Postemergence Herbicide Treatments Research Articles

Effect of weed control technologies on chickpeas (Cicer arietinum L.) and weeds

Purpose. In our experiment, effect of weed technologies on chickpeas (Cicer arietium L.) was set up in 2018 and 2019 at the Szeged-Othalom experimental area.Methods. In the first year we applied mechanical weed control in addition to pre-emergence herbicide (May 19, 2018) and 6–8 leaf chickpeas (June 20, 2018) in addition to post-emergence herbicide treatments. The year 2019 was different in that after the pre-emergence treatment (April 10, 2019), the post-emergence treatment of chickpeas with 6–8 leaf condition (May 15, 2019) was repeated in the budding state (June 18, 2019). The yield components one way analysis of variance was prepared using SPSS 22 software and graphic representation of the development of the plants was carried out Svab's cumulative yield analysis.Results. The effect of the treatments of 2018 and 2019 on the yield elements of chickpeas can be illustrated graphically in Figure 1 and Figure 2. For both years, the data are from plots of the ʻRealeʼ variety, where the 100% level is made up of the yield elements of the weed-free plots, and the yield elements of the other treatments are compared to this. Figure 1 shows that the number of shoots per unit area (1 m2) of weed-free plots that did not control weeds was 15%, the number of pods 45%, the number of seeds 58% and the weight of seeds 49% less than the weed-free control plots the same crop elements. Weeds were also significantly present in the plots treated only with pre-emergence treatment in the second half of the growing season, so the number of shoots per unit area was 3 %, the number of pods 23 %, the number of seeds 34% and the seed weight 35 % lower, as on weed-free plots. In the case of herbicide treatments, the decrease in yield elements was much smaller: the number of plants per unit area by 1%, the number of shoots by 3–10%, the number of pods by 5–12%, the number of seeds by 13–18%, the seed weight was by 1–5% less than on mechanically weed-controlled plots. Conclusions. Our two-year weed survey results show that the later sowing time of chickpeas favored warm-loving weeds. This is in complete agreement with the opinion of Nagy (2017), who found that sowing time determines the predominant weed species in a given area. At the same time, the statement of Kurnik (1970) was not confirmed, since in our experiment we proved in the case of ʻRealeʼ cultivar that the later sowing stock in 2018 gave higher yields than the plots with earlier sowing time in 2019. The changing weather caused by climate change makes the site characteristics of the given period much more unpredictable, so the yield is determined much more by the field factors developed during the growing season than by the calendar period.

Pre-and post-emergence herbicide sequences for management of multiple herbicide-resistant littleseed canary grass in wheat

Littleseed canary grass (Phalaris minor) is the ubiquitous and pernicious grass weed of wheat in rice-wheat cropping system in north-western Indo- Gangetic plains of India. A field experiment was conducted during Rabi 2014–15 and 201516 in a farmers field infested with P. minor having history of poor control with acetyl-CoA-carboxylase inhibitors in village Nangla, district Fatehabad, Haryana, India with an objective to compare pre-emergence only, postemergence only and pre-emergence followed by post-emergence herbicide treatments for control of P. minor in wheat. The sequential application of preemergence pendimethalin 1.5 kg/ha fb post-emergence pinoxaden + metsulfuron 64 g/ha and pre-emergence pendimethalin 1.5 kg/ha fb post-emergence mesosulfuron + iodosulfuron 14.4 g/ha provided 88–93% control of P. minor compared to alone pre- and post-emergence herbicide treatments. Grain yield of wheat increased significantly by 69–78% with pre-emergence pendimethalin 1.5 kg/ha fb post-emergence pinoxaden + metsulfuron 64 g/ha or pre-emergence pendimethalin 1.5 kg/ha fb post-emergence mesosulfuron + iodosulfuron 14.4 g/ha due to significant increase in yield attributes. Alone pre- or post-emergence herbicides provided ineffective control of P. minor (44–66%) and recorded lower grain yield. It was concluded that herbicide sequences having both pre- and postemergence herbicides would be better option as compared to their alone applications in order to manage resistant populations of P minor in wheat.

