Soil pH affects imazethapyr sorption-desorption, which in turn can affect persistence and bioavailability. Long-term imazethapyr carry-over has been observed in soil that is below pH 6.5, resulting in significant sugarbeet damage. Imazethapyr concentration decreased rapidly in field soil, regardless of pH. Despite similar amounts of imazethapyr remaining in aged soils at different pH levels, there were differences in bioavailability, which can be explained by sorption-desorption. At low pH more imazethapyr was sorbed than at high pH, but it readily desorbed. At high pH less imazethapyr was sorbed initially, but it did not readily desorb. Thus, after 3 months, the remaining 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 carry-over.

No abstract

Long‐term carry‐over of some imidazolinone herbicides has been observed in soil that is below pH 6.5, resulting in significant damage to sugarbeet. In a field study in south‐west Minnesota, imazamox concentration decreased rapidly in soil, regardless of pH. Despite similar amounts of aged soil residues of imazamox remaining at different pH levels, bioavailability differed with pH as a result of pH effects on sorption–desorption interactions. At low pH, more imazamox was sorbed than at high pH, but it was readily desorbed. At high pH, less imazamox was sorbed initially, but it did not readily desorb. Thus, after 3 months, the remaining imazamox in low‐pH soil was desorbable and bioavailable, resulting in injury to oilseed rape and sugarbeet. In aged, low‐pH soil, adding lime released bound imazamox, which was then degraded, resulting in less carry‐over.

Glyphosate is a nonselective herbicide used as a harvest aid in a variety of crops. Glyphosate is absorbed into the foliage and translocated to metabolically active regions in the plant where it interferes with the shikimic acid pathway. Experiments were conducted to determine the accumulation and distribution of shikimic acid in wheat treated with glyphosate at soft and hard dough stages of kernel development and to determine the fate of shikimic acid during milling and bread making. Elevated levels of shikimic acid were detected throughout the wheat plant. Shikimic acid concentrations peaked 3-7 days after treatment and then declined until harvest. Shikimic acid content was 3-fold greater in flour and 2-fold greater in the bread derived from treated wheat than nontreated wheat. Similarly, elevated levels of shikimic acid were found in the crumbs and crust of bread made with flour from glyphosate treated wheat. Glyphosate applied preharvest resulted in shikimic acid accumulation in hard red spring wheat and subsequent end-use products.

Isoxaflutole is a relatively new herbicide used for weed control in maize. The objective of this research was to increase the understanding of the behaviour and environmental fate of isoxaflutole and its diketonitrile (DKN) degradate in soil, including determination of the strength of sorption to soil and whether sorption is affected by ageing. In sandy loam (SL) and silty clay (SiCl) soils, 14 C-isoxaflutole was found to dissipate rapidly after application to soil; recovery ranged from 42% to 68% at week 0, and recovery had decreased to <10% at week 12. Decreases in 14 C isoxaflutole residues over time in SL and SiCl soils are consistent with hydrolysis of isoxaflutole and formation of bound DKN residues in the soil. DKN recovery from freshly treated SiCl and SL soils was 41% to 52%. After a 12-week incubation in SL soil at pH 7.1 and 8.0, recoveries were similar, 40%. However, at week 12 in SL soil pH 5.7, DKN recovery decreased to 28%. DKN recovery in SiCl soil at week 12 was <10%. Increases in sorption of DKN in SL at pH 5.7 and SiCl soil over time indicate that the DKN degradate is tightly bound to the soil and sorption is affected by soil pH and soil type. Sorption of 14 C-DKN in the SiCl soil more than doubled with ageing compared with the lower K d sorption coefficient values of the SL soils. In the SiCl soil at time 0, the K d was 0.6; at 1 week, K d increased to 2; and at the end of the 12-week incubation period, K d was 4.5. This strong binding of DKN to the soil may be due to chelate formation in the interlayer of the clay.