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Plant extract-based nanoemulsion for controlling sweet potato pests and weeds
(2026-12-01)
Pumnuan, Jarongsak
;
Ruddit, Anusart
;
Lakyat, Anuwat
;
Doungnapa, Thanaporn
;
Deemak, Jantra
The sweet potato weevil (Cylas formicarius) is the most destructive pest of sweet potato and is often associated with diseases and weeds. The use of plant extracts as pest control agents is a promising, eco-friendly approach, but their effectiveness often declines under field conditions. Therefore, nanoemulsion technology was applied to improve the dispersion and bioefficacy of active compounds. In this study, we aimed to develop plant extract-based nanoemulsions as multifunctional biopesticides capable of controlling insect pests, fungal pathogens, and weeds. Twenty-one plant extracts were screened for their effects adult SPW via contact methods. The most potent extracts were then formulated into nanoemulsions and evaluated for insecticidal efficacy—including contact toxicity, repellency, and oviposition inhibition. In addition to insecticidal effects, antifungal and herbicidal activities were systematically assessed against Fusarium sp. and two common weed species in sweet potato fields, Amaranthus tricolor and Echinochloa crus-galli. The major chemical constituents of key extracts were identified using gas chromatography–mass spectrometry (GC–MS). Among all extracts, the hexane extracts of star anise and long pepper exhibited the highest contact toxicity, with LC50 values ranging from 2.051 to 2.415% at 24 h. When formulated into nanoemulsions (NHEF-1 and NHEH-2), toxicity increased 16- to 18-fold, lowering LC<inf>50</inf> values to 0.114–0.150%, and at above 0.1%, oviposition was inhibited by more than 85%. Both formulations also demonstrated significant antifungal activity against Fusarium sp. (44.6–56.8% growth inhibition) and completely inhibited the germination of A. tricolor (at 0.01%) and E. crus-galli (at 1.0%). GC–MS analysis revealed anethole (84.49%) as the predominant compound in the star anise extract, with long pepper extract containing moderate amounts of several compounds. These findings demonstrate the potential of plant extract-based nanoemulsions as eco-friendly, multifunctional biopesticides for sustainable sweet potato management, integrating enhanced insecticidal, antifungal, and herbicidal effects.
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Field Performance and ecological safety of botanical nanoemulsions against sweet potato weevil in Tropical smallholder systems
(2026-06-01)
Pumnuan, Jarongsak
;
Lakyat, Anuwat
;
Name, Janejira
;
Deemak, Jantra
;
Phutphat, Sudjai
This study investigated the effectiveness of two nanoemulsion-based plant hexane extract formulations, S4L0 and S3L1, for managing sweet potato weevils (SPW) under field conditions. The formulations, derived from star anise and long pepper hexane extracts, were tested alongside a synthetic insecticide (imidacloprid) and an untreated control using a randomized complete block design (RCBD) on farmer plots in Sa Kaeo Province, Thailand. Key determination parameters included SPW infestation levels, crop yield, pesticide residue levels, diversity of non-target soil arthropods, and soil physicochemical properties. Field applications of S4L0 and S3L1 reduced SPW infestations to 3.6 ± 4.3 and 11.1 ± 5.0 insects per plant, respectively, significantly lower than in untreated plots (33.9 ± 11.8 insects/plant). No detectable imidacloprid residues were found in tubers treated with S4L0 or S3L1, whereas imidacloprid-treated tubers retained residues of 0.335 and 0.144 ppm at 5 and 7 days after application. Sweet potato yields ranged from 310 to 440 g/plant, with no significant differences among treatments. The untreated plots supported greater diversity and abundance of non-target soil arthropods, while the imidacloprid-treated plots showed the lowest diversity. Soil properties, including bulk density, pH, electrical conductivity, and organic matter content, remained stable across treatments. Overall, S4L0 and S3L1 demonstrated effective pest suppression and minimal environmental impact, highlighting their potential as sustainable alternatives to synthetic insecticides for integrated pest management in sweet potato production.
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Insecticidal activities of long pepper (Piper retrofractum Vahl) fruit extracts against seed beetles (Callosobruchus maculatus Fabricius, Callosobruchus chinensis Linnaeus, and Sitophilus zeamais Motschulsky) and their effects on seed germination
(2022-12-01)
Pumnuan, J.
;
Namee, D.
;
Sarapothong, K.
;
Doungnapa, T.
;
Phutphat, S.
Bruchid beetles (Callosobruchus maculatus and Callosobruchus chinensis), and maize weevil (Sitophilus zeamais) are important insect pests during the postharvest period. Botanical insecticide is an alternative solution for controlling these insects, and long pepper (Piper retrofractum) has been reported as having insecticidal potential against general insect pests. Film seed coatings with various concentrations of hexane extracts were made for mung bean (Vigna radiata) and corn (Zea mays) seeds. Insecticidal activities of these treatments were assessed at before and after storage period of six months, and seed germination was also evaluated. The hexane extract was subjected to analysis of the bioactive components by using Gas Chromatography-Mass Spectrometry (GC-MS). Results revealed that the hexane extract presented extreme toxicity to both bruchid beetles higher compared to maize weevil at 24 h with LC<inf>50</inf> values of 5.57–6.75 and 58.04 μg⋅cm<sup>−2</sup>, respectively. Bruchid beetles presented significant response to ethanol, acetone and hexane extracts, whereas maize weevil showed relatively low responsibility. Film seed coating with hexane extract at 1% and 3% concentrations with six-month storage presented high insecticidal activity against bruchid beetles by more than 88% mortality but had low kill rates against maize weevil. The coated mung bean seeds presented non-seed germination effect, whereas high effect was observed on coated corn. Isolation of bioactive components demonstrated that there were 74 compounds, where pentadecane was the main compound. Film seed coating technology for mung bean seed preservation by using 1% hexane extract from long pepper fruit presented to be an extremely effective method to control bruchid beetles without any seed germination effect. It could serve as one of the green insecticides of the future.

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