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BACKGROUND: Johnsongrass (Sorghum halepense) is one of the weeds that evolves resistance to glyphosate [N‐(phosphonomethyl)‐glycine], the most widely used herbicide, and the weed may cause agronomic troublesome in the southern USA. This paper reports a study on developing a hyperspectral plant sensing approach to explore the spectral features of glyphosate‐resistant (GR) and glyphosate‐sensitive (GS) plants to evaluate this approach using machine learning algorithms to differentiate between GR and GS plants. RESULTS: On average, GR plants have higher spectral reflectance compared with GS plants. The sensitive spectral bands were optimally selected using the successive projections algorithm respectively wrapped with the machine learning algorithms of k‐nearest neighbors (KNN), random forest (RF), and support vector machine (SVM) with Fisher linear discriminant analysis (FLDA) to classify between GS and GS plants. At 3 weeks after transplanting (WAT) KNN and SVM could not acceptably classify the GR and GS plants but they improved significantly with the stages to have their overall accuracies reaching 73% and 77%, respectively, at 5 WAT. RF and FLDA had a better ability to classify the plants at 3 WAT but RF was low in accuracy at 2 WAT while FLDA dropped accuracy to 50% at 4 WAT from 57% at 3 WAT and raised it to 73% at 5 WAT. CONCLUSIONS: Previous studies were conducted developing the hyperspectral imaging approach to differentiate GR Palmer amaranth from GS Palmer amaranth and GR Italian ryegrass from GS Italian ryegrass with classification accuracies of 90% and 80%, respectively. This study demonstrated that the hyperspectral plant sensing approach could be developed to differentiate GR johnsongrass from glyphosate‐sensitive GS johnsongrass with the highest classification accuracy of 77%. The comparison with our previous studies indicated that the similar hyperspectral approach could be used and transferred from classification across different GR and GS weed biotypes, such as Palmer amaranth, Italian ryegrass and johnsongrass, so it is highly possible for classification of more other GR and GS weed biotypes as well. On the basis of classic pattern recognition approaches the process of plant classification can be enhanced by modeling using machine learning algorithms. © 2022 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: There has been controversy as to whether the glyphosate resistance gene and/or glyphosate applied to glyphosate‐resistant (GR) soybean affect the content of cationic minerals (especially Mg, Mn and Fe), yield and amino acid content of GR soybean. A two‐year field study (2013 and 2014) examined these questions at sites in Mississippi, USA. RESULTS: There were no effects of glyphosate, the GR transgene or field crop history (for a field with both no history of glyphosate use versus one with a long history of glyphosate use) on grain yield. Furthermore, these factors had no consistent effects on measured mineral (Al, As, Ba, Cd, Ca, Co, Cr, Cs, Cu, Fe, Ga, K, Li, Mg, Mn, Ni, Pb, Rb, Se, Sr, Tl, U, V, Zn) content of leaves or harvested seed. Effects on minerals were small and inconsistent between years, treatments and mineral, and appeared to be random false positives. No notable effects on free or protein amino acids of the seed were measured, although glyphosate and its degradation product, aminomethylphosphonic acid (AMPA), were found in the seed in concentrations consistent with previous studies. CONCLUSIONS: Neither glyphosate nor the GR transgene affect the content of the minerals measured in leaves and seed, harvested seed amino acid composition, or yield of GR soybean. Furthermore, soils with a legacy of GR crops have no effects on these parameters in soybean. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND We report results of the last two years of a 7 year field experiment designed to test the null hypothesis: applications of glyphosate on glyphosate-resistant ( GR) and non-resistant (non- GR) corn ( Zea mays L.) under conventional tillage and no-till would have no effect on soil exoenzymes and microbial activity. RESULTS Bulk soil ( BS) and rhizosphere soil ( RS) macronutrient ratios were not affected by either GR or non- GR corn, or glyphosate applications. Differences observed between exoenzyme activities were associated with tillage rather than glyphosate applications. In 2013, nutrient acquisition ratios for bulk and rhizosphere soils indicated P limitations, but sufficient assimilable N. In 2014, P limitations were observed for bulk and rhizosphere soils, in contrast to balanced C and N acquisition ratios in rhizosphere soils. Stoichiometric relationships indicated few differences between glyphosate and non-glyphosate treatments. Negative correlations between C:P and N:P nutrient ratios and nutrient acquisition ratios underscored the inverse relation between soil nutrient status and microbial community exoenzyme activities. CONCLUSIONS Inconsistent relationships between microbial community metabolic activity and exoenzyme activity indicated an ephemeral effect of glyphosate on BS exoenzyme activity. Except for ephemeral effects, glyphosate applications appeared not to affect the function of the BS and RS exoenzymes under conventional tillage or no-till. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

