Pre-emergence weed control methods continue to grow in Iowa, particularly in soybean production. It is estimated that 70 to 75 percent of Iowa’s soybean acres now receive a residual herbicide application.

That is up from only 20 percent in 2008. Corn residual acres have grown as well to 83 percent, but have been historically much higher than soybeans.

With the weed resistance issues that have grown in Iowa, we are now starting to see multiple applications of residual...