Resistance of Eleusine Indica (L.) Gaertn to Paraquat and Glyphosate in Oil Palm Plantations and Evaluation of Propaquizafop as an Alternative Control

1. INTRODUCTION

The provinces of West Kalimantan and Riau are among the largest oil palm-producing areas in Indonesia. West Kalimantan covers an area of 1.829.533 hectares, with a production of 5,332, 338 tonnes in 2023. Riau province covers an area of 3.494.583 hectares, with a production of 8.961.940 tons in 2023 [1]. Presently, Indonesia stands as the foremost palm oil producer on a global scale, boasting a plantation area that encompasses 14.17 million hectares [2]. In Indonesian oil palm farms, herbicide application for weed management is more prevalent than alternative methods. Weed control using herbicides is more practical and profitable, as it requires less time and labour [3]. It has been reported to be up to 80% more profitable than traditional weeding methods [4].

Weed is a major factor affecting oil palm plantations by reducing the quality and quantity of production due to competition for nutrients, 40% of the damage to crops, both in terms of quality and quantity, was attributable to diverse types of weeds, diseases, insects, and animals [5]. Weed has a greater economic impact on production than insects, fungi, or other plant pests [6]. The presence of Eleusine indica weed causes losses to oil palm cultivation in both producing mature plants, immature plants, and main nursery areas [7]. Weed infestations in oil palm plantations may reduce production by 25-40% [8]. A typical example of a weed frequently predominant in oil palm farms is E. indica.

The emergence of herbicide-resistant weeds significantly reduces the number of effective herbicide options, leading to increased failure rates in weed control efforts [9]. Furthermore, resistant weed renders herbicide applications ineffective, prompting farmers to adopt alternative control methods that may be more expensive. This situation affects both production costs and the effectiveness of weed control [10].

Resistance to herbicides occurs due to a lack of herbicide rotation and continuous application over a long period [3]. A previous study defined weed resistance to herbicides as the ability to survive after the administration of herbicide, even at higher doses. The persistent use of herbicides with the same active ingredient or mechanism of action can lead to a substantial rise in the population of resistant weeds that endure. This condition may result in larger populations of resistant weeds, making herbicide control ineffective [9].

Cases of weed resistance have increased globally each year, reducing the number of effective herbicide options available [11]. In 2017, there were 494 resistant weed biotypes, experiencing an increase in 2024 to 531. Presently, there are 27 documented instances of E. indica exhibiting resistance to several herbicides worldwide, including resistance to propaquizafop (1 case), paraquat (1 case), and glyphosate (16 cases). An example of this case is E. indica resistance to glyphosate in the oil palm fields of Serdang Begadai, North Sumatra province, Indonesia [12]. The rotation of herbicide types with different modes of action represents a potential strategy for the management of resistant weeds [13].

The rationale for this study is based on the limited availability of information on resistant weeds in Indonesia. However, there is a substantial body of knowledge from local farmers showing that effective herbicides have become ineffective against some weed species, including E. indica. This lack of information is attributable to the limited study conducted and the low level of knowledge among farmers regarding weed resistance. The framework of this study is to confirm the resistant nature of E. indica weed from West Kalimantan and Riau to various herbicides, thereby elucidating the suitability for use in a rotation programme aimed at controlling the resistant weed.

2. MATERIALS AND METHODS

2.3. Measurements of Morphological Parameters

In each experimental unit, weed dry weights were determined by destruction. Weed was harvested 4 weeks after application. Samples of E. indica that remained alive in each treatment were severed at the stem's base and subsequently subjected to an oven at 80 °C for 48 hours to achieve a consistent dry weight [13]. The data of the dry weight were converted into a percentage of growth reduction by making a comparison between E. indica treated with herbicide (T) and E. indica without herbicide application (C) in each region of origin. The formula used in this case for percentage conversion is (Eq. 1) [13]

(1)

3. RESULT

3.1. Growth Reduction of Eleusine Indica Weed to Various Herbicide

The effects of glyphosate on growth reduction in E. indica are presented in Table 1. When E. indica was treated with glyphosate at 2 to 8 times the recommended dose (1500–6000 g a.i. ha⁻¹), a 100% growth reduction was observed. This indicates that the weeds were completely controlled at these treatment levels. Glyphosate application reduced growth in ER1 and ER2 populations; however, no complete weed mortality was observed even at the highest dose (6000 g a.i. ha⁻¹). In contrast, the ES population exhibited complete mortality at just twice the recommended dose (1500 g a.i. ha⁻¹).

