Duration: 10/01/2025 to 09/30/2030

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Herbicide-resistant weeds pose a serious challenge to the production of agronomic crops. Widespread evolution of herbicide-resistant weed populations can substantially reduce crops' yields/qualities and increase production costs. Several new weed species, including Palmer amaranth, common waterhemp, and Johnsongrass, have recently invaded and established in the northeastern United States. In addition, horseweed, common lambsquarters, common ragweed, redroot pigweed, annual ryegrass, foxtails (giant, green and yellow), and fall panicum are also troublesome weed species in the region. More recently, glyphosate resistance has been confirmed in Palmer amaranth, waterhemp and horseweed. However, limited information exists on the distribution and frequency of herbicide resistance among these dominant weed species in the Northeast. Knowledge of underlying mechanism(s) of resistance and alternative preemergence (PRE) and postemergence (POST) herbicides for controlling herbicide-resistant weed populations is also lacking. This applied multistate research project aims to fill these knowledge gaps. Information on the status of herbicide-resistant weed populations, underlying mechanism (s) of resistance, and alternative PRE and POST herbicides will help in developing effective weed control strategies for herbicide-resistant weed populations in the Northeastern US.

Statement of Issues and Justification

 

Rapid adoption of herbicide-resistant crops, especially those resistant to glyphosate, fundamentally changed weed management strategies. Reliance on residual pre-emergence herbicides and alternative post-emergence herbicides with diverse mechanisms of action was reduced. For example, the number of available herbicide mechanisms of action dropped from six in corn and nine in soybeans in 1995 to only one in 2004 (NASS 2013 cited in Shaner 2014). Pre-emergent herbicides were largely forsaken, particularly in corn, cotton, and soybeans, and multiple applications of glyphosate were used for managing a broad spectrum of weeds (Hurley et al. 2009; Johnson, 2006; Johnson et al., 2007; Prince et al. 2012). The consequence of intense glyphosate use in glyphosate-resistant (GR) crops was a greater selection pressure on weed populations resulting in the evolution of glyphosate resistance in several weed species (Heap, 2024). Currently, there are > 30 glyphosate-resistant weed species in the United States (Heap, 2024). Several of these GR weed populations (especially Palmer amaranth, waterhemp, and horseweed) have evolved resistance to multiple herbicides (Heap, 2024). Resistance to synthetic auxins (2,4-D and dicamba) in GR Palmer amaranth and waterhemp populations has also been confirmed in the US (Figueiredo et al. 2018; Foster et al. 2023; Shayam et al. 2021; Shergill et al. 2018). The multiple herbicide-resistant Palmer amaranth and waterhemp have caused severe yield losses in the two major U.S. crops, corn and soybean, and increased the production costs (Soltani et al. 2016; 2017). For instance, control of glyphosate-resistant Palmer amaranth incurs an additional cost of $40 per ha in corn, $52 per ha in soybean, and $74 per ha in cotton (Carpenter & Gianessi, 2010; Legleiter et al. 2009).

Resistance to glyphosate and/or ALS inhibitors has been confirmed in Palmer amaranth and common waterhemp in the Northeast (NE) and is suspected in common lambsquarters, common ragweed, fall panicum, foxtails (green, yellow, or giant), giant ragweed, horseweed, Kochia, and annual ryegrass populations. Enlist soybean and corn growers in the NE also reported a control failure of waterhemp with 2,4-D, glufosinate, and mesotrione herbicides in summer 2024. Herbicide resistance in weeds in the NE region is increasing and warrants timely evaluation of the suspected weed populations for herbicide resistance evolution, determination of underlying resistance mechanisms, and discovery of alternate PRE and POST herbicides for their timely, economical, and effective control.