BACKGROUND Glyphosate drift onto off-target sensitive crops can reduce growth and yield and is of great concern to growers and pesticide applicators. Detection of herbicide injury using biological responses is tedious, so more convenient and rapid detection methods are needed. The objective of this research was to determine the effects of glyphosate on biological responses of non-glyphosate-resistant (non- GR) soybean and to correlate vegetation indices ( VIs) derived from aerial multispectral imagery. RESULTS Plant height, shoot dry weight and chlorophyll ( CHL) content decreased gradually with increasing glyphosate rate, regardless of weeks after application ( WAA). Accordingly, soybean yield decreased by 25% with increased rate from 0 to 0.866 kg AI ha−1. Similarly to biological responses, the VIs derived from aerial imagery - normalized difference vegetation index, soil adjusted vegetation index, ratio vegetation index and green NDVI - also decreased gradually with increasing glyphosate rate, regardless of WAA. CONCLUSION The VIs were highly correlated with plant height and yield but poorly correlated with CHL, regardless of WAA. This indicated that indices could be used to determine soybean injury from glyphosate, as indicated by the difference in plant height, and to predict the yield reduction due to crop injury from glyphosate. Published2014.Thisarticle is a U.S.Government work and is in the public domainin the USA. [ABSTRACT FROM AUTHOR]

BACKGROUND Palmer amaranth ( Amaranthus palmeri S. Wats.) is a troublesome agronomic weed in the southern United States, and several populations have evolved resistance to glyphosate. This paper reports on spectral signatures of glyphosate-resistant ( GR) and glyphosate-sensitive ( GS) plants, and explores the potential of using hyperspectral sensors to distinguish GR from GS plants. RESULTS GS plants have higher light reflectance in the visible region and lower light reflectance in the infrared region of the spectrum compared with GR plants. The normalized reflectance spectrum of the GR and GS plants had best separability in the 400-500 nm, 650-690 nm, 730-740 nm and 800-900 nm spectral regions. Fourteen wavebands from within or near these four spectral regions provided a classification of unknown set of GR and GS plants, with a validation accuracy of 94% for greenhouse-grown plants and 96% for field-grown plants. CONCLUSIONS GR and GS Palmer amaranth plants have unique hyperspectral reflectance properties, and there are four distinct regions of the spectrum that can separate the GR from GS plants. These results demonstrate that hyperspectral imaging has potential application to distinguish GR from GS Palmer amaranth plants (without a glyphosate treatment), with future implications for glyphosate resistance management. Published 2014. This article is a U.S. Government work and is in the public domain in the USA [ABSTRACT FROM AUTHOR]

Early detection of crop injury from herbicide glyphosate is of significant importance in crop management. In this paper, we attempt to detect glyphosate-induced crop injury by PROSPECT (leaf optical PROperty SPECTra model) inversion through leaf hyperspectral reflectance measurements for non-Glyphosate-Resistant (non-GR) soybean and non-GR cotton leaves. The PROSPECT model was inverted to retrieve chlorophyll content ( C a+b ), equivalent water thickness ( C w ), and leaf mass per area ( C m ) from leaf hyperspectral reflectance spectra. The leaf stress conditions were then evaluated by examining the temporal variations of these biochemical constituents after glyphosate treatment. The approach was validated with greenhouse-measured datasets. Results indicated that the leaf injury caused by glyphosate treatments could be detected shortly after the spraying for both soybean and cotton by PROSPECT inversion, with C a+b of the leaves treated with high dose solution decreasing more rapidly compared with leaves left untreated, whereas the C w and C m showed no obvious difference between treated and untreated leaves. For both non-GR soybean and non-GR cotton, the retrieved C a+b values of the glyphosate treated plants from leaf hyperspectral data could be distinguished from that of the untreated plants within 48 h after the treatment, which could be employed as a useful indicator for glyphosate injury detection. These findings demonstrate the feasibility of applying the PROSPECT inversion technique for the early detection of leaf injury from glyphosate and its potential for agricultural plant status monitoring. [ABSTRACT FROM AUTHOR]

