) frequency and distribution of volunteers, and effect on gene flow; (3) effect of adventitious double herbicide‐resistant seed presence in seedlots planted; and (4) a comparison of various marker systems to track gene flow events. At 11 sites in 1999, gene flow was determined by sampling seeds from plants located at 0, 50, 100, 200, 400, 600, or 800 m along a transect perpendicular to the common border in the paired fields, spraying seedlings with glyphosate and glufosinate, and confirming the presence of the transgenes using commercial test strips and PCR analysis. In the spring of 2000, putative double herbicide‐resistant volunteers that survived sequential herbicide applications were mapped at three of the sites using GPS and resistance in sampled plants was characterized. In 1999, gene flow between the paired fields was detected to a maximum distance of 400 m. Values ranged from 1.4% outcrossing at the border common to the paired fields to 0.04% at 400 m. In 2000, gene flow as a result of pollen flow in 1999 was detected to the limits of the study areas (800 m). Large variation in gene flow levels and patterns among the three sites was evident. Adventitious presence of double herbicide‐resistant seed in glyphosate‐resistant seedlots planted at two of the sites in 1999 contributed to the occurrence of double herbicide‐resistant volunteers in 2000. The results of this study suggest that gene stacking in B. napus canola volunteers in western Canada may be common, and reflects pollen flow between different herbicide‐resistant canola, presence of double herbicide‐resistant off‐types in seedlots, and/or agronomic practices typically employed by Canadian growers.

Common Waterhemp (Amaranthus rudis) Control in Corn (Zea mays) with Single Preemergence and Sequential Applications of Residual Herbicides1

Control of common waterhemp in corn with chloroacetamide and dinitroaniline herbicides can be inconsistent. Common waterhemp control by dimethenamid, S-metalochlor, pendimethalin, and three formulations of acetochlor, applied alone or with atrazine as single preemergence (PRE) or sequential PRE followed by postemergence (POST) treatment, was determined. The manufacturer's suggested use rate (1 time) of PRE herbicides was compared with sequential applications (0.66 time PRE followed by 0.34 time POST) of herbicides. POST applications included dicamba to control emerged common waterhemp. Single and sequential herbicide applications controlled common waterhemp at least 98%, 28 d after planting (DAP). But herbicides applied sequentially were more effective than PRE treatments by 56 DAP. Encapsulated acetochlor formulations controlled common waterhemp at least 85% by 56 DAP regardless of application method. Sequential applications of S-metolachlor controlled common waterhemp greater than 83%. Atrazine improved common waterhemp control regardless of herbicide or application method 56 DAP. Sequential applications of dimethenamid or S-metolachlor alone or with atrazine were more effective than single PRE applications of these herbicides.Nomenclature: Acetochlor; atrazine; chloroacetamide; dimethenamid; dinitroaniline; pendimethalin; S-metalochlor; common waterhemp, Amaranthus rudis Sauer #3 AMATA; corn, Zea mays L. ‘Pioneer 34R07’.Additional index words: Chloroacetamide, dinitroaniline, herbicide application timing, sequential applications.Abbreviations: DAP, days after planting; POST, postemergence; PRE, preemergence.

Change in weed control studies of rice paddy fields in Korea

This paper was reviewed on the research status of weed control according to cultivating patterns of rice in Korea. Weed control study in a nursery bed was chiefly carried out to control the species of barnyardgrass at the times of machine transplanting. Propanil and nitrofen were applied successfully in wet‐nursery beds, and chlornitrofen and pyrazolate/butachlor were also successfully applied in protected semi‐irrigated rice nursery beds in the 1970s. Sequential application of herbicides in the mid‐1980s has resulted in the end of hand weeding. In machine transplanting, basic research such as the selection of herbicides was conducted in the early 1970s, and its related research including crop injury, seedling age, and reaction of cultivars were done in the late 1970s to early 1980s. Effects of the continuous application of herbicides and its methods of labor saving for rice cultivation were studied in the mid to late 1980s. When the rice planting methods were newly established, such as transplanting when seedlings were 10‐days‐old and direct seeding from the early 1990s, weed control research relating to herbicides was carried out (e.g. herbicide registration, crop injury, water management, appropriate application time, and neighboring application with insecticide). Weed control for the dill seeding of fields in wetted and reclaimed saline land have been experimented with, particularly in terms of the physio‐ecological characteristics and the control of problematic weeds, and the resistance of weeds to herbicides was also investigated systematically.

