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The new triketone herbicide, tembotrione, provides excellent weed control in corn fields. To evaluate its safety, we established a modified QuEChERSpretreatment and ultra-high performance liquid chromatography-mass spectrometry method, using acetonitrile with 2% formic acid as the extractant and C18 as absorbent. The dissipation dynamics of tembotrionein corn straw and the terminal residual levels in all three corn matrices were studied in Henan and Jilin provinces. The linearity was excellent in the range of 0.01 to1 mg L−1, with the determination coefficient (R2) ≥0.9954. The average recovery was between 74% and 117%, with intra-day relative standard deviation less than 18.9 and the inter-day relative standard deviation less than 17.5. The degradation dynamic experiment showed that tembotrione decreased over time and followed the first-order kinetic equation. Our results showed that the regression coefficients of the dynamic equations were 0.9906 and 0.9897, with half-lives of 0.7 and 0.8 d, respectively. The final residue results showed that the maximum residues of tembotrione detected in corn in Jilin and Henan were 0.041 and 0.051 mg kg−1, respectively. The risk quotient (RQ) were calculated as 0.186 and 0.246, both of which were less than 1, which indicated an acceptable risk. [ABSTRACT FROM AUTHOR]