Browsing by Author "Jha, Prashant"

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Discrimination of herbicide-resistant kochia with hyperspectral imaging
(2018-03) Nugent, Paul W.; Shaw, Joseph A.; Jha, Prashant; Scherrer, Bryan; Donelick, Andrew; Kumar, Vipan
A hyperspectral imager was used to differentiate herbicide-resistant versus herbicide-susceptible biotypes of the agronomic weed kochia, in different crops in the field at the Southern Agricultural Research Center in Huntley, Montana. Controlled greenhouse experiments showed that enough information was captured by the imager to classify plants as either a crop, herbicidesusceptible or herbicide-resistant kochia. The current analysis is developing an algorithm that will work in more uncontrolled outdoor situations. In overcast conditions, the algorithm correctly identified dicamba-resistant kochia, glyphosate-resistant kochia, and glyphosate-and dicamba-susceptible kochia with 67%, 76%, and 80% success rates, respectively. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.
Effective Preemergence and Postemergence Herbicide Programs for Kochia Control
(2015-03) Kumar, Vipan; Jha, Prashant
Field experiments were conducted in 2011 through 2013 at the MSU Southern Agricultural Research Center near Huntley, MT, to evaluate the effectiveness of various PRE and POST herbicide programs for kochia control in the absence of a crop. PRE herbicides labeled for corn, grain sorghum, soybean, wheat/barley, and/or in chemical fallow were applied at recommended field-use rates. Acetochlor + atrazine, S-metolachlor + atrazine + mesotrione, and sulfentrazone applied PRE provided ≥91% control of kochia at 12 wk after treatment (WAT). Metribuzin, metribuzin + linuron, and pyroxasulfone + atrazine PRE provided 82% control at 12 WAT. PRE control with acetochlor + flumetsulam + clopyralid, pyroxasulfone alone, and saflufenacil + 2,4-D was ≤23% at 12 WAT. Paraquat + atrazine, paraquat + linuron, and paraquat + metribuzin controlled kochia ≥98% at 5 WAT. POST control with bromoxynil + fluroxypyr, paraquat, tembotrione + atrazine, and topramezone + atrazine treatments averaged 84% at 5 WAT, and did not differ from glyphosate. Control with POST-applied bromoxynil + pyrasulfotole, dicamba, diflufenzopyr + dicamba + 2,4-D, saflufenacil, saflufenacil + 2,4-D, saflufenacil + linuron was 67 to 78% at 5 WAT. Because of the presence of kochia resistant to acetolactate synthase-inhibiting herbicides at the test site, cloransulam-methyl was not a viable option for kochia control. In a separate greenhouse study, kochia accessions showed differential response to the POST herbicides (labeled for corn or soybean) tested. Tembotrione + atrazine, topramezone + atrazine, lactofen, or fomesafen effectively controlled the glyphosate-resistant kochia accession tested. Growers should utilize these effective PRE- or POST-applied herbicide premixes or tank mixtures (multiple modes of action) to control herbicide-resistant kochia accessions in the field. PRE herbicides with 8 wk of soil-residual activity on kochia would be acceptable if crop competition were present; however, a follow-up herbicide application may be needed to obtain season-long kochia control in the absence of crop competition. Nomenclature: 2,4-D; acetochlor; atrazine; bromoxynil; carfentrazone-ethyl; clopyralid; cloransulam-methyl; dicamba; diflufenzopyr; flumetsulam; flumioxazin; fluroxypyr; fomesafen; glufosinate; glyphosate; isoxaflutole; lactofen; linuron; MCPA; mesotrione; metolachlor; paraquat; pyrasulfotole; pyroxasulfone; saflufenacil; sulfentrazone; tembotrione; thifensulfuron; tribenuron; topramezone; kochia, Kochia scoparia (L.) Schrad.
Emerging Challenges and Opportunities for Education and Research in Weed Science
(2017-09) Chauhan, Bhagirath S.; Matloob, Amar; Mahajan, Gulshan; Aslam, Farhena; Florentine, Singarayer K.; Jha, Prashant
In modern agriculture, with more emphasis on high input systems, weed problems are likely to increase and become more complex. With heightened awareness of adverse effects of herbicide residues on human health and environment and the evolution of herbicide-resistant weed biotypes, a significant focus within weed science has now shifted to the development of eco-friendly technologies with reduced reliance on herbicides. Further, with the large-scale adoption of herbicide-resistant crops, and uncertain climatic optima under climate change, the problems for weed science have become multi-faceted. To handle these complex weed problems, a holistic line of action with multi-disciplinary approaches is required, including adjustments to technology, management practices, and legislation. Improved knowledge of weed ecology, biology, genetics, and molecular biology is essential for developing sustainable weed control practices. Additionally, judicious use of advanced technologies, such as site-specific weed management systems and decision support modeling, will play a significant role in reducing costs associated with weed control. Further, effective linkages between farmers and weed researchers will be necessary to facilitate the adoption of technological developments. To meet these challenges, priorities in research need to be determined and the education system for weed science needs to be reoriented. In respect of the latter imperative, closer collaboration between weed scientists and other disciplines can help in defining and solving the complex weed management challenges of the 21st century. This consensus will provide more versatile and diverse approaches to innovative teaching and training practices, which will be needed to prepare future weed science graduates who are capable of handling the anticipated challenges of weed science facing in contemporary agriculture. To build this capacity, mobilizing additional funding for both weed research and weed management education is essential.
