scholarly journals Confirmation and Control of HPPD-Inhibiting Herbicide–Resistant Waterhemp (Amaranthus tuberculatus) in Nebraska

2017 ◽  
Vol 31 (1) ◽  
pp. 67-79 ◽  
Author(s):  
Maxwel C. Oliveira ◽  
Amit J. Jhala ◽  
Todd Gaines ◽  
Suat Irmak ◽  
Keenan Amundsen ◽  
...  
Keyword(s):  
Dose Response ◽  
Field Conditions ◽  
Effective Control ◽  
Herbicide Resistant ◽  
Greenhouse Experiments ◽  
Amaranthus Tuberculatus ◽  
Sites Of Action ◽  
And Control ◽  
Herbicide Programs

Field and greenhouse experiments were conducted in Nebraska to (1) confirm the 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting resistant-waterhemp biotype (HPPD-RW) by quantifying the resistance levels in dose-response studies, and (2) to evaluate efficacy of PRE-only, POST-only, and PRE followed by POST herbicide programs for control of HPPD-RW in corn. Greenhouse dose-response studies confirmed that the suspected waterhemp biotype in Nebraska has evolved resistance to HPPD-inhibiting herbicides with a 2- to 18-fold resistance depending upon the type of HPPD-inhibiting herbicide being sprayed. Under field conditions, at 56 d after treatment, ≥90% control of the HPPD-RW was achieved with PRE-applied mesotrione/atrazine/S-metolachlor+acetochlor, pyroxasulfone (180 and 270 g ai ha−1), pyroxasulfone/fluthiacet-methyl/atrazine, and pyroxasulfone+saflufenacil+atrazine. Among POST-only herbicide programs, glyphosate, a premix of mesotrione/atrazine tank-mixed with diflufenzopyr/dicamba, or metribuzin, or glufosinate provided ≥92% HPPD-RW control. Herbicide combinations of different effective sites of action in mixtures provided ≥86% HPPD-RW control in PRE followed by POST herbicide programs. It is concluded that the suspected waterhemp biotype is resistant to HPPD-inhibiting herbicides and alternative herbicide programs are available for effective control in corn. The occurrence of HPPD-RW in Nebraska is significant because it limits the effectiveness of HPPD-inhibiting herbicides.

Characterization of multiple herbicide–resistant waterhemp (Amaranthus tuberculatus) populations from Illinois to VLCFA-inhibiting herbicides

Weed Science ◽  
2019 ◽  
Vol 67 (4) ◽  
pp. 369-379 ◽  
Author(s):  
Seth A. Strom ◽  
Lisa C. Gonzini ◽  
Charlie Mitsdarfer ◽  
Adam S. Davis ◽  
Dean E. Riechers ◽  
...  
Keyword(s):  
Dose Response ◽  
Field Experiments ◽  
Survival Rates ◽  
Acetolactate Synthase ◽  
Field Studies ◽  
Complete Control ◽  
Herbicide Resistant ◽  
Amaranthus Tuberculatus ◽  
Als Inhibitors ◽  
And Control