Table 1.

Herbicide	Biotypes	Herbicide
		0	0.25	0.5	1	2	4	8
Glyphosate	ES	0.00 a,D	43.50 a,C	50.59 a,C	85.19 a,B	100.00 a,A	100.00 a,A	100.00 a.A
	ER1	0.00 a,F	9.84 b,E	37.21 b,D	52.78 b,C	66.52 b,B	88.34 a,A	97.68 a,A
	ER2	0.00 a,F	13.6 b,E	24.35 c,D	31.33 c,D	55.42 b,C	71.99 b,B	98.73 a,A
Paraquat	ES	0.00 a,D	46.75 a,C	58.21 a,B	97.49 a,A	100.00 a,A	100.00 a,A	100.00 a,A
	ER1	0.00 a,G	33.71 b,F	40.91 b,E	54.48 b,D	69.00 b,C	79.91 b,B	96.36 a,A
	ER2	0.00 a,F	15.87 c,E	27.97 c,D	43.30 c,C	67.79 b,B	100.00 a,A	100.00 a,A
Propaquizafop	ES	0.00 a,D	43.09 b,C	68.20 b,B	100.00 a,A	100.00 a,A	100.00 a,A	100.00 a,A
	ER1	0.00 a,E	37.51 c,D	60.14 c,C	79,76 b,B	100.00 a,A	100.00 a,A	100.00 a,A
	ER2	0.00 a,B	100.00 a,A	100.00 a,A	100.00 a,A	100.00 a,A	100.00 a,A	100.00 a,A

Note: The values in each column denoted by identical lowercase letters (vertically) and uppercase letters (horizontally) are not statistically different at p < 0.05, as determined by the Scott-Knott Test for each herbicide.

Table 2.

Herbicide	Biotype	p	r2	GR50	Resistance Index	Level of Resistance
Glyphosate	ES	1.50	0.92	271.97	-	Susceptible
	ER1	1.28	0.97	702.92	2.58	Low Resistance
	ER2	1.24	0.96	1,187.59	4.36	Low Resistance
Paraquat	ES	1.70	0.91	122.68	-	Susceptible
	ER1	0.85	0.97	283.04	2.30	Low Resistance
	ER2	1.53	0.96	414.25	3.37	Low Resistance
Propaquizafop	ES	2.08	0.96	30.01	-	Susceptible
	ER1	1.58	0.98	36.58	1.21	Susceptible
	ER2	-	-	-	-	Susceptible

The result in Table 1 shows that plants treated with paraquat at doses ranging from 1-8 times the recommended dosage (400 to 3200 g a.i. ha^-1) had a 97 to 100% reduction in growth or mortality. However, plants treated with ER1 and following the application of the recommended dose of paraquat, ER2 showed survival, even at the highest dose. The growth reduction value was 96.36% for ER1 and up to twice the recommended dose, with 67.79% for ER2. This result suggested that ER1 and ER2 were not susceptible to the effects of paraquat. Table 1 showed that plants treated with propaquizafop at the recommended dosage (100 g a.i. ha^-1) experienced a reduction in growth, with values of 100, 79.76, and 100% observed for ES, ER1, and ER2, respectively. This result showed that ES and ER2 could be effectively controlled by propaquizafop at the recommended dose.

4. DISCUSSION

The application of paraquat and glyphosate was generally effective in controlling the growth of E. indica weed. Glyphosate inhibits the enzyme 5- enolpyruvyl shikimate -3-phosphate synthase (EPSPS), integral to the shikimate pathway in plants. This route is required for the biosynthesis of aromatic amino acids, such as tryptophan, tyrosine, and phenylalanine, which are vital for plant growth and development [16]. Paraquat inhibits the photosynthetic process, particularly photosystem I, disrupting the reduction of NADP⁺ to NADPH. This disruption leads to the generation of free radicals, which react with oxygen to form hydrogen peroxide. The accumulation of hydrogen peroxide damages cell membranes and plant tissues, ultimately causing weed death characterized by leaf necrosis and signs of wilting [17, 18].

