Adsorption of 14C-imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} and imazethapyr [2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-5-ethyl-3-pyridinecarboxylic acid] to soil increased as soil pH decreased from 8.0 to 3.0 in laboratory studies. Significantly more imazethapyr3 (AC-263,499) than imazaquin was adsorbed at soil pH levels 3.0 and 5.5, while the greatest difference in adsorption behavior between the two herbicides was observed at a soil pH of 5.5. In greenhouse studies, phytotoxicity to corn (Zea mays L.) was greater for imazaquin than AC-263,499 applied at 26 and 53 g ai/ha. There were significant pH by herbicide and pH by rate interactions, but in trend analysis only a small proportion of the corn response (r2 = 0.01 to 0.35) was attributed to increasing soil pH values. In field studies where imazaquin was applied to soil pH levels of 4.2 to 4.8, 5.4 to 5.5, and 5.8 to 6.2, injury to corn across all pH levels decreased as the time delay between herbicide application and corn planting increased. There was no significant effect of soil pH on imazaquin injury to corn planted in July or August. Decreased injury from imazaquin was observed in 1985 on corn planted in June on the soil pH of 5.8 to 6.2. Imazaquin injury was less for June-planted corn in 1984 than in 1985, across all soil pH levels.

The fate of imazamox, imazethapyr, and imazaquin in soil was evaluated at various soil moisture levels and at soil pH levels of 5 and 7. The percentage of each herbicide sorbed, desorbed, dissipated, and metabolized over time was compared. Soil was kept at its field pH (pH 7) or modified to a lower pH (pH 5) and equilibrated to field moisture contents ranging from 0.27 to 0.21 g water/ g soil, at and below the field capacity of the soil. Soil moisture in the range studied did not affect the fate of the herbicides. The percentage of applied herbicide found in soil solution was greatest for imazamox and least for imazaquin (imazamox > imazethapyr > imazaquin) and was greater at pH 7 than at pH 5 for all three herbicides. Over time, less herbicide was in the soil solution and less was desorbed. Metabolism followed the same pattern. Among the herbicides, metabolism followed the following sequence, imazamox > imazethapyr > imazaquin with metabolism greater at pH 7 than at pH 5 for all three herbicides. At pH 7, the half-life for imazamox was 1.4 wk and for imazethapyr was 16 wk, and the estimated half-life for imazaquin was 191 wk.