Postemergence Glyphosate Research Articles

The silver bullet that wasn't: Rapid agronomic weed adaptations to glyphosate in North America.

The rapid adoption of glyphosate-resistant crops at the end of the 20th century caused a simplification of weed management that relied heavily on glyphosate for weed control. However, the effectiveness of glyphosate has diminished. A greater understanding of trends related to glyphosate use will shed new light on weed adaptation to a product that transformed global agriculture. Objectives were to (1) quantify the change in weed control efficacy from postemergence (POST) glyphosate use on troublesome weeds in corn and soybean and (2) determine the extent to which glyphosate preceded by a preemergence (PRE) improved the efficacy and consistency of weed control compared to glyphosate alone. Herbicide evaluation trials from 24 institutions across the United States of America and Canada from 1996 to 2021 were compiled into a single database. Two subsets were created; one with glyphosate applied POST, and the other with a PRE herbicide followed by glyphosate applied POST. Within each subset, mean and variance of control ratings for seven problem weed species were regressed over time for nine US states and one Canadian province. Mean control with POST glyphosate alone decreased over time while variability in control increased. Glyphosate preceded by a labeled PRE herbicide showed little change in mean control or variability in control over time. These results illustrate the rapid adaptation of agronomically important weed species to the paradigm-shifting product glyphosate. Including more diversity in weed management systems is essential to slowing weed adaptation and prolonging the usefulness of existing and future technologies.

Multiple herbicide resistance in waterhemp (Amaranthus tuberculatus) accessions from Wisconsin

AbstractA comprehensive, Wisconsin state-wide assessment of waterhemp response to a diverse group of herbicide sites of action has not been conducted. Our objective was to characterize the response of a state-wide collection of waterhemp accessions to postemergence (POST) and preemergence (PRE) herbicides commonly used in corn and soybean in Wisconsin. Greenhouse experiments were conducted with more than 80 accessions from 27 counties. POST treatments included 2,4-D, atrazine, dicamba, fomesafen, glufosinate, glyphosate, imazethapyr, and mesotrione at 1× and 3× label rates. PRE treatments included atrazine, fomesafen, mesotrione, metribuzin, and S-metolachlor at 0.5×, 1×, and 3× label rates. Ninety-eight percent and 88% of the accessions exhibited ≥50% plant survival after exposure to imazethapyr and glyphosate POST 3× rate, respectively. Seventeen percent, 16%, and 3% of the accessions exhibited ≥50% plant survival after exposure to 2,4-D, atrazine, and dicamba, respectively, applied POST at the 1× rate. Survival of all accessions was ≤25% after exposure to 2,4-D or dicamba applied POST at the 3× rate, or glufosinate, fomesafen, and mesotrione applied POST at either rate evaluated. No plant of any accession survived exposure to glufosinate at either rate. Forty-five percent and 3% of the accessions exhibited <90% plant density reduction after exposure to atrazine applied PRE at the 3× rate and fomesafen PRE at the 1× rate, respectively. Plant density reduction of all accessions was ≥96% after exposure to fomesafen applied PRE at the 3× rate, or metribuzin, S-metolachlor, and mesotrione applied PRE at the 1× rate. Our results suggest that waterhemp resistance to imazethapyr and glyphosate applied POST is widespread in Wisconsin, whereas resistance to 2,4-D, atrazine, and dicamba applied POST is present to a lower extent. One accession (A75, Fond du Lac County) exhibited multiple resistance to imazethapyr, atrazine, glyphosate, and 2,4-D when applied POST. Overall, atrazine applied PRE was ineffective for waterhemp control in Wisconsin. Proactive resistance management and the use of effective PRE and POST herbicides are fundamental for waterhemp management in Wisconsin.