Control of ALS- and EPSPS-Resistant Amaranthus palmeri by Alternative Herbicides Applied in PRE- and POST-Emergence

ABSTRACT: The emergence of resistant biotypes of the Amaranthus palmeri species in cotton production areas of the state of Mato Grosso, Brazil, generated the need for correct identification of this species and information on viable herbicidal tools for their management. Thus, greenhouse experiments were conducted to evaluate the efficacy of alternative herbicides applied to A. palmeri in pre and post emergence. A randomized block design with four replications was used. The efficacy of herbicides applied in pre emergence was evaluate in two experiments, one in a clayey and other in a sandy soil; 9 herbicide treatments (8 with herbicide application and a control without application) were applied on each soil. Subsequently, two experiments with different populations of A. palmeri were conducted, using a 13 x 2 factorial arrangement, to evaluate the efficacy of herbicides applied in post emergence. The factors consisted of 13 herbicide treatments (12 with herbicide application and a control without application) and two weed development stages (2-4 and 6-8 leaves). Pre-emergence application of the flumioxazin, S-metolachlor, isoxaflutole, and trifluralin herbicides controlled the weed satisfactorily in both evaluated soils. The sulfentrazone and metribuzin herbicides were effective in the sandy soil, and diuron was effective in the clayey soil. The clomazone herbicide did not successfully controlled the A. palmeri plants in any of the soils. All post-emergence herbicide treatments were effective for the management of A. palmeri plants, when they were applied at the 2-4 leaf stage.

INTEGRATING PRE AND POST-EMERGENCE HERBICIDES FOR CONTROLLING WEEDS IN DRILL-SEEDED RICE (ORYZA SATIVA L.)

Two field experiments were carried out at the experimental farm of Sakha Agricultural Research Station, Kafrelsheikh, Egypt during the summer seasons of 2015 and 2016 to find out the optimum pre and post-emergence herbicide treatments from the recommended herbicides to control weeds under drillseeded rice conditions (Giza179 cv). Fourteen weed control treatments included two pre-emergence herbicides i.e. thiobencarb 50% at the rate of 3.57 kg ai ha-1 alone and followed by six weed control treatments included; penoxsulam 2.5% at 0.0238 kg ai ha- 1 , bispyribac-sodium 2% at 0.0381 kg ai ha-1 and fenoxaprop-ethyl 7.5% at 0.0625 kg ai ha-1 alone and mixed with halosulfuron 75% at 0.0357 kg ai ha-1, also pendimethalin 50% at rate of 2.023 kg ai ha-1 alone and followed by the previous six post-emergence weed control treatments as compared to weedy check (untreated). Randomized Complete Block Design (RCBD) with three replications was used. The results revealed that, spraying pendimethalin as pre-emergence herbicides at 4 days after seeding (DAS) recorded the best weed control, highest rice growth characters and grain yields, as compared to thiobencarb. Each of penoxsulam 2.5% or bispyribac-sodium 2% or fenoxaprop-ethyl 7.5% mixed with halosulfuron 75% gave the lowest dry weights of grasses, broadleaves and total weeds in addition to rice dry biomass, grain yield and its studied attributes. Based on obtained results, it can be concluded that pendimethalin as pre-emergence herbicide at 4 DAS followed by spraying any of penoxsulam 2.5% or bispyribac-sodium 2% or fenoxaprop-ethyl 7.5% mixed with halosulfuron 75% at recommended doses applied at 15, 22 and 35 DAS, respectively were the best combinations for controlling weeds and gave the highest grain yield in drill-seeded rice.

