EFFECT OF SOIL TYPE AND PH ON PERSISTENCE AND CARRYOVER OF IMIDAZOLINONE HERBICIDES

Field studies were conducted in 1988 through 1990 to determine the effect of soil pH, over a 4.5 to 6.5 range, on imazethapyr persistence and on imazaquin and imazethapyr carryover to 'Pioneer 3377' com in a Crosby silt loam (1.6% organic matter) and a Hoytville clay (3.3% organic matter). Imazethapyr appeared to be more persistent in Hoytville clay than in Crosby silt loam. In Crosby silt loam, imazethapyr persistence increased as pH decreased, whereas soil pH did not affect persistence in Hoytville clay. Imazaquin or imazethapyr did not affect com grown the year following application to Crosby silt loam. Imazethapyr applied to Hoytville clay did not cause significant injury or yield reduction to com. Carryover of imazaquin in Hoytville clay caused com injury and yield reduction, increased as pH decreased, and was more evident at 280 g ai ha-1 than at 140 g ha-1.