<b>HRAC Group 2</b> <font size='2'> (Legacy B) </font> resistant Panicum dichotomiflorum from Spain

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

HRAC GROUP 2 (LEGACY B) RESISTANT FALL PANICUM
(Panicum dichotomiflorum)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Spain, Aragón and Catalonia

INTRODUCTION		FALL PANICUM
Fall Panicum (Panicum dichotomiflorum) is a monocot weed in the Poaceae family. In Spain this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2022 and infests Corn (maize). Group 2 (Legacy B) herbicides are known as Inhibition of Acetolactate Synthase (Inhibition of Acetolactate Synthase ). Research has shown that these particular biotypes are resistant to nicosulfuron and they may be cross-resistant to other Group 2 (Legacy B) herbicides. The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

QUIK STATS (last updated May 30, 2025 )
Common Name	Fall Panicum
Species	Panicum dichotomiflorum
Group	Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicides	nicosulfuron
Location	Spain, Aragón and Catalonia
Year	2022
Situation(s)	Corn (maize)
Contributors - (Alphabetically)	Jose María Montull , GERMAN MORA MARIN, Maria D. Osuna, and Joel Torra
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NOTES ABOUT THIS BIOTYPE

GENERAL

GERMAN MORA MARIN

Panicum dichotomiflorum
Resistance to ALS inhibitors (nicosulfuron) was characterized in two populations of P. dichotomiflorum collected in 2022 from maize fields in Aragón and Catalonia, Spain. This study has been accepted for presentation at the upcoming 20th European Weed Research Society Symposium (2025). This resistance was mediated by enhanced metabolism

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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Fall Panicum biotype with this Fall Panicum biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on HRAC Group 2 resistant Fall Panicum have not been reported to the site. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

Studies on the mechanism of resistance of Group 2 (Legacy B) resistant Fall Panicum from Spain indicate that resistance is due to enhanced metabolism. There may be a note below or an article discussing the mechanism of resistance in the Fact Sheets and Other Literature

Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes. If you have any information pertaining to the fitness of Group 2 (Legacy B) resistant Fall Panicum from Spain please update the database.

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CONTRIBUTING WEED SCIENTISTS

JOSE MARÍA MONTULL

Universitat de Lleida. Agrotecnio Rovira Roure 191 Lleida, Catalonia Spain Email Jose María Montull

GERMAN MORA MARIN

PhD student Universitat de Lleida HBJ - Maleherbologia Carrer ROCA LABRADOR 12. Piso 5, puerta 3A Lleida, 25003, Cataluña Spain Email GERMAN MORA MARIN Web : Web Site Link

MARIA D. OSUNA

Researcher CICYTEX Crop Protection Finca La Orden Crta AV, km 372 Guadajira, 06187, Badajoz Spain Email Maria D. Osuna Web : Web Site Link

JOEL TORRA

Research Assistant University Of Lleida Depart. Hortofructicultura Botànica I Jardineria Rovira Roure 191, Etsea, Ed. 1 Lleida, 25198, Badajoz Spain Email Joel Torra Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Spain have been instrumental in providing you this information. Particular thanks is given to Jose María Montull , GERMAN MORA MARIN, Maria D. Osuna, and Joel Torra for providing detailed information.

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Herbicide Resistant Fall Panicum Globally
(Panicum dichotomiflorum)

Country

FirstYear

Situation

Active Ingredients

Site of Action

Spain

1981

Corn (maize), and Cropland

atrazine

PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)

Spain

2022

Corn (maize)

nicosulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Illinois)

2019

Sweet corn

nicosulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Literature about Similar Cases

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Gardner, A. P. ; York, A. C. ; Jordan, D. L. ; Monks, D. W.. 2006. Glufosinate antagonizes postemergence graminicides applied to annual grasses and johnsongrass. Journal of Cotton Science 10 : 319 - 327.