In this paper, we aim to detect crop injury from glyphosate, a herbicide, by both traditionally used spectral indices and newly extracted features with leaf hyperspectral reflectance data for non-Glyphosate-Resistant (non-GR) soybean and non-GR cotton. The new features were extracted by canonical analysis technique, which could provide the largest separability to distinguish the injured leaves from the healthy ones. Spectral bands used for constructing these new features were selected based on the sensitivity analysis results of a physically-based leaf radiation transfer model (leaf optical PROperty SPECTra model, PROSPECT), which could help extend the effectiveness of these features to a wide range of leaf structures and growing conditions. This approach has been validated with greenhouse measured data acquired in glyphosate treatment experiments. Results indicated that glyphosate injury could be detected by NDVI (Normalized Difference Vegetation Index), RVI (Ratio Vegetation Index), SAVI (Soil Adjusted Vegetation Index), and DVI (Difference Vegetation Index) in 48 h After the Treatment (HAT) for soybean and in 72 HAT for cotton, but the other spectral indices either showed little use for separation, or did not show consistent separation for healthy and injured soybean and cotton. Compared with the traditional spectral indices, the new features were more feasible for the early detection of glyphosate injury, with leaves sprayed with a higher rate of glyphosate solution having larger feature values. This trend became more and more pronounced with time. Leaves sprayed with different glyphosate rates showed some separability 24 HAT using the new features and could be totally distinguished at and beyond 48 HAT for both soybean and cotton. These findings demonstrated the feasibility of applying leaf hyperspectral reflectance measurements for the early detection of glyphosate injury using these newly proposed features. [ABSTRACT FROM AUTHOR]

Abstract: Laboratory and field studies were conducted to assess the effects of glyphosate on Macrophomina phaseolina culture growth in vitro and the disease severity of charcoal rot in soybean fields at Stoneville, MS and Jackson, TN. Glyphosate inhibited M. phaseolina growth in a linear dose dependent manner when technical grade glyphosate acid (GlyCry) was used; however, growth was inhibited in an exponential dose dependent manner when a commercial formulation of glyphosate-potassium salt (Gly-K salt) was used. The glyphosate GR50 values (glyphosate concentration required to cause a 50% reduction) in culture radial growth ranged from 0.25 to 9.94 mM among the M. Phaseolina isolates, temperatures, and formulations. The three isolates differed in response to various concentrations across the three temperature regimes. Among the three isolates, TN 410 was the most sensitive for both GlyCry (GR50 = 7.74 mM) and Gly-K salt (GR50 = 0.25 mM) at 30 °C. This research indicates that glyphosate has the ability to inhibit growth of M. phaseolina in culture in vitro. The preliminary field studies demonstrated that application of glyphosate to glyphosate-resistant soybeans did not enhance or reduce the severity of charcoal rot in a no-till field in TN but had some suppressing effect in a tilled environment in MS when single applications were made at growth stage V3 and V6. [Copyright &y& Elsevier]