Sicklepod (Senna obtusifolia) Control and Soybean (Glycine max) Response to Soybean Row Spacing and Population in Three Weed Management Systems1

Studies were conducted with one glyphosate-resistant and three conventional soybean cultivars to determine the effects of reducing row spacing from 76 to 38 and 19 cm, in combination with increased soybean population and herbicide applications (single and sequential), on sicklepod control and soybean yield. ‘Hutcheson’ was the only cultivar, and only under adverse conditions (1998), for which the 19-cm rows provided greater sicklepod control than the 38-cm rows. It was only under optimum conditions (1997), and only with conventional cultivars and sequential herbicide applications, that the 19-cm–row yield of 3,350 kg/ha was 21% greater than the 38-cm–row yield in medium population (455,375 plants/ha), and 21 and 64% greater than the 19- and 76-cm–row yield in low populations (241,000 plants/ha), respectively. In 1998, the same treatment showed similar late-season sicklepod control (> 80%) and a yield of 1,890 kg/ha, with no difference between the 19- and the 38-cm rows; but the yields were 15 and 24% greater than the yield of the narrow (19 and 38 cm) and that of the 76-cm row in low populations, respectively. Low populations with sequential applications in narrow rows and in the 76-cm row showed similar late-season sicklepod control (59 to 70%) and yield in 1998; but in 1997, the narrow rows showed 18 and 32% greater late-season control and yield than the 76-cm row, respectively. In 1997 and 1998, for ‘Hartz 5088RR’ (glyphosate resistant) with medium population and narrow rows, the single and sequential applications provided similar late-season sicklepod control (> 80%) and yield, and at least 10 and 24% greater yield than the narrow and the 76-cm rows in low populations, respectively.Nomenclature: Glyphosate; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby #3 CASOB; soybean, Glycine max (L.) Merr.Additional index words: Chlorimuron, flumetsulam, glyphosate-resistant soybean, metolachlor, sequential herbicide applications.Abbreviations: MG, maturity group; POST, postemergence; PRE, preemergence; WAP, weeks after planting.

Productivity of winter (rabi) onion (Allium cepa) as influenced by sole and sequential application of herbicides

A field experiment was conducted during the winter (rabi) seasons of 201415 and 201516 to study the effect of sole and sequential application of different herbicides on weed control in onion (Allium cepa L.). Sequential ap- plication of pendimethalin @ 750 g/ha at 3 days after transplanting (DAT) + oxyfluorfen @ 100 g/ha at 20 DAT controlled the grasses, sedges and broad-leaf weeds most efficiently and was at par with oxadiargyl @ 90 g/ha at 3 DAT + oxyfluorfen @ 100 g/ha at 20 DAT. Weed competition resulted in about 54.8% yield loss of onion in weedy check plot. The lowest values of total weed density (18.6/m 2), dry weight (6.8 g/m 2), weed index (6.2%) and the highest values of weed control efficiency (89.2%), bulb yield (21.89 t/ha) and benefit: cost ratio (2.84) were registered with sequential application of pendimethalin @ 750 g/ha at 3 DAT + oxyfluorfen @ 100 g/ha at 20 DAT. In weedy check, weeds removed 23.9 kg N, 3.8 kg P and 27.6 kg K/ha.

Effect of sequential application of herbicides on weed control indices and productivity of rainy-season greengram (Vigna radiata) in north Indian plains

A field experiment was conducted at New Delhi during rainy season (JulyOctober) of 2013, to determine the effect of sequential application of herbicides on weed growth and weed- control indices, productivity and profitabil- ity of greengram [Vigna radiata (L.) Wilczek]. The experiment had 12 weed-control treatments, viz. pendimethalin @ 1 kg/ha pre-emergence (PE), pendimethalin @ 1 kg/ha PE followed by (fb) 1 hand-weeding (HW) at 30 days af- ter sowing (DAS), pendimethalin @ 0.75 kg/ha PE fb imazethapyr @ 50 g/ha post-emergence (PoE) at 30 DAS, pendimethalin @ 0.75 kg/ha PE fb imazethapyr @ 75 g/ha PoE at 30 DAS, imazethapyr @ 50 g/ha PoE at 20 DAS, imazethapyr @ 75 g/ha at PoE at 20 DAS, pendimethalin @ 0.75 kg/ha PE fb quizalofop @ 50 g/ha PoE at 30 DAS, pendimethalin @ 0.75 kg/ha PE fb quizalofop @ 75 g/ha PoE at 30 DAS, quizalofop @ 50 g/ha PoE at 20 DAS, quizalofop @ 75 g/ha PoE at 20 DAS, weed free and weedy check. The treatments were randomly allocated in a randomized complete block design with 3 replications. The sequential application of herbicides was found to be more effective than their 1 time application in decreasing weed dry weight. pendimethalin @ 1 kg/ha PE fb 1 HW at 30 DAS resulted in the highest seed yield (1.1 t/ha), weed-control efficiency (75.2%), herbicide-efficiency index (4.5%), benefit: cost ratio (2.91), net return ( 41,167/ha) and lowest weed dry weight (6.0 g/m2) and weed index (8.3%). However, this treatment did not differ significantly from pendimethalin @ 0.75 kg/ha PE fb imazethapyr @ 75 g/ha PoE at 30 DAS indicating that sequential application of herbicides could be an efficient op- tion to manage weeds in greengram, particularly under labour-constrained conditions.