Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem

Topic Information

Dear Colleagues,

Weed resistance to herbicides is one of the most critical threats to sustainable global food production. The speed of their evolution and spread of resistant weeds is overcoming the industry's capacity to provide new herbicides for effective weed control. To cope with this threat, it is vital to assess and bring new solutions to this complex problem. We are pleased to announce this special Topic on “Weed Resistance to Herbicides” at MDPI. This Topic will span across five journals: Agriculture, Agronomy, Crops, Genes, and Plants. The authors can choose in which journal to publish, and all the manuscripts will be assembled under a unique Topic. Please check on the journal webpage the instructions for authors to find details on what is expected of a manuscript.

In this Topic, we will accept manuscripts dealing with the aspects related to weed resistance below:

• Weed resistance detection;
• Ecology and biology of resistant weeds;
• Weed resistance mechanisms;
• Weed resistance management;
• Weed resistance and environmental aspects;
• Agronomic and sociological impact of weed resistance.

Prof. Dr. Nilda Roma Burgos
Prof. Dr. Luis Antonio de Avila
Dr. Harry Strek
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Agriculture agriculture	3.3	4.9	2011	19.2 Days	CHF 2600
Agronomy agronomy	3.3	6.2	2011	17.6 Days	CHF 2600
Crops crops	-	-	2021	22.1 Days	CHF 1000
Genes genes	2.8	5.2	2010	14.9 Days	CHF 2600
Plants plants	4.0	6.5	2012	18.9 Days	CHF 2700

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Published Papers (11 papers)

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14 pages, 4050 KiB  

Open AccessArticle

Conyza bonariensis’ Resistance to Glyphosate, Diclosulam, and Chlorimuron: Confirmation and Alternative Control for the First Case of Multiple and Cross-Resistance in Uruguay

by Tiago Edu Kaspary, Mauricio Emanuel Waller Barcena, Milton Alejandro García, Maurico Cabrera and Sofía Marques Hill

Agronomy 2024, 14(1), 79; https://doi.org/10.3390/agronomy14010079 - 28 Dec 2023

Cited by 2 | Viewed by 1817

Abstract

Conyza bonariensis L. (hairy fleabane) is a significant weed in production systems, especially due to its evolving resistance to various herbicides. In Uruguay, control failures of C. bonariensis have been reported following the use of glyphosate and ALS inhibitors. The objective of this [...] Read more.

Conyza bonariensis L. (hairy fleabane) is a significant weed in production systems, especially due to its evolving resistance to various herbicides. In Uruguay, control failures of C. bonariensis have been reported following the use of glyphosate and ALS inhibitors. The objective of this study was to investigate the occurrence of the multiple and cross-resistance of C. bonariensis to glyphosate, chlorimuron, and diclosulam, and to assess the efficacy of alternative herbicides against these resistant biotypes. Seeds were collected from sites where plants had survived herbicide applications during the 2019/2020 and 2020/2021 seasons. Following initial screenings, biotypes were selected to establish independent dose–response curves for glyphosate, diclosulam, and chlorimuron. For each herbicide, four biotypes of C. bonariensis were tested: one susceptible (S), two putatively moderately resistant (MR) biotypes, and one putatively highly resistant (R) biotype. In each assay, eight herbicide doses were used (1/32; 1/16; 1/8; 1/2; 1; 2; and 4X for S and MR biotypes, and 1/8; 1/2; 1; 2; 4; 8; and 16X for R biotypes) based on the recommended dose (1x) for each herbicide, with four repetitions per treatment. Each assay was completely replicated twice. Resistance was confirmed through testing in two plant generations (G1 and G2). The findings reveal high levels of multiple and cross-resistance in C. bonariensis to glyphosate, diclosulam, and chlorimuron. In general, herbicides with alternative action mechanisms effectively controlled C. bonariensis exhibiting multiple and cross-resistance. This study confirms the first case of C. bonariensis cross-resistance to diclosulam and chlorimuron, and the first occurrence of multiple and cross-resistance to glyphosate, diclosulam, and chlorimuron in this species. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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10 pages, 717 KiB  

Open AccessArticle

Herbicide Program to Control Parthenium hysterophorus in Grain Sorghum in an Arid Environment

by Ali Ahsan Bajwa, Ahmad Nawaz, Muhammad Farooq, Bhagirath Singh Chauhan and Steve Adkins

Crops 2023, 3(4), 292-301; https://doi.org/10.3390/crops3040026 - 16 Nov 2023

Cited by 1 | Viewed by 2056

Abstract

Parthenium weed (Parthenium hysterophorus L.) is an emerging production constraint in many summer crops including sorghum (Sorghum bicolor L. Moench), but limited control options are available. In this field study, the efficacy of sole and sequential applications of a pre-emergence (pendimethalin) [...] Read more.