 

Related, Current and Previous Work

Evolution and widespread occurrence of herbicide-resistant weeds is a significant threat to the sustainable production of field and horticultural crops across the U.S. Palmer amaranth and waterhemp are the most competitive and widespread pigweed species in many central, southern, and western states in the U.S. Several Palmer amaranth and waterhemp populations in the US are multiple herbicide resistant (MHR) involving ALS-inhibitors, EPSPS-synthase inhibitors, HPPD inhibitors, long-chain fatty acid inhibitors, microtubule inhibitors, photosystem-II inhibitors, PPO inhibitors, and synthetic auxins groups of herbicides (Heap, 2024). Furthermore, certain biotypes of both Palmer amaranth and waterhemp are resistant to more than five different herbicide sites-of-action (Chahal et al., 2015; Faleco et al., 2022; Heap, 2024; Kumar et al., 2019). Both Palmer amaranth and waterhemp are relatively new but fast spreading pigweed species in Connecticut (CT), Massachusetts (MA), New York (NY), and other NE states. Resistance to glyphosate and ALS-inhibiting herbicides in Palmer amaranth and waterhemp biotypes has already been confirmed in the NE (Aulakh et al. 2021; 2024; Kumar, 2024). Confirmation of pigweed populations with resistance to glyphosate and ALS inhibitors poses a serious concern for NE producers. Additionally, common lambsquarters, horseweed, common ragweed, giant ragweed, foxtails (green, yellow, or giant), fall panicum, and Italian ryegrass are also the most problematic summer/winter annual weeds with suspected herbicide resistance in agronomic and horticultural crops. Recently, kochia (tumbleweed) has also been found along roadsides and in other non-crop areas in parts of the NE. It is one of the most troublesome summer annual broadleaf weeds in the western U.S., known for its invasiveness and propensity to evolve herbicide resistance. Johnsongrass populations have also been recently identified in southern counties of NY. As of now, there is lack of information on the prevalence of herbicide resistance among these problematic weed species (Palmer amaranth, waterhemp, common lambsquarters, horseweed, common ragweed, giant ragweed, kochia, johnsongrass, foxtails, fall panicum, and Italian ryegrass) across the NE region.

Weeds have evolved multiple resistance mechanisms to resist control by diverse herbicide modes-of-action. A majority of MHR Palmer amaranth and waterhemp populations have evolved target site- and/or non-target site-based resistance mechanisms. For instance, several glyphosate-resistant Palmer amaranth and waterhemp populations have enhanced EPSPS gene copy numbers (Chahal et al. 2015; Gaines et al. 2010; Shergill et al. 2018), whereas resistance to ALS inhibitors has commonly been due to single point mutations in the ALS gene. More recently, resistance to synthetic auxins (2,4-D and dicamba) in Palmer amaranth and waterhemp populations has been attributed to enhanced herbicide metabolism (Figueiredo et al. 2018; Foster et al. 2023; Shayam et al. 2021; Shergill et al. 2018). Glyphosate-resistant Palmer amaranth biotypes from the NE possess a target site-based resistance mechanism involving amplification of the EPSPS gene. There were 33 to 111 and 25 to 135 fold higher relative copies of the EPSPS gene in CT and NY biotypes, respectively, compared to a susceptible biotype (Aulakh et al. 2024; Butler-Jones et al. 2024). Common waterhemp biotypes resistant to multiple herbicides have been confirmed in CT and NY, and may occur more broadly across the NE, but the resistance mechanisms are still not known. Therefore, it is necessary to elucidate the underlying mechanism(s) of resistance (target site or non-target site-based) to devise economical and effective integrated strategies for herbicide-resistant weed management.

Weed population shifts typically occur more rapidly in response to herbicides than to other types of weed control practices because herbicides impose a greater selection pressure on the weed community (Culpepper, 2006; Westra et al., 2008; Wilson et al., 2007). Factors such as herbicide chemistry, application rate, weed size, type of adjuvant etc., strongly influence the crop safety and weed efficacy of herbicides. Increasing spread of multiple herbicide-resistant (MHR) weeds coupled with declining new herbicide chemistries warrants alternative cost-effective and sustainable integrated weed management strategies. Therefore, evaluation of new and old herbicides (multiple modes of action) is required to tackle the ever-increasing problem of MHR weed populations in agronomic and horticultural crops in the NE. It is crucial to determine the effective herbicide premixes or tank-mixtures (multiple modes of action) in conjunction with new crop traits to manage and mitigate the spread of herbicide-resistant weed populations in field and horticultural crops in the NE region.