Saflufenacil is a new herbicide on the market and its effectiveness on horseweed, several populations of which have evolved resistance to glyphosate, is not clear. In this research, the effect of adjuvants on the control of horseweed with saflufenacil in the field, the effect of the interaction between glyphosate and saflufenacil on glyphosate-resistant and glyphosate-susceptible horseweed and the patterns of uptake and translocation of glyphosate applied alone and in combination with saflufenacil in horseweed were evaluated. The addition of methylated seed oil to saflufenacil provided the best control of horseweed, with crop oil concentrate being intermediate in effect and non-ionic surfactant ranking as the least-effective adjuvant. The interaction between glyphosate and saflufenacil was additive with regards to the control of glyposate-resistant horseweed. The glyphosate-susceptible horseweed population absorbed 6-13% more 14C-glyphosate than the glyphosate-resistant population. The addition of saflufenacil reduced 14C-glyphosate translocation in both the glyphosate-resistant and the glyphosate-susceptible horseweed populations by at least 6%; however, due to the exceptional efficacy of saflufenacil, these reductions did not reduce the level of control. Saflufenacil holds great potential as an alternative control option for glyphosate-resistant horseweed and is a valuable tool in the management of resistant weeds. [ABSTRACT FROM AUTHOR]

Information on long-term glyphosate- and glufosinate-resistant corn (Zea mays L.) production on weed control and rotation benefits is lacking. A six-year field study was conducted from 2004 to 2009 at Stoneville, MS, to examine the effects of rotating glyphosate-resistant and glufosinate-resistant corn under reduced tillage conditions on weed control, soil weed seedbanks, and yield. The four rotation systems were glyphosate-resistant and glufosinate-resistant corn grown continuously and in rotation with two herbicide programs, post-emergence-only herbicides (POST) and preemergence herbicides followed by POST (PRE + POST). Control of 13 predominant weed species in glyphosate-resistant and glufosinate-resistant corn was >95%, regardless of herbicide program, with the exception of johnsongrass and yellow nutsedge, both perennial weeds. Johnsongrass and yellow nutsedge control was lower in the continuous glufosinate-resistant corn system compared with other rotation systems. Yellow nutsedge control was higher with the PRE + POST (89% to 99%) compared with the POST-only (72% to 86%) treatment. Corn yields were similar regardless of rotation when a corn cultivar stacked with both glyphosate-resistant and glufosinate-resistant traits was used. The PRE + POST program gave 5% to 10% higher yield than the POST-only program in four of six years. The seedbank for yellow nutsedge and predominant grass and broadleaf weeds was not significant among the four rotation systems. Seedbanks for grasses and yellow nutsedge were higher in the POST-only program (20.5 and 1.8 per core of 678 cm3, respectively) compared with the PRE + POST program (9.5 and 0.4 per core, respectively). These results indicate that johnsongrass and yellow nutsedge control could be reduced in continuous glufosinate-resistant corn and could be mitigated by rotating with glyphosate-resistant corn. [ABSTRACT FROM PUBLISHER]

When glyphosate is applied to glyphosate-resistant (GR) crops, drift on to off-target sensitive crops may cause injury and mortality. An aerial application drift study was conducted in 2009 to determine biological effects of glyphosate on non-glyphosate-resistant (non-GR) cotton (Gossypium hirsutum L.) and non-GR soybean [Glycine max (L.) Merr.]. Glyphosate at 866 g ae/ha was applied using an Air Tractor 402B agricultural aircraft in an 18.3 m spray swath to crops at the two- to three-leaf stage. Visual plant injury, chlorophyll, shikimate, plant height, and shoot dry weight were determined at one, two, and three weeks after application (WAA) of glyphosate. Biological responses differed between crops as a function of downwind drift distance. For example, at 3 WAA soybean was dead 6 m downwind from the spray swath, whereas cotton sustained 85% visual injury. Plant injury was not observed beyond 25.6 m downwind in soybean and 35.4 m downwind in cotton at 3 WAA. Chlorophyll reduction was higher (80%) in soybean compared with cotton (43%) at 0 m from the edge of the spray at 1 WAA. Shikimate levels 1 WAA decreased from 1518% at 0 m to 209% at 35.4 m downwind in soybean; at the same sampling time shikimate levels in cotton decreased from 464% at 0 m to 0% at 35.4 m. At 35.4 m downwind, shoot dry weight (5-13%) and plant height (6-8%) were reduced in both crops at 3 WAA. The biological response of soybean and cotton to glyphosate drift decreased with increased distance from the edge of spray swath. These biological data suggested that soybean was more susceptible to glyphosate drift than cotton and elevated shikimate level could be used as a sensitive indicator to confirm plant exposure to glyphosate drift. [ABSTRACT FROM AUTHOR]