Multiple resistance to imazethapyr, atrazine, and glyphosate in a recently introduced Palmer amaranth (Amaranthus palmeri) accession in Wisconsin

AbstractThe continued dispersal of Palmer amaranth can impose detrimental impacts on cropping systems in Wisconsin. Our objective was to characterize the response of a recently introduced Palmer amaranth accession in southern Wisconsin to postemergence (POST) and preemergence (PRE) herbicides commonly used in corn and soybean. Greenhouse experiments were conducted with the Wisconsin putative herbicide-resistant accession (BRO) and two additional control accessions from Nebraska, a glyphosate-resistant (KEI2) and a glyphosate-susceptible (KEI3) accession. POST treatments were 2,4-D, atrazine, dicamba, glufosinate, glyphosate, imazethapyr, lactofen, and mesotrione at 1X and 3X label rates. PRE treatments were atrazine, mesotrione, metribuzin, S-metolachlor, and sulfentrazone at 0.5X, 1X, and 3X label rates. Plant survival of each accession was ≥63% after exposure to imazethapyr POST 3X rate. Survival of BRO and KEI2 was 44% (±13) and 50% (±13), respectively, after exposure to atrazine POST 3X rate. Survival of BRO was 69% (±12) after exposure to glyphosate POST 1X rate, whereas survival of KEI2 was 44% (±13) after exposure to glyphosate POST 3X rate. After exposure to 2,4-D POST 1X rate, KEI2 and KEI3 survival was 38% (±13) and 50% (±13), respectively. Survival of all accessions was ≤31% after exposure to 2,4-D POST 3X rate or dicamba, glufosinate, lactofen, and mesotrione POST at either rate. Plant density reduction of KEI2 was 77% (±13) after exposure to atrazine PRE 1X rate, whereas density reduction of BRO was 56% (±13) after exposure to atrazine PRE 3X rate. Plant density reduction of all accessions was ≥94% after exposure to mesotrione PRE 1X and 3X rates or metribuzin, S-metolachlor, and sulfentrazone PRE at either rate. Our results suggest that each accession is resistant (≥50% survival) to imazethapyr POST, that BRO and KEI2 are resistant to atrazine and glyphosate POST, and that KEI2 and KEI3 are resistant to 2,4-D POST. The recently introduced BRO accession exhibited multiple resistance to imazethapyr, atrazine, and glyphosate POST. In addition, atrazine PRE was ineffective for BRO control, suggesting that diversified resistance management strategies will be critical for its effective management.

Effect of Preplant Application of Post Emergent Herbicide Glyphosate on the Events of Germination, Growth and Biochemical Composition of Blackgram Seedlings

Weed causes heavy yield loss when it competes with crops especially for light, water, nutrient and space. In crop production, weed management is a necessary operation to get a higher yield. Manual weeding operation is an easy and environmentally friendly method but it increases the cost of cultivation and makes the crop production practice a non-profitable business venture. Under this situation, the herbicide can be used as the most practical and effective alternative means of weed control. In intensive agriculture heavy use of herbicide affects the growth and biochemical composition of the crop. The objective of this study was to find out the effect of pre-plant soil application of post emergence glyphosate on the germination, growth and biochemical composition of blackgram seedlings. Results showed that glyphosate 1000 ppm did not significantly affect the germination of blackgram seeds. However, the higher concentration of 1000 ppm affects the root (1.08 cm) and shoot length (6.16 cm) compared to control (6.16 and 12.27 cm, respectively) and the lower concentration at the rate of 10 ppm enhance the root (6.26 cm) and shoot length (12.49 cm). Soluble protein content was higher in glyphosate 1000 ppm (70.60 mg g-1) compare to control (59.40 mg g-1). The finding concludes that the pre-plant application of post emergence herbicide glyphosate didn’t affect the germination. However it has reduced the root and shoot length of blackgram when applied at higher concentrations. Contrary to the higher dose the lower dose of glyphosate stimulates the growth and development of blackgram seedlings.

Single and Split Herbicide Applications for Efficacy in Corn

The objective of this study was to compare season-long weed control from single and sequential herbicide applications in corn. Control of all weed species was generally good (90% or more) early in the season regardless of preemergence (PRE) herbicide. However, Russian thistle and Palmer amaranth control was best later in the season when a PRE herbicide was followed by a postemergence (POST) treatment. While all herbicide treatments increased yields compared to the untreated control, yields were greatest when Lumax EZ PRE (atrazine/mesotrione/metolachlor) was followed by Acuron (atrazine/bicyclopyrone/mesotrione/metolachlor) and glyphosate POST.