Objectives

1. Confirmation and characterization of herbicide resistance in the troublesome weed species in the Northeastern region
   
2. Elucidate the underlying genetic and molecular mechanism(s) of herbicide resistance among these weed species
   
3. Determine the effectiveness of alternative post-emergence (POST) herbicide mixtures for control of herbicide-resistant weed populations
   

Methods

 

Objective 1. Seeds of common lambsquarters, common ragweed, fall panicum, foxtails (green, yellow and giant), giant ragweed, horseweed, annual ryegrass, kochia, Palmer amaranth, redroot pigweed, Powell amaranth, and waterhemp, etc. will be collected (2025-2028) from growers’ farms with suspected herbicide resistance in the Northeastern U.S.. To achieve this goal, we will collaborate with extension specialists, producers, crop consultants, and industry scientists. Herbicide resistance screening experiments will be conducted in the greenhouse at Cornell University to determine the response of suspected weed species to herbicides from ALS-inhibitors (Synchrony, Firstrate), EPSPS-inhibitors (Roundup PowerMax), GS inhibitors (Liberty), HPPD-inhibitors (Callisto, Laudis), PPO-inhibitors (Flexstar, Cobra), PS II inhibitors (Atrazine, Tough), and synthetic auxins (2,4-D and glyphosate) groups. Preliminary tests will involve exposure to the field use (1x) rate of these herbicides. Weed populations surviving the 1x rate will be further tested in dose-response studies at rates spanning from 0.125x to 16x to determine the resistance levels in each population. Both pre-emergence (PRE) and post-emergence (POST) dose response experiments will be conducted for herbicides (ALS-, EPSPS-, HPPD-, PPO-, and PS II-inhibitors etc.) having both PRE and POST activity. Greenhouse conditions will be maintained as close as possible to 26/23 °C day/night with a 16/8 h (day/night) photoperiod; natural sunlight will be supplemented with mercury halide lamps, providing a minimum of 450 to 750 µmol m^-2 s^-1 photon flux. At least 6 plants (8 to 10 cm tall) from each weed population will be treated with the given herbicide and application rate. Visual weed control assessments will be made on 7, 14, and 21 days after treatment (DAT) on a 0 to 100% scale, where 0 = no control/injury and 100 = a dead plant. Approximately 21 DAT, the aboveground biomass will be harvested to record the fresh shoot weight. The harvested weed biomass will be dried at 65 C for 5 days to determine the dry weight. The aboveground shoot dry weight reduction will be recorded as percentage of the nontreated control. The visual weed control and dry shoot weight data will be analyzed to determine 50 and 90% growth reduction (GR₅₀ and GR₉₀) using a three-parameter log-logistic model (Ritz et al. 2015):

 y = d / {1+exp[b (log(x) - log(c))]}   (1)

Where y is the visual control or shoot dry weight reduction (% of nontreated), d is the maximum visual control or shoot dry weight, b represents the slope of each curve, x is the herbicide dose, and c is the herbicide dose required for 50 or 90% visual control or reduction in shoot dry weights.

Objective 2.  To elucidate the underlying mechanism(s) of herbicide resistance, lab experiments will be conducted at the University of Florida (UFL, Dr. Jugpreet Singh), Connecticut Agricultural Experiment Station (CAES, Dr. Nathaniel Westrick), and Pennsylvania State University (PSU, Dr. Caio Brunharo). Both target and non-target site-based mechanism(s) of resistance will be investigated. Young leaf tissue from 8 to 10 plants each of the herbicide susceptible and confirmed herbicide-resistant weed populations will be collected and shipped to CAES, UFL and PSU lab facilities. The harvested leaf tissue (100 mg) will be immediately flash-frozen in liquid nitrogen (−195.79 C) and stored at −80 C for genomic DNA (gDNA) isolation and extraction. The gDNA extraction will be performed following the Wizard^® Genomic DNA purification kit (Promega Corporation. Madison, WI) protocol for plant tissue. Quantification of extracted DNA will be performed with a Nanodrop™ One C (Thermo Fisher Scientific, Waltham, MA).

2.1 Sequencing of Target Genes for Point Mutations: Based on the confirmed resistance to herbicide site of action, the collected gDNA from each population will be used to amplify and sequence the target genes (ALS, EPSPS, PSII, HPPD, PPO, GSI) to determine any possible known or new novel point mutations in those target genes conferring herbicide resistance. Lab experiments will be conducted at UFL and PSU for polymerase chain reaction (PCR) on confirmed herbicide-resistant and herbicide-susceptible weed populations using previously reported protocols. Sequencing results will be aligned and visually analyzed using Geneoius Prime software (Biomatters Inc., Boston, MA) to compare and identify any known point mutations.   

