Multiple Herbicide Resistance in Annual Ryegrass (Lolium rigidum Gaudin) in the Southeastern Cropping Region of Australia

Abstract

Annual ryegrass (Lolium rigidum) is a problematic weed in winter crops and fallows in the southeastern cropping region (SCR) of Australia. This weed has evolved resistance to multiple herbicide groups, globally. In Australia, L. rigidum is more prevalent in the western and southern regions than in SCR. To assess the herbicide resistance status of L. rigidum, the response of five L. rigidum populations (collected from the SCR) to glyphosate, glufosinate, paraquat, haloxyfop-P-ethyl, and clethodim is determined using dose–response curves. Three parametric logistic models are used to determine the herbicide dose required to achieve 50% survival (LD₅₀) and 50% growth reduction (GR₅₀). The LD₅₀ values for 50% survival at 28 days after treatment range from 1702 g a.e. ha⁻¹ to 8225 g a.e. ha⁻¹ for glyphosate, 1637 g a.i. ha⁻¹ to 1828 g a.i. ha⁻¹ for glufosinate, 141 g a.i. ha⁻¹ to 307 g a.i. ha⁻¹ for paraquat, 11 g a.i. ha⁻¹ to 107 g a.i. ha⁻¹ for haloxyfop-P-ethyl, and 17 g a.i. ha⁻¹ to 48 g a.i. ha⁻¹ for clethodim. The resistance factor, based on GR₅₀ value, is highest in the S7 population (2.2 times) for glyphosate, the S11 population (2.3 times) for glufosinate, the S11 population (2.0 time) for paraquat, the S7 population (3.9 times) for haloxyfop-P-ethyl, and the S3 population (3.1 times) for clethodim, compared with the susceptible or less tolerant population. The S11 population is found to be resistant to five tested herbicides, based on resistance factors. Similarly, the S3 population is highly resistant to glyphosate, haloxyfop-P-ethyl, and clethodim compared with the W4 population. These results suggest that L. rigidum populations in the SCR exhibit resistance to multiple herbicide groups at labelled field rates. The findings highlight the necessity of adopting an integrated management approach, including the use of residual herbicides, tank mixing herbicides with different modes of action, and rotating herbicides in conjunction with cultural and mechanical control methods.

1. Introduction

Lolium rigidum Gaud. (annual ryegrass) is a winter annual weed prevalent in Australian cropping fields, causing an annual revenue loss of over AU$93 million to Australian grain growers [1]. Globally, L. rigidum has evolved resistance to 11 distinct herbicide groups [2], with herbicide resistance against this weed reported in 12 countries, including Australia.

The intensive use of herbicides for L. rigidum control in cropping situations, along with frequent applications of nonselective herbicides in fallows and as knockdowns before pre-seeding, has exacerbated the problem of herbicide-resistant L. rigidum in Australia. Notably, the world’s first case of glyphosate-resistant L. rigidum was reported in a cropping region of northern Victoria, Australia, in 1996 [3,4].

Initially, L. rigidum was a problematic weed in western and southern Australia. However, due to its adaptability to climate change, it has also become a significant weed in the southeastern cropping region (SCR) of Australia. A recent study in Australia demonstrated that L. rigidum can germinate across a wide range of temperatures (15/5 °C to 35/25 °C; day/night temperature), confirming its adaptability to changing seasonal conditions [5]. Notably, this weed has been observed during the summer season in the SCR, particularly in cotton (Gossypium hirsutum L.) paddocks, suggesting its ability to produce seeds throughout the year [5,6,7]. Furthermore, the widespread adoption of glyphosate-tolerant canola (Brassica napus L.) in Australia has increased the incidence of glyphosate-resistant L. rigidum populations.

While resistant populations of L. rigidum to nonselective herbicides, such as glyphosate, paraquat, and glufosinate, are less prevalent in Australia compared to resistance against Group 1 and 2 herbicides [8,9,10,11], even small herbicide-resistant populations in fallows, fencelines, and cropping areas can produce seeds and invade the agroecosystem. Lolium rigidum in wheat crops can produce up to 45,000 seeds m⁻² [12], suggesting that this weed can produce even more seeds under fallow conditions when not competing with crops.