First report of Ser653 Asn mutation endowing high-level resistance to imazamox in downy brome (Bromus tectorum L.)
(2017-08) Kumar, Vipan; Jha, Prashant
BACKGROUND Bromus tectorum L. is one of the most troublesome grass weed species in cropland and non-cropland areas of the northwestern United States. In summer 2016, a B. tectroum accession (R) that survived imazamox at the field-use rate (44â€‰gâ€‰ha-1 ) in an imidazolinone-tolerant (IMI-tolerant or Clearfieldâ„¢ ) winter wheat field was collected near Hammond, Carter County, MT, USA. The aim of this study was to determine the resistance profile of the B. tectroum R accession to imazamox and other ALS inhibitors, and investigate the mechanism of resistance to imazamox. RESULTS The R B. tectorum accession had a high-level resistance (110.1-fold) to imazamox (IMI) and low to moderate-levels cross-resistance to pyroxsulam (TP) (4.6-fold) and propoxycarbazone (SCT) (13.9-fold). The R accession was susceptible to sulfosulfuron (SU) and quizalofop and clethodim (ACCase inhibitors), paraquat (PS I inhibitor), glyphosate (EPSPS inhibitor), and glufosinate (GS inhibitor). Sequence analysis of the ALS gene revealed a single, target-site Ser653 Asn mutation in R plants. The pre-treatment of malathion followed by imazamox at 44 or 88â€‰gâ€‰ha-1 did not reverse the resistance phenotype. CONCLUSION This is the first report of evolution of cross-resistance to ALS-inhibiting herbicides in B. tectorum. A single-point mutation, Ser653 Asn, was identified, conferring the high-level resistance to imazamox.
Growth & Reproduction of Glyphosate-Resistant & Susceptible Populations of Kochia scoparia
(2015-11) Kumar, Vipan; Jha, Prashant
Evolution of glyphosate-resistant kochia is a threat to no-till wheat-fallow and glyphosate-resistant (GR) cropping systems of the US Great Plains. The EPSPS (5-enol-pyruvylshikimate-3-phosphate synthase) gene amplification confers glyphosate resistance in the tested Kochia scoparia (L.) Schrad populations from Montana. Experiments were conducted in spring to fall 2014 (run 1) and summer 2014 to spring 2015 (run 2) to investigate the growth and reproductive traits of the GR vs. glyphosate-susceptible (SUS) populations of K. scoparia and to determine the relationship of EPSPS gene amplification with the level of glyphosate resistance. GR K. scoparia inbred lines (CHES01 and JOP01) exhibited 2 to 14 relative copies of the EPSPS gene compared with the SUS inbred line with only one copy. In the absence of glyphosate, no differences in growth and reproductive parameters were evident between the tested GR and SUS inbred lines, across an intraspecific competition gradient (1 to 170 plants m-2). GR K. scoparia plants with 2 to 4 copies of the EPSPS gene survived the field-use rate (870 g ha-1) of glyphosate, but failed to survive the 4,350 g ha-1 rate of glyphosate (five-times the field-use rate). In contrast, GR plants with 5 to 14 EPSPS gene copies survived the 4,350 g ha-1 of glyphosate. The results from this research indicate that GR K. scoparia with 5 or more EPSPS gene copies will most likely persist in field populations, irrespective of glyphosate selection pressure.