2.2 EPSPS Gene Amplification. Increase in the EPSPS gene copy numbers is the most common mechanism of resistance to glyphosate among Palmer amaranth, waterhemp, kochia and Italian ryegrass previously reported in the mid-western and western U.S (Gaines et al. 2010; Shergill et al. 2018). For newly confirmed glyphosate resistance among weed populations from the NE, the relative qPCR will be conducted to determine the EPSPS copy number using ALS as a reference (single copy) gene using primers: ALS (FP, 5′-GCTGCTGAAGGCTACGCT-3′; RP, 5′-GCGGGACTGAGTCAAGAAGTG-3′; 118-bp product) and EPSPS (FP, 5′-ATGTTGGACGCTCTCAGAACTCTTGGT-3′; RP, 5′-TGAATTTCCTCCAGCAACGGCAA-3′; 195-bp product). The qPCR will be performed using QuantStudio 3 (Thermo Fisher Scientific) real-time PCR. The 20 μl qPCR reaction mixture comprised: 10 μl of GoTaq® Probe qPCR Master Mix (2X, Promega, USA), 1 µl each of forward and reverse primers (10 μm, Integrated DNA Technologies, USA), 2 μl of gDNA (20 ng/μl), 0.2 µl CXR Reference Dye (30µM, Promega), and 5.8 μl of nuclease-free water to make up the volume. A minimum of three technical replicates and negative controls will be included. The ΔΔCt method will be used to quantify copy number variation of EPSPS gene relative to ALS gene. The EPSPS gene copies in glyphosate-resistant populations will be assessed relative to a known glyphosate-susceptible biotype.

2.3 Non-target site mechanisms. Greenhouse experiments will be conducted at Cornell University to elucidate the possibility of any metabolic-based mechanisms (via cytochrome P450 genes or Glutathione-s-transferase gene) using malathion and GST inhibitors in confirmed herbicide-resistant weed populations. Lab experiments will be conducted at CAES, UFL and PSU to further confirm the possibility of other non-target-site-based mechanisms (alteration in absorption and translocation of herbicides).     

Objective 3. Response of the confirmed herbicide-resistant weed populations to alternate POST herbicides will be determined in greenhouse and field experiments in CT and NY and potentially other Northeastern states. At least 8 to 10 plants from each of the confirmed herbicide resistant weed populations will be treated at two growth stages, 8- to 10-cm and 10- to 15-cm height in greenhouse studies.  Available alternative POST herbicides (premixes or tank-mixes) will be applied at the field use rate (1x) in both greenhouse and field studies. Herbicide treatments will be applied using a chamber sprayer, or research plot sprayer equipped with a flat-fan nozzle tips (TeeJet 8002XR, Spraying System Co., Wheaton, IL) calibrated to deliver 187 L ha^-1 of spray solution at 276 kPa. Experiments will be conducted in a  randomized complete block design with at least six replicates in greenhouse and three to four replications in field studies and repeated for consistency of results. Greenhouses will be maintained as close as possible to 26/23 °C day/night with a 16/8 h (day/night) photoperiod; natural sunlight will be supplemented with mercury halide lamps, providing a minimum of 450 to 750 µmol m^-2 s^-1 photon flux. Visual weed control assessments will be made on 7, 14, and 21 days after treatment (DAT). Approximately 21 DAT, the aboveground biomass will be harvested to record the fresh shoot weight. In field experiments, visual assement of weed contorl will be recorded at bi-weekly inntervals throughought the growing season and the aboveground shoot dry weights of weeds using one square meter quadrats will be collected at the end of the growing season. The harvested weed biomass will be dried at 65 C for 5 days to determine the dry weight. The aboveground shoot dry weight reduction will be recorded as percentage of the nontreated control. Visual weed control and shoot dry weight data will be analyzed using the PROC GLIMMIX procedure in SAS software to test treatment significance. Treatment differences will be determined using Fisher’s protected LSD test at P ≤ 0.05. 

 

Measurement of Progress and Results

Outputs

• Information generated through all three research objectives will be summarized annually in extension publications and shared among NE stakeholders. Comments: Publications will include bulletins, blogs, news articles, fact sheets, presentations, and Cornell field crop guidelines. Other methods for sharing results will be via Cornell weed science website, annual state Extension events such as annual corn/soybean conference, growers’ workshops, Ag in-service trainings, CAES Annual Plant Science Day, Certified Crop Advisor training, dealer meetings, etc.
• On-farm field studies will be utilized to demonstrate and educate stakeholders on the performance of alternative herbicide premixes/tank-mixes. Comments: Demonstration and education will be via annual crop field days, field tours, soil health field days, small grain field days, field demonstrations, etc.

Outcomes or Projected Impacts

• Information gained through this multistate research project will contribute to better understanding the prevalence and spread of herbicide-resistant (HR) weed populations across the northeastern U.S. This baseline information on the distribution of herbicide resistance in the NE region will further help in monitoring the shifts in weed populations' responses to commonly used herbicides in the future.
• Further understanding of resistance evolution, mechanisms of herbicide resistance, and effects of herbicide resistance on growth and reproductive fitness will help in devising diversified ecological-based integrated weed management (IWM) in the NE region.
• Research-based information on the efficacy of various alternative herbicide premixes/tank-mixes for controlling herbicide-resistant weed biotypes will help to provide improved weed management guidelines. Testing new herbicide premixes/tank-mixes will help label use recommendations for new herbicides and expanded/new uses of previously registered herbicides for potential use in NE field crops.
• With successful implementation of the project goals, we anticipate enhanced understanding and collaborations across geographical boundaries and enhanced stakeholder interest and participation in herbicide resistance management for the most troublesome weed species. The project will help to develop alternative herbicide premixes/tank-mixes that could aid in improving the long-term sustainability and economic viability of NE field crops. The information generated through this project will also be useful to Extension specialists, researchers, policy makers, and agro-industry for a more focused information delivery on herbicide resistance management.
• Long-term impacts will focus on region-wide issues relating to occurrence of herbicide-resistant weed populations, status of newly introduced invasive weed species (Palmer amaranth, waterhemp, Johnsongrass, kochia, etc.), environmental impacts and the sustainability of agricultural production. All these outcomes will result in measurable changes (mitigating further spread of resistance, reduction in herbicide inputs by implementing most effective herbicides, increased crop yields, enhanced adoption of IWM tactics by producers, reduced environmental impact of pesticides, etc.).

Milestones

(1):Starting in year 1 and continuing throughout the project, multi-year field surveys will be conducted to collect seeds of predominant weed species from NE field crops for subsequent greenhouse screening to test herbicide resistance status.

(2):Starting in year 2 and continuing throughout the project, suspected herbicide-resistant weed populations will further be evaluated to determine the herbicide resistance levels in dose-response studies.

(2):Starting in year 2 and continuing throughout the project, confirmed herbicide-resistant weed populations will subsequently be analyzed to determine the underlying mechanism(s) of resistance.

(2):Starting in year 2 and continuing throughout the project, alternative pre-emergence and post-emergence herbicides will be evaluated on selected confirmed herbicide-resistant weed populations with known mechanism(s) of resistance.

Projected Participation

View Appendix E: Participation

Outreach Plan

This research will help in understanding the geographical distribution of herbicide-resistant weed populations in NE field crops, characterizing underlying mechanism(s) of herbicide resistance, and developing alternative cost-effective chemical-based premixes/tank-mixes for control of herbicide-resistant weed populations. This research-based information will be delivered by workshops, certified crop advisor (CCA) seminars, and field days, which will align with the extension and outreach responsibilities of the project participants. For example, Dr. Kumar will be engaged with NY Corn and Soybean Growers Association, New York Farm Viability Institute, NE SARE, New York State IPM, Northeast IPM Center, and Getting Rid of Weeds (GROW) IWM. Similarly, Dr. Jatinder Aulakh (Co-PI) will be actively engaged in disseminating project findings among CT stakeholders, researchers, extension specialists, and industry partners. Project findings will be communicated through popular press articles across the Northeastern region, conference proceedings and peer-reviewed refereed journal articles.

Organization/Governance

The recommended Standard Governance for multistate research activities will be followed, including the election of a Chair, a Chair-elect, and a Secretary. All officers are to be elected for at least two-year terms to provide continuity. Administrative guidance will be provided by an assigned Administrative Advisor and a NIFA Representative.