Weed management through early post-emergence herbicides to improve productivity and nutrient uptake in greengram

A field experiment was conducted at College of Agriculture, PJTSAU, Rajendranagar, Hyderabad (Telangana) during rainy season 2015–16 on sandy loam soil to study the weed growth, yield and nutrient uptake in greengram under different early post-emergence herbicide treatments. Lower density and dry matter of weeds was recorded with hand weeding at 20 and 40 DAS followed by haloxyfop-p-methyl 135 g/ha + imazethapyr 75 g/ha at 12–15 DAS as early post-emergence, which remained at par with quizalofop-ethyl 50 g/ha + imazethapyr 75 g/ha at 12–15 DAS. Hand weeding twice at 20 and 40 DAS showed the highest uptake of N, P and K, which was comparable with haloxyfop-p-methyl 135 g/ha + imazethapyr 75 g/ha at 12–15 DAS and quizalofop-ethyl 50 g/ha + imazethapyr 75 g/ha at 12–15 DAS. Significantly higher seed yield was observed with hand weeding at 20 and 40 DAS (1.09 t/ha) which remained at par with haloxyfop-p-methyl 135 g/ha + imazethapyr 75 g/ha at 12–15 DAS (1.03 t/ha) and quizalofop-ethyl 50 g/ha + imazethapyr 75 g/ha at 12–15 DAS (1.01 t/ha).

Best timing for glyphosate treatments and possible combinations with pre and post-emergence weed control practices in no-till maize

Use of reduced and no-tillage systems has increased in recent years due to concerns for ecological and economic sustainability of agricultural production. Effective weed control is a serious concern in reduced tillage production. This study was conducted to investigate weed control practices in reduced and no-till maize production. The most effective timing of glyphosate application, either before or after sowing, was investigated in combination with pre-emergence application of acetochlor (840 g a.i/L), post-emergence application of foramsulfuron (22.5 g a.i/L), and two hoeing treatments. The treatments were maintained on the same plots during 2011 and 2012 to evaluate the cumulative effects of the treatments. Main plot treatments consisted of four timings of glyphosate application: 20 or 10 days before sowing, day of sowing, 5 days after sowing, and an untreated control. Sub-plot treatments were: pre- plus post-emergence herbicides, pre-emergence herbicide plus rotary hoeing, post-emergence herbicide plus rotary hoeing, and post-emergence herbicide plus two hoeing treatments (rotary and lister hoe). In the main plots, the lowest weed biomass was produced in glyphosate treatments at sowing and 5 days after sowing; the highest biomass was produced in control plots and in the plots with glyphosate treatments 20 days before sowing. In the sub-plots, the greatest weed biomass was produced in plots with two hoeing treatments (rotary and lister hoe). Glyphosate treatments at sowing and post-emergence herbicide treatment combinations produced the best weed control. Economic analysis revealed that pre-sowing, non-selective herbicide treatments provided a slight increase in net profit. Mechanical hoeing decreased net income due to increased production costs. The highest income was obtained from the pre-emergence plus post-emergence herbicide treatment combinations with no glyphosate.

Control químico de malezas en frijol (Phaseolus vulgaris L.) en el estado de Veracruz.

Two experiments wiht herbicides were carried out during the Fall-Winter seasons of 1990-91 and 1991-92. The objective was to determine the best preemergence and/or postemergence herbicide treatments for controlling the dominant weed species in the residual moisture growing sistem of beans. The experiments were established in the central area of the state of Veracruz, Mexico.In both experiments, treatments were distributed in a CRBD with 12 treatments and four replications. Melampodium divaricatum and Cyperus rotundus were the dominant weed species in both experimental sites. Euphorbia heterophylla and Sorghum halepense were dominant in one location each. In preemergence, the maximum control of M. divaricatum was obtained with alachlor (2 kg a.i./ha) and linuron (2 kg/ha), the last herbicide was also efficient to control E. heterophylla. In postemergence, fomesafen (0.25 kg/ha) showed an efficient control of the two dominant weed species. No treatment controlled C. rotundus, and S. halepense was only controlled with a treatment included fluazifop-butyl. Linuron and alachlor caused toxicity to the bean plants when the residual moisture of the soil was high. However, and contrary to the response observed with these two herbicides, fomesafen caused a higher toxicity when the residual moisture in the soil was low.