For weed control in fallows, paraquat has been used by growers in a ‘double-knock strategy’ (glyphosate followed by paraquat), particularly for controlling glyphosate-resistant L. rigidum populations [13,14]. The incidence of L. rigidum populations resistant against different herbicide modes of action is rising in Australia, necessitating careful investigation and a diversified weed control program to restrict its spread. Australian growers have shown interest in using glufosinate for nonselective weed control in fallows despite its higher cost [15].

The lack of information on L. rigidum populations resistant to multiple nonselective herbicides is a concern for SCR growers cultivating winter crops. The control of L. rigidum is crucial before planting no-till winter crops, especially in dryland regions, where residual soil moisture is essential for crop growth. Lolium rigidum populations are highly competitive and can severely reduce crop yield if not controlled in a timely manner. Several studies have reported significant yield losses (50–80%) due to L. rigidum infestations in various crops [16,17].

Therefore, this study aims to determine the level of resistance to glyphosate, glufosinate, paraquat, haloxyfop-P-ethyl (thereafter haloxyfop), and clethodim in L. rigidum populations in the SCR of Australia.

2. Materials and Methods

2.1. Population and Seed Collection

Five populations (S0, S3, S7, S11, and W4) of L. rigidum were used in this study. Seeds of the S0 population were collected from a cotton field in Griffith, New South Wales (NSW) (S 34°43.417; E 146°03.409) in February 2017. Seeds of the S3 (S 34°30.019; E 146°08.611) and S7 (S 34°689617; E 145°7852) populations were collected from the fenceline of a cotton field in Griffith in March 2019. Seeds of the S11 (S 35°03.195; E 147°18.591) population were collected from wheat fallows in Griffith in March 2019. The W4 population was collected in December 2018 from fallow areas in Croppa Creek, NSW, Australia (S 27°36.980; E 152°12.486). Seeds were stored under laboratory conditions (25 °C) until May 2022, when they were grown together at the Gatton Research Farm, University of Queensland, Queensland, Australia. Fresh seeds from these populations were used for this study.

2.2. Experimental Setup and Observations

For the experimental study, seeds of L. rigidum populations (S0, S3, S7, S11, and W4) were sown in trays containing potting mix (Centenary Landscape, Queensland, Australia) and then transplanted into pots (12 cm diameter and 14 cm height) immediately after emergence. The pots were filled with potting mix before transplanting, and six plants were transplanted into each pot. The pots were kept on benches in an open environment under natural light and temperature conditions.

The experiment was conducted following a randomized block design with six replicates for each population. In the glyphosate dose–response experiment, doses were 0X (no herbicide; control), 0.25X, 0.5X, 1X (recommended dose, 450 g a.e. ha⁻¹), 2X, 4X, and 8X. In the paraquat dose response experiment, doses were 0X (no herbicide; control), 0.25X, 0.5X, 1X (recommended field rate, 300 g a.i. ha⁻¹), 2X, 4X, and 8X. In the glufosinate dose response experiment, doses were 0X (no herbicide; control), 0.25X, 0.5X, 1X (recommended field rate, 750 g a.i. ha⁻¹), 2X, and 4X. In the haloxyfop dose–response experiment, doses were 0X (no herbicide; control), 0.25X, 0.5X, 1X (recommended field rate, 39 g a.i. ha⁻¹), 2X, 4X, and 8X. In the clethodim dose–response experiment, doses were 0X (no herbicide; control), 0.25X, 0.5X, 1X (recommended field rate, 36 g a.i. ha⁻¹), 2X, 4X, and 8X.

The commercial product of glyphosate, named ‘Roundup UltraMAX’, with an active constituent of 570 gL⁻¹ was used, and, under fallow conditions in Australia, its labelled rate for controlling L. rigidum was 625–795 mL ha⁻¹ (commercial dose). For paraquat, a commercial product named ‘Genfarm Paraquat’ (Landmark Operations Limited, Macquarie Park, NSW, Australia), with an active constituent of 250 gL⁻¹, was used, and, under fallow conditions in Australia, its labelled rate for controlling L. rigidum was 1200 mL ha⁻¹ (commercial dose). Similarly, for glufosinate, a commercial product named ‘Biffo’ (Nufarm Australia Limited, Laverton North, VIC, Australia), with an active constituent of 200 gL⁻¹, was used at a labelled rate of 3750 mL ha⁻¹ for controlling L. rigidum under fallow conditions. For clethodim, a commercial product named ‘Platinum^® XTRA’ (ADAMA, St Leonards, NSW, Australia), with an active constituent of 360 gL⁻¹, was used at a labelled rate of 100 mL ha⁻¹ for controlling L. rigidum. For haloxyfop, a commercial product named ‘Verdict’ (Corteva Agriscience Australia Pty Ltd., Chatswood, NSW, Australia), with an active constituent of 520 gL⁻¹, was used at a labelled rate of 75 mL ha⁻¹ for controlling L. rigidum.