Influence of Postemergence Dicamba/Glyphosate Timing and Inclusion of Acetochlor as a Layered Residual on Weed Control and Soybean Yield

Roundup Ready 2 Xtend® [glyphosate- and dicamba-resistant (DR)] soybean is a novel trait option for postemergence (POST) control of herbicide-resistant broadleaf weeds in soybean. With increased use of labeled dicamba products POST in DR soybean and recommendations to include a soil-residual herbicide POST (e.g., layered residual approach), research on how combinations of these approaches influence weed control, weed seed production, and soybean grain yield is warranted. The objective of this research was to evaluate the effects of (1) flumioxazin applied preemergence (PRE) followed by (fb) dicamba plus glyphosate applied POST at different crop developmental stages and (2) acetochlor POST as a layered residual approach on weed control, weed seed production, and soybean yield to determine the optimal POST timing in DR soybean. A field study was conducted in Wisconsin at three sites in 2018 and four sites in 2019 to evaluate flumioxazin (43.4 g ai ha−1, WDG 51%) PRE fb dicamba (560 g ae ha−1, SL) plus glyphosate (1,101 g ae ha−1, SL) POST in DR soybean at three stages: early-POST (EPOST, V1-V2), mid-POST (MPOST, V3-V4), and late-POST (LPOST, V5-V6/R1) with or without a soil-residual herbicide POST (acetochlor, 1,262 g ai ha−1, ME). Weed community composition was site-specific; difficult-to-control broadleaf species included giant ragweed (Ambrosia trifida L.) and waterhemp [Amaranthus tuberculatus (Moq.) J.D. Sauer]. Dicamba plus glyphosate applied MPOST and LPOST provided greater control, weed biomass reduction, and density reduction of giant ragweed and waterhemp when compared with EPOST treatments. Giant ragweed and waterhemp had not reached 100% cumulative emergence at EPOST, and plants that emerged after EPOST produced seed. There was some benefit to including acetochlor as a layered residual at EPOST as indicated by a residual by POST timing interaction for waterhemp density reduction. Complete waterhemp control was not attained at one site-year. For remaining site-years, dicamba plus glyphosate applied MPOST (V3-V4) provided season-long weed control, reduced weed seed production, and optimized soybean grain yield compared with other POST treatments. Results highlight the importance of timely POST applications and suggest utilization of a POST layered residual needs to be timed appropriately for the window of active weed species emergence.

Wheat and Cereal Rye Inter-Row Living Mulches Interfere with Early Season Weeds in Soybean.

Rapid growth of cool-season weeds in the spring exacerbates weed interference during early soybean (Glycine max (L.) Merr.) establishment in northern climates. This study tested the utility of spring-seeded inter-row living mulches in soybean for early season weed suppression using volunteer canola (Brassica napus L.) as a representative model weed species. The effects of the presence or absence of spring wheat (Triticum aestivum L.) or winter cereal rye (Secale cereale L.) living mulches (mulch type) that had been seeded simultaneously with soybean grown using 38 or 76 cm row spacing (spatial arrangement) and the presence or absence of herbicides used for mid-season mulch termination (herbicide regime) were evaluated in three environments in Manitoba, Canada, in 2013 and 2014. Soybean yield was similar in the presence and absence of the living mulches. In the environment that received the lowest precipitation (Carman 2013), the mulches terminated with post-emergence glyphosate resulted in a 55% greater soybean yield compared to the mulches that remained live throughout the growing season. Inter-row mulches that had been living or terminated mid-season reduced volunteer canola seed production by about one-third (up to 9000 seeds m−2). This study demonstrates the utility of wheat or cereal rye inter-row living mulches for enhanced interference with weeds during early soybean establishment.