Strip Tillage and Early-Season Broadleaf Weed Control in Seeded Onion (Allium cepa)

Field experiments were conducted in 2007 and 2008 near Oakes, North Dakota (ND), USA, to evaluate if strip tillage could be incorporated into a production system of seeded onion (Allium cepa) to eliminate the standard use of a barley (Hordeum vulgare) companion crop with conventional, full width tillage, yet support common early-season weed control programs. A split-factor design was used with tillage (conventional and strip tillage) as the main plot and herbicide treatments (bromoxynil, DCPA, oxyfluorfen, and pendimethalin) as sub-plots. Neither tillage nor herbicide treatments affected onion stand counts. Common lambsquarters (Chenopodium album) densities were lower in strip tillage compared to conventional tillage up to three weeks after the post-emergence applied herbicides. In general, micro-rate post-emergence herbicide treatments provided greater early-season broadleaf weed control than pre-emergence herbicide treatments. Onion yield and grade did not differ among herbicide treatments because the mid-season herbicide application provided sufficient control/suppression of the early-season weed escapes that these initial weed escapes did not impact onion yield or bulb diameter. In 2007, onion in the strip tillage treatment were larger in diameter resulting in greater total and marketable yields compared to conventional tillage. Marketable onion yield was 82.1 Mg ha−1 in strip tillage and 64.9 Mg ha−1 in conventional tillage. Results indicate that strip tillage use in direct-seeded onion production was beneficial, especially when growing conditions were conducive to higher yields and that the use of strip tillage in onion may provide an alternative to using a companion crop as it did not interfere with either early-season weed management system.

Weed Management in Autumn Fresh Market Spinach: A Nonchemical Alternative

Physical rather than chemical treatments are preferred for integrated production and are required for organic production to ensure a sustainable production. Weed management in many horticultural crops is heavily constrained by the limited number of herbicides available. Physical weed control strategies, on the other hand, are essential to organic vegetable production and greatly assist conventional vegetable farmers. A physical weed control strategy was developed and compared with a standard chemical strategy within an integrated farming system in fresh market spinach (Spinacia oleracea). The experiment was conducted on a farm in the Serchio Valley (Tuscany, central Italy) in 2004 and 2005, where spinach is one of the most important crops. The physical weed control strategy consisted of a stale seedbed technique and postemergence treatments using various mechanical and thermal machines. The chemical weed control strategy consisted of a single postemergence herbicide treatment using phenmedipham at 15.8% in compliance with integrated production norms in Italy. Strategy performance was assessed in terms of weed density and biomass, total labor requirement, and crop yield. Compared with the chemical system, the physical system required a substantially larger labor input (19 vs. 6 h·ha−1), but like the chemical system, did not require hand weeding. In addition, the physical system reduced weed dry biomass at harvest by 50% and increased spinach fresh yield by 35%. Physical strategies therefore are a valid alternative to the use of herbicides in fresh market spinach and may be especially desirable given the increasing importance of nonchemical weed control in integrated, organic, and conventional farming systems in Europe and the United States.

Herbicide Evaluation for Control of Kochia and Palmer Amaranth in Teff Grass

Eleven postemergence herbicide treatments were applied to teff grown for forage to evaluate Palmer amaranth and kochia control, as well as crop tolerance. Effective Palmer amaranth control was achieved with all herbicide treatments, while less than satisfactory kochia control was obtained with atrazine and Harmony. Clarity, 2,4-D, and Huskie applied alone appeared to control kochia, but kochia density was low in the plots. Had the kochia population been higher, similar efficacy ratings may have been attained. Huskie or atrazine caused the most injury to teff. The first harvest suggests these herbicides reduced forage yield to less than 3,000 lb/a.