Parthenium weed (Parthenium hysterophorus L.) is an emerging production constraint in many summer crops including sorghum (Sorghum bicolor L. Moench), but limited control options are available. In this field study, the efficacy of sole and sequential applications of a pre-emergence (pendimethalin) and a post-emergence (bromoxynil) herbicide was evaluated for parthenium weed control in grain sorghum over two years. Pendimethalin or bromoxynil alone could only provide 54% and 63% control, whereas their sequential application provided 86% control of parthenium weed over the weedy treatment. The sorghum plants in pendimethalin followed by bromoxynil treatment had the highest leaf fresh weight per plant, plant dry biomass, plant height, and the number of heads among the herbicide treatments. Sorghum fresh forage yield, dry fodder yield, 1000-grain weight, and grain yield were highest in the weed-free treatment followed by the pendimethalin followed by (fb) bromoxynil treatment. Overall, the herbicide treatment performance was in an order of pendimethalin fb bromoxynil > bromoxynil > pendimethalin for weed control and sorghum yield improvement. These results suggest that pendimethalin followed by bromoxynil may provide acceptable control (>85%) of parthenium weed and may improve sorghum grain yield (up to 23%). Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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17 pages, 4851 KiB  

Open AccessArticle

Identification and Expression Analysis of EPSPS and BAR Families in Cotton

by Zhao Li, Zhen Zhang, Yinbo Liu, Yuanqi Ma, Xing Lv, Dongmei Zhang, Qishen Gu, Huifeng Ke, Liqiang Wu, Guiyin Zhang, Zhiying Ma, Xingfen Wang and Zhengwen Sun

Plants 2023, 12(19), 3366; https://doi.org/10.3390/plants12193366 - 23 Sep 2023

Cited by 2 | Viewed by 1975

Abstract

Weeds seriously affect the yield and quality of crops. Because manual weeding is time-consuming and laborious, the use of herbicides becomes an effective way to solve the harm caused by weeds in fields. Both 5-enolpyruvyl shikimate-3-phosphate synthetase (EPSPS) and acetyltransferase genes [...] Read more.

Weeds seriously affect the yield and quality of crops. Because manual weeding is time-consuming and laborious, the use of herbicides becomes an effective way to solve the harm caused by weeds in fields. Both 5-enolpyruvyl shikimate-3-phosphate synthetase (EPSPS) and acetyltransferase genes (bialaphos resistance, BAR) are widely used to improve crop resistance to herbicides. However, cotton, as the most important natural fiber crop, is not tolerant to herbicides in China, and the EPSPS and BAR family genes have not yet been characterized in cotton. Therefore, we explore the genes of these two families to provide candidate genes for the study of herbicide resistance mechanisms. In this study, 8, 8, 4, and 5 EPSPS genes and 6, 6, 5, and 5 BAR genes were identified in allotetraploid Gossypium hirsutum and Gossypium barbadense, diploid Gossypium arboreum and Gossypium raimondii, respectively. Members of the EPSPS and BAR families were classified into three subgroups based on the distribution of phylogenetic trees, conserved motifs, and gene structures. In addition, the promoter sequences of EPSPS and BAR family members included growth and development, stress, and hormone-related cis-elements. Based on the expression analysis, the family members showed tissue-specific expression and differed significantly in response to abiotic stresses. Finally, qRT-PCR analysis revealed that the expression levels of GhEPSPS3, GhEPSPS4, and GhBAR1 were significantly upregulated after exogenous spraying of herbicides. Overall, we characterized the EPSPS and BAR gene families of cotton at the genome-wide level, which will provide a basis for further studying the functions of EPSPS and BAR genes during growth and development and herbicide stress. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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11 pages, 2327 KiB  