Pre‐plant and in‐crop herbicide programs for prickly sida control in soybean

AbstractPrickly sida (Sida spinosa L.) is emerging as a prevalent and troublesome weed in the Mid‐South glyphosate‐resistant (GR) soybean [Glycine max (L.) Merr.] cropping systems as reliance on residual herbicides has decreased. It emerges throughout the growing season and postemergence (POST) control has been reported to be variable. Combinations of residual herbicides applied pre‐plant and at‐planting followed by POST herbicides in‐crop may be needed to maximize control. This research utilized separate studies to address the value of currently available residual herbicides applied pre‐plant, at‐planting, and POST in glyphosate‐resistant soybean prickly sida management systems. At 35 days after application (DAA), prickly sida control from glyphosate plus 2,4‐D pre‐plant with flumioxazin plus chlorimuron‐ethyl, flumioxazin plus pyroxasulfone, flumioxazin plus chlorimuron‐ethyl plus thifensulfuron‐methyl, metribuzin plus chlorimuron‐ethyl or metribuzin plus sulfentrazone was 70–89% and similar among treatments. In a separate study, based on prickly sida control and density 21 days after late postemergence (LPOST) application, improvement in control was most affected by inclusion of glyphosate or glyphosate plus residual herbicides flumioxazin, chlorimuron‐ethyl, and thifensulfuron‐methyl at‐planting. Weed control was not improved when residual herbicides chlorimuron‐ethyl plus tribenuron‐methyl were included pre‐plant or when residual herbicides chlorimuron‐ethyl, s‐metolachlor, and fomesafen were applied with glyphosate POST. Late‐season prickly sida control was as high as 93% following at‐planting and POST applications that did not include residual herbicides. Soybean yield was maximized with glyphosate applied both at‐planting and POST, whether or not residual herbicides flumioxazin, chlorimuron‐ethyl, and thifensulfuron‐methyl were included at‐planting or residual herbicides chlorimuron‐ethyl, s‐metolachlor, or fomesafen were included POST. When averaged across at‐planting and POST treatments, a 10% yield increase was observed when residual herbicides chlorimuron‐ethyl and tribenuron‐methyl were applied with glyphosate plus 2,4‐D pre‐plant compared with glyphosate plus 2,4‐D alone.

Multiple-resistant waterhemp control in herbicide-resistant 3 (HT3) soybean

Herbicide-resistant (HR) crops, specifically glyphosate-, glufosinate-, and dicamba-resistant (HT3) soybean, will offer producers a new weed management option for the control of some HR weeds in soybean. Four field experiments were conducted near Cottam and on Walpole Island, ON, Canada, during 2017 and 2018 to assess the control of multiple-resistant (MR) waterhemp (herbicide groups 2, 5, and 9) in HT3 soybean treated with various herbicide programs. Pyroxasulfone/flumioxazin, flumioxazin plus metribuzin, or S-metolachlor/metribuzin applied preemergence (PRE) and followed by (fb) glyphosate postemergence (POST) controlled MR waterhemp at 94%, 66%, and 78%, respectively, in early September. Pyroxasulfone/flumioxazin, flumioxazin plus metribuzin, or S-metolachlor/metribuzin applied PRE controlled MR waterhemp 86%–97% when fb glufosinate POST; 100% when fb glyphosate plus dicamba POST; 99%–100% when fb glufosinate plus dicamba POST; and 100% when fb glyphosate plus dicamba POST and fb glufosinate POST2 (before the R2 soybean growth stage) in early September. Reduced MR waterhemp interference with all herbicide programs resulted in an increase in HT3 soybean yield (up to 59%) relative to the weedy control. Results indicate that pyroxasulfone/flumioxazin, flumioxazin plus metribuzin, or S-metolachlor/metribuzin applied PRE fb glufosinate POST, glyphosate plus dicamba POST, glufosinate plus dicamba POST, or glyphosate plus dicamba POST fb glufosinate POST2 provides similar and excellent season-long control of MR waterhemp in HT3 soybean.

Transgenik Olmayan Mısırda (Zea mays L.) Yabancı Ot Mücedesinde Yaygın Olarak Kullanılan Herbisitlerin Karşılaştırılması

