Ludwigia decurrens Walter is a dicotyledonous plant belonging to the family Onagraceae. It is native to Central Eastern USA but has been spreading quickly and has naturalized in aquatic and riparian ecosystems (including rice paddy fields) in many countries; therefore, it is now considered an invasive noxious weed. L. decurrens is highly competitive with rice and causes a significant reduction in rice production. The objective of the present study was to evaluate the efficacy of the herbicide penoxsulam for the control of L. decurrens in rice fields. The seeds of L. decurrens were collected from four villages in Indonesia, and penoxsulam was applied to L. decurrens in seven dosages (0, 2.5, 5, 10, 20, 40, and 80 g a.i. /ha) 3 weeks after seed sowing. The plant populations from Hegarmanah, Jatisari, and Joho showed complete mortality at the recommended dosage of penoxsulam (10 g a.i. /ha). However, the plants from Demakan grew, flowered, and produced seeds 56 days after treatment with 40 g a.i. /ha of penoxsulam. The resistance index value of the population was 36.06.
1. Introduction
Ludwigia decurrens Walter, belonging to the Onagraceae family, is a synonym of
Jussiaea decurrens Walter D.C. It is an annual or woody perennial herb that stands upright reaching 2 m of height, with alternate branches. The leaves are opposite, narrowly elliptical, 4–12 cm long, and 1–3 cm wide. A single flower with four bright yellow petals is produced in the upper leaf axis. A seed capsule develops immediately below the flower and contains up to 1000 seeds per capsule
[1][2][3][1,2,3]. The species grows in wetlands including paddy fields, riverbanks, ponds, and slow-moving streams
[1][4][1,4]. It has adapted to these aquatic habitats through the development of rhizomes with aerenchyma
[5].
L. decurrens is native to Central Eastern USA but has been introduced accidentally into many countries in South and East Asia and Africa, where it is now considered an invasive noxious weed
[1][2][4][6][7][1,2,4,6,7]. It produces a large number of seeds and spreads rapidly in the wet zone through seeds and plant fragments floating on water
[1][4][8][1,4,8]. It has also allelopathic properties. The exudates of the plants inhibited the growth of
Corchorus olitorius L. and increased its mortality
[9]. Allelopathy may also be involved in
L. decurrens invasion
[10][11][12][10,11,12]. The severe invasion of some plant species often causes a significant reduction of biodiversity in the invaded ecosystems
[13][14][13,14]. The risk of a negative environmental impact for
L. decurrens is high because of its pest dispersal potential
[4].
L. decurrens emerges along with rice seedlings and grows in rice paddy fields. It is highly competitive with rice due to its fast growth rate and a life cycle similar to that of rice and causes a significant reduction in rice production
[1][15][1,15].
L. decurrens suppresses the development of tillers, panicles, leaves, and spikelets of rice plants. Consequently, the risk of an economic impact due to lower crop yields and quality is high
[4]. For example,
L. decurrens has been reported to reduce rice grain yield by around 30%
[15]. Penoxsulam is one of the pre-emergence herbicides widely used in rice cultivation
[16]. It is an acetolactate synthase (ALS; EC 4.6.3.8) inhibitor and is an efficient broad-spectrum herbicide against grass and broadleaf weeds
[17]. This herbicide has been effective in controlling
L. decurrens. However, excessive application of herbicides increases the potential to develop resistant weeds
[18][19][20][18,19,20]. The appearance of herbicide-resistant weeds was predicted by Harper in 1956
[21], and a herbicide resistant-weed was first observed in sugarcane plantations in Hawaii
[22]. Following this, triazine-resistant
Senecio vulgaris L.
[23] and 2,4-D-resistant
Convolvulus arvensis L.
[24] were recorded. Currently, 264 herbicide-resistant weed species—522 cases (species × site of action) for 164 herbicides—have been reported in 94 crops in 71 countries
[25]. The present study was conducted due to reports of
L. decurrens becoming difficult to control in rice paddy fields of Central Java, Indonesia. The efficiency of penoxsulam on
L. decurrens collected from four Central Java villages was evaluated, and a penoxsulam-resistant
L. decurrens population was confirmed for the first time.
2. Discussion on Ludwigia decurrens Walter
An invasive plant species,
L. decurrens, has been spreading quickly and naturalized into aquatic and riparian ecosystems including rice paddy fields in many countries
[1][2][4][6][7][1,2,4,6,7]. This species has been reported to occupy 50% of the invaded plant community, and thus is considered one of the most aggressive weed species
[3][8][3,8]. Consequently, the risks associated with
L. decurrens invasion are high from both an environmental and an economic perspective
[4]. Management of
L. decurrens relies on physical and chemical methods
[26][30], and penoxsulam has effectively controlled
L. decurrens so far. However, we identified penoxsulam-resistant
L. decurrens plants from a Demakan population for the first time in this study (
Figure 1,
Table 1). The resistance index value of the population was 36.06 (
Table 2), and the plants made flowers and produced seeds (
Figure 2).
Figure 1. Effect of penoxsulam on four populations of L. decurrens 28 days after herbicide application.
Table 1. Effect of penoxsulam on the percentage of damage to L. decurrens.
|
Penoxsulam Dosage (g a.i. ha−1) |
Population |
0 |
2.5 |
5 |
10 |
10 |
40 |
80 |
Hegarmanah |
0 a,A |
51.2 b,D |
72.85 b,E |
100 a,F |