IMAZETHAPYR BIOACTIVITY AND MOVEMENT IN SOIL

A bioassay using red beet root length indicated an increase in imazeth apyr bioactivity in Berryland sand (BLS) as soil pH increased from 3.7 to 6.5. Increasing pH above 6.5 had no effect on imazethapyr bioactiv ity. The lowest imazethapyr concentrations detected by the bioassay at pH 6.5 were 0.5, 1, 2.5, and 5 to 10 mu g kg(-1) in acid-washed quart z sand, BLS, Aura loamy sand, and muck soil, respectively After applic ation of 0.07 kg ae ha(-1) with 12.5 mm of simulated rainfall at 3-d i ntervals, imazethapyr remained in the 0 to 15 cm soil in BLS soil colu mns. Under this rainfall regime, the herbicide moved 30 cm deep 5 mo a fter application, but residues decreased significantly in surface soil . Imazethapyr bioactivity was highest and mobility was lowest at low s oil temperature (10 C) and low moisture (4 to 6% w/w). Imazethapyr mov ement was monitored successfully using the red beet root length bioass ay, and an herbicide residue map was developed to show the pattern of imazethapyr bioactivity in soil columns.