Spartina alterniflora is a globally invasive plant that has caused significant damage to coastal ecosystems, including biodiversity loss, decline of native vegetation, alteration of benthic communities, and degradation of bird habitats. Effective control of S. alterniflora is therefore critical for coastal ecological conservation. Current control methods—physical, chemical, biological, and integrated—have limitations: physical removal alone is often inefficient, and chemical control poses risks of ecological pollution. This study evaluates an integrated approach combining mechanical cutting with low-dose herbicide application to improve control efficacy and assesses its impact on soil microbial diversity. In August 2022, two sites with uniformly growing S. alterniflora were selected, each divided into 21 quadrats of 1 m × 1 m. One site was mowed at the end of August, while the other remained uncut. In September, three concentrations of Haloxyfop-P-methyl (HP) and Glyphosate (GP) were applied. Plant responses were monitored during the flowering stage (September), seed-setting stage (October), the end of the growing season (December), and the following April. Four treatments were compared: HP alone, GP alone, cutting followed by HP, and cutting followed by GP. Soil samples were collected from herbicide-treated and control quadrats for physicochemical analysis. High-throughput sequencing was used to characterize bacterial and fungal community structure and diversity. Data were analyzed using one-way ANOVA with LSD post-hoc tests following validation of homogeneity of variances (Levene’s test). Results showed that: (1) Cutting followed by HP application during the flowering stage effectively controlled S. alterniflora, with a dose of 150 mg/m2 achieving 98.93% control efficiency by the end of the growing season, while doses of 300 mg/m2 and 600 mg/m2 achieved complete plant mortality; all doses significantly inhibited regrowth the following year, with suppression rates of 93.49%, 92.68%, and 96.48%, respectively. (2) Cutting during flowering significantly reduced the sexual reproduction capacity of regenerated plants. (3) Although the combined treatment reduced the relative abundance of Ascomycota in soil fungi, it did not significantly affect overall bacterial or fungal diversity. The combined treatment of cutting followed by Haloxyfop-P-methyl application at 150 mg/m2 effectively controls S. alterniflora and strongly suppresses its regrowth without causing significant adverse effects on soil microbial diversity, supporting the development of efficient and environmentally sustainable management strategies for this invasive species.
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