Auxinic herbicides and glyphosate inhibit horseweed seed production and germination

Novello, Bruna D.; Barroso, Arthur A. M.; Silva, Diecson R. O. da; Bacha, Allan L.; Roncatto, Eduardo; Albrecht, Alfredo J. P.

doi:10.51694/AdvWeedSci/2025;43:00002

Brazil

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RESEARCH ARTICLE • Adv. Weed Sci. 43 • 2025 • https://doi.org/10.51694/AdvWeedSci/2025;43:00002 linkcopy

Auxinic herbicides and glyphosate inhibit horseweed seed production and germination

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Background Horseweed (Conyza bonariensis) is an important weed species infesting soybean plantations. Some biotypes with multiple herbicide resistance have been recently reported. One way to avoid weed dispersion and spread to adjacent areas is by reducing and preventing seed germination.

Objective We aimed to evaluate the effects of auxinic herbicides (2,4-D, dicamba, triclopyr and halauxifen-methyl), with or without mixing with glyphosate, on the production, germination and morphology of horseweed seeds.

Methods With the recent release of the transgenic soybean event DAS-44406-6 in Brazil, we conducted three experiments with different horseweed biotypes (Canguiri, Palotina and Palmeira) and application stages (early and late vegetative, and early reproductive).

Results Auxinic herbicides, applied alone or mixed with glyphosate, reduced the germination and production of horseweed seeds, regardless of the stage of application. The application of herbicides caused morphological changes in the seeds, such as darkening, damaged achenes and papillae, and absence of embryos.

Conclusions For plants that produced seeds, there was a 100% reduction in germination, showing that the application of these herbicides can be a viable strategy in the integrated management of this species.

Conyza bonariensis; Seed Viability; Dicamba; Triclopyr; Halauxifen-Methyl

Orthogonal contrasts	Plant development stage
Orthogonal contrasts	Early vegetative	Late vegetative	Early reproductive
(glyphosate) x (other herbicides)	100 x 100^ns	90.0 x 68.6*	100 x 69.8*
(glyphosate) x (auxinic herbicides)	100 x 100^ns	90.0 x 43.2*	100 x 47.5*
(glyphosate) x (auxinic herbicides + glyphosate)	100 x 100^ns	90.0 x 94.1*	100 x 92.1*
(auxinic herbicides) x (auxinic herbicides +glyphosate)	100 x 100^ns	43.2 x 94.1*	47.5 x 92.1*
(2,4-D and dicamba) x (triclopyr and halauxifen-methyl)	100 x 100^ns	43.3 x 43.1*	50.0 x 45.0*
(2,4-D and dicamba) x (2,4-D+glyphosate and dicamba+ glyphosate)	100 x 100^ns	43.3 x 100*	50.0 x 96.6*
(triclopyr and halauxifen-methyl) x (triclopyr+ glyphosate and halauxifen-methyl +glyphosate)	100 x 100^ns	43.1 x 88.1*	45.0 x 87.7*
(2,4-D+glyphosate and dicamba+ glyphosate) x (triclopyr+glyphosate and halauxifen-methyl +glyphosate)	100 x 100^ns	100 x 88.1*	96.6 x 87.7*
CV %	1.82	5.26	8.00

Orthogonal contrasts	Plant development stage
Orthogonal contrasts	Early vegetative	Late vegetative	Early reproductive
(glyphosate) x (other herbicides)	100 x 100^ns	35.0 x 70.6*	76.2 x 72.8*
(glyphosate) x (auxinic herbicides)	100 x 100^ns	35.0 x 59.6*	76.2 x 74.0*
(glyphosate) x (auxinic herbicides +glyphosate)	100 x 100^ns	35.0 x 81.5*	76.2 x 70.5*
(auxinic herbicides) x (auxinic herbicides +glyphosate)	100 x 100^ns	59.6 x 81.5*	74.0 x 70.5*
(2,4-D and dicamba) x (triclopyr and halauxifen-methyl)	100 x 100^ns	51.2 x 68.1*	75.1 x 73.0*
(2,4-D and dicamba) x (2,4-D+glyphosate and dicamba+ glyphosate)	100 x 100^ns	51.2 x 83.7*	75.1 x 65.5*
(triclopyr and halauxifen-methyl) x (triclopyr+ glyphosate and halauxifen-methyl+ glyphosate)	100 x 100^ns	68.1 x 79.3^ns	73.0 x 75.5*
(2,4-D+glyphosate and dicamba+ glyphosate) x (triclopyr+glyphosate and halauxifen- methyl+glyphosate)	100 x 100^ns	83.7 x 79.3^ns	65.5 x 75.5*
CV %	1.82	16.55	4.67