Influence of herbicides applied postharvest in wheat stubble on control, fecundity, and progeny fitness of Kochia scoparia in the US Great Plains
(2015-05) Kumar, Vipan; Jha, Prashant
Field, greenhouse, and laboratory experiments were conducted at the Montana State University Southern Agricultural Research Center, Huntley, MT, USA, in 2012 and 2013, to evaluate the effectiveness of various postharvest-applied herbicides on late-season control, fecundity, seed viability, and progeny fitness of Kochia scoparia (kochia) in wheat stubble. Paraquat + atrazine, paraquat + linuron, and paraquat + metribuzin applied at the early bloom stage were the most effective postharvest treatments for late-season control (100%) at 28 d after treatment (DAT), biomass reduction (70â€“73%), and seed prevention of K. scoparia, and did not differ from glyphosate, glufosinate, saflufenacil + 2, 4-D, saflufenacil + atrazine, tembotrione + atrazine, or topramezone + atrazine treatments. Dicamba alone, dicamba + 2, 4-D, or diflufenzopyr + dicamba + 2, 4-D applied at the early bloom stage were ineffective, with <70% late-season control, <45% biomass reduction, and <55% seed reduction of K. scoparia. In the absence of a postharvest herbicide, uncontrolled kochia plants at a density of 8â€“10 plants mâˆ’2 contributed >100,000 seeds mâˆ’2. Addition of atrazine to dicamba improved late-season control (80%) and seed reduction (78%) compared to dicamba alone, and reduced seed viability and 100-seed weight. There was no significant effect of any of the dicamba-containing herbicides applied at the early bloom stage on K. scoparia progeny fitness, including height, width, primary branches, and shoot dry weight of seedlings at 42 d after planting (DAP). The effective postharvest-applied herbicides investigated in this research should be utilized to prevent late-season K. scoparia seed bank replenishment in wheat, and as a component of herbicide resistance management program for the containment of glyphosate- and/or acetolactate synthase (ALS)-inhibitor-resistant K. scoparia in wheat-based crop rotations in the US Great Plains.
Influence of Nitrogen Rate, Seeding Rate, and Weed Removal Timing on Weed Interference in Barley and Effect of Nitrogen on Weed Response to Herbicides
(2017-01) Kumar, Vipan; Jha, Prashant
Field experiments were conducted at the Montana State University Southern Agricultural Research Center, Huntley, MT, in 2011 through 2013 to determine the effect of nitrogen (N) rate, seeding rate, and weed removal timing on weed interference in barley. A delay in weed removal timing from the 3- to 4-leaf (LF) stage to the 8- to 10-LF stage of barley resulted in up to 3.5-fold increase in total weed biomass and 10% reduction in barley biomass, and this was unaffected by a N rate that ranged from 56 (low) to 168 (high) kg ha^sup -1^. The effect of N rate on barley biomass was more pronounced when weed removal was delayed from the 3- to 4-LF stage to the 8- to 10-LF stage of barley and in nontreated plots. Increasing the barley seeding rate from 38 to 152 kg ha^sup -1^ increased the barley plant density by 50%, biomass by 13%, and grain yield by 29%, averaged over N rates and weed removal timing. On the basis of 5 and 10% levels of acceptable yield loss, the addition of â‰¥112 kg N ha^sup -1^ delayed the critical timing of weed removal by at least 1.3 wk in barley, compared with the 56 kg N ha^sup -1^ rate. A medium or high N rate prevented reduction in barley grain quality (plumpness and test weight) observed when the seeding rate was increased from 38 to 76 or 152 kg ha^sup -1^ at the low N rate. In a separate greenhouse study, the effect of N rate on the effectiveness of various herbicides for controlling wild oat, green foxtail, kochia, or Russian thistle was investigated. Results highlighted that wild oat or green foxtail grown under 56 kg N ha^sup -1^ (low N) soil required 1.4 to 2.6 times higher doses of clodinafop, fenoxaprop, flucarbazone, glyphosate, glufosinate, pinoxaden, or tralkoxydim for 50% reduction in shoot dry weights (GR^sub 50^) compared with plants grown under 168 kg N ha^sup -1^ (high N). Similarly, a reduced efficacy of thifensulfuron methyl + tribenuron methyl, metsulfuron methyl, or bromoxynil + pyrasulfotole was observed (evident from the GR^sub 50^ values) for kochia or Russian thistle grown under low- vs. high-N soil. Information gained from this research will aid in developing cost-effective, integrated weed management (IWM) strategies in cereals and in educating growers on the importance of fertilizer N management as a component of IWM programs.
