Below are some pictures from the field, taken July 20, 2009.
These plants were sprayed with Pursuit (imazethapyr) and glyphosate on July 14 (photos 1 and 2) or July 11 (photos 3 and 4).
The chlorosis of the leaves and purpling of veins is characteristic of ALS inhibitor injury in soybean. Severity of injury is determined by environmental characteristics at the time of application and thereafter. Recovery is often slower with low soil moisture and high air temperatures. Injury symptoms are generally gone 21 days after application.
The Univeristy of Illinois found that in over 95% of fields with ALS injury, no yield loss was observed. The fields where yield loss occured were late planted and/or the herbicide application was late in the season. These are times when the crop is more likely to be in conditions of low soil moisture and warmer air temperatures. The risk of yield loss due to labeled applications of these herbicides is far less than allowing for crop competition with weeds or failing to adequately control weeds.
References: University of Illinois Extension Purdue University Extension Weed Science