Abstract: To investigate the effect of 28-homobrassinolide on procymidone residue levels in Allium tuberosum, seven treatments were established using 28-homobrassinolide as the test agent, with a control group sprayed with procymidone but not 28-homobrassinolide.Samples were pretreated using the QuEChERS technique, and procymidone residue levels in Allium tuberosum were determined by GC-MS. Results showed that procymidone residue levels in Allium tuberosum at 1 day post-treatment were higher in the 28-homobrassinolide-treated groups than in the control.Under high-dose conditions (0.20 and 0.10 mg/L), procymidone residue levels at 1 day post-treatment exceeded the other treatments, regardless of whether 28-homobrassinolide was applied once before treatment or twice (pre- and post-treatment), indicating that high-dose 28-homobrassinolide temporarily enhanced procymidone absorption.At 2 days post-treatment, all treatments exhibited rapid reductions in procymidone residue levels, but residues remained higher than the control in groups treated with 0.20 mg/L 28-homobrassinolide (once or twice) and 0.10 mg/L 28-homobrassinolide (twice).From 3 days post-treatment onward, procymidone residue levels in 28-homobrassinolide-treated Allium tuberosum declined rapidly, with faster degradation observed in the double-application groups compared to single-application groups.Under natural conditions, procymidone residue levels in Allium tuberosum gradually decreased post-treatment, with a degradation curve equation of y=8.934 4e^-0.197t, correlation coefficient (r)=0.985 4, and a half-life (T_1/2) of 3.52 days. All 28-homobrassinolide-treated groups exhibited shorter procymidone degradation half-lives than the control, demonstrating that 28-homobrassinolide effectively accelerated procymidone degradation in Allium tuberosum.

Key words: 28-homobrassinolide, Allium tuberosum, procymidone, residue levels