Abstract: Aminomethylphosphonic acid (AMPA) is formed in glyphosate-treated glyphosate-resistant (GR) and glyphosate-sensitive (GS) soybean [Glycine max (L.) Merr.] plants and is known to cause yellowing in soybean. Although, AMPA is less phytotoxic than glyphosate, its mode of action is different from that of glyphosate and is still unknown. Greenhouse studies were conducted at Stoneville, MS to determine the effects of AMPA on plant growth, chlorophyll content, photosynthesis, nodulation, nitrogenase activity, nitrate reductase activity, and shoot nitrogen content in GR and GS soybeans. AMPA was applied to one- to two-trifoliolate leaf stage soybeans at 0.1 and 1.0kgha−1, representing a scenario of 10% and 100% degradation of glyphosate (1.0kgaeha−1 use rate) to AMPA, respectively. Overall, AMPA effects were more pronounced at 1.0kgha−1 than at 0.1kgha−1 rate. Visual plant injury (18–27%) was observed on young leaves within 3d after treatment (DAT) with AMPA at the higher rate regardless of soybean type. AMPA injury peaked to 46–49% at 14 DAT and decreased to 17–18% by 28 DAT, in both soybean types. AMPA reduced the chlorophyll content by 37%, 48%, 66%, and 23% in GR soybean, and 17%, 48%, 57%, and 22% in GS soybean at 3, 7, 14, and 28 DAT, respectively. AMPA reduced the photosynthesis rate by 65%, 85%, and 77% in GR soybean and 59%, 88%, and 69% in GS soybean at 3, 7, and 14 DAT, respectively, compared to non-treated plants. Similarly, AMPA reduced stomatal conductance to water vapor and transpiration rates at 3, 7, and 14 DAT compared to non-treated plants in both soybean types. Photosynthesis rate, stomatal conductance, and transpiration rate recovered to the levels of non-treated plants by 28 DAT. Plant height and shoot dry weight at 28 DAT; nodulation, nitrogenase activity at 10 DAT, and nitrate reductase activity at 3 and 14 DAT were unaffected by AMPA. AMPA reduced root respiration and shoot nitrogen content at 10 DAT. These results suggest that a foliar application of AMPA could indirectly reduce photosynthesis through decreased chlorophyll content in GR and GS soybean up to 14 DAT, but affected plants can recover to normal growth by 28 DAT. [Copyright &y& Elsevier]

The article presents a study which examines the implication to the chlorophyll content, plant height, and shikimate level of corn crops regarding the single aerial application of glyphosate drift. The aerial application of glyphosate was conducted to the corn area of U.S. Department of Agriculture-Agricultural Research on August 12, 2009 in Mississippi. The study reveals that the plant height, chlorophyll, and the plant dry weight can be affected by the aerial spray of glyphosate.

The article reviews the impact on soil of conservation practices and glyphosate-resistant crops. It presents data from a Mississippi field trial comparing glyphosate-resistant and non-glyphosate resistant maize (Zea mays L.) and cotton (Gossypium hirsutum L.) under the limited tillage management. The review concludes that there are minor effects of glyphosate use on soil biological/chemical properties. On the other hand, enhanced organic carbon and plant residues in surface soils under conservation practices can influence potential effects of glyphosate. It is recommended that a long-term research under various cropping systems and ecological reasons be made for the critical assessment of glyphosate-resistant crop and conservation practice interactions.

The article presents a study that determined the impact of glyphosate on the structure, activity, and function of soil microbial community. The study collected soil samples from soil microbial communities on a silt loam soil in Stoneville, Mississippi. It analyzed the soil samples' fatty acid methyl esters (FAMEs) and discovered that there is no differentiation between field treatments of the total FAME profile. The study also found out that there is no significant herbicide effect in community shifts or bulk soil. It concludes that glyphosates did not create significant whole microbial community shifts.