The mean growth reduction values observed for ER1 and ER2 were found to be lower than ES in herbicide treatments using glyphosate and paraquat. A similar phenomenon was observed in E. indica weed from Adolina Plantation PTPN IV Serdang Bedagai, North Sumatra Province. This weed was previously documented to exhibit resistance and showed a lower average growth reduction compared to susceptible biotype E. indica weed following exposure to herbicides that inhibit photosystem 1 processes [19]. The reduction in dry weight of E. indica weed observed at each treatment dose was attributed to the application of herbicides in conjunction with higher doses and the mechanism of action [20]. The E. indica population from oil palm plantations at the Adolina Plantation of PTPN IV Serdang Bedagai was determined to be resistant to glyphosate and paraquat [21].

The study reported that E. indica ER1 and ER2 exhibited resistance to glyphosate and paraquat. This result is consistent with a report that showed E. indica from China had resistance to glyphosate, paraquat, and glufosinate herbicides [16]. The information regarding this resistance case increases the difficulty of controlling E. indica weed in oil palm plantations, as glyphosate and paraquat were the most widely used [22]. In addition, the E. indica population in oil palm farms within Batu Bara Regency exhibited a glyphosate resistance rate of 63.33% [12].

The history of herbicide use, dose, frequency, and application method were among the factors that increased resistance in weed [23]. The populations of ER1 and ER2 were gathered from oil palm fields in Riau and West Kalimantan, where the persistent application of glyphosate and paraquat has been a prevalent practice for the last decade. According to farmers in these locations, the application of glyphosate and paraquat existed for the last 10 years with a frequency of 4-6 times annually. This result is consistent with the report that E. indica exhibited multiple resistance to fluazifop-P-butyl, paraquat, glufosinate, and glyphosate herbicides in Malaysia [23]. A previous study confirmed that weed was resistant to glyphosate with a moderate category [24]. The present study is substantiated by the documented findings of E. indica, which has been identified as exhibiting resistance to paraquat with index values of 5 and 9 in Benjire Village and Perlamben Sub-district, Tigabinaga Karo District [25].

The result of this study showed that both ER1 and ER2 were vulnerable to ACCase enzyme inhibitor herbicide, containing propaquizafop as the principal component. Therefore, ACCase inhibitor is a viable alternative to conventional herbicides for the control of E. indica, which has been identified as having multiple resistance to aromatic amino acid and photosystem I inhibitor herbicides. ACCase-inhibiting herbicide has been shown to provide effective weed control against grass-type weeds [26]. This outcome aligns with a report that the use of propaquizafop herbicide can control E. indica weed [27]. The result was also consistent with a report that showed that the ACCase inhibitor effectively lowers the dry weight of certain grass weeds [5].

The application of herbicide rotation is important in controlling weeds to minimize the occurrence of resistance in the agricultural sector. According to a previous study, the phenomenon of multiple resistance occurs when a weed is resistant to different types of herbicides and modes of action [28]. Therefore, the control of E. indica weed resistant to glyphosate and paraquat can be achieved through the use of propaquizafop as an alternative [13]. Based on the results, farmers are required to have insight and knowledge about herbicide rotation and type selection in order to avoid the development of more complex resistance cases in the future.

CONCLUSION

Eleusine indica biotypes from Riau and West Kalimantan were identified as resistant to glyphosate with resistance index values of 2.58 and 4.36, and to paraquat, with values of 2.30 and 3.37. However, these biotypes were effectively controlled by the herbicide propaquizafop. This study demonstrates that propaquizafop herbicide can be utilized as an alternative herbicide to manage glyphosate and paraquat-resistant E. indica. However, further research is needed to identify mixed herbicides and those with different modes of action that can effectively control resistant weeds. A comprehensive evaluation of the underlying resistance mechanisms is also essential to support effective management strategies, including herbicide rotation.

REFERENCE