 

Collaborators:

Vipan Kumar, Associate Profesor of Weed Science, Cornell University

Jatinder Aulakh, Associate Agricultural Scientist, Connecticut Agricultural Experiment Station

Antonio DiTommaso, Professor of Weed Science, Cornell University

Lynn Sosnoskie, Assistant Professor of Weed Science, Cornell University

Bryan Brown, Senior Extension Associate, Integrated Pest Management, Cornell University

Mike Stanyard, Senior Extension Associate, Cornell Cooperative Extension

Mike Hunter, Senior Extension Associate, Integrated Pest Management, Cornell University

Erik A. Smith, Field Crops Specialist, Cornell Cooperative Extension

Janice Degni, Field Crops Specialist, Cornell Cooperative Extension

Jeff Miller, Agronomy Specialist, Cornell Cooperative Extension

Katelyn Miller, Field Crops and Forage Specialist, Cornell Cooperative Extension

Jason Norsworthy, Professor of Weed Science, University of Arkansas

Prashant Jha, Professor of Weed Science, Louisiana State University

Jugpreet Singh, Assistant Professor, University of Florida

Caio Brunharo, Assistant Professor of Weed Science, The Pennsylvania State University

Literature Cited

Aulakh, J.S., P.S. Chahal, V. Kumar, A.J. Price, K. Guillard. 2021. Multiple herbicide-resistant Palmer amaranth (Amaranthus palmeri) in Connecticut: confirmation and response to POST herbicides. Weed Technol. 35:457–463 

Aulakh J.S., Kumar, V., Brunharo, C.A.C.G., Vernon, A., Price A.J. 2024. EPSPS gene amplification confers glyphosate resistance in Palmer amaranth in Connecticut. Weed Technol. 38(1), 1-7.

[NASS] National Agricultural Statistics Service (2013) http://usda01.library.cornell.edu/usda/nass/AgriChemUSFC. Accessed Dec 7, 2024.

Butler-Jones, A.L., E.C. Maloney, M. McClements, et al. 2024. Confirmation of glyphosate-resistant Palmer amaranth (Amaranthus palmeri) populations in New York and responses to alternative chemistries. Weed Sci doi:10.1017/wsc.2024.48

Carpenter, J., L. Gianessi. 2010. Economic impact of glyphosate-resistant weeds. Pages 297–312 in Nandula VK, ed. Glyphosate Resistance in Crops and Weeds: History, Development, and Management. John Wiley & Sons, Inc.

Chahal, P.S., J.S. Aulakh, M. Jugulam, A. J. Jhala. 2015. Herbicide-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) in the United States -Mechanisms of resistance, impact, and management. https://www.intechopen.com/chapters/49229

Culpepper, A.S. 2006. Glyphosate-induced weed shifts. Weed Technol. 20:277-281.

Duke, S.O. and S.B. Powles. 2009. Glyphosate-resistant crops and weeds: now and in the future. AgBioForum 12:346-357.

Faleco, F.A., M.C. Oliveira, N.J. Arneson, M. Renz, D.E. Stoltenberg, R. Werle. 2022. Multiple resistance to imazethapyr, atrazine, and glyphosate in a recently introduced Palmer amaranth (Amaranthus palmeri) accession in Wisconsin. Weed Technol. 36(3):344-351.

Figueiredo, M.R., L.J. Leibhart, Z.J. Reicher, P.J. Tranel, S.J. Nissen, P. Westra, M.L. Bernards, G.R. Kruger, T.A. Gaines, M. Jugulam. 2018. Metabolism of 2,4-dichlorophenoxyacetic acid contributes to resistance in a common waterhemp (Amaranthus tuberculatus) population. Pest Manag Sci. 74(10):2356-2362. doi: 10.1002/ps.4811.