Glufosinate controls a broad spectrum of weeds in glufosinate-resistant cotton (Gossypium hirsutum). Control of grassy weeds, however, can sometimes be inadequate, especially when grasses are large or growing under dry conditions. In situations where less than adequate control of grasses by glufosinate alone is anticipated, growers may consider mixing a postemergence graminicide with glufosinate. Most herbicides mixed with graminicides antagonize grass control. Research was conducted in North Carolina to determine the potential for antagonism with mixtures of glufosinate and four postemergence graminicides and to determine if antagonism could be alleviated by increasing the rate of graminicide in mixtures, by adding ammonium sulfate to mixtures, or by applying glufosinate and graminicides sequentially. Antagonism was noted on johnsongrass (Sorghum halepense) and on mixtures of annual grasses, broadleaf signalgrass (Brachiaria platyphylla [Urochloa platyphylla]), fall panicum (Panicum dichotomiflorum), goosegrass (Eleusine indica), and large crabgrass (Digitaria sanguinalis), when glufosinate was mixed with clethodim, fluazifop-P, quizalofop-P, or sethoxydim. Antagonism was not alleviated by increasing the graminicide rate in the mixture by 50% or by including ammonium sulfate in the mixture. Antagonism was not observed when graminicides were applied 3 or more days before glufosinate or 5 or more days after glufosinate..

Parker, R. G. ; York, A. C. ; Jordan, D. L.. 2006. Weed control in glyphosate-resistant corn as affected by preemergence herbicide and timing of postemergence herbicide application. Weed Technology 20 : 564 - 570.

Field studies were conducted at three locations in North Carolina, USA, during both 2002 and 2003 to evaluate weed control and response of glyphosate-resistant (GR) maize (Zea mays) to glyphosate or nicosulfuron plus atrazine applied POST at three application timings with and without alachlor plus atrazine applied PRE. The POST herbicides were applied timely (5- to 9-cm weeds) or applications were delayed one or two weeks. All treatments, except the weedy control, were followed by glyphosate postemergence-directed (PDIR) 4 weeks after the timely POST application. Common lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia), Palmer amaranth (Amaranthus palmeri), prickly sida (Sida spinosa), and smooth pigweed (Amaranthus hybridus) were controlled at least 94% regardless of PRE or POST treatments. Large crabgrass (Digitaria sanguinalis) and fall panicum (Panicum dichotomiflorum) were controlled at least 96% by glyphosate regardless of PRE herbicide or POST application timing. In contrast, control by nicosulfuron plus atrazine POST in the absence of PRE herbicide decreased as application was delayed. Sicklepod (Senna obtusifolia [Cassia obtusifolia]) was controlled at least 94% when POST herbicides were applied timely, but control by both POST herbicide treatments decreased with delayed application regardless of PRE herbicide. Tall morningglory (Ipomoea purpurea [Pharbitis purpurea]) was controlled 93% or greater by POST herbicides applied timely. Control by both POST herbicide treatments decreased as application was delayed, with glyphosate being affected more by timing than nicosulfuron plus atrazine. Maize grain yield was similar with glyphosate and nicosulfuron plus atrazine. Yield was unaffected by POST application timing when PRE herbicides were included. Without PRE herbicide, grain yield decreased as POST herbicide application was delayed..

Bunting, J. A. ; Sprague, C. L. ; Riechers, D. E.. 2005. Incorporating foramsulfuron into annual weed control systems for corn. Weed Technology 19 : 160 - 167.

Field studies were conducted in 2000, 2001, and 2002 at Brownstown, DeKalb, Perry and Urbana, in Illinois, USA, to evaluate the weed control and maize (Zea mays) tolerance from postemergence (POST) applications of foramsulfuron in sequential and total-POST herbicide programmes. Foramsulfuron applied alone controlled giant foxtail (Setaria faberi), fall panicum (Panicum dichotomiflorum) and redroot pigweed (Amaranthus retroflexus) by 88, 99 and 99%, respectively, 28 days after treatment (DAT), which was comparable with the standard treatment of nicosulfuron. However, the control of common cocklebur (Xanthium strumarium), velvetleaf (Abutilon theophrasti) and common lambsquarters (Chenopodium album) was significantly higher with foramsulfuron compared with nicosulfuron. Sequential herbicide programmes of atrazine, S-metolachlor or isoxaflutole applied preemergence (PRE) followed by a POST application of foramsulfuron provided greater than 85% control of giant foxtail, fall panicum, common cocklebur, velvetleaf, common waterhemp (Amaranthus rudis [A. tuberculatus]), and redroot pigweed. Of the sequential herbicide treatments, atrazine applied PRE followed by a POST application of foramsulfuron provided the greatest Pennsylvania smartweed (Polygonum pennsylvanicum) control. A PRE application of either atrazine or isoxaflutole was needed before a POST application of foramsulfuron to control common lambsquarters. POST tank mixtures of foramsulfuron with atrazine, dicamba, and dicamba plus diflufenzopyr improved the control of Pennsylvania smartweed, common cocklebur, velvetleaf, common lambsquarters, and common waterhemp when compared with foramsulfuron applied alone. The tank mixture of foramsulfuron with mesotrione improved control of all species, except Pennsylvania smartweed, common lambsquarters, and common cocklebur. Foramsulfuron tank mixtures with carfentrazone did not improve control of any weed species to commercial acceptance. Adjuvant selection was important for POST tank mixtures. The control of giant foxtail and fall panicum was reduced when atrazine was tank mixed with foramsulfuron and crop oil concentrate (COC). However, when methylated seed oil (MSO) was added to the atrazine-foramsulfuron tank mixture instead of COC, giant foxtail and fall panicum control were similar to foramsulfuron applied alone..

Dalley, C. D. ; Kells, J. J. ; Renner, K. A.. 2004. Effect of glyphosate application timing and row spacing on corn (Zea mays) and soybean (Glycine max) yields. Weed Technology 18 : 165 - 176.

Studies were carried out in 1998-2001 in Michigan, USA, to determine the effect of glyphosate application timing and row spacing (38 and 76 cm for glyphosate-resistant maize hybrid DK 493RR and 19, 38 and 76 cm for soyabean cv. 92B71) on the yield of these crops. Glyphosate was applied when average weed canopy height reached 5, 10, 15, 23, and 30 cm. The weeds present in these studies included velvetleaf (Abutilon theophrasti), redroot pigweed (Amaranthus retroflexus), common ragweed (Ambrosia artemisiifolia), common lambsquarters (Chenopodium album), jimsonweed (Datura stramonium), barnyardgrass (Echinochloa crus-galli), fall panicum (Panicum dichotomiflorum), giant foxtail (Setaria faberi), yellow foxtail (Setaria glauca [S. pumila]), green foxtail (Setaria viridis), and eastern black nightshade (Solanum ptycanthum). Under highly competitive growing conditions (below normal rainfall and high weed density), maize yield was first reduced when weeds reached 10 and 15 cm in height with maize planted in 38- and 76-cm row widths, respectively. Under similar conditions, soyabean yield was first reduced when weeds reached 15 and 23 cm with soyabean planted in 19- and 38-cm row widths, respectively. Yield losses occurred only in the untreated control when soyabean was planted in 76-cm rows. When growing conditions were less competitive (adequate rainfall and lower weed density), yield losses occurred only when weeds reached 30 cm or more in maize and only in the untreated control in soyabean. Maize and soyabean yields were higher when planted in narrow rows in 3 of 4 years but were more susceptible to early-season weed interference than maize and soyabean in wide rows. Maize yield was affected more by weed interference than was soyabean yield. The product of weed height by weed density, as the independent variable, resulted in the best linear fit for both maize and soyabean yields. High weed densities increase the risk of yield loss and must be considered when determining the appropriate timing for total post-emergence herbicide applications such as glyphosate. Sequential glyphosate applications in maize did not increase yield..

Dalley, C. D. ; Kells, J. J. ; Renner, K. A.. 2004. Effect of glyphosate application timing and row spacing on weed growth in corn (Zea mays) and soybean (Glycine max). Weed Technology 18 : 177 - 182.

Glyphosate-resistant maize hybrid DK 493RR and soyabean cv. 92B71 were planted in narrow- and wide-row spacings in East Lansing, Michigan, USA, during 1998-2001 to study the effects of glyphosate application timing and row spacing on light interception and subsequent weed growth. The weeds in the experimental area included Setaria faberi, S. viridis, S. glauca [S. pumila], Echinochloa crus-galli, Panicum dichotomiflorum, Chenopodium album, Amaranthus retroflexus and Abutilon theophrasti. Glyphosate was applied when weeds were 5, 10, 15, 23 and 30 cm in height. Maize planted in narrow rows (38 cm) had greater light interception than maize planted in wide rows (76 cm) from 35 to 55 days after crop emergence. Soyabean planted in narrow rows (both 19 and 38 cm) had greater light interception throughout the growing season than soyabean in 76-cm row. At maximum canopy closure, narrow-row (both 19 and 38 cm) soyabean intercepted more light than narrow-row maize. Biomass of weeds after glyphosate application was greater when soyabean was planted in 76-cm than in 19- or 38-cm rows. However, weed biomass was generally similar in both row spacings of maize. Sequential glyphosate applications reduced weed biomass in maize each year compared with a single glyphosate application at the 5-cm weed height. Sequential glyphosate applications that followed initial glyphosate application to 10- or 15-cm tall weeds did not reduce weed biomass compared with a single application..

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