Yabancı otlar mısır üretiminde önemli ekonomik kayıplara neden olmaktadır. Yabancı ot mücadelesinde en yaygın kullanılan yöntem pratik olması bakımından herbisit kullanımıdır. Transgenik (GDO’lu) mısır üretiminde yabancı ot mücadelesi genellikle çıkış sonrası glyphosate ve 2.4-D herbisitlerinin kullanımına bağlı olarak yapılmaktadır. Ancak transgenik mısır üretiminin yasak olduğu Avrupa birliği ve Türkiye gibi ülkelerde mısır tarlalarında yabancı ot mücadelesi farklı herbisitlere bağlı olarak; ekim öncesi, çıkış öncesi ve çıkış sonrası olmak üzere üç ayrı dönemde yapılabilmektedir. Bu çalışmada transgenik olmayan mısır üretiminde sorun olan yabancı otlara karşı yaygın olarak kullanılan herbisitlerin yabancı ot kontrolüne ve mısır verimine etkisi araştırılmıştır. En yüksek verim sırasıyla dimethenamid-P 280 g/l + terbuthylazine 250 g/l (13.055 kg ha-1), mesotrione 75 g/l + nicosulfuron 30 g/l (12.979 kg ha-1) ve terbutylazine 270 g/l + pendimethalin 64 g/l (12.746 kg ha-1) uygulamalarından elde edilmiştir. Maksimum hasat indeksi sırasıyla dimethenamid-P 280 g/l + terbuthylazine 250 g/l (%53), mesotrione 75 g/l + nicosulfuron 30 g/l (%52) ve terbutylazine 270 g/l + pendimethalin 64 g/l (%50) uygulamalarında saptanmıştır. Yabancı ot indeksi sırasıyla dimethenamid-P 280 g/l + terbuthylazine 250 g/l (%7), mesotrione 75 g/l + nicosulfuron 30 g/l (%8) ve terbutylazine 270 g/l + pendimethalin 64 g/l (%10) uygulamalarında en iyi sonucu verdiği belirlenmiştir. Sonuçlar bir bütün olarak değerlendirildiğinde sırasıyla dimethenamid-P 280 g/l + terbuthylazine uygulamalarının öncelikli olarak tercih edilebileceği sonucuna varılmıştır. Ancak sadece kimyasallara bağlı mücadelelerin uzun dönemde çıkarabileceği çevresel sorunlar nedeniyle mısır üretiminde sürdürülebilir yabancı ot mücadelesi için münavebe, malçlama, solarizasyon, buhar ile toprak dezenfeksiyonu, akıllı kültivatörler ve sensörlü pülverizatörler kullanılması, dron ve dijital teknoloji gibi çevre dostu uygulamaların herbisit uygulamalarına entegre edilmesi gerekmektedir.

A lack of response of irrigated soybean (Glycine max L. Merr.) in rotation with cotton (Gossypium hirsutum L.) in the Mississippi Delta, USA

The effects of cotton (Gossypium hirsutum L.): soybean [Glycine max (L.) Merr.] rotations on the respective crops are limited. This manuscript discusses the response of irrigated soybean in crop rotation with cotton. An irrigated soybean: cotton rotation experiment was conducted from the year 2012 through 2015 near Elizabeth, MS. The crop rotation sequences were included continuous soybean (SSSS), continuous cotton (CCCC), cotton followed by soybean (SCSC), soybean followed by cotton (CSCS), soybean followed by two year of cotton (SCCS), and cotton followed by two year of soybean (CSSC). The rotations were grown under two production systems conventional and transgenetic with respect to weed control. During this study, a weed control treatment of (pendimethalin pre-emergence vs. glyphosate post-emergence) as included on the soybean plots was used. The soybean yields across rotations within a year were not significantly different. The means yields differed among years (3655.1, 3023.6, 3500.6 and 2600.3 Kg ha-1 for the year 2012, 2013, 2014 and 2015, respectively) and appear related to difference in rainfall/irrigation amounts. The results revealed that the weights of 100 seed samples averaged 13.9g in the year 2015 which differed from the previous years (16.2, 15.6, and 16.2g; 2012, 2013 and 2014, respectively). Therefore, the rotations of cotton with soybean appear to have neither a beneficial or negative effect on soybean yield.

Response of Three Chloris elata Populations to Herbicides Sprayed in Pre- and Post-Emergence

ABSTRACT: In agricultural areas of Brazil, where there is no establishment of cover crops in the off-season and in fruit orchards, an increase in Chloris elata infestations, syn. Chloris polydactyla, has been observed. With the purpose to evaluate the response of three populations (Itaberaí - GO, Matão - SP e Jaboticabal - SP) of C. elata to herbicides sprayed before and after emergence, four experiments were conducted. In the first one, the differential tolerance of three C. elata populations to the herbicide glyphosate (0, 0.18, 0.36, 0.72, 0.96, 1.44, 2.88, 5.76 and 11.52 kg a.e. ha-1) was studied. In the other experiments, the control of the three populations by herbicides applied in pre-emergence (clomazone, diclosulam, flumioxazin, isoxaflutole, chlorimuron-ethyl, metribuzin, S-metolachlor, sulfentrazone and trifluralin) or in post-emergence (clethodim, fenoxaprop-p-ethyl, fluazifop-p-butyl, haloxyfop-methyl, quizalofop-p-tefuryl, mesotrione, nicosulfuron, tembotrione, glufosinate-ammonium, paraquat and glyphosate) was evaluated. The population from Jaboticabal was more susceptible to glyphosate than Itaberaí and Matão, at smaller doses. In pre-emergence, clomazone, isoxaflutole, metribuzin, S-metolachlor and trifluralin were effective in controlling the three populations. The same results were observed for clethodim, fenoxaprop, fluazifop, haloxyfop, quizalofop, paraquat and glyphosate, when sprayed on plants with 2-6 tillers. C. elata populations differed for the herbicides flumioxazin, chlorimuron-ethyl and nicosulfutron.