Open AccessArticle

Divergence in Glyphosate Susceptibility between Steinchisma laxum Populations Involves a Pro106Ser Mutation

by Veronica Hoyos, Guido Plaza, Candelario Palma-Bautista, Jose G. Vázquez-García, José Alfredo Dominguez-Valenzuela, Ricardo Alcántara-de la Cruz and Rafael De Prado

Plants 2023, 12(18), 3315; https://doi.org/10.3390/plants12183315 - 20 Sep 2023

Viewed by 1917

Abstract

The characterization of the mechanisms conferring resistance to herbicides in weeds is essential for developing effective management programs. This study was focused on characterizing the resistance level and the main mechanisms that confer resistance to glyphosate in a resistant (R) Steinchisma laxum population [...] Read more.

The characterization of the mechanisms conferring resistance to herbicides in weeds is essential for developing effective management programs. This study was focused on characterizing the resistance level and the main mechanisms that confer resistance to glyphosate in a resistant (R) Steinchisma laxum population collected in a Colombian rice field in 2020. The R population exhibited 11.2 times higher resistance compared to a susceptible (S) population. Non-target site resistance (NTSR) mechanisms that reduced absorption and impaired translocation and glyphosate metabolism were not involved in the resistance to glyphosate in the R population. Evaluating the target site resistance mechanisms by means of enzymatic activity assays and EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) gene sequencing, the mutation Pro106Ser was found in R plants of S. laxum. These findings are crucial for managing the spread of S. laxum resistance in Colombia. To effectively control S. laxum in the future, it is imperative that farmers use herbicides with different mechanisms of action in addition to glyphosate and adopt Integrate Management Programs to control weeds in rice fields of the central valleys of Colombia. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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11 pages, 2694 KiB  

Open AccessArticle

A Double Mutation in the ALS Gene Confers a High Level of Resistance to Mesosulfuron-Methyl in Shepherd’s-Purse

by Huan Lu, Yingze Liu, Dexiao Bu, Fan Yang, Zheng Zhang and Sheng Qiang

Plants 2023, 12(14), 2730; https://doi.org/10.3390/plants12142730 - 23 Jul 2023

Cited by 8 | Viewed by 2154

Abstract

Shepherd’s-purse (Capsella bursa-pastoris), a globally distributed noxious weed species often found in wheat, has evolved resistance to ALS-inhibiting herbicides mainly due to single mutations in the ALS gene. In the present study, dose–response bioassays showed that a shepherd’s-purse population (R), collected [...] Read more.

Shepherd’s-purse (Capsella bursa-pastoris), a globally distributed noxious weed species often found in wheat, has evolved resistance to ALS-inhibiting herbicides mainly due to single mutations in the ALS gene. In the present study, dose–response bioassays showed that a shepherd’s-purse population (R), collected from Xinghua, Jiangsu Province, China, had high level of resistance to the ALS-inhibiting herbicide, mesosulfuron-methyl (800-fold), and even much higher resistance levels to other reported ALS-inhibiting herbicides, tribenuron-methyl (1313-fold), bensulfuron-methyl (969-fold) and penoxsulam (613-fold). Sequencing of the open reading frame of the ALS gene revealed a double ALS gene mutation (Pro197-Ser plus Trp574-Leu) conferring the high resistance in the R plants. Docking analysis of the ALS protein and mesosulfuron-methyl predicts that the two amino acid substitutions in the R samples reduces the binding energy to the herbicide by decreasing the hydrogen bonds (H-bonds) and other interactions, thus endowing resistance to ALS-inhibiting herbicides. These results demonstrate that the double ALS mutation confers high resistance levels to ALS-inhibiting herbicides. To our knowledge, this is the first evidence of the double ALS mutation in shepherd’s-purse endowing ALS-inhibiting herbicide resistance. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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10 pages, 6481 KiB  

Open AccessCommunication

A New V361A Mutation in Amaranthus palmeri PPX2 Associated with PPO-Inhibiting Herbicide Resistance

by Haozhen Nie, Nick T. Harre and Bryan G. Young

Plants 2023, 12(9), 1886; https://doi.org/10.3390/plants12091886 - 5 May 2023

Cited by 6 | Viewed by 2258

Abstract

Weeds resistant to PPO-inhibiting herbicides threaten the profitability of crop producers relying on this chemistry. In Amaranthus palmeri, mutations at G210 (∆G210) and R128 (R128G/M) of the PPX2 gene were reported to confer PPO-inhibitor resistance. Here, A. palmeri samples from nine states [...] Read more.