The experiment assessing the dose–response curve of glyphosate, glufosinate, and paraquat began in early April 2024 and was concluded in May 2024. The experiment for clethodim and haloxyfop began in late April 2024 and was harvested in June 2024. Plants were kept well-watered (four times daily with a sprinkler system for ten minutes).

Herbicides were applied using a research track sprayer. Plants were treated at the two-to-three leaf stage using a spray volume of 108 L ha⁻¹ and Teejet XR 110,015 flat fan nozzles. After herbicide application, plants were left without water for 24 h. Plant survival was assessed 28 days after herbicide application and the aboveground biomass was harvested, dried for 72 h at 70 °C, and weighed.

2.3. Statistical Analyses

Visual survival percentage (as a percentage compared to the nontreated control) and shoot biomass data were regressed separately for each population against herbicide treatments using a three-parameter logistic model:

y = a/[1 + (x/x₀)b]

where y is the response variable (percent survival or shoot biomass), a is the upper limit, b is the slope of the line, x₀ is the dose resulting in a 50% survival rate or biomass reduction (known as LD₅₀ or GR_50, respectively), and x is the herbicide rate.

Dose–response curves were analyzed separately for each population, and LD₅₀ and GR₅₀ values were determined using the Sigma-Plot software (Sigma Plot 15.0, Systat Software, San Jose, CA, USA). The ANOVA function was used to perform the lack-of-fit test, and a p-value ≥ 0.05 was used, indicating that the fitted nonlinear model adequately described the data.

The resistance factor of herbicide was calculated by dividing the LD₅₀ or GR₅₀ of the resistant population by LD₅₀ or GR₅₀ of the susceptible populations. The population with the lowest LD₅₀ or GR₅₀ value was considered to be the susceptible population. While the resistance factor is typically compared to the most susceptible population, we did not have access to the most susceptible population, so we used the population with the lowest available LD₅₀ or GR₅₀ value as the reference population.

3. Results

The dose–response assay revealed that a glyphosate rate of 1700 g a.e. ha⁻¹ resulted in a 50% mortality (LD₅₀) in the W4 population, whereas the same mortality was achieved with rates of 3840, 8225, 7650, and 7590 g a.e. ha⁻¹ in the S0, S3, S7, and S11 populations, respectively (

Table 1. Parameters of the equations used to calculate the herbicide dose (g a.e./a.i. ha⁻¹) required for a 50% reduction in the survival percentage (LD₅₀).

Herbicide	Population	a ± Standard Error	b ± Standard Error	LD50 ± Standard Error	R2	Resistance Factor
Glyphosate	S0	100 ± 5.0	1.4 ± 0.3	3846 ± 641	0.96	2.25
	S3	93 ± 3.4	8.4 ± 1.4	8225 ± 2032	0.94	4.83
	S7	97 ± 1.8	4.5 ± 1.2	7656 ± 329	0.99	4.50
	S11	98 ± 1.8	4.2 ± 1.0	7593 ± 334	0.99	4.46
	W4	98 ± 1.5	4.6 ± 0.9	1702 ± 53	0.99	-
Glufosinate	S0	103 ± 4.2	1.5 ± 0.3	1703 ± 197	0.98	1.04
	S3	101 ± 4.6	1.8 ± 0.4	1637 ± 195	0.97	-
	S7	97 ± 1.7	3.6 ± 0.5	1641 ± 60	0.99	1.00
	S11	100 ± 3.4	2.1 ± 0.4	1804 ± 159	0.98	1.10
	W4	98 ± 0.6	3.3 ± 0.1	1828 ± 24	0.99	1.12
Paraquat	S0	101 ± 4.6	2.2 ± 0.3	139 ± 12	0.99	1.10
	S3	97 ± 8.1	2.2 ± 0.6	126 ± 19	0.97	-
	S7	99 ± 9.0	1.4 ± 0.4	126 ± 28	0.96	1.00
	S11	100 ± 3.2	1.8 ± 0.2	307 ± 23	0.99	2.40
	W4	98 ± 4.5	2.7 ± 0.40	141 ± 11	0.99	1.10
Haloxyfop	S0	102 ± 9.4	2.1 ± 0.6	31 ± 6	0.96	2.80
	S3	104 ± 17	0.6 ± 0.3	107 ± 84	0.73	9.70
	S7	105 ± 9.5	1.1 ± 0.2	46 ± 13	0.94	4.20
	S11	104 ± 12	1.2 ± 0.4	35 ± 11	0.93	3.20
	W4	99 ± 6	1.8 ± 0.4	11 ± 1.6	0.98	-
Clethodim	S0	94 ± 9	2.6 ± 0.9	26 ± 4.5	0.95	1.50
	S3	102 ± 8.1	1.4 ± 0.3	48 ± 10	0.96	2.80
	S7	101 ± 6.6	1.4 ± 0.2	34 ± 6	0.97	2.00
	S11	95 ± 3	4.1 ± 0.6	28 ± 1.5	0.99	1.60
	W4	95 ± 14	2.1 ± 1.0	17 ± 4.4	0.92	-