Manejo de plantas daninhas em milho RR® com herbicidas aplicados isoladamente ou associados ao glyphosate

The objective of this work was to evaluate the effectiveness, selectivity and effect on yield components of RR® maize as a function of herbicide application, applied alone or in a tank mix. The experiment was conducted in a randomized block design, with four replications, and treatments were control without weeding, control with weeding, glyphosate, glyphosate + [atrazine+simazine], glyphosate + [atrazine + simazine], glyphosate + tembotrione, glyphosate+mesotrione, T8-glyphosate + nicosulfuron, glyphosate + 2,4-D, glyphosate + [atrazine + S-metolachlor], T11-glyphosate + (atrazine + S-metolachlor), glyphosate + S-metolachlor, glufosinate ammonium, [nicosulfuron + mesotrione], glyphosate + [nicosulfuron + mesotrione] and glyphosate + [nicosulfuron+mesotrione] + [atrazine + simazine]. Herbicide phytotoxicity to a SYN Supremo VIP3 maize hybrid and control of Urochloa plantaginea and Digitaria ciliaris were evaluated at 7, 14, 21 and 28 days after treatment application. Prior to crop harvest, we determined weed control and, in ten plants per experimental unit, the variables related to grain yield components such as ear insertion height, ear length, number of rows and grains per rows on the ears of corn. During harvest, the mass of one thousand grains and yield were evaluated. It was observed that all herbicide treatments caused low phytotoxicity in maize, except for the post-emergence tank mix composed of glyphosate + 2,4-D and glyphosate + mesotrione, that showed the highest injuries in the four evaluated periods. Most of the herbicides showed good control of D. ciliaris and U. plantaginea, except for the pre-harvest mixture of glyphosate + 2,4-D. The post-emergence glyphosate + [atrazine + simazine] tank mix demonstrated the highest grain yield. It can be concluded, therefore, that depending on the association of herbicides, synergistic effect occurs for both weed control and crop phytotoxicity, being productivity being the main influenced variable.

Effects of Rotation of Cotton (Gossypium Hirsutum L.) and Soybean [Glycine Max (l.) Merr.] Crops on Soil Fertility in Elizabeth, Mississippi, USA

The effects of cotton (Gossypium hirsutum L.): soybean [Glycine max (L.) Merr.] rotation on the soil fertility levels are limited. An irrigated soybean: cotton rotation experiment was conducted from 2012 through 2015 near Elizabeth, Mississippi, USA. The crop rotation sequences were included continuous cotton (CCCC), continuous soybean (SSSS), cotton-soybean-cotton-soybean (CSCS), cotton-soybean-soybean-cotton (CSSC), soybean-cotton-cotton-soybean (SCCS), soybean-cotton-soybean-cotton (SCSC). The crop rotation sequences were followed continuous soybean, continuous cotton, cotton followed by soybean, soybean followed by cotton, soybean followed by two years of cotton, and cotton followed by two years of soybean. A weed control treatment of a non-glyphosate post-emergence vs. glyphosate post emergence was used in both crops. Soil samples taken prior to planting each year and in 2016 showed no differences in cation exchange capacity, organic matter, pH, or macro nutrient levels among the rotations, over the five sampling periods nor weed control methods used for either crop.

