Pokeweed Management Update

May 28, 2014

Research conclusions for pokeweed control in corn and soybean.

Common pokeweed berry cluster. Each berry contains about 9 seeds (Image by Kelly Patches).

Common pokeweed berry cluster. Each berry contains about 9 seeds (Image by Kelly Patches).

Some of you have seen and heard Kelly Patches present on her research over the last 2+ years. She recently successfully defended her MS Thesis titled “Common Pokeweed (Phytolacca americana L.) Management in Pennsylvania Field Crops”. Kelly’s research was supported in part by our Pennsylvania soybean growers through the checkoff program working with the PA Soybean Board. We greatly appreciate the support. Kelly will soon be starting her next challenge as a new member of the Penn State Extension Field and Forage Crops team based in Franklin County, PA so you can continue to direct your pokeweed question to her.  

In her research, Kelly focused in several areas that included herbicide evaluation as well as trying to learn more about the biology of common pokeweed. The Penn State weed science group all learned a great deal more about this weed through Kelly’s research. Here are just a few take home points from her work:

Common pokeweed is called a simple herbaceous perennial, which means that each plant establishes a taproot from which it can emerge each growing season. This is similar to dandelion. It does not creep like Canada thistle, so each plant is an individual that originally germinated from seed. Individuals may live a year or two or for several years depending on their environment. A cold winter like this last one can greatly reduce the persistence of these perennial plants (one positive thing about cold winters). One thing we observed from Kelly’s work was how important seed production and dispersal are for pokeweed success. A single pokeweed berry contains 9 or 10 seeds. If plant’s do not successfully flower and set seed, the population will not grow. Birds and other animals help disperse seeds into new locations. In one of Kelly’s studies, she monitored the effect of the date of seedling emergence on pokeweed flowering and seed production. A single pokeweed seed that emerged in May or June grew into a perennial plant that first season that produced up to about 2500 seeds per plant at the end of the season. So, preventing berry/seed production is an important management tactic for this weed, much like for annual species.

Kelly examined a number of herbicide programs for pokeweed control in corn and soybean. Most of this work was conducted in Centre County PA. She discovered that a number of systemic post corn herbicides (glyphosate, 2,4-D, Banvel