a is the upper limit, b is the slope of the line, LD₅₀ is the dose resulting in a 50% survival rate.

and Figure 1). The GR₅₀ values for glyphosate in the W4, S0, and S11 populations ranged from 1300 to 1600 g a.e. ha⁻¹, whereas these values for the S3 and S7 populations were between 2200 g a.e. and 2900 g a.e. ha⁻¹ (

Table 2. Parameters of the equations used to calculate the herbicide dose (g a.e./a.i. ha⁻¹) required for a 50% reduction in biomass (GR₅₀).

Herbicide	Population	a ± Standard Error	b ± Standard Error	GR50 ± Standard Error	R2	Resistance Factor
Glyphosate	S0	0.6 ± 0.03	1.2 ± 0.20	1367 ± 205	0.98	1.04
	S3	0.7 ± 0.04	0.7 ± 0.05	2210 ± 551	0.96	1.70
	S7	0.8 ± 0.04	1.4 ± 0.40	2923 ± 652	0.94	2.20
	S11	1.0 ± 0.07	0.8 ± 0.10	1607 ± 5	0.99	1.20
	W4	1.0 ± 0.01	1.3 ± 0.04	1307 ± 375	0.99	-
Glufosinate	S0	0.7 ± 0.02	1.3 ± 0.01	590 ± 57	0.99	1.10
	S3	0.6 ± 0.04	0.9 ± 0.20	535 ± 117	0.97	-
	S7	0.6 ± 0.01	1.9 ± 0.20	1102 ± 64	0.99	2.00
	S11	0.7 ± 0.05	1.9 ± 0.50	1237 ± 199	0.97	2.30
	W4	0.7 ± 0.04	1.9 ± 0.40	1110 ± 137	0.98	2.10
Paraquat	S0	0.6 ± 0.01	2.1 ± 0.10	111 ± 4	0.99	1.50
	S3	0.6 ± 0.03	1.6 ± 0.40	74 ± 13	0.98	-
	S7	0.7 ± 0.01	1.6 ± 0.10	78 ± 4	0.99	1.05
	S11	0.9 ± 0.03	1.5 ± 0.10	152 ± 12	0.99	2.05
	W4	0.8 ± 0.02	2.3 ± 0.20	100 ± 4	0.99	1.30
Haloxyfop	S0	1.0 ± 0.09	1.0 ± 0.20	36 ± 10	0.95	2.30
	S3	1.1 ± 0.02	0.7 ± 0.05	140 ± 12	0.99	10.70
	S7	1.2 ± 0.03	0.98 ± 0.06	51 ± 4	0.99	3.90
	S11	1.3 ± 0.08	1.0 ± 0.01	37 ± 7	0.98	2.80
	W4	1.4 ± 0.07	1.9 ± 0.30	13 ± 1.4	0.99	-
Clethodim	S0	1.3 ± 0.05	1.6 ± 0.20	24 ± 2	0.99	2.00
	S3	1.0 ± 0.05	1.1 ± 0.10	37 ± 6	0.98	3.10
	S7	1.2 ± 0.03	1.5 ± 0.10	31 ± 2	0.99	2.60
	S11	0.9 ± 0.03	1.5 ± 0.10	18 ± 1.4	0.99	1.50
	W4	1.1 ± 0.07	2.1 ± 0.40	12 ± 1.3	0.98	-

a is the upper limit, b is the slope of the line, LD₅₀ is the dose resulting in a 50% biomass reduction.

and Figure 2). Based on LD₅₀ values, the resistance factors for glyphosate in the S0, S3, S7, and S11 populations were 2.2, 4.8, 4.5, and 4.5 times greater, respectively, compared to the W4 population.