Abstract: Transgenic glyphosate-resistant (GR) soybean [Glycine max (L.) Merr.] expressing a glyphosate-insensitive 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) enzyme has provided new opportunities for weed control in soybean production. However, glyphosate is toxic to the soybean nitrogen-fixing symbiont, Bradyrhizobium japonicum, as its EPSPS enzyme is sensitive to glyphosate. The effects of glyphosate on symbiotic parameters, nitrogen accumulation, and yield in GR soybean under weed-free conditions were determined in a 3-yr field study during 2002–2004. Four glyphosate (0.84, 1.68, 2.52+2.52, and 0.84+0.84kgae/ha) treatments applied at 4 and 6 weeks after planting (WAP) soybean were compared to a no glyphosate, hand weeded (weed-free) control. In 2002 and 2003, soybean plants were harvested at 5, 6, 7, and 8WAP, and roots assessed for nitrogenase activity (acetylene reduction assay, ARA), root respiration, nodulation, and root biomass. Soybean seed yield, leaf and seed nitrogen content were determined in all three years. No consistent effect of glyphosate was observed on either ARA or root respiration. In 2002, both ARA and respiration were about a third of that in 2003, attributed to early-season drought in 2002. All glyphosate treatments reduced foliar nitrogen content (26–42%) in 2002. In 2003 and 2004, three and two glyphosate treatments, respectively, reduced foliar nitrogen content (8–13%), with the greatest reduction when glyphosate was applied at the highest rate. Soybean yield was reduced by 11% with two applications of 2.52kgae/ha glyphosate compared to hand weeded control in 2002, but seed yield was not affected in 2003 and 2004. Total seed nitrogen harvested in 2002 and 2003 was reduced by 32% and 17%, respectively, when two applications of 2.52kgae/ha glyphosate were applied compared to hand weeded soybean. These studies indicate that nitrogen fixation and/or assimilation in GR soybean was only slightly affected at label use rate, but was consistently reduced at above label use rates of glyphosate and the greatest reductions occurred with soil moisture stress following glyphosate application. [Copyright &y& Elsevier]

In controlled environment experiments, the bioherbicidal fungus Myrothecium verrucaria (Alb. & Schwein.) Ditmar:Fr. was tested alone, in combination with, prior to, and following treatment with glyphosate [N-(phosphonomethyl)glycine] for control of kudzu [Pueraria lobata (Willd.) Ohwi], redvine [Brunnichia ovata (Walt.) Shinners], and trumpetcreeper [Campsis radicans (L.) Seem. ex Bureau] at temperatures of 20, 30, and 40°C. At all temperatures, kudzu was most adversely affected by the fungus, followed by trumpetcreeper and redvine, as indicated by greater mortality and dry weight reductions. Trumpetcreeper and redvine mortalities and dry weight reductions significantly increased when the fungus was applied 2 days after the glyphosate treatment. Application of the fungus combined with or prior to glyphosate treatment resulted in reduced weed control. Although pathogenesis and mortality also occurred at 20°C, disease development was favored by higher temperatures (30 and 40°C). Infected weeds of each species exhibited similar disease symptomatology within 12 h following treatment at incubation temperatures of 30 and 40°C. Disease symptomatology was characterized by necrotic flecking on leaves that coalesced into large lesions. Symptoms progressed, initially infecting cotyledons and leaves, and later (within 48 h) producing stem lesions. The fungus sporulated profusely on infected tissue and was easily reisolated. These results suggest that timing of glyphosate application in relation to combined treatment with the bioherbicide M. verrucaria can improve the control of kudzu, redvine, and trumpetcreeper. [ABSTRACT FROM AUTHOR]