Weeds resistant to PPO-inhibiting herbicides threaten the profitability of crop producers relying on this chemistry. In Amaranthus palmeri, mutations at G210 (∆G210) and R128 (R128G/M) of the PPX2 gene were reported to confer PPO-inhibitor resistance. Here, A. palmeri samples from nine states in America, having survived a field application of a PPO-inhibitor, were genotyped to determine the prevalence of these mutations. Less than 5% of the 1828 A. palmeri plants screened contained the ∆G210 mutation. Of the plants lacking ∆G210, a R128 substitution was only found in a single plant. An A. palmeri population from Alabama without mutations at G210 or R128 had a resistance ratio of 3.1 to 3.5 for fomesafen. Of the candidate PPX2 mutations identified in this population, only V361A conferred resistance to lactofen and fomesafen in a transformed bacterial strain. This is the first report of the V361A substitution of PPX2 conferred PPO-inhibiting herbicide resistance in any plant species. Future molecular screens of PPO-inhibitor resistance in A. palmeri and other species should encompass the V361A mutation of PPX2 to avoid false-negative results. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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17 pages, 3635 KiB  

Open AccessArticle

Unravelling the Phytotoxic Effects of Glyphosate on Sensitive and Resistant Amaranthus palmeri Populations by GC–MS and LC–MS Metabolic Profiling

by Ainhoa Zulet-Gonzalez, Karin Gorzolka, Stefanie Döll, Miriam Gil-Monreal, Mercedes Royuela and Ana Zabalza

Plants 2023, 12(6), 1345; https://doi.org/10.3390/plants12061345 - 16 Mar 2023

Cited by 12 | Viewed by 2534

Abstract

Glyphosate, the most successful herbicide in history, specifically inhibits the activity of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS; EC 2.5.1.19), one of the key enzymes in the shikimate pathway. Amaranthus palmeri is a driver weed in agriculture today that has evolved glyphosate-resistance through increased [...] Read more.

Glyphosate, the most successful herbicide in history, specifically inhibits the activity of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS; EC 2.5.1.19), one of the key enzymes in the shikimate pathway. Amaranthus palmeri is a driver weed in agriculture today that has evolved glyphosate-resistance through increased EPSPS gene copy number and other mechanisms. Non-targeted GC–MS and LC–MS metabolomic profiling was conducted to examine the innate physiology and the glyphosate-induced perturbations in one sensitive and one resistant (by EPSPS amplification) population of A. palmeri. In the absence of glyphosate treatment, the metabolic profile of both populations was very similar. The comparison between the effects of sublethal and lethal doses on sensitive and resistant populations suggests that lethality of the herbicide is associated with an amino acid pool imbalance and accumulation of the metabolites of the shikimate pathway upstream from EPSPS. Ferulic acid and its derivatives were accumulated in treated plants of both populations, while quercetin and its derivative contents were only lower in the resistant plants treated with glyphosate. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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18 pages, 4846 KiB  

Open AccessArticle

Widespread Occurrence of Glyphosate-Resistant Hairy Fleabane (Erigeron bonariensis L.) in Colombia and Weed Control Alternatives

by Edwin Granados, Ian Zelaya and Guido Plaza

Agronomy 2023, 13(3), 683; https://doi.org/10.3390/agronomy13030683 - 26 Feb 2023

Cited by 2 | Viewed by 2827

Abstract

Glyphosate, the most applied herbicide globally, offers effective non-selective and post-emergent weed control. Evolution of herbicide-resistant weeds is commonly associated with the recurrent application of herbicides with the same mode of action. Native to South America, hairy fleabane (Erigeron bonariensis L.) is [...] Read more.