The dose–response trial for glufosinate confirmed poor control of the S11 and W4 populations. The LD₅₀ values for these populations were 1800 g a.i. ha⁻¹ and 1830 g a.i. ha⁻¹, respectively, while the S0, S3, and S7 populations had slightly lower LD₅₀ values ranging from 1600 g a.i. ha⁻¹ to 1700 g a.i. ha⁻¹ (Table 1 and Figure 1). The GR₅₀ values for S0 and S3 were 590 g a.i. ha⁻¹ and 530 g a.i. ha⁻¹, respectively, both of which were lower than those for the S7, S11, and W4 populations (1100–1200 g a.i. ha⁻¹).

The paraquat dose–response trial demonstrated poor control of the S11 population, with LD₅₀ and GR₅₀ values of 300 g a.i. ha⁻¹ and 150 g a.i. ha⁻¹, respectively (Table 1 and Table 2). The LD₅₀ values for paraquat in the S0 and W4 populations were 139 g a.i. ha⁻¹ and 141 g a.i. ha⁻¹, respectively (Table 2). The resistance factors based on GR₅₀ values in the S0 and S11 populations were 1.5 and 2.0 times greater, respectively, compared to those for the S3 population (Table 2).

The dose–response assays for haloxyfop and clethodim confirmed a very poor control of the S3 population based on both LD₅₀ and GR₅₀ values (Table 1 and Table 2). The W4 population was found to be susceptible to both clethodim and haloxyfop (Table 1 and Table 2). Given the W4 population’s susceptibility to haloxyfop, the resistance factors for haloxyfop in the S0, S3, S7, and S11 populations were calculated to be 2.8, 9.7, 4.2, and 3.2 times greater, respectively, based on LD₅₀ values (Table 1). The GR₅₀ values for haloxyfop in the S3 and S7 populations were 140 g a.i. ha⁻¹ and 51 g a.i. ha⁻¹ (Table 2 and Figure 2).

The resistance factors for haloxyfop in the S0, S3, S7, and S11 were 2.3, 10.7, 3.9, and 2.8 times greater, respectively, based on GR₅₀ values compared to those for the W4 population (Table 2). The S3 population had a higher LD₅₀ value (107 g a.i. ha⁻¹) than the field rate (39 g a.i. ha⁻¹) for haloxyfop (Table 1). The S3 population also had greater LD₅₀ than the field rate (36 g a.i. ha⁻¹) for clethodim (Table 1 and Figure 1). The LD₅₀ value for clethodim in the S3 population was 48 g a.i. ha⁻¹, while the W4 population had the lowest LD₅₀ value of 17 g a.i. ha⁻¹ (Table 1).

4. Discussion

This study provides evidence of confirmed resistance in L. rigidum populations to glyphosate, glufosinate, paraquat, haloxyfop, and clethodim in the SCR. The glyphosate resistance factor was greater than four based on LD₅₀ values in the S3, S7, and S11 populations, suggesting that these populations require four times the herbicide dose compared to the least resistant population (W4) to achieve the same level of control. Similarly, the haloxyfop resistance factor was greater than nine based on LD₅₀ values in the S3 population, indicating that this population requires nine times the herbicide dose compared to the susceptible W4 population for effective control. These findings underscore the need for regular monitoring of herbicide-resistant populations in the SCR to detect shifts in dose–response curves, facilitating early detection of resistance and timely intervention. By regularly assessing resistance factors, growers and agronomists can effectively manage herbicide-resistant L. rigidum populations and maintain sustainable weed control in the SCR of Australia.

The occurrence of multiple-herbicide resistance in L. rigidum populations in the SCR may be attributed to the limited crop and herbicide rotation programs followed in this region. This could explain why the W4 population collected from fencelines remained susceptible to haloxyfop and clethodim, as these herbicides are rarely used for weed control in such areas. Multiple-herbicide resistance in Lolium spp. has been widely reported globally [9,18,19]. Lolium rigidum exhibits a wide genetic variability, and its outcrossing pollination system may allow herbicide resistance alleles to accumulate at an individual or population level [20].

