Penn State recently completed a two-year study on pokeweed management in corn and soybeans that provides some useful information. Some of the highlights:
- pokeweed is a perennial that regrows from a large taproot, and individuals may live a year or two, or for several years, depending on their environment. Harsh winters such as the last one can reduce plant survival.
- seed production and dispersal are essential for pokeweed success. A pokeweed berry contains 9 or 10 seeds. Pokeweed plants that emerged in May or June grew into perennial plants that first season, and produced up to about 2500 seeds. Preventing berry/seed production is an important management tactic for this weed, much like for annual species.
- systemic postemergence corn herbicides (glyphosate, 2,4-D, dicamba, Status, Callisto + atrazine, etc) can provide at least 80% control by the end of the season. None of the herbicides provided complete control, indicating the potential for recovery and regrowth the following year, and the need for a multi-year management approach.
- similar results occurred with postemergence soybean herbicides, but effective options were fewer. Research showed the value of Roundup Ready and glyphosate as a foundation herbicide for managing common pokeweed in soybean; the non-glyphosate treatments (Classic, Harmony, Synchrony, FirstRate, and Raptor) provided only 39 to 62% control.
- application in late June through the rest of the summer provided good control of pokeweed, while late spring application was less effective. At least 90% control occurred when glyphosate was applied at 600 to 800 GDD (48 F base temperature) or later. The late June and later applications coincide with pokeweed flowering, and herbicide translocation to below ground vegetative structures is probably much greater with the later applications.
- results are summarized in a Penn State newsletter article -http://extension.psu.edu/plants/crops/news/2014/05/pokeweed-management-update.