Soil pH affects imazethapyr sorption-desorption, which in turn can affect p
ersistence and bioavailability. Long-term imazethapyr carry-over has been o
bserved in soil that is below pH 6.5, resulting in significant sugarbeet da
mage. Imazethapyr concentration decreased rapidly in held soil, regardless
of pH. Despite similar amounts of imazethapyr remaining in aged soils at di
fferent pH levels, there were differences in bioavailability, which can be
explained by sorption-desorption. At low pH more imazethapyr was sorbed tha
n at high pH, but it readily desorbed. At high pH less imazethapyr was sorb
ed initially, but it did not readily desorb. Thus, after 3 months, the rema
ining imazethapyr in low-pH soil was desorbable and bioavailable, resulting
in injury to canola and sugarbeet. Liming aged, low-pH soil released bound
imazethapyr residues, which would then be degraded and result in less carr
y-over.