Orthogonal contrasts	Plant development stage
Orthogonal contrasts	Late vegetative	Early reproductive
(glyphosate) x (other herbicides)	47.5 x 94.0*	45.0 x 95.7*
(glyphosate) x (auxinic herbicides)	47.5 x 88.6*	45.0 x 97.9*
(glyphosate) x (auxinic herbicides +glyphosate)	47.5 x 99.3*	45.0 x 93.5^ns
(auxinic herbicides) x (auxinic herbicides + glyphosate)	88.6 x 99.3*	97.9 x 93.5*
(2,4-D and dicamba) x (triclopyr and halauxifen-methyl)	82.3 x 94.8*	96.6 x 99.2*
(2,4-D and dicamba) x (2,4-D+glyphosate and dicamba+glyphosate)	82.3 x 100*	96.6 x 93.3*
(triclopyr and halauxifen-methyl) x (triclopyr+glyphosate and halauxifen-methyl+ glyphosate)	94.8 x 98.7^ns	99.2 x 93.6*
(2,4-D+glyphosate and dicamba+glyphosate) x (triclopyr+glyphosate and halauxifen- methyl+glyphosate)	94.8 x 98.7^ns	99.2 x 93.6*
C.V. (%)	16.55	4.67

Orthogonal contrasts	Canguiri biotype	Palotina biotype
(glyphosate) x (other herbicides)	88.7 x 90.1*	83.0 x 71.0*
(glyphosate) x (auxinic herbicides)	88.7 x 84.9*	83.0 x 66.0*
(glyphosate) x (auxinic herbicides +glyphosate)	88.7 x 95.3*	83.0 x 77.0^ns
(auxinic herbicides) x (auxinic herbicides +glyphosate)	84.9 x 95.3*	66.0 x 77.0*
(2,4-D and dicamba) x (triclopyr and halauxifen-methyl)	81.2 x 89.4*	64.0 x 67.0*
(2,4-D and dicamba) x (2,4-D+glyphosate and dicamba+glyphosate)	81.2 x 98.6*	64.0 x 91.0*
(triclopyr and halauxifen-methyl) x (triclopyr+glyphosate and halauxifen- methyl+glyphosate)	89.4 x 92.0^ns	67.0 x 63.0*
(2,4-D+glyphosate and dicamba+glyphosate) x (triclopyr+glyphosate and halauxifen- methyl+glyphosate)	98.6 x 92.0^ns	91.0 x 63.0*
C.V. (%)	7.81	22.68

Orthogonal contrasts	Plant development stage
Orthogonal contrasts	Late vegetative	Early reproductive
(glyphosate) x (other herbicides)	94.8 x 99.9*	84.8 x 95.2*
(glyphosate) x (auxinic herbicides)	94.8 x 99.8*	84.8 x 97.7*
(glyphosate) x (auxinic herbicides+glyphosate)	94.8 x 100*	84.8 x 92.8^ns
(auxinic herbicides) x (auxinic herbicides +glyphosate)	99.8 x 100^ns	97.7 x 92.8^ns
(2,4-D and dicamba) x (triclopyr and halauxifen-methyl)	100 x 100^ns	95.5 x 99.9^ns
(2,4-D and dicamba) x (2,4-D+glyphosate and dicamba+glyphosate	100 x 100^ns	95.5 x 85.7*
(triclopyr and halauxifen-methyl) x (triclopyr+glyphosate and halauxifen- methyl+glyphosate)	100 x 100^ns	99.9 x 100^ns
(2,4-D+glyphosate and dicamba+glyphosate) x (triclopyr+glyphosate and halauxifen- methyl+glyphosate)	100 x 100^ns	85.7 x 100^ns
C.V. (%)	2.26	8.33

Orthogonal contrasts	7 DAS	14 DAS
(glyphosate) x (other herbicides)	36.1 x 100*	57.9 x 100*
(glyphosate) x (auxinic herbicides)	36.1 x 100*	57.9 x 100*
(glyphosate) x (auxinic herbicides+glyphosate)	36.1 x 100*	57.9 x 100*
(auxinic herbicides) x (auxinic herbicides +glyphosate)	100 x 100^ns	100 x 100^ns
(2,4-D and dicamba) x (triclopyr and halauxifen-methyl)	100 x 100^ns	100 x 100^ns
(2,4-D and dicamba) x (2,4-D+glyphosate and dicamba+ glyphosate)	100 x 100^ns	100 x 100^ns
(triclopyr and halauxifen-methyl) x (triclopyr+glyphosate and halauxifen- methyl+glyphosate)	100 x 100^ns	100 x 100^ns
(2,4-D+glyphosate and dicamba+ glyphosate) x (triclopyr+glyphosate and halauxifen- methyl+glyphosate)	100 x 100^ns	100 x 100^ns
C.V. (%)	6.12	3.26

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[TFN1] Values relative to the percentage in relation to the non-treated control. * or ns = significant and non-significant contrasts, respectively (p<0.05); + = indicates herbicide mixtures; C.V. = Coefficient of variation.