AbstractField experiments were conducted in 2016 and 2017 in Champaign County, IL, to study a waterhemp [Amaranthus tuberculatus (Moq.) J. D. Sauer] population (CHR) resistant to 2,4-D and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-, photosystem II–, acetolactate synthase (ALS)-, and protoporphyrinogen oxidase–inhibiting herbicides. Two field experiments were designed to investigate the efficacy of very-long-chain fatty-acid (VLCFA)-inhibiting herbicides, including a comparison of active ingredients at labeled use rates and a rate titration experiment. Amaranthus tuberculatus density and control were evaluated at 28 and 42 d after treatment (DAT). Nonencapsulated acetochlor, alachlor, and pyroxasulfone provided the greatest PRE control of CHR (56% to 75%) at 28 DAT, while metolachlor, S-metolachlor, dimethenamid-P, and encapsulated acetochlor provided less than 27% control. In the rate titration study, nonencapsulated acetochlor controlled CHR more than equivalent field use rates of S-metolachlor. Subsequent dose–response experiments with acetochlor, S-metolachlor, dimethenamid-P, and pyroxasulfone in the greenhouse included three multiple herbicide–resistant (MHR) A. tuberculatus populations: CHR-M6 (progeny generated from CHR), MCR-NH40 (progeny generated from Mclean County, IL), and ACR (Adams County, IL), in comparison with a sensitive population (WUS). Both CHR-M6 and MCR-NH40 are MHR to atrazine and HPPD, and ALS inhibitors and demonstrated higher survival rates (LD50) to S-metolachlor, acetochlor, dimethenamid-P, or pyroxasulfone than ACR (atrazine resistant but HPPD-inhibitor sensitive) and WUS. Based on biomass reduction (GR50), resistant to sensitive (R:S) ratios between CHR-M6 and WUS were 7.5, 6.1, 5.5, and 2.9 for S-metolachlor, acetochlor, dimethenamid-P, and pyroxasulfone, respectively. Values were greater for MCR-NH40 than CHR-M6, and ACR was the most sensitive to all VLCFA inhibitors tested. Complete control of all populations was achieved at or below a field use rate of acetochlor. In summary, field studies demonstrated CHR is not controlled by several VLCFA-inhibiting herbicides. Greenhouse dose–response experiments corroborated field results and generated R:S ratios (LD50) ranging from 4.5 to 64 for CHR-M6 and MCR-NH40 among the four VLCFA-inhibiting herbicides evaluated.

Herbicide Programs for Control of Waterhemp (Amaranthus tuberculatus) Resistant to Three Distinct Herbicide Sites of Action in Corn

2020 ◽  
pp. 1-28
Author(s):  
Christian Willemse ◽  
Nader Soltani ◽  
Lauren Benoit ◽  
David C. Hooker ◽  
Amit J. Jhala ◽  
...  
Keyword(s):  
Field Experiments ◽  
Field Trials ◽  
Effective Control ◽  
High Fecundity ◽  
Field Corn ◽  
Amaranthus Tuberculatus ◽  
Excellent Control ◽  
Density And Biomass ◽  
Sites Of Action ◽  
Herbicide Programs

Abstract Control of waterhemp is becoming more difficult in Ontario as biotypes have evolved resistance to four herbicide sites of action (SOA) including groups 2, 5, 9, and 14. The objective of this study was to compare PRE, POST, and PRE followed by (fb) POST herbicide programs and their effect on control, density, and biomass of multiple herbicide-resistant (MHR) waterhemp as well as corn injury and grain yield. Two separate field experiments, each consisting of five field trials, were conducted over a two-year period (2018 and 2019) in corn in Ontario, Canada. The first experiment evaluated MHR waterhemp control with 4-hydroxyphenyl-pyruvate dioxygenase (HPPD) inhibitor containing programs applied PRE, HPPD-inhibitor containing programs applied PRE fb glufosinate applied POST, and glufosinate applied POST. The second experiment evaluated MHR waterhemp control with non-HPPD inhibitor containing programs applied PRE, non-HPPD inhibitor containing programs applied PRE fb atrazine + mesotrione applied POST, and atrazine + mesotrione applied POST. Atrazine + isoxaflutole caused 3 to 5% corn injury at E1; no corn injury was observed with PRE and POST herbicide programs at other environments. In general, atrazine/bicyclopyrone/mesotrione/S-metolachlor and dimethenamid-P/saflufenacil, applied PRE, controlled MHR waterhemp ≥ 95% 12 weeks after POST application (WAA). A POST application of glufosinate following atrazine + tolpyralate PRE, and a POST application of atrazine + mesotrione following atrazine/dicamba or atrazine/S-metolachlor PRE, improved control at 4, 8, and 12 WAA in most environments. In general, PRE fb POST applications resulted in better control of MHR waterhemp throughout the growing season than PRE and POST applications (P<0.05). It is concluded that herbicide programs based on multiple effective SOA are available for effective control of MHR waterhemp in field corn and it is advisable that when choosing a herbicide program, excellent control of MHR waterhemp should be the goal given its high fecundity and competitive ability.

Protoporphyrinogen oxidase (PPO) inhibitor–resistant waterhemp (Amaranthus tuberculatus) from Nebraska is multiple herbicide resistant: confirmation, mechanism of resistance, and management

Weed Science ◽  
2019 ◽  
Vol 67 (05) ◽  
pp. 510-520 ◽  
Author(s):  
Debalin Sarangi ◽  
Trey Stephens ◽  
Abigail L. Barker ◽  
Eric L. Patterson ◽  
Todd A. Gaines ◽  
...  
Keyword(s):  
Dose Response ◽  
Aboveground Biomass ◽  
Acetolactate Synthase ◽  
Effective Control ◽  
Weed Species ◽  
Protoporphyrinogen Oxidase ◽  
Robust Detection ◽  
Specific Pcr ◽  
Amaranthus Tuberculatus ◽  
Sites Of Action

AbstractA waterhemp [Amaranthus tuberculatus (Moq.) J. D. Sauer] biotype (designated as “NER”) collected from a soybean [Glycine max (L.) Merr.] production field in eastern Nebraska survived the POST application of fomesafen at the labeled rate. The objectives of this study were to (1) quantify the level of resistance to protoporphyrinogen oxidase (PPO) inhibitors (acifluorfen, fomesafen, and lactofen) applied POST, (2) determine the mechanism of PPO-inhibitor resistance in the NER biotype, (3) determine whether NER possessed multiple resistance to acetolactate synthase (ALS)-, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS)-, and photosystem II (PSII)-inhibiting herbicides, and (4) control NER with POST soybean herbicides. A whole-plant dose–response bioassay revealed that the NER biotype was 4- to 6-fold resistant to PPO-inhibiting herbicides depending on the known susceptible biotype (S1 or S2) used for comparison. A Kompetitive Allele Specific PCR (KASP™) assay was developed and performed for rapid and robust detection of the ΔG210 mutation (deletion of a codon) in the PPX2L gene. All samples of the NER biotype tested positive for the ΔG210 mutation. Dose–response bioassays confirmed that the NER biotype was resistant to three additional herbicide sites of action. Chlorimuron and imazethapyr, both ALS inhibitors, applied at 32X the labeled rate resulted in &lt;80% reduction in the aboveground biomass of the NER biotype. The same biotype was 3- and 7-fold resistant to glyphosate (EPSPS inhibitor) and atrazine (PSII inhibitor), respectively. Glufosinate, 2,4-D choline plus glyphosate, and dicamba were the only soybean POST herbicides that controlled NER effectively (≥92% aboveground biomass reduction). Amaranthus tuberculatus is the first confirmed weed species in Nebraska to evolve resistance to four distinct herbicide sites of action, leaving no POST herbicide choice for effective control in glyphosate-resistant and conventional (non-transgenic) soybean.

scholarly journals Investigating the Efficacy of Selected Very-Long-Chain Fatty Acid-Inhibiting Herbicides on Iowa Waterhemp (Amaranthus tuberculatus) Populations with Evolved Multiple Herbicide Resistances

Agronomy ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 595
Author(s):  
Eric A. L. Jones ◽  
Micheal D. K. Owen
Keyword(s):  
Fatty Acid ◽  
Dose Response ◽  
Chain Fatty Acid ◽  
Long Chain Fatty Acid ◽  
Midwest United States ◽  
Herbicide Resistant ◽  
Amaranthus Tuberculatus ◽  
The 1960S ◽  
Sites Of Action ◽  
Long Chain

