Soybean Rust Developing Slowly in the United States

Published: August 1, 2011

Each year, from about the beginning of July through the middle of August, there isn't a lot of variety to the calls I get related to weed management in soybeans. The questions usually have to do with essentially one issue, "How do I control big weeds in soybean?" Obviously "big" is a relative term but my definition is usually way different from everyone else's. This is primarily due to the fact that if you have weeds over 6-inches or so in height, it is highly likely that you are already losing soybean yield. But that is a topic for another time. Most of the calls I get don't have to do with 6-inch weeds; more commonly the questions have to do with weeds double or even triple that height. Either these weeds never got sprayed because of the wet season we've had, or the weeds have already been sprayed one or more times with glyphosate (sold as Roundup, Touchdown, or a variety of other trade names) and they are still living. In recent years, the vast majority of the questions have to do with this latter scenario. I believe we have now moved into an era where glyphosate-resistant weeds like waterhemp, palmer pigweed, marestail, and giant ragweed have taken over as the predominant weed problems in Missouri soybean production fields. Based on all of the research I have conducted or seen over the years on both resistant and non-resistant weed populations, I have to divide my answer to the question of controlling "big" weeds in Roundup Ready soybean into the following two categories: