Marestail Control in Soybeans

This article is devoted to one of the most problematic weeds in soybeans: marestail. Marestail is an upright growing plant and can reach 4 feet if not mowed or controlled. Marestail begins as a basal rosette similar to other winter annuals. Following the rosette stage, Marestail expereinces a stage of rapid vertical growth refered to as ‘bolting’. The leaves are 3 – 4 inches in length, and have widely toothed margings. And the stem of marestail is simple and unbranched, and covered with hair.

In a recent fall weed-scouting project, I noted marestail in nearly 20% of the soybean fields in Van Wert County. For those who are battling this weed already, you know that marestail is difficult to control. Marestail is diffiuclt to control for many reasons. First, marestail has the ability to germinate throughout the year. In fact, marestail is typically classified as both a winter annual and a summer annual because it can germinate in the fall and throughout the summer. Next, marestail is tolerant and in some cases resistant to glyphosate. So an application of glyphosate may have little to no effect on marestail. Last, marestail is a prolific seed producer. Weed scientists have reported seed production up to 200,000 seeds per marestail plant. Yes, that’s per single plant. The seeds are small (typically 2mm) and are dispersed easily by wind and equipment.

In OSU research, the most effective control of marestail in soybeans has occurred from a combination of 2,4-D ester, residual herbicides and either glyphosate or paraquat applied in April, when the marestail is still in the rosette stage or has only an inch or two of stem elongation. But even with this ‘loaded’ herbicide package, expect a few marestail escapes. If marestail populations are heavy, OSU researchers recommend delaying the herbicide application until very late-April or early-May to catch as many emerged marestail plants as possible.

Below is the full podcast on marestail.