The harsh realities of poor marestail control with burndown herbicides applied before soybean planting were widespread during the 2013 growing season. We anticipated even more challenges with this species for the 2014 growing season, but by and large the forecasted marestail “train wreck” did not materialize in much of the state. Fall herbicide applications coupled with a harsh winter that caused a high degree of mortality to winter annual weed species probably contributed to a reduced population of marestail last spring. However, it is unwise to assume that a lower marestail population last year will translate into a low marestail population this year.
It’s not too early to apply herbicides to control emerged marestail in fields that will be planted to soybean. The small marestail plants we have currently will be much easier to control than the larger plants that will be encountered in several weeks. Consider an early herbicide application targeted for marestail control, and application of soil-residual herbicides for summer annual weeds closer to soybean planting. Dr. Mark Loux, extension weed scientist at The Ohio State University, recently published suggestions to improve marestail control with burndown herbicides; you can read these suggestions at http://corn.osu.edu/newsletters/2015/2015-08/managing-marestail-this-spring-2013-the-perfect-storm