Very long chain fatty acid (VLCFA)-inhibiting herbicides (Herbicide group (HG) 15) have been applied to corn and soybean fields in Iowa since the 1960s. The VLCFA-inhibiting herbicides are now applied more frequently to control multiple herbicide-resistant (MHR) waterhemp (Amaranthus tuberculatus Moq. J.D. Sauer) populations that are ubiquitous across the Midwest United States as resistance to the VLCFA-inhibiting herbicides is not widespread. Waterhemp has evolved multiple resistances to herbicides from seven sites of action (HG 2, 4, 5, 9, 14, 15, and 27), and six-way herbicide-resistant populations have been confirmed. Thus, the objective of this study was to determine if selected Iowa waterhemp populations are less sensitive to VLCFA-inhibiting herbicides when additional herbicide resistance traits have evolved within the selected population. Dose–response assays were conducted in a germination chamber to determine the efficacy of three selected VLCFA-inhibiting herbicides (acetochlor, S-metolachlor, and flufenacet) on selected Iowa MHR waterhemp populations. An herbicide-susceptible, three-way, four-way, and five-way herbicide-resistant waterhemp population responded to the herbicide treatments differently; however, several of the four-way and five-way herbicide-resistant populations exhibited resistance ratios greater than 1 when treated with acetochlor and S-metolachlor. Selected four-way herbicide-resistant waterhemp populations from Iowa were subjected to a dose–response assay in the field using the same VLCFA-inhibiting herbicides, and all herbicides achieved control greater than 80% at the maximum labeled rate. The results of the experiments provide evidence that some MHR waterhemp populations may exhibit decreased susceptibility the VLCFA-inhibiting herbicides, but generally, these herbicides remain efficacious on Iowa MHR waterhemp populations.

A Waterhemp (Amaranthus tuberculatus) Population Resistant to 2,4-D

Weed Science ◽  
2012 ◽  
Vol 60 (3) ◽  
pp. 379-384 ◽  
Author(s):  
Mark L. Bernards ◽  
Roberto J. Crespo ◽  
Greg R. Kruger ◽  
Roch Gaussoin ◽  
Patrick J. Tranel
Keyword(s):  
Dose Response ◽  
Dry Weight ◽  
Population Based ◽  
Susceptible Population ◽  
Herbicide Resistant ◽  
Synthetic Auxins ◽  
Resistant Population ◽  
Amaranthus Tuberculatus ◽  
Susceptible Populations ◽  
Dose Response Study

A waterhemp population from a native-grass seed production field in Nebraska was no longer effectively controlled by 2,4-D. Seed was collected from the site, and dose-response studies were conducted to determine if this population was herbicide resistant. In the greenhouse, plants from the putative resistant and a susceptible waterhemp population were treated with 0, 18, 35, 70, 140, 280, 560, 1,120, or 2,240 g ae ha−12,4-D. Visual injury estimates (I) were made 28 d after treatment (DAT), and plants were harvested and dry weights (GR) measured. The putative resistant population was approximately 10-fold more resistant to 2,4-D (R:S ratio) than the susceptible population based on both I50(50% visual injury) and GR50(50% reduction in dry weight) values. The R:S ratio increased to 19 and 111 as the data were extrapolated to I90and GR90estimates, respectively. GR50doses of 995 g ha−1for the resistant and 109 g ha−1for the susceptible populations were estimated. A field dose-response study was conducted at the suspected resistant site with 2,4-D doses of 0, 140, 280, 560, 1,120, 2,240, 4,480, 8,960, 17,920, and 35,840 g ha−1. At 28 DAT, visual injury estimates were 44% in plots treated with 35,840 g ha−1. Some plants treated with the highest rate recovered and produced seed. Plants from the resistant and susceptible populations were also treated with 0, 9, 18, 35, 70, 140, 280, 560, or 1,120 g ae ha−1dicamba in greenhouse bioassays. The 2,4-D resistant population was threefold less sensitive to dicamba based on I50estimates but less than twofold less sensitive based on GR50estimates. The synthetic auxins are the sixth mechanism-of-action herbicide group to which waterhemp has evolved resistance.