Weed management in turmeric

Pre-emergence metribuzin 0.7 kg/ha, pendimethalin 1.0 kg/ha and atrazine 0.75 kg/ha each followed by i) hand weeding (HW) (45 and 75 DAP, days after planting), ii) fenoxaprop 67 g/ha + metsulfuron-methyl 4 g/ha (45 DAP) and iii) mulch + HW (75 DAP); pre-emergence oxyflourfen 0.3 kg/ha and oxadiargyl 0.25 kg/ha and post-emergence glyphosate 1.23 and 1.85 kg/ha (25 DAP) each followed by HW (45 and 75 DAP); HW (25, 45 and 75 DAP) and untreated control were evaluated at Palampur during 2014, 2015 and 2016 to develop an effective weed management strategy in turmeric for mid hill conditions of Himachal Pradesh. Treatments constituting fenoxaprop + metsulfuron-methyl were phyto-toxic resulting in poor turmeric crop canopy formation thereby more growth of Ageratum sp. and lower plant height, plant stand, daughter corms/mother corm, rhizome yield and economics. Other weed control treatments were effective in controlling Echinochloa colona and other grassy weeds. With every g/m2 increase in weed dry weight, the fresh turmeric rhizome yield was reduced by 64.2 kg/ha. Pre-emergence atrazine/metribuzin/pendimethalin fb mulch fb hand weeding had effectively controlled weeds and increased the fresh rhizome yield by 54.1 to 54.9%, cured rhizome yield by 57.6 to 59.4% and net return by 66.4 to 68.3% being comparable to hand weeding thrice. However, hand weeding thrice was the costliest treatment. Atrazine/metribuzin/pendimethalin fb mulch fb hand weeding had lower weed persistence index and weed index and higher weed management index, agronomic management index, integrated weed management index and overall impact index than other treatments. Residues of metribuzin, atrazine, pendimethalin, oxyfluorfen and metsulfuron--methyl in soil and rhizomes of turmeric were found below detectable level. Based on overall impact index metribuzin fb mulch fb hand weeding, atrazine fb mulch fb hand weeding and pendimethalin fb mulch fb hand weeding in that order are recommended as an alternative to hand weeding thrice in turmeric.

Manejo de plantas voluntárias em sistemas de cultivo com soja, milho e algodão resistentes ao glyphosate

A introdução de novas tecnologias de cultivo em lavouras de soja, milho e algodão contribuíram para um aumento significativo da produtividade dessas culturas. Dentre os avanços tecnológicos, pode-se destacar a resistência dessas culturas ao herbicida glyphosate, que a princípio proporcionou um melhor controle de plantas daninhas, sobretudo em áreas com uma grande diversidade de espécies. Adicionalmente, também se pode destacar do ponto de vista prático, o aumento do lapso temporal para o controle das plantas daninhas, visto a possibilidade de aplicação do glyphosate em vários estádios fenológicos da cultura RR®. Entretanto, a “comodidade” proporcionada pela possibilidade de aplicação em pós-emergência de glyphosate em culturas como a soja, o milho e algodão, elevou o consumo dessa molécula, acarretando em uso contínuo por parte dos produtores. Tal efeito decorrente desse uso foi o aumento de pressão de seleção e consequentemente a seleção de biótipos resistentes a essa molécula. Adicionalmente a esse aspecto, recentemente têm se verificado a presença de plantas voluntárias de soja, milho e algodão resistentes ao glyphosate em sistemas de manejo principalmente em sucessão de soja-milho e soja-algodão. Tal fato tem elevado os custos de controle e demandado o uso de alternativas para o manejo dessas plantas voluntárias. Nesse contexto, objetivou-se com esse trabalho abordar e apresentar algumas estratégias de manejo para o controle de soja, milho e algodão RR® voluntário em sistemas de cultivo em sucessão soja-milho e soja-algodão.

Evaluation of two chemical weed control systems in sugar beet in Germany and the Russian Federation

Roundup Ready® sugar beets are widely grown in the USA since their market introduction in 2005. The system has proven to be cost-efficient and reliable. However, the negative social image among consumers and politicians has prohibited the adoption of this technology in Europe. Seven field experiments were conducted over three years in Germany and the Russian Federation to compare weed control efficacy and sugar beet yields of post-emergent glyphosate applications with conventional selective herbicides. Although weed infestations at the Russian sites were higher than in Germany, weed control efficacies were similar at both locations ranging between 78% and 100%. Glyphosate applications resulted in significantly higher weed control efficacies than the conventional herbicides in four out of 7 experiments. In five experiments, a single glyphosate application gave equal weed control efficacy as two and three glyphosate applications. White sugar yield was always higher in the weed control treatments than in the untreated plots. There was no yield difference between treatments based on glyphosate and conventional herbicide applications in 6 out of 7 experiments. The results demonstrate a slight benefit of the glyphosate-based weed control program compared to the conventional herbicide system in terms of weed control efficacy.