The negative impact of the evolution of multiple-herbicide-resistant populations of L. rigidum in the SCR could lead to difficulties in the management of this weed with cost-effective solutions [21,22]. The increasing number of L. rigidum populations with high-level resistance to glyphosate, glufosinate, and paraquat (as seen in the S7 and S11 populations in this study) necessitates a diversified weed management program for crops, fallows, and fencelines. This study highlights the rapid evolution of herbicide resistance in L. rigidum populations in the SCR, a phenomenon which demands careful consideration and high prioritization in weed management programs.

Nonselective herbicides have been widely used in Australia to manage weeds in fallows and no-till paddocks, typically as a preplant knockdown spray. Effective weed control during the fallow period is crucial in the SCR, especially in dryland regions where residual soil moisture is crucial for subsequent crops. Therefore, an effective management strategy is needed for these populations. This study suggests that L. rigidum populations in the SCR are resistant to nonselective herbicides, particularly glyphosate and glufosinate. As a result, a residual or double-knock strategy must be adopted to better control these populations.

With the evolution of multiple-herbicide-resistant L. rigidum populations in the SCR (as the S11 population in this study), growers’ options for effectively controlling L. rigidum have diminished. There is a need to diversify existing herbicide programs by incorporating residual and post-emergent herbicides. To avoid selection pressure from herbicides with different modes of action, growers should adopt an integrated weed management approach that includes residual herbicides, tank mixing herbicides with different modes of action, and rotating herbicides in conjunction with cultural and mechanical weed control methods [22,23,24]. Furthermore, multiple-herbicide-resistant populations of L. rigidum can move from fencelines to adjacent cropping areas, posing considerable challenges to growers.

This study suggests that regions with observed multiple-herbicide-resistant L. rigidum populations require critical surveying. Regular monitoring and resistance testing of these populations may provide useful information for management and help prevent further spread. It is imperative to discontinue the practice of using glyphosate, paraquat, and glufosinate as standalone treatments in these areas, whether on fencelines, fallows, or before crop seeding. A double-knock strategy should be employed to control such multiple-herbicide-resistant populations, particularly when the weeds are small and actively growing. Introducing new herbicide options could prevent the buildup of herbicide resistance genes in the weed seed bank. To manage these resistant populations, alternative nonherbicide strategies, such as electric weeding, slashing, grazing, or baling around the field perimeter, as well as the use of cover crops, should be considered to prevent seed set.

Given that growers in the SCR rely on glyphosate, paraquat, and glufosinate to control weeds in fallow areas, the demonstrated resistance in L. rigidum populations (such as S11) means that these populations can survive and produce seeds that enter the soil seed bank and germinate over multiple seasons. This situation may increase costs for farmers and reduce crop productivity. Therefore, integrated control measures to reduce the seed bank are essential to prevent further spread.

5. Conclusions

In conclusion, the dose–response curves from this study can assist growers and researchers in making informed decisions regarding herbicide selection and dose optimization for effective weed control. This study highlights that some L. rigidum populations of southeastern Australia (such as S11) are resistant to five herbicides: glyphosate, glufosinate, paraquat, haloxyfop, and clethodim. Further, the S3 population was found to be highly resistant to glyphosate, haloxyfop, and clethodim compared to the W4 population. These findings suggest that these populations require careful management to prevent further invasion. By optimizing the dose of effective herbicides, growers can control L. rigidum effectively, enhance agricultural productivity, reduce the buildup of weed seed banks, and ensure environmental sustainability and safety. Managing multiple-herbicide-resistant L. rigidum populations requires a multifaceted approach that integrates various control methods, including herbicide rotation, herbicide mixtures, and the double-knock approach. By combining cultural, chemical, and biological strategies, growers can reduce the L. rigidum seed bank, delay resistance development, and maintain effective control. Implementing an integrated L. rigidum management plan tailored to specific farm conditions is crucial for long-term sustainability and productivity in the SCR. This study also notes that the response of tested populations in terms of shoot biomass reduction to different herbicide rates (glyphosate, paraquat, glufosinate, clethodim, and haloxyfop) observed in these pot studies might differ under field conditions. Therefore, field efficacy trials are necessary to determine the effect of spray parameters and environmental conditions on herbicide efficacy in controlling these resistant populations.