scholarly journals Evaluation of the time-of-day effect of herbicides applied POST on protoporphyrinogen IX oxidase–resistant and –susceptible Palmer amaranth (Amaranthus palmeri)

2019 ◽  
Vol 33 (5) ◽  
pp. 651-657
Author(s):  
J. Drake Copeland ◽  
Garret B. Montgomery ◽  
Lawrence E. Steckel
Keyword(s):  
Early Morning ◽  
Time Of Day ◽  
Palmer Amaranth ◽  
Amaranthus Palmeri ◽  
Application Time ◽  
Herbicide Resistant ◽  
Consistent Performance ◽  
Sites Of Action ◽  
And Control

AbstractStudies to evaluate the effect of application time of day (TOD) and protoporphyrinogen IX oxidase (PPO)-inhibiting herbicide–resistant Palmer amaranth on the efficacy of commonly used herbicides was conducted in Tennessee in 2017 and 2018. Treatments of fomesafen, lactofen, acifluorfen, paraquat, glufosinate, glufosinate plus fomesafen, paraquat plus fomesafen, and paraquat plus metribuzin were applied to PPO-resistant (PPO-R) and PPO-susceptible (PPO-S) Palmer amaranth at sunrise and midday. Control of Palmer amaranth with acifluorfen, glufosinate, and glufosinate plus fomesafen was greater with the midday application. However, control of Palmer amaranth with paraquat-based treatments was greater with the sunrise application. TOD effects on PPO-inhibiting herbicides and paraquat-based treatments were more prominent for the PPO-R Palmer amaranth biotype. The TOD effect observed when applying glufosinate in early morning hours on PPO-S Palmer amaranth can be minimized by adding fomesafen to the tank mix. However, this strategy did not provide consistent performance on PPO-R Palmer amaranth. The percentages of living Palmer amaranth plants and control were greater when paraquat plus metribuzin was applied to both biotypes. These results highlight the necessity of at least two effective herbicide sites of action for POST applications intended for controlling PPO-R Palmer amaranth. In addition, the timing of herbicide applications can affect their activity in both PPO-R and PPO-S Palmer amaranth populations.

Confirmation and Control of Propanil-Resistant and Quinclorac-Resistant Barnyardgrass (Echinochloa crus-galli) in Rice

2010 ◽  
Vol 24 (3) ◽  
pp. 226-233 ◽  
Author(s):  
Mayank S. Malik ◽  
Nilda R. Burgos ◽  
Ronald E. Talbert
Keyword(s):  
Field Studies ◽  
Herbicide Resistant ◽  
Composite Field ◽  
Field Samples ◽  
Rice Yields ◽  
Repeated Use ◽  
Clearfield Rice ◽  
Extension Center ◽  
And Control ◽  
Herbicide Programs

Intensive selection pressure from repeated use of propanil and quinclorac led to the evolution of herbicide-resistant barnyardgrass biotypes. Twenty-two composite field samples were tested for level of resistance in 2002 and 2003, and field studies were conducted at the Rice Research and Extension Center, Stuttgart, AR, in 2002 and 2003 to evaluate alternative rice herbicides to control propanil-resistant (PR) and quinclorac-resistant (QR) barnyardgrass. Of the 22 composite samples, four were PR (30 to 40% control); four had a mixed population of PR, QR, and susceptible (S) barnyardgrass; and two had multiple resistance to propanil and quinclorac (P/QR), with control from propanil of 15 to 30% and control from quinclorac of 5 to 10%. ‘Wells’ rice was used where conventional herbicide programs were evaluated, and Clearfield rice ‘CL-161’ (imidazolinone-resistant) was used for herbicide programs involving imazethapyr. All PR and QR barnyardgrass were controlled > 90% by alternative herbicides, including all preemergence (PRE) and delayed preemergence (DPRE) treatments. By 56 d after emergence (DAE), cyhalofop or fenoxaprop applied to two- to three-leaf barnyardgrass (early postemergence [EPOST]), followed by (fb) a preflood application, controlled barnyardgrass > 93%. Pendimethalin controlled PR barnyardgrass 21 DAE, but not all season long. In contrast, imazethapyr in Clearfield rice controlled all grass weeds 100% all season long. Midpostemergence (MPOST) bispyribac application at the four- to five-leaf stage also provided season-long control of all barnyardgrass biotypes (> 88%, 56 DAE). Rice yields ranged from 5,300 to 5,700 kg ha−1in conventional weed-control treatments and from 2,800 to 5,000 kg ha−1in imazethapyr-treated plots. Nontreated plots yielded 1,500 kg ha−1.

