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Differential response of horseweed (Conyza canadensis) to halauxifen-methyl, 2,4-D, and dicamba

  • Cara L. McCauley (a1) and Bryan G. Young (a2)


Halauxifen-methyl is an auxin herbicide for broadleaf weed control in preplant applications to corn and soybean. Our objective for this research was to characterize the phytotoxicity of halauxifen-methyl on horseweed, relative to 2,4-D and dicamba, in terms of weed height, the response to an auxin synergist, and root activity. The 50% reduction in plant growth (GR50) value for halauxifen-methyl on rosette-sized plants was 0.05 g ae ha−1, 100 times less than the labeled use rate of 5 g ae ha−1, compared with 36 and 31 g ha−1 for 2,4-D and dicamba, respectively. In a whole-plant bioassay, 240 g ae ha−1 of 2,4-D was calculated as the GR50 value on horseweed 20-cm tall, whereas applications of only 53 and 0.40 g ae ha−1 were necessary for dicamba and halauxifen-methyl, respectively, to achieve the same response. As weed size decreased, there was a concomitant reduction in the estimated herbicide dose for the GR50 with similar differences observed between halauxifen-methyl and the other two auxin herbicides. The addition of diflufenzopyr, an auxin synergist, to 2,4-D and dicamba resulted in a synergistic response on horseweed. However, the addition of diflufenzopyr to halauxifen-methyl resulted in an additive or antagonistic effect, depending on rate of diflufenzopyr, demonstrating a distinctive physiological pathway for halauxifen-methyl compared with 2,4-D and dicamba. In the agar-based bioassays, GR50 values for horseweed root length for 2,4-D and dicamba were 0.16 and 0.19 µM, respectively, whereas only 0.004 µM halauxifen-methyl was required for a comparable root response. These results indicate that horseweed exhibits a high level of sensitivity to halauxifen-methyl and suggest the activity of halauxifen-methyl is different from that of 2,4-D and dicamba. These differences in herbicide activity may reflect differential absorption, translocation, metabolism, or targeting of auxin receptors found in horseweed.


Corresponding author

Author for correspondence: Cara L. McCauley, Corteva Agriscience, Indianapolis, IN 46268. (Email:


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Anonymous (2010) Clarity® herbicide. Accessed: December 29, 2017
Anonymous (2015) Distinct® herbicide. Accessed: December 29, 2017
Anonymous (2017a) Status® herbicide. Accessed: December 29, 2017
Anonymous (2017b) Elevore™ herbicide. Accessed: December 29, 2017
Anonymous (2018) Weedar 64 herbicide. Accessed: July 1, 2019
Barampuram, S, Allen, G, Krasnyanski, S (2014) Effect of various sterilization procedures on the in vitro germination of cotton seeds. Plant Cell Tissue Organ Cult 118:179185
Bell, JL, Burke, IC, Prather, TS (2011) Uptake, translocation and metabolism of aminocyclopyrachlor in prickly lettuce, rush skeletonweed and yellow starthistle. Pest Manag Sci 67:13381348
Bell, JL, Schmitzer, PR, Robinson, AE (2014) Arylex™ mode and site of action characterization. Proceedings of the 2014 meeting of the Weed Science Society of America and Canadian Weed Science Society/Société Canadienne de Malherbologie. Vancouver, British Columbia, February 3–6, 2014
Bowe, S, Landes, M, Best, J, Schmitz, F, Graben, M (1999) BAS 662 H: an innovative herbicide for weed control in corn. Proc. Brighton Pest Control Conf.—Weeds Pp 3540.
Braz, GBP, Oliveira, RS, Zobiole, LHS, Rubin, RS, Voglewede, C, Constantin, J, Takano, HK (2017) Sumatran fleabane (Conyza sumatrensis) control in no-tillage soybean with diclosulam plus halauxifen-methyl. Weed Technol 31:184192
Brosnan, JT, Vargas, JJ, Reasor, EH, Viggiani, R, Breeden, GK, Zobel, JM (2017) A diagnostic assay to detect herbicide resistance in annual bluegrass (Poa annua). Weed Technol 31:609616
Bukun, B, Gaines, TA, Nissen, SJ, Westra, P, Brunk, G, Shaner, DL, Sleugh, BB, Peterson, VF (2009) Aminopyralid and clopyralid absorption and translocation in Canada thistle (Cirsium arvense). Weed Sci 57:1015
Burgos, NR, Tranel, PJ, Streibig, JC, Davis, VM, Shaner, D, Norsworthy, JK, Ritz, C (2013) Review: confirmation of resistance to herbicides and evaluation of resistance levels. Weed Sci 61:420
Byrd, SA, Collins, GD, Culpepper, AS, Dodds, DM, Edmisten, KL, Wright, DL, Morgan, GD, Baumann, PA, Dotray, PA, Manuchehri, MR, Jones, A, Grey, TL, Webster, TM, Davis, JW, Whitaker, JR, Roberts, PM, Snider, JL, Porter, WM (2016) Cotton stage of growth determines sensitivity to 2,4-D. Weed Technol 30:601610
Colby, S (1967) Calculating synergistic and antagonistic responses of herbicide combinations. Weeds 15:2022
Craigmyle, BD, Ellis, JM, Bradley, KW (2013) Influence of weed height and glufosinate plus 2,4-D combinations on weed control in soybean with resistance to 2,4-D. Weed Technol 27:271280
Davis, VM, Gibson, KD, Johnson, WG (2008) A field survey to determine distribution and frequency of glyphosate-resistant horseweed (Conyza canadensis) in Indiana. Weed Technol 22:331338
Devkota, P, Whitford, F, Johnson, WG (2016) Influence of spray-solution temperature and holding duration on weed control with premixed glyphosate and dicamba formulation. Weed Technol 30:116122
Dowler, CC (1969) A cucumber bioassay test for the soil residues of certain herbicides. Weed Sci 17:309310
Enloe, SF, Kniss, AR (2009) Influence of diflufenzopyr addition to picolinic acid herbicides for Russian knapweed (Acroptilon repens) control. Weed Technol 23:450454
Flint, JL, Cornelius, PL, Barrett, M (1988) Analyzing herbicide interactions: A statistical treatment of Colby’s method. Weed Technol 2:304309
Gibson, KD, Johnson, WG, Hillger, DE (2006) Farmer perceptions of weed problems in corn and soybean rotation systems. Weed Technol 20:751755
Grossmann, K, Caspar, G, Kwiatkowski, J, Bowe, SJ (2002) On the mechanism of selectivity of the corn herbicide BAS 662H: a combination of the novel auxin transport inhibitor diflufenzopyr and the auxin herbicide dicamba. Pest Manag Sci 58:10021014
Heap, I (2018) International survey of herbicide resistant weeds. Accessed: February 20, 2018
Hugie, JA, Bollero, GA, Tranel, PJ, Riechers, DE (2008) Defining the rate requirements for synergism between mesotrione and atrazine in redroot pigweed (Amaranthus retroflexus). Weed Sci 56:265270
Johnston, CR, Eure, PM, Grey, TL, Culpepper, AS, Vencill, WK (2018) Time of application influences translocation of auxinic herbicides in Palmer amaranth (Amaranthus palmeri). Weed Sci 66:414
Kaundun, SS, Hutchings, SJ, Harris, SC, Jackson, LV, Shashi-Kiran, R, Dale, RP, McIndoe, E (2014) A simple in-season bioassay for detecting glyphosate resistance in grass and broadleaf weeds prior to herbicide application in the field. Weed Sci 62:597607
Kaundun, SS, Hutchings, SJ, Dale, RP, Bailly, GC, Glanfield, P (2011) Syngenta “RISQ” test: a novel in-season method for detecting resistance to post-emergence ACCase and ALS inhibitor herbicides in grass weeds. Weed Res 51:284293
Knezevic, SZ, Streibig, JC, Ritz, C (2007) Utilizing R software package for dose-response studies: the concept and data analysis. Weed Technol 21:840848
Kruger, GR, Davis, VM, Weller, SC, Johnson, WG (2010) Control of horseweed (Conyza canadensis) with growth regulator herbicides. Weed Technol 24:425429
Lym, RG, Deibert, KJ (2005) Diflufenzopyr influences leafy spurge (Euphorbia esula) and Canada thistle (Cirsium arvense) control by herbicides. Weed Technol 19:329341
Matocha, ME, Baumann, PA, Matocha, MA (2013) Western ragweed (Ambrosia psilostachya) control and bermudagrass response to diflufenzopyr tank-mix combinations. Weed Technol 27:757761
Mayo, CM, Horak, MJ, Peterson, DE, Boyer, JE (1995) Differential control of four Amaranthus species by six postemergence herbicides in soybean (Glycine max). Weed Technol 9:141147
McCauley, CL, Johnson, WG, Young, BG (2018) Efficacy of halauxifen-methyl on glyphosate-resistant horseweed (Erigeron canadensis). Weed Sci 66:758763
Mellendorf, TG, Young, JM, Matthews, JL, Young, BG (2013) Influence of plant height and glyphosate on saflufenacil efficacy on glyphosate-resistant horseweed (Conyza canadensis). Weed Technol 27:463467
Monaco, J, Weller, S, Ashton, M (2002) Weed science principles and practices. 4th edn. New York, NY: John Wily & Sons. 671 p.
Roskamp, JM, Chahal, GS, Johnson, WG (2013) The effect of cations and ammonium sulfate on the efficacy of dicamba and 2,4-D. Weed Technol 27:7277
Shrestha, A, Hembree, KJ, Va, N (2007) Growth stage influences level of resistance in glyphosate-resistant horseweed. Calif Agric 61:6770
VanGessel, MJ, Scott, BA, Johnson, QR, White-Hansen, SE (2009) Influence of glyphosate-resistant horseweed (Conyza canadensis) growth stage on response to glyphosate applications. Weed Technol 23:4953
Van Wychen, L (2017) WSSA survey ranks most common and most troublesome weeds in broadleaf crops, fruits and vegetables. Accessed: June 27, 2019
Walsh, TA, Neal, R, Merlo, AO, Honma, M, Hicks, GR, Wolff, K, Matsumura, W, Davies, JP (2006) Mutations in an auxin receptor homolog AFB5 and in SGT1b confer resistance to synthetic picolinate auxins and not to 2,4-dichlorophenoxyacetic acid or indole-3-acetic acid in Arabidopsis. Plant Physiol 142:542552
Wiese, AF, Salisbury, CD, Bean, BW (1995) Downy brome (Bromus tectorum), jointed goatgrass (Aegilops cylindrica) and horseweed (Conyza canadensis) control in fallow. Weed Technol 9:249254
Zimmer, M, Young, BG, Johnson, WG (2018) Weed control with halauxifen-methyl applied alone and in mixtures with 2,4-D, dicamba, and glyphosate. Weed Technol 32:597602


Differential response of horseweed (Conyza canadensis) to halauxifen-methyl, 2,4-D, and dicamba

  • Cara L. McCauley (a1) and Bryan G. Young (a2)


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