Decay and Nutrient Release Patterns of Weeds Following Post-Emergent Glyphosate Control

The role of weed biomass in the nutrient balance of agro-ecosystems remains poorly understood. To measure the rate of decomposition and nutrient release of common weeds, litterbag methodology was employed using waterhemp and giant foxtail desiccated by glyphosate at heights of 10, 20, 30, and 45 cm in two southern Illinois soybean fields. Losses were then expressed as a decay constant (k) regressed over time according to the single exponential decay model. Concentrations of the recalcitrant cell wall components (cellulose, hemicellulose, and lignin) were generally greatest as weed height (maturity) increased in giant foxtail compared with waterhemp. Sixteen weeks after desiccation by glyphosate, 10-cm waterhemp and giant foxtail detritus had lost 10 and 12% more mass, respectively, compared to the 45-cm height of each species. Decomposition rates revealed mass loss was highest for 10-cm waterhemp (kD = 0.022) and lowest for 45-cm giant foxtail (kD = 0.011) and this process was negatively correlated to the overall amount of cell wall constituents (r = −0.73). Nutrient release rates followed a similar trend in that both shorter (younger) weeds and waterhemp liberated nutrients more readily. Across all tested plant material, K was the nutrient most rapidly released, whereas, Ca was the most strongly retained nutrient.

Weed control with postemergence glyphosate tank mixes in glyphosate-resistant soybean

Walsh, K. D., Soltani, N., Brown, L. R. and Sikkema, P. H. 2014. Weed control with postemergence glyphosate tank mixes in glyphosate-resistant soybean. Can. J. Plant Sci. 94: 1239–1244. Six field trials were conducted over a 3-yr period (2011, 2012 and 2013) in Ontario, Canada, to evaluate various postemergence (POST) glyphosate tank mixes for weed management in glyphosate-resistant (GR) soybean. Herbicide treatments included glyphosate applied alone or mixed with acifluorfen, fomesafen, bentazon and thifensulfuron-methyl. Glyphosate tank mixtures with acifluorfen, fomesafen, bentazon and thifensulfuron-methyl caused GR soybean injury of up to 21, 11, 4 and 14% at 7 d after treatment (DAT), which was reduced to 5, 0, 0 and 2% by 28 DAT, respectively. Velvetleaf, green pigweed, common ragweed and common lambsquarters control ranged from 55 to 95, 93 to 100, 70 to 92 and 81 to 98% at 28 DAT respectively. Relative to glyphosate alone, tank mixtures with thifensulfuron-methyl provided equivalent to increased weed control, while acifluorfen, fomesafen and bentazon provided equivalent to reduced weed control. All herbicide tank mixtures resulted in higher yields (3.8–4.0 t ha−1) than the untreated check (2.7 t ha−1), and were generally equivalent to glyphosate alone (4.1 t ha−1). Results from this study indicate that the glyphosate tank mixtures evaluated did not provide a benefit over glyphosate alone.

Efficacy of POST glyphosate applications in combination with other POST herbicides in glyphosate-resistant corn (Zea mays L.)

The use of glyphosate-resistant corn has facilitated a shift from a reliance on preemergence residual herbicides to postemergence (POST) herbicides, and in some cases exclusively glyphosate. Glyphosate is a non-selective herbicide that is relatively slow-acting, which may allow weeds to continue to compete with corn after application and potentially decrease crop yield. The addition of several POST corn herbicides, with some residual control, to an early-season glyphosate application was examined to determine if the tankmix combination would improve the speed of weed control compared to glyphosate applied alone. Seven field trials were conducted over three years (2009, 2010 and 2011) near Ridgetown and Exeter, Ontario. The control of common ragweed was improved 3 days after application (DAA) with three POST glyphosate tankmixes compared to glyphosate alone. However control was still less than 55%. Depending on the weed species examined, at 28 DAA two of the glyphosate tankmix treatments tested provided better common ragweed, common lambsquarters, or green foxtail control than glyphosate alone. Treatments providing better weed control at 28 DAA also typically decreased weed density compared to glyphosate alone.