Skip to main content Accessibility help

Glyphosate-Resistant Horseweed (Conyza canadensis) Control with Dicamba in Alabama

  • Michael L. Flessner (a1), J. Scott McElroy (a2), James D. McCurdy (a3), Jordan M. Toombs (a2), Glenn R. Wehtje (a2), Charles H. Burmester (a2), Andrew J. Price (a4) and Joyce T. Ducar (a2)...


The development and spread of glyphosate-resistant (GR) horseweed has increased the use of dicamba as an alternative herbicide treatment. Research evaluated suspected glyphosate-resistant horseweed populations from DeKalb (GR-1) and Cherokee (GR-2) counties, Alabama, for response to glyphosate, dicamba, and glyphosate + dicamba. Populations used for resistance determination were tested at rosette and bolt growth stages. Glyphosate resistance evaluation treatments ranged from 0 to 36.0 kg ae ha−1. Data confirmed that GR-1 and GR-2 horseweed populations were 3.0 to 38 times more resistant to glyphosate than the susceptible population, according to population, data type, and growth stage at treatment. GR-1 and GR-2 populations were further evaluated for response to dicamba. Dicamba was applied at 0 to 1.12 kg ai ha−1, both with and without the addition of glyphosate at 1.12 kg ae ha−1. All populations had similar tolerance to dicamba, with the exception of GR-2 treated at the rosette growth stage, which had ~2-fold greater tolerance. When glyphosate was tank-mixed with dicamba, the response of GR populations was similar to that of dicamba alone. Therefore, any potential resistance-management benefit of tank-mixing dicamba with glyphosate may be negated when one is attempting to control GR horseweed. Conversely, adding glyphosate to dicamba drastically enhanced control of the susceptible population at both growth stages.

El desarrollo y dispersión de Conyza canadensis resistente a glyphosate (GR) ha incrementado el uso de dicamba como un tratamiento herbicida alternativo. Esta investigación evaluó poblaciones de C. canadensis provenientes de los condados DeKalb (GR-1) y Cherokee (GR-2) en Alabama, que se sospechaba eran resistentes a glyphosate, para determinar su respuesta a glyphosate, dicamba, y glyphosate + dicamba. Las poblaciones usadas para la determinación de resistencia fueron evaluadas en los estadios de desarrollo de roseta y de producción de tallo floral. Los tratamientos para la evaluación de resistencia a glyphosate variaron de 0 a 36.0 kg ae ha−1. Los datos confirmaron que las poblaciones de C. canadensis GR-1 y GR-2 fueron 3.0 a 38 veces más resistentes a glyphosate que la población susceptible, según la población, el tipo de dato, y el estadio de crecimiento al momento del tratamiento. Las poblaciones GR-1 y GR-2 fueron además evaluadas para determinar su respuesta a dicamba. Dicamba fue aplicado de 0 a 1.12 kg ai ha−1, con y sin la adición de glyphosate a 1.12 kg ae ha−1. Todas las poblaciones tuvieron tolerancia similar a dicamba, con la excepción de GR-2 tratada en el estadio de roseta, la cual tuvo una tolerancia ~2 veces mayor. Cuando glyphosate fue mezclado en tanque con dicamba, la respuesta de las poblaciones GR fue similar a la de dicamba solo. De esta forma, cualquier beneficio potencial para el manejo de resistencia al mezclar en tanque dicamba con glyphosate, podría ser negado cuando uno trate de controlar C. canadensis GR. En cambio, el agregar glyphosate a dicamba drásticamente mejoró el control de las población susceptible en ambos estadios de desarrollo.


Corresponding author

Corresponding author's E-mail:


Hide All

Associate Editor for this paper: Lawrence E. Steckel, University of Tennessee.



