Fate of fluroxypyr in soil

Summary: Fluroxypyr‐MHE (methylheptyl ester) was added to four soils and incubated at 26 ± 1°C and approximately 0.1 MPa moisture. After initial rapid hydrolysis of the ester to fluroxypyr, fluroxypyr degraded with half‐lives of 12, 12, 23, and 7 days in Barnes loam, Catlin silt loam, Hanford sandy loam, and Mhoon clay soils, respectively. Two metabolites (4‐amino‐3,5‐dichloro‐6‐fluoro‐pyridin‐2‐ol and 4‐amino‐3, 5‐dichloro ‐ 6 ‐ fluoro ‐ 2 ‐methoxypyridine) were identified, with the pyridinol at its maximum concentration after 2 to 4 weeks of incubation, and the methoxypyridine after 8 weeks. Degradation rates of fluroxypyr and its pyridinol were not significantly altered by diurnally varying soil temperature (21°C to 32°C) or moisture, nor by the presence of growing grass. Methoxypyridine dissipation was more rapid under greenhouse conditions, suggesting that laboratory studies underestimated the dissipation rate of this metabolite.