By Harold Watters, Ohio State University Extension, Champaign County
Several years ago I attended a Montgomery County Extension Weed Tour and saw the marestail problem there. I saw their plots, saw the attempts to clean up the weed with glyphosate in Roundup Ready soybeans and recognized that it was virtually impossible.
Today our soybean fields look as bad in Champaign County (and surrounding areas in western Ohio) as I remember those Montgomery County fields. What our Extension weed specialists, Mark Loux, Jeff Stachler (was still here then), and Tony Dobbels learned was that once you have glyphosate resistant marestail plants, we can only kill about 50% or less with a glyphosate application. Other post products that once upon a time worked on marestail, such as First Rate or Classic lost their effectiveness in the mid-1990s for the most part. So a planned post program today to kill marestail in soybeans is foolish.