scholarly journals Herbicide Program Approaches for Managing Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) and Waterhemp (Amaranthus tuberculatusandAmaranthus rudis) in Future Soybean-Trait Technologies

2015 ◽  
Vol 29 (4) ◽  
pp. 716-729 ◽  
Author(s):  
Christopher J. Meyer ◽  
Jason K. Norsworthy ◽  
Bryan G. Young ◽  
Lawrence E. Steckel ◽  
Kevin W. Bradley ◽  
...  
Keyword(s):  
Palmer Amaranth ◽  
Amaranthus Palmeri ◽  
Single Experiment ◽  
Herbicide Resistant ◽  
Synthetic Auxin ◽  
Wide Range ◽  
Soybean Genetics ◽  
Sites Of Action ◽  
Herbicide Programs ◽  
Weed Emergence

Herbicide-resistantAmaranthusspp. continue to cause management difficulties in soybean. New soybean technologies under development, including resistance to various combinations of glyphosate, glufosinate, dicamba, 2,4-D, isoxaflutole, and mesotrione, will make possible the use of additional herbicide sites of action in soybean than is currently available. When this research was conducted, these soybean traits were still regulated and testing herbicide programs with the appropriate soybean genetics in a single experiment was not feasible. Therefore, the effectiveness of various herbicide programs (PRE herbicides followed by POST herbicides) was evaluated in bare-ground experiments on glyphosate-resistant Palmer amaranth and glyphosate-resistant waterhemp (both tall and common) at locations in Arkansas, Illinois, Indiana, Missouri, Nebraska, and Tennessee. Twenty-five herbicide programs were evaluated; 5 of which were PRE herbicides only, 10 were PRE herbicides followed by POST herbicides 3 to 4 wks after (WA) the PRE application (EPOST), and 10 were PRE herbicides followed by POST herbicides 6 to 7 WA the PRE application (LPOST). Programs with EPOST herbicides provided 94% or greater control of Palmer amaranth and waterhemp at 3 to 4 WA the EPOST. Overall, programs with LPOST herbicides resulted in a period of weed emergence in which weeds would typically compete with a crop. Weeds were not completely controlled with the LPOST herbicides because weed sizes were larger (≥ 15 cm) compared with their sizes at the EPOST application (≤ 7 cm). Most programs with LPOST herbicides provided 80 to 95% control at 3 to 4 WA applied LPOST. Based on an orthogonal contrast, using a synthetic-auxin herbicide LPOST improves control of Palmer amaranth and waterhemp over programs not containing a synthetic-auxin LPOST. These results show herbicides that can be used in soybean and that contain auxinic- or HPPD-resistant traits will provide growers with an opportunity for better control of glyphosate-resistant Palmer amaranth and waterhemp over a wide range of geographies and environments.

Glyphosate-Resistant Common Ragweed (Ambrosia artemisiifolia) in Nebraska: Confirmation and Response to Postemergence Corn and Soybean Herbicides

2017 ◽  
Vol 31 (2) ◽  
pp. 225-237 ◽  
Author(s):  
Zahoor A. Ganie ◽  
Amit J. Jhala
Keyword(s):  
United States ◽  
Dose Response ◽  
Acetolactate Synthase ◽  
Ambrosia Artemisiifolia ◽  
Effective Control ◽  
Common Ragweed ◽  
Agronomic Crops ◽  
Whole Plant ◽  
And Control ◽  
Biomass Reduction

Common ragweed is an important broadleaf weed in agronomic crops in the northcentral United States. A common ragweed biotype in glyphosate-resistant (GR) soybean production field in southeast Nebraska was not controlled after sequential applications of glyphosate at the labeled rate. The objectives of this study were to confirm GR common ragweed in Nebraska by quantifying the level of resistance in greenhouse and field whole-plant dose-response studies and to evaluate the response of the putative GR common ragweed to POST corn and soybean herbicides. Greenhouse whole-plant dose-response studies confirmed 7- and 19-fold resistance to glyphosate compared to the known glyphosate-susceptible (GS) biotype based on biomass reduction and control estimates, respectively. Field dose-response studies conducted in 2015 and 2016 at the putative GR common ragweed research site suggested that glyphosate doses equivalent to 15- and 40-times the labeled rate (1,260 gaeha–1) were required for 90% control and biomass reduction, respectively. Response of GR common ragweed to POST soybean herbicides in greenhouse studies indicated ≥89% control with acifluorfen, fomesafen, fomesafen plus glyphosate, glyphosate plus dicamba or 2,4-D choline, glufosinate, imazamox plus acifluorfen, and lactofen. POST corn herbicides, including 2,4-D, bromoxynil, diflufenzopyr plus dicamba, glufosinate, halosulfuron-methyl plus dicamba, mesotrione plus atrazine, and tembotrione provided ≥87% control, indicating that POST herbicides with distinct modes of action are available in corn and soybean for effective control of GR common ragweed. Results also suggested a reduced efficacy of the acetolactate synthase (ALS)-inhibiting herbicides tested in this study for control of GR and GS biotypes, indicating further research is needed to determine whether this biotype has evolved multiple herbicide resistance.

Identification of a Tall Waterhemp (Amaranthus tuberculatus) Biotype Resistant to HPPD-Inhibiting Herbicides, Atrazine, and Thifensulfuron in Iowa

2011 ◽  
Vol 25 (3) ◽  
pp. 514-518 ◽  
Author(s):  
Patrick M. McMullan ◽  
Jerry M. Green
Keyword(s):  
Photosystem Ii ◽  
Field Tests ◽  
Acetolactate Synthase ◽  
Field Conditions ◽  
Herbicide Resistant ◽  
Seed Corn ◽  
Modes Of Action ◽  
Henry County ◽  
Amaranthus Tuberculatus ◽  
Als Inhibitors

Seeds of a putative 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide–resistant tall waterhemp biotype from Henry County, IA, were collected from a seed corn field in fall 2009 after plants were not controlled following a POST application of mesotrione plus atrazine. The response of this biotype to various herbicide modes of action was evaluated in greenhouse and field tests. Under greenhouse conditions, the suspect biotype showed an eightfold decrease in sensitivity to mesotrione with a 50% control rate of 21 g ha−1compared with 2.7 g ha−1for the susceptible biotype. The biotype also had a 10-fold decrease in sensitivity to atrazine and a 28-fold decrease in sensitivity to thifensulfuron. Under field conditions, tall waterhemp was not controlled POST at the label rate of 1,100 g ha−1of atrazine. Tall waterhemp control was less than 60% at the label rates of three commonly used POST HPPD-inhibiting herbicides in seed corn: 105 g ha−1of mesotrione, 92 g ha−1of tembotrione, or 18 g ha−1of topramezone. Thus, this new tall waterhemp biotype is resistant to three herbicide modes of action: HPPD inhibitors, photosystem-II inhibitors, and acetolactate synthase (ALS) inhibitors.

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