Foster, D.C., P. A. Dotray, S. Culpepper, L.E. Steckel. 2023. Response of dicamba-resistant Palmer amaranth and cotton to malathion applied in conjunction with dicamba. Weed Technol. doi:10.1017/wet.2023.62

Gaines, T.A., W. Zhang, D. Wang, B. Bukun, S.T. Chisholm, D.L. Shaner, S.J. Nissen, W.L. Patzoldt, P.J. Tranel, A.S. Culpepper, T.L. Grey, T.M. Webster, W. K. Vencill, R.D. Sammons, J. Jiang, C. Preston, J.E. Leach, P. Westra. 2010. Gene amplification confers glyphosate resistance in Amaranthus palmeri. Proc Natl Acad Sci USA. 107(3):1029-34. doi: 10.1073/pnas.0906649107 

Heap, I. 2024. The International Survey of Resistant Weeds. http://www.weedscience.com. Accessed: May 14, 2024.

Hurley, T.M., P.D. Mitchell, G.B. Frisvold. 2009. Weed management costs weed best management practices, and the Roundup Ready^® weed management program. AgBioForum 12:281-290.

Johnson, B.G. 2006. Changes in herbicide use patterns and production practices resulting from glyphosate-resistant crops. Weed Technol. 20:301–307.

Johnson, W.G., M.D.K. Owen, G.R. Kruger, B.G. Young, D.R. Shaw, R.G. Wilson, J.W. Wilcut, D.L. Jordan, S.C. Weller. 2007. Does weed size matter” An Indiana grower perspective about weed control timing. Weed Technol. 21:542–546.

Kumar, V., R. Liu, G. Boyer, P.W. Stahlman. 2019. Confirmation of 2,4-D resistance and identification of multiple resistance in a Kansas Palmer amaranth (Amaranthus palmeri) population. Pest Manage. Sci. DOI 10.1002/ps.5400.

Kumar, V. 2024. Glyphosate-resistant Palmer amaranth and tall waterhemp in Northeast-A new frontier. https://ecommons.cornell.edu/items/a43ed24f-08d8-41a5-b746-12e4f013ba62

Legleiter, T., K. Bradley, R. Massey. 2009. Glyphosate-resistant waterhemp (Amaranthus rudis) control and economic returns with herbicide programs in soybean. Weed Technol. 23:54–61.

Prince, J.M., D.R. Shaw, W.A. Givens, M.E. Newman, M.D.K. Owen, S.C. Weller, B.G. Young, R.G. Wilson, D.L. Jordan. 2012. Benchmark Study: III. Survey on changing herbicide use patterns in glyphosate-resistant cropping systems. Weed Technol. 26:536–542.

Ritz, C., F. Baty, J.C. Streibig, D. Gerhard. 2015. Dose-response analysis using R. PLoS ONE 10:1–13.

Shaner, D.L. 2014. Lessons learned from the history of herbicide resistance. Weed Sci. 62(2): 427-432.

Shergill, L.S., B. R. Barlow, M.D. Bish, K.W. Bradley. 2018. Investigations of 2,4-D and multiple herbicide resistance in a Missouri waterhemp (Amaranthus tuberculatus) population. Weed Sci 66(3):386-394.

Shyam, C., E.A. Borgato, D.E. Peterson, J.A. Dille, M. Jugulam. 2021. Predominance of metabolic resistance in a six-way-resistant Palmer amaranth (Amaranthus palmeri) population. Front Plant Sci. doi: 10.3389/fpls.2020.614618.

Soltani, N., J.A. Dille, I. Burke, W. Everman, M. VanGessel, V. Davis, P. Sikkema. 2016. Potential corn yield losses from weeds in North America. Weed Technol. 30: 979–984.

Soltani, N., J. A. Dille, I. Burke, W. Everman, M. VanGessel, V. Davis, P. Sikkema. 2017. Perspectives on potential soybean yield losses from weeds in North America. Weed Technol. 31: 148–154.

Westra, P., R.G. Wilson, S.D. Miller, P.W. Stahlman, G.W. Wicks, P.L. Chapman, J. Withrow, D. Legg, C. Alford, T.A. Gaines. 2008. Weed population dynamics after six years under glyphosate and conventional herbicide-based weed control strategies. Crop Sci. 48:1170–1177.

Wilson, R.G., S.D. Miller, P. Westra, A.R. Kniss, P.W. Stahlman, G.W. Wicks, S.D. Kachman. 2007. Effect of glyphosate use over six years in glyphosate-resistant corn or a rotation of glyphosate-resistant corn, sugarbeet and spring wheat. Weed Technol. 21:900–909.

Attachments

Land Grant Participating States/Institutions

CT, NY

Non Land Grant Participating States/Institutions