Glyphosate, the most applied herbicide globally, offers effective non-selective and post-emergent weed control. Evolution of herbicide-resistant weeds is commonly associated with the recurrent application of herbicides with the same mode of action. Native to South America, hairy fleabane (Erigeron bonariensis L.) is the most problematic weed in this sub-continent and has previously been confirmed glyphosate resistant. This research aimed at characterizing glyphosate-resistant populations, thus estimating the frequency of resistance, resistance levels and identifying effective herbicide alternatives to control glyphosate-resistant populations. Glyphosate resistance characterization was initially conducted on ten suspected populations collected in plantain, banana, cassava, passionfruit, papaya, and drybean crops. Two resistant populations were selected and further characterized through dose-response tests; in addition, response to alternative herbicides (paraquat, glufosinate, 2,4-D, pyraflufen-ethyl, and mesotrione) was determined. All surveyed hairy fleabane populations survived (≥80% of individuals) the recommended glyphosate rate of 1080 g ae ha⁻¹; conversely, five populations collected from non-cropping areas were effectively controlled at this same rate. Dose-response tests estimated resistance factors of 3.15- to 22.3-fold versus the most susceptible population. Interestingly, resistance profile and dose-response tests detected hormesis responses at field-recommended rates. The most effective herbicide alternatives to control glyphosate-resistant hairy fleabane were pyraflufen-ethyl and mesotrione. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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8 pages, 254 KiB  

Open AccessArticle

Response of Soybean (Glycine max (L.) Merr.) and Weed Control with Postemergence Herbicides and Combinations of Cytokinin Mixtures

by Hunter D. Bowman, Huntington T. Hydrick, Jason A. Bond and Thomas W. Allen

Agronomy 2022, 12(12), 3086; https://doi.org/10.3390/agronomy12123086 - 6 Dec 2022

Cited by 2 | Viewed by 1811

Abstract

A field study was conducted in 2015 and 2016 in Stoneville, MS, to evaluate the influence of cytokinin products on soybean injury and weed control when combined with common POST soybean herbicide treatments. Cytokinin treatments included no cytokinin mixture and two formulated cytokinin [...] Read more.

A field study was conducted in 2015 and 2016 in Stoneville, MS, to evaluate the influence of cytokinin products on soybean injury and weed control when combined with common POST soybean herbicide treatments. Cytokinin treatments included no cytokinin mixture and two formulated cytokinin mixtures (kinetin-1 and kinetin-2) applied at 0.000227 kg ai ha⁻¹. Herbicide treatments were no herbicide, glyphosate at 1.37 kg ae ha⁻¹ alone and in combination with S-metolachlor at 1.42 kg ai ha⁻¹ or fomesafen 0.395 kg ai ha⁻¹. The addition of cytokinin treatments had no impact on soybean injury, plant height, or yield. Glyphosate plus fomesafen provided the greatest level of Palmer amaranth control, between 84 and 67%., 7 days and 28 days after treatment, respectively. Barnyardgrass control with glyphosate plus fomesafen was antagonized by one of two cytokinin products. To prevent possible reductions in herbicide efficacy, tank mixtures with cytokinin products should not be applied to soybean in POST herbicide applications. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

10 pages, 1204 KiB  

Open AccessArticle

Weed Control, Rice Safety, and Mechanism of the Novel Paddy Field Herbicide Glyamifop

by Haitao Gao, Haowen Zheng, Pu Zhang, Jiaxing Yu, Jun Li and Liyao Dong

Agronomy 2022, 12(12), 3026; https://doi.org/10.3390/agronomy12123026 - 30 Nov 2022

Cited by 3 | Viewed by 2382

Abstract

Glyamifop (R&D code: FG001), (R)-(2-(4-(6-chlorobenzoxazol-2-oxy) phenoxy) propionyl) glycine ethyl ester is a newly developed aryloxyphenoxypropionate (HRAC Group 1) herbicide for weed control in paddy fields. This work determined the effect of Glyamifop on weeds and its safety for rice in the [...] Read more.