Response of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) to alternative herbicides

Burton, N., Shirriff, S. W. and Beckie, H. J. 2014. Response of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) to alternative herbicides. Can. J. Plant Sci. 94: 1407–1411. A greenhouse study was conducted to examine the response of glyphosate-resistant (GR) plus acetolactate synthase (ALS) inhibitor-resistant kochia to five post-emergence herbicide treatments commonly used to control the weed species in chemical fallow, cereals, or oilseed crops in western Canada. The treatments, which were applied to two GR kochia biotypes and one non-GR (susceptible) biotype, included the labeled rate of dicamba, dicamba/fluroxypyr, dicamba/diflufenzopyr, MCPA/bromoxynil, and glufosinate. Both GR and non-GR biotypes responded similarly to each of the herbicide treatments. Although both GR biotypes were sensitive to the herbicides, MCPA/bromoxynil was the most effective treatment in reducing shoot biomass 3 wk after application (99%), followed by glufosinate (91%) then the dicamba mixtures (82%). Dicamba alone only suppressed kochia biomass (76% reduction).

Effects of post emergence herbicides on weed control and yields of field pea and their residual effect on succeeding sorghum and mungbean crop.

A field experiment was conducted during 2008-09 and 2009-10 to evaluate different post emergence herbicides applied against weeds in field pea and their residual effect on succeeding sorghum and mungbean crop. Pendimethalin herbicide applied 1.5 kg ha-1 as pre-emergence gave effective control against all the weeds whereas, among post emergence herbicides imazethapyr was found effective against broadleaf weeds and quizalofop-ethyl was effective only against grassy weeds. During both the years, application of imazethapyr 50 g ha-1 at 30 days after sowing gave effective control of weeds and resulted minimum density and dry biomass of weeds compared to all the post emergence herbicide treatments. During second year, residual effect of imazethapyr was observed only on sorghum crop.

Comparison of sequential preemergence-postemergence and postemergence-alone weed management strategies for red beet (Beta vulgaris L.)

Robinson, D. E., McNaughton, K. E. and Bilyea, D. 2013. Comparison of sequential preemergence-postemergence and postemergence-alone weed management strategies during critical period of red beet ( Beta vulgaris L.). Can. J. Plant Sci. 93: 863–870. Weed management during the first 4 wk after red beet emergence is critical to prevent yield loss. The purpose of this research was to compare weed control and red beet tolerance of postemergence (POST) treatments alone (full, split- and micro-rates of pyrazon plus triflusulfuron) with sequential preemergence (PRE) applications of s-metolachlor followed by these POST herbicide treatments. The experiment was carried out for 4 yr as a randomized complete block with four replications. Of the POST alone treatments examined, control of velvetleaf (Abutilon theophrasti Medik.), redroot pigweed (Amaranthus retroflexus L.), common lambsquarters (Chenopodium album L.) and green foxtail [Setaria viridis L. (Beauv.)] was 98, 86, 97 and 62%, respectively. Much more consistent control of all species (i.e., greater than 96%) was measured where the sequential treatment of s-metolachlor was applied PRE followed by POST split- or micro-rates in all study years. Red beet density and soluble solid levels were not different than the weed-free check in any of the POST or sequential treatments. However, red beet yield in the POST single and split-rate treatments alone ranged from 9500 to 12100 kg ha−1, and was significantly less than in the weed-free check (19400 kg ha−1). Yields in the sequential treatments were comparable to the weed-free check. The results of this study confirm that a sequential treatment of PRE s-metolachlor followed by POST split- and micro-rate applications of pyrazon plus triflusulfuron can be safely applied to red beet and control annual weed species.

Cutleaf Groundcherry (Physalis angulata) Density, Biomass and Seed Production in Peanut (Arachis hypogaeaL.) Following Regrowth Due to Inadequate Control

ABSTRACTA 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.).

Weed management in winter wheat ( Triticum aestivum L.) influenced by different soil tillage systems

In this study, weed management in winter wheat influenced by different soil tillage systems was investigated. The experiment was carried out under Mediterranean conditions on a Luvisol, during two growing seasons (1996/1997 and 1999/2000). Two factors (different soil tillage systems and post-emergence weed control) were studied, with two levels each: Two soil tillage systems and two levels of post-emergence weed control. The conventional soil tillage system, performed for seedbed preparation after the emergence of a high percentage of weeds, increases the appearance of monocotyledons, especially Lolium rigidum Gaud. in wheat crops, when compared to their establishment in no-till system. As a consequence of the higher number of monocotyledons there is an increase in weed-crop competition. Without post-emergence herbicide treatment, the wheat crop yield is lower in the treatments with the conventional soil tillage system and yield reduction is less under no-till system compared to the respective treatments with post-emergence herbicide application. Key words: No-till system, weeds, wheat, herbicides.

Potential of a terrestrial LiDAR-based system to characterise weed vegetation in maize crops

LiDAR (Light Detection And Ranging) is a remote-sensing technique for the measurement of the distance between the sensor and a target. A LiDAR-based detection procedure was tested for characterisation of the weed vegetation present in the inter-row area of a maize field. This procedure was based on the hypothesis that weed species with different heights can be precisely detected and discriminated using non-contact ranging sensors such as LiDAR. The sensor was placed in the front of an all-terrain vehicle, scanning downwards in a vertical plane, perpendicular to the ground, in order to detect the profile of the vegetation (crop and weeds) above the ground. Measurements were taken on a maize field on 3m wide (0.45m2) plots at the time of post-emergence herbicide treatments. Four replications were assessed for each of the four major weed species: Sorghum halepense, Cyperus rotundus, Datura ferox and Xanthium strumarium. The sensor readings were correlated with actual, manually determined, height values (r2=0.88). With canonical discriminant analysis the high capabilities of the system to discriminate tall weeds (S. halepense) from shorter ones were quantified. The classification table showed 77.7% of the original grouped cases (i.e., 4800 sampling units) correctly classified for S. halepense. These results indicate that LiDAR sensors are a promising tool for weed detection and discrimination, presenting significant advantages over other types of non-contact ranging sensors such as a higher sampling resolution and its ability to scan at high sampling rates.

MANAGEMENT OF RED RICE (ORYZA SATIVA) AND BARNYARDGRASS (ECHINOCHLOA CRUS-GALLI) GROWN WITH SORGHUM WITH REDUCED RATE OF ATRAZINE AND MECHANICAL METHODS

SUMMARYThe weedy variety ofOryza sativaoccurs in several rice cultivation areas reducing both grain yield and quality. Prevention and crop rotation are considered the basic means to reduce its presence. Weed control in sorghum is generally attained with atrazine. In this study, the efficacy of both chemical and mechanical methods for control, under different soil tillage conditions, of weedy rice and barnyardgrass during sorghum cultivation was evaluated with the aim to reduce the application rate of atrazine. In the case of chemical control, the atrazine rate (1000, 1500, 2000, 2500 and 3000 ga.i.ha−1) and application timing (pre- and post-emergence) were assessed. With the mechanical control method, the number of interventions (inter-row hoeing with sorghum at 3, 4–5 and 6–8 leaves) to avoid weed competition was determined. The effect of the tillage system on weed population was investigated comparing conventional (ploughing), minimum-tillage (disc harrowing) and sod seeding (no-tillage) in combination with pre- and post-emergence herbicide treatments. The results showed that efficient control of weedy rice and barnyardgrass was achieved in lowlands with sorghum in rotation with rice. Both chemical and mechanical methods of weed control in sorghum gave a level of efficiency higher than 60%. The application of atrazine was more efficient in pre-emergence application, rather than in post-emergence treatments, in all soil tillage systems tested. On both weed species, the most suitable application rate was the pre-emergence treatment with 1500 ga.i.ha−1, and the adoption of higher rates did not significantly increase the herbicidal efficacy. The adoption of two or three mechanical interventions resulted in sorghum yield higher than the chemical post-emergence application, and similar to the application of atrazine in pre-emergence. Higher yield results were in accordance to greater weed control, being obtained in the conventional tillage system.