Molecular Basis of Evolved Resistance to Glyphosate & Acetolactate Synthase-Inhibitor Herbicides in Kochia (Kochia scoparia) Accessions from Montana
(2015-10) Kumar, Vipan; Jha, Prashant; Giacomini, Darci; Westra, Eric P.; Westra, Philip
The rapid evolution and spread of glyphosate-resistant (GR) kochia in the Northern Great Plains is an increasing threat to GR cropping systems and conservation tillage practices common in this region. GR kochia accessions with 4.6- to 11-fold levels of resistance to glyphosate have recently been reported in Montana. Those GR kochia accessions were also suspected to be resistant to acetolactate synthase (ALS) inhibitors, i.e., multiple herbicide-resistant (MHR) kochia. In this research, the level of resistance to the ALS-inhibitor herbicides (sulfonylureas) and the molecular mechanisms conferring resistance to glyphosate and ALS-inhibitor herbicides in MHR kochia was investigated. On the basis of whole-plant doseâ€“response assays, MHR kochia accessions (GIL01, JOP01, and CHES01) were 9.3- to 30-fold more resistant to premixed thifensulfuron methyl + tribenuron methyl + metsulfuron methyl than the susceptible (SUS) accession. In an in vivo leaf-disk shikimate assay, MHR plants accumulated less shikimate than the SUS plants at a discriminate dose of 100 Î¼M glyphosate. Sequencing of the conserved region of EPSPS revealed no target-site mutation at Thr102 or Pro106 residue. MHR kochia accessions had increased relative EPSPS gene copies (~â€‰4 to 10) compared with the SUS accession (single copy). Furthermore, MHR kochia accumulated higher EPSPS protein compared with the SUS plants. Resistance to the ALS-inhibitor herbicides was conferred by Pro197 amino acid substitution (proline to glutamine). EPSPS gene amplification and a single target-site mutation at Pro197 in ALS gene confer resistance to glyphosate and ALS-inhibitor herbicides, respectively, in MHR kochia accessions from Montana. This is the first confirmation of occurrence of MHR kochia in Montana.
Occurrence and Characterization of Kochia (Kochia scoparia) Accessions with Resistance to Glyphosate in Montana
(2014-01) Kuman, Vipan; Jha, Prashant; Reichard, Nicholas
Herbicide-resistant kochia is an increasing concern for growers in the northwestern United States. Four suspected glyphosate-resistant (Gly-R) kochia accessions (referred to as GIL01, JOP01, CHES01, and CHES02) collected in fall 2012 from four different chemical-fallow fields in northern Montana were evaluated. The objectives were to confirm and characterize the level of glyphosate resistance in kochia accessions relative to a glyphosate-susceptible (Gly-S) accession and evaluate the effectiveness of various POST herbicides for Gly-R kochia control. Whole-plant dose–response experiments indicated that the four Gly-R kochia accessions had 7.1- to 11-fold levels of resistance relative to the Gly-S accession on the basis of percent control ratings (I50 values). On the basis of shoot dry weight response (GR50 values), the four Gly-R kochia accessions exhibited resistance index (R/S) ratios ranging from 4.6 to 8.1. In a separate study, the two tested Gly-R accessions (GIL01 and JOP01) showed differential response (control and shoot dry weight reduction) to various POST herbicides 21 d after application (DAA). Paraquat, paraquat þ linuron, carfentrazone þ 2,4-D, saflufenacil alone or with 2,4-D, and bromoxynil þ fluroxypyr effectively controlled (99 to 100%) and reduced shoot dry weight (88 to 92%) of the GIL01 accession, consistent with the Gly-S kochia accession; however, bromoxynilþMCPA and bromoxynilþpyrasulfotole provided 76% control and 83% shoot dry weight reduction of the GIL01 accession and were lower compared with the Gly-S accession. The JOP01 accession exhibited lower control or shoot dry weight reduction to all herbicides tested, except dicamba, diflufenzopyr þ dicamba þ 2,4-D, paraquat þ linuron, and bromoxynil þ pyrasulfotole, compared with the Gly-S or GIL01 population. Furthermore, paraquat þlinuron was the only treatment with 90% control and shoot dry weight reduction of the JOP01 kochia plants. Among all POST herbicides tested, glufosinate was the least effective on kochia. This research confirms the first evolution of Gly-R kochia in Montana. Future research will investigate the mechanism of glyphosate resistance, inheritance, ecological fitness, and alternative strategies for management of Gly-R kochia. Nomenclature: 2,4-D; bromoxynil; carfentrazone; dicamba; diflufenzopyr; fluroxypyr; glufosinate; glyphosate; linuron; MCPA; paraquat; pyrasulfotole; saflufenacil; kochia, Kochia scoparia (L.) Schrad. Key words: Glyphosate resistance, postemergence herbicides, resistance management.