A 3-year field research was conducted in 1997, 1998, and 1999 at Stoneville, MS on a Dundee silt loam soil to study efficacy and economics of glyphosate with or without preemergence (PRE) herbicides in glyphosate-resistant soybean under conventional tillage (CT) and no-tillage (NT) systems. Single or sequential glyphosate postemergence (POST) applications provided at least 91% control of Echinochloa crusgalli (L.) Beauv. (barnyardgrass), Brachiaria platyphylla (Griseb.) Nash (broadleaf signalgrass), Brachiaria ramosa (L.) Stapf (browntop millet), Sesbania exaltata (Raf.) Rydb. ex A.W. Hill (hemp sesbania), Sorghum halepense (L.) Pers. (johnsongrass), Senna obtusifolia (L.) Irwin and Barneby (sicklepod), Ipomoea lacunosa L. (pitted morningglory), Sida spinosa L. (prickly sida), and Cyperus esculentus L. (yellow nutsedge), and POST-only programs were as effective as PRE followed by POST programs. Two POST applications of glyphosate produced highest soybean yield (2,710 kg/ha) and net return ($280/ha). Single POST application of glyphosate resulted in greater net return ($226/ha) compared to the conventional standard (pendimethalin, imazaquin, acifluorfen, bentazon, and clethodim) herbicide program ($58/ha), although both had similar yields. Addition of PRE herbicides tend to increase herbicide costs and decrease net returns compared to two POST applications of glyphosate. Soybean yield and net return were lower in NT compared to CT systems, due to a lower soybean stand establishment in NT systems. These results suggest that when yields are comparable among various herbicide programs, net return is dictated by the cost of the herbicide program, including seeds and associated technology fee. [ABSTRACT FROM PUBLISHER]

Greenhouse and growth chamber experiments were conducted to examine glyphosate [isopropylamine salt of N-(phosphonomethyl) glycine] effects on growth, chlorophyll content, nodulation, and nodule leghemoglobin content of glyphosate-resistant and susceptible soybean (Glycine max [L.] Merr.) varieties. In susceptible soybean, a single application of 0.28 kg/ha reduced chlorophyll content (49%), and shoot and root dry weight (50 and 57%, respectively) at 2 wk after treatment. In glyphosate-resistant soybean, there were no significant effects on these parameters by single application up to 1.12 kg/ha, but 2.24 kg/ha reduced shoot and root dry weight by 25 to 30%. Application of glyphosate 1.12 kg/ha, followed by sequential applications at 0.56 or 1.12 kg/ha, did not affect plant growth and chlorophyll content, but application of 2.24 kg/ha followed by sequential application of 2.24 kg/ha reduced root growth. In glyphosate-resistant soybean, an application of 1.12 kg/ha 3 wk after planting did not affect nodule number or mass, but 2.24 kg/ha reduced these parameters by 30 and 39%, respectively, compared to untreated. Leghemoglobin content of nodules was reduced (6 to 18%) by both glyphosate rates, but effects were inconsistent with rate. At post-treatment temperatures of 18/13_C (day/night), glyphosate at 1.12 kg/ha or 2.24 kg/ha did not affect chlorophyll and growth of glyphosate-resistant soybean. However, at 25/20 and 32/27_C (day/night), glyphosate at 2.24 kg/ha reduced both chlorophyll content and growth of glyphosate-resistant soybean. Overall, treatment of glyphosate- resistant soybean with glyphosate at 1.12 had little or no effect on chlorophyll content and dry weight of shoots and roots in five of five trials. But treatment of glyphosate at 2.24 kg/ha reduced these parameters in three of five trials, suggesting potential for soybean injury at higher rates. Results showed subtle reductions of nodulation in glyphosate- resistant soybean using label rates of glyphosate, but these effects may be of minimal consequence due to the potential of soybean to compensate after short durations of stress. [ABSTRACT FROM PUBLISHER]

Glyphosate is the most widely used herbicide in crop production due to the widespread adoption of glyphosate-resistant (GR) crops. However, the spray of glyphosate onto non-target crops from ground or aerial applications can cause severe injury to non-GR corn plants. To evaluate the crop damage of the non-GR corn plants from glyphosate and the recoverability of the damaged plants, we used the hyperspectral imaging (HSI) technique in field experiments with different glyphosate application rates. This study investigated the spectral characteristic of corn plants and assessed the corn plant damage from glyphosate. Based on HSI image analysis, a spectral variation pattern was observed at 1 week after treatment (WAT), 2 WAT, and 3 WAT from the glyphosate-treated non-GR corn plants. It was further found that the corn plants treated with glyphosate rates equal to or higher than 0.5X (X = 0.866 kilograms acid equivalents/hectare (kg ae/ha) represents the recommended spray rate for GR corn) would suffer unrecoverable damage. Using the Jeffries–Matusita distance as the spectral sensitivity criterion, three sensitive bands from the measured spectra were selected to create two spectral indices for crop recoverability differentiation in band ratio and normalization forms, respectively. With the two spectral indices, the corn plants recoverable and unrecoverable from damage were classified with an overall accuracy greater than 95%. Then, three machine learning algorithms (k-nearest neighbors, random forest, and support vector machine) were respectively combined with the successive projections algorithm to create models to relate selected feature spectral bands to glyphosate spray rates. The results indicated that the models achieved reasonable accuracy, especially in the group of recoverable plants. This study illustrated the potential of the hyperspectral imaging technique for evaluating crop damage from herbicides and recoverability of the injured plants using different data analysis and machine learning modeling approaches for practical weed management in crop fields. [ABSTRACT FROM AUTHOR]

Despite glyphosate's wide use for weed control in agriculture, questions remain about the herbicide's effect on soil microbial communities. The existing scientific literature contains conflicting results, from no observable effect of glyphosate to the enrichment of agricultural pathogens such as Fusarium spp. We conducted a comprehensive field-based study to compare the microbial communities on the roots of plants that received a foliar application of glyphosate to adjacent plants that did not. The 2-year study was conducted in Beltsville, MD, and Stoneville, MS, with corn and soybean crops grown in a variety of organic and conventional farming systems. By sequencing environmental metabarcode amplicons, the prokaryotic and fungal communities were described, along with chemical and physical properties of the soil. Sections of corn and soybean roots were plated to screen for the presence of plant pathogens. Geography, farming system, and season were significant factors determining the composition of fungal and prokaryotic communities. Plots treated with glyphosate did not differ from untreated plots in overall microbial community composition after controlling for other factors. We did not detect an effect of glyphosate treatment on the relative abundance of organisms such as Fusarium spp. [ABSTRACT FROM AUTHOR]

Abstract: Glyphosate is a non-selective, systemic herbicide highly toxic to sensitive plant species. Its use has seen a significant increase due to the increased adoption of genetically modified glyphosate-resistant crops since the mid-1990s. Glyphosate application for weed control in glyphosate-resistant crops can drift onto an off-target area, causing unwanted injury to non-glyphosate resistant plants. Thus, early detection of crop injury from off-target drift of herbicide is critical in crop production. In non-glyphosate-resistant plants, glyphosate causes a reduction in chlorophyll content and metabolic disturbances. These subtle changes may be detectable by plant reflectance, which suggests the possibility of using optical remote sensing for early detection of drift damage to plants. In order to determine the feasibility of using optical remote sensing, a greenhouse study was initiated to measure the canopy reflectance of soybean plants using a portable hyperspectral image sensor. Non-glyphosate resistant soybean (Glycine max L. Merr.) plants were treated with glyphosate using a pneumatic track sprayer in a spray chamber. The three treatment groups were control (0kg ae/ha), low dosage (0.086kg ae/ha), and high dosage (0.86kg ae/ha), each with four 2-plant pots. Hyperspectral images were taken at 4, 24, 48, and 72h after application. The extracted canopy reflectance data was analyzed with vegetation indices. The results indicated that a number of vegetation indices could identify crop injury at 24h after application, at which time visual inspection could not distinguish between glyphosate injured and non-treated plants. To improve the results a modified method of spectral derivative analysis was proposed and applied to find that the method produced better results than the vegetation indices. Four selected first derivatives at wavelength 519, 670, 685, and 697nm could potentially differentiate crop injury at 4h after treatment. The overall false positive rate was lower than the vegetation indices. Furthermore, the derivatives demonstrated the ability to separate treatment groups with different dosages. The study showed that hyperspectral imaging of plant canopy reflectance could be a useful tool for early detection of soybean crop injury from glyphosate, and that the modified spectral derivative analysis had a better performance than vegetation indices. [Copyright &y& Elsevier]