Glyamifop (R&D code: FG001), (R)-(2-(4-(6-chlorobenzoxazol-2-oxy) phenoxy) propionyl) glycine ethyl ester is a newly developed aryloxyphenoxypropionate (HRAC Group 1) herbicide for weed control in paddy fields. This work determined the effect of Glyamifop on weeds and its safety for rice in the glasshouse. Glyamifop controlled the common gramineous weeds in paddy fields at 100 g a.i. ha⁻¹: the fresh weight inhibition rates of Echinochloa crus-galli, Leptochloa chinensis, Setaria viridis, Eragrostis japonica, Digitaria sanguinalis and Panicum bisulcatum were all above 90%. It has almost no inhibitory effect on broad-leaved and cyperaceae weeds, such as Eclipta prostrata and Cyperus iria. Glyamifop inhibited cyhalofop-butyl-resistant L. chinensis, penoxsulam-resistant E. crus-galli and quinclorac-resistant E. crusgalli var. zelayensis by 100%, 99.98% and 96.37%, respectively, at 100 g a.i. ha⁻¹, based on the fresh weight. The selectivity index of Glyamifop foliage treatment in the rice varieties japonica ‘Huaidao 5’, indica ‘Xiangliangyou 900’ and glutinous ‘Zhennuo 29’ was 5.93, 6.81 and 4.91, respectively; therefore, Glyamifop is safe for the 3 different rice varieties. Fresh weight rice inhibition rates were 7.18%, 2.99% and 7.93% at the 2.5-, 3.5- and 5.5-leaf stage, respectively, and the selectivity index was 5.18, 6.04 and 7.93, respectively, indicating that Glyamifop was safe for rice at these leaf stages. L. chinensis ACCase activity decreased with increasing Glyamifop concentration, and the inhibitory effect was similar to that of cyhalofop acid; this confirmed that Glyamifop is an ACCase inhibitor. In conclusion, Glyamifop has potential for the management of gramineous weeds as it has good activity against weeds that are resistant to common herbicides in paddy fields. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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13 pages, 1379 KiB  

Open AccessArticle

Glyphosate Efficacy in Chloris virgata Sw. in Response to Temperature and Tank Mixing

by Gulshan Mahajan and Bhagirath Singh Chauhan

Plants 2022, 11(23), 3190; https://doi.org/10.3390/plants11233190 - 22 Nov 2022

Cited by 2 | Viewed by 1911

Abstract

Glyphosate alone or a tank mixture of glyphosate and 2,4-D is commonly used for broad-spectrum weed control under fallow conditions in Australia. Air temperature or mixing glyphosate with 2,4-D, may influence the efficacy of glyphosate on feather fingergrass (Chloris virgata Sw.), a [...] Read more.

Glyphosate alone or a tank mixture of glyphosate and 2,4-D is commonly used for broad-spectrum weed control under fallow conditions in Australia. Air temperature or mixing glyphosate with 2,4-D, may influence the efficacy of glyphosate on feather fingergrass (Chloris virgata Sw.), a problematic summer-season weed of Australia. Dose–response studies were conducted with four populations of feather fingergrass under temperature-controlled glasshouse conditions (35/25 °C and 25/15 °C at 12 h/12 h) to assess the level of glyphosate resistance in relation to temperature regimes. Four parameter log-logistic models were used to develop dose–response curves. Based on plant mortality percentage, LD₅₀ (lethal dose for 50% mortality) values of glyphosate at 25/15 °C for populations Ch, SGM2, SGW2, and CP2 were 137, 60, 650, and 1067 g ae ha⁻¹, respectively. However, at 35/25 °C, the corresponding LD₅₀ values were 209, 557, 2108, and 2554 g ae ha⁻¹, respectively. A similar response was observed for the parameter GR₅₀ (dose for 50% growth reduction) values of glyphosate. These results indicate that populations SGW2 and CP2 are highly glyphosate-resistant and in the summer season, it may be very difficult to control these populations due to poor glyphosate efficacy. These results further suggest that the efficacy of glyphosate for feather fingergrass control can be improved if applied during cooler temperatures (25/15 °C) or the spring season compared with warmer temperatures (35/25 °C) or the summer season. In another study, 2,4-D antagonized glyphosate remarkably in the CP2 (glyphosate-resistant) population but only marginally in the Ch (glyphosate-susceptible) population. Thus, it is not advisable to mix 2,4-D with glyphosate for the control of glyphosate-resistant feather fingergrass populations. The results further suggest that the use of this mixture is useful if the feather fingergrass is not glyphosate-resistant; however, the use of the mixture is to be avoided if the population is glyphosate-resistant in order to not exacerbate the potential resistance problem. Full article

(This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem)

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