Tank Mixing Pendimethalin with Pyroxasulfone and Chloroacetamide Herbicides Enhances In-Season Residual Weed Control in Corn
(2015-05) Jha, Prashant; Kumar, Vipan; Garcia, Josefina; Reichard, Nicholas
Kochia, common lambsquarters, and wild buckwheat are major problem weeds in glyphosate-resistant corn production in the northern Great Plains of the United States. Field research was conducted in 2011 and 2012 near Huntley, MT to investigate effective PRE herbicides applied alone or in premixes with or without tank-mixed pendimethalin for extended in-season residual control of the selected broadleaf weeds in glyphosate-resistant corn. Control of kochia, common lambsquarters, and wild buckwheat with recently registered herbicide premixes, including saflufenacil + dimethenamid-P and S-metolachlor + mesotrione, was as high as 95 and 90% at 21 and 63 d after treatment (DAT), and mostly similar to the standard atrazine treatment. Residual control of common lambsquarters and wild buckwheat from pyroxasulfone was higher at 298 compared with 149 g ai haâˆ’1 rate. Pyroxasulfone and other chloroacetamide herbicides (acetochlor or dimethenamid-P) applied alone failed to provide greater than 79, 70, and 54% residual control at 21, 35, and 63 DAT, respectively, of the weed species investigated. Residual weed control throughout the growing season was significantly improved with the addition of pendimethalin to pyroxasulfone (149 g haâˆ’1), acetochlor, or dimethenamid-P when compared with any of the three herbicides applied alone. Kochia control by pyroxasulfone, acetochlor, or dimethenamid-P tank mixed with pendimethalin was as high as 94, 92, and 81% at 21, 35, and 63 DAT, respectively. Control of common lambsquarters with the addition of pendimethalin to pyroxasulfone or acetochlor was improved to 94, 89, and 81% at 21, 35, and 63 DAT, respectively. Similarly, wild buckwheat control with acetochlor plus pendimethalin was improved to 87, 85, and 82% at 21, 35, and 63 DAT, respectively. Consistent with the extended in-season (up to 9 wk) residual weed control, pyroxasulfone, acetochlor, or dimethenamid-P treatments when tank mixed with pendimethalin had higher corn yields compared with the herbicides applied alone. The investigation on residual herbicides that provide extended in-season weed control should be continued as an important aspect of glyphosate stewardship and to mitigate the occurrence of glyphosate-resistant weed populations in grower fields.
Variable response of kochia [Kochia scoparia (L.) Schrad.] to auxinic herbicides dicamba and fluroxypyr in Montana
(2015-09) Jha, Prashant; Kumar, Vipan; Lim, Charlemagne A.
Herbicide-resistant kochia is an increasing concern for growers in the Northern Great Plains of United States and Canada. The objective of the research was to characterize the response of the three putative auxinic herbicide-resistant kochia inbreds (derived from accessions collected from wheat/ chemical fallow fields in northern Montana) to dicamba and fluroxypyr relative to a susceptible (SUS) inbred. A dicamba dose-response study indicated that the three putative resistant inbreds (Chot-01, Chot-02, and Chot-03) had R/S ratios of 1.3 to 6.1 based on the visible control response (I50 values), and R/S ratios of 1.5 to 6.8 based on the shoot dry weight response (GR50 values). Dose-response experiments with fluroxypyr determined I50 R/S ratios of 1.4 to 5.7 and GR50 R/S ratios of 1.6 to 4.0 for the three putative resistant inbreds. The selected inbreds showed variable symptomology (phenotype) in response to dicamba and fluroxypyr. Among the three inbreds, Chot-01 exhibited the least epinasty, stem curling/swelling, and chlorosis/necrosis symptoms, and was resistant to dicamba and fluroxypyr. Growers should diversify their weed management tools to manage further spread of auxinic or multiple herbicide-resistant kochia in the region.
Weed management using crop competition in the United States: A review
(2016-07) Jha, Prashant; Kumar, Vipan; Godara, Rakesh K; Chauhan, Bhagirath S.
Exploiting the competitive ability of crops is essential to develop cost-effective and sustainable weed management practices. Reduced row spacing, increased seeding rates, and selection of competitive cultivars can potentially manage crop-weed competition in cotton, soybean, wheat, and corn. These cultural weed management practices facilitate a more rapid development of crop canopy that adversely affect the emergence, density, growth, biomass, and subsequently the seed production of weeds during a growing season. These cultural practices can also favour the weed suppressive ability of the crop by influencing the canopy architecture traits (plant height, canopy density, leaf area index, rate of leaf area development, and leaf distribution). These crop-competition attributes can potentially reduce the risk of crop yield losses due to interference from weed cohorts that escape an early- or a late-season post-emergence herbicide application. Furthermore, reduced row spacing, increased seeding rates, and weed-competitive cultivars are effective in reducing reliance on a single site-of-action herbicides, thereby reducing the selection pressure for development of herbicide-resistant weed populations in a cropping system.