Validation of a Management Program Based on A Weed Cover Threshold Model: Effects on Herbicide Use and Weed Populations

Weed management decisions based on weed threshold models offer the opportunity to reduce herbicide use by allowing the possibility of forgoing treatment or lowering rates. Weed thresholds based on a relative leaf-cover model were tested during a 4-yr period at two locations. Two 1.62-ha fields, planted to conventional and glyphosate-resistant corn (2004, 2005, 2007) or soybean (2006), were divided in 900 m2sections. Herbicides were applied postemergence to each of these sections with either variable rates based on weed thresholds, or constant full rates. Variable herbicide rates included: no application, half rate, or full rate. Relative weed cover values of 0.2 and 0.4 (corn) or 0.1 and 0.3 (soybean) served as thresholds for incremental rates. Digital images were used to evaluate the relative weed cover. Weed density was assessed before and after herbicide application. Weed seed production was estimated for two species in 2004 and 2005. No difference in crop yield, relative weed cover, weed density, or weed seed production was observed between conventional and glyphosate-resistant cropping systems. During the first year, herbicide use reduction was obtained (−85.4%) with marginal crop yield loss (5 to 15%). In the subsequent 3 yr, preherbicide weed densities increased and concomitant increases in relative weed cover values did not allow more than a 10% overall reduction in herbicide use. This threshold model designed to maintain crop yields within a given year did not allow significant reduction in herbicide use during the following 3 yr. Residual weed populations most likely replenished the seed bank to levels that allowed weed densities to increase afterward. Increased weed density over time in plots treated with full rates of herbicide every year also indicated that a single postemergence herbicide treatment was not sufficient to contain weed populations at low levels every year in this corn–soybean rotation.

Effect of Herbicides for the Control of Fimbristylis miliacea (L.) Vahl. in Rice

The experiment was conducted in the glasshouse at Universiti Putra Malaysia to determine the efficacy of herbicides with different modes of action against a Fimbristylis miliacea population and increased rice yield potentiality. Nine early post emergence herbicide treatments such as bensulfuron, cinosulfuron, pyrazosulfuron, cinosulfuron+pretilachlor+safener, 2, 4-D (amine), pretilachlor+safener, bentazone, fentrazamide+propanil and bispyribac-sodium were applied singly or in mixtures. A weed-free (hand-weeded) treatment and an unweeded treatment served as controls. The treatments were arranged in a randomized complete block design with four replications. A weed-free (hand-weeded) treatment and an unweeded treatment served as controls. The treatments were arranged in a randomized complete block design with four replications. Data on crop phytotoxicity, weed control, chlorophyll content, plant height, productive tillers, total tillers, panicle length, grains per panicle, 1000 grain weight, % filled grains per panicle, grain yield and straw biomass were recorded to evaluate efficacy of the different treatments. All tested herbicides were effective in controlling F. miliacea, but the herbicides bensulfuron and fentrazamide+propanil increased grain yield by more than 80% compared to the unweeded treatment and were comparable to the weed-free treatment.

Integrated analysis of weed control practices for reducing atrazine contamination in an agricultural watershed

Atrazine has been detected in more than 90% of raw drinking water samples in northern Missouri, including the Route J watershed, and half of those samples had atrazine concentrations that exceeded the drinking water standard of three parts per billion. An integrated bioeconomic-weed management model was used to evaluate the effects on water quality and profitability of 46 preplant and preemergence herbicide treatments, 67 postemergence herbicide treatments, and 260 two-pass herbicide treatments for weed control in corn production in the watershed. The percentage of total treatments that were profitable was the highest with postemergence treatment (38%), the second highest with preemergence treatment (36%), and the lowest with two-pass treatment (27%). The latter only allows postemergence application of atrazine. Of the nine weed population scenarios evaluated, atrazine was used in 15% to 28% of the profitable two-pass treatments, 27% to 38% of the profitable postemergence treatments, and 81% to 100% of the profitable preemergence treatments. Using average rainfall, a simulation model indicated that the atrazine concentration in surface runoff in the watershed generally exceeded three parts per billion for the profitable preemergence treatments, and was less than three parts per billion for the profitable postemergence and two-pass treatments. Two-pass treatment offers farmers in the watershed additional flexibility in maintaining the profitability of corn production while reducing the atrazine contamination of surface runoff.