Hide All
Behrens, MR, Mutlu, N, Chakraborty, S, Dumitru, R, Jiang, WZ, LaVallee, BJ, Herman, PL, Clemente, TE, Weeks, D (2007) Dicamba resistance: enlarging and preserving biotechnology-based weed management strategies. Science 316:11851188
Bradshaw, LD, Padgette, SR, Kimball, SL, Wells, BH (1997) Perspectives on glyphosate resistance. Weed Technol 11:189198
Byker, HP, Soltani, N, Robinson, DE, Tardif, FJ, Lawton, MB, Sikkema, PH (2013) Control of glyphosate-resistant horseweed (Conyza canadensis) with dicamba applied preplant and postemergence in dicamba-resistant soybean. Weed Technol 27:492496
Davis, VM, Johnson, WG (2008) Glyphosate-resistant horseweed (Conyza canadensis) emergence, survival, and fecundity in no-till soybean. Weed Sci 56:231236
Davis, VM, Kruger, GR, Stachler, JM, Loux, MM, Johnson, WG (2009) Growth and seed production of horseweed (Conyza canadensis) populations resistant to glyphosate, ALS-inhibiting, and multiple (glyphosate + ALS-inhibiting) herbicides. Weed Sci 57:494504
Diggle, AJ, Neve, PB, Smith, FP (2003) Herbicides used in combination can reduce the probability of herbicide resistance in finite weed populations. Weed Res 43:371382
Dinelli, G, Marotti, I, Bonetti, A, Minelli, M, Catizone, P, Barnes, J (2006) Physiological and molecular insight on the mechanisms of resistance to glyphosate in Conyza canadensis (L.) Cronq. biotypes. Pestic Biochem Physiol 86:3041
Everitt, JD, Keeling, JW (2007) Weed control and cotton (Gossypium hirsutum) response to preplant applications of dicamba, 2,4–D, and diflyfenzopyr plus dicamba. Weed Technol 21:506510
Feng, PCC, Tran, M, Chiu, T, Sammons, RD, Heck, GR, Jacob, CA (2004) Investigations into glyphosate-resistant horseweed (Conyza canadensis): retention, uptake, translocation, and metabolism. Weed Sci 52:498505
Ge, X, d'Avignon, DA, Ackerman, JJH, Sammons, RD (2010) Rapid vacuolar sequestration: the horseweed glyphosate resistance mechanism. Pest Manag Sci 66:345348
Green, JM (2009) Evolution of glyphosate-resistant crop technology. Weed Sci 57:108117
Heap, I (2015) The International Survey of Herbicide Resistant Weeds. Accessed January 19, 2015
Johnson, B, Young, B, Matthews, J, Marquart, P, Slack, C, Bradley, K, York, A, Culpepper, S, Haper, A, Al-Khatib, K, Steckel, L, Moechnig, M, Loux, M, Bernards, M, Smeda, R (2010) Weed Control in dicamba-resistant soybeans. Crop Manage 9:1
Koger, CH, Poston, DH, Hayes, RM, Montgomery, RF (2004) Glyphosate-resistant horseweed (Conyza canadensis) in Mississippi. Weed Technol 18:820825
Koger, CH, Reddy, KN (2005) Role of absorption and translocation in the mechanism of glyphosate resistance in horseweed (Conyza canadensis). Weed Sci 53:8489
Kruger, GR, Davis, VM, Weller, SC, Johnson, WG (2010a) Control of horseweed (Conyza canadensis) with growth regulator herbicides. Weed Technol 24:425429
Kruger, GR, Davis, VM, Weller, SC, Johnson, WG (2010b) Growth and seed production of horseweed (Conyza canadensis) populations after exposure to postemergence 2,4–D. Weed Sci 58:413419
Kruger, GR, Johnson, WG, Weller, SC, Owen, MDK, Shaw, DR, Wilcut, JW, Jordan, DL, Wilson, RG, Bernards, ML, Young, BG (2009) U.S. grower views on problematic weeds and changes in weed pressure in glyphosate-resistant corn, cotton and soybean cropping systems. Weed Technol 23:162166
Main, CL, Mueller, TC, Hayes, RM, Wilkerson, JB (2004) Response of selected horseweed (Conyza canadensis (L.) Cronq.) populations to glyphosate. J Agric Food Chem 52:879883
Mueller, TC, Massey, JH, Hayes, RM, Main, CL, Stewart, CN (2003) Shikimate accumulates in both glyphosate-sensitive and glyphosate-resistant horseweed (Conyza canadensis (L.) Cronq.). J Agric Food Chem 51:680684
Owen, LN, Steckel, LE, Koger, CH, Main, CL, Mueller, TC (2009) Evaluation of spring and fall burndown application timings on control of glyphosate-resistant horseweed (Conyza canadensis) in no-till cotton. Weed Technol 23:335339
Powles, SB (2008) Evolved glyphosate-resistant weeds around the world: lessons to be learnt. Pest Manage Sci 64:360365
Powles, SB, Preston, C, Bryan, IB, Jutsum, AR (1997) Herbicide resistance: impact and management. Adv Agron 58:5793
Steckel, LE, Craig, CC, Hayes, RM (2006) Glyphosate-resistant horseweed (Conyza canadensis) control with glufosinate prior to planting no-till cotton (Gossypium hirsutum). Weed Technol 20:10471051
VanGessel, MJ (2001) Glyphosate-resistant horseweed from Delaware. Weed Sci 49:703705
Walsh, M, Newman, P, Powles, S (2013) Targeting weed seeds in-crop: a new weed control paradigm for global agriculture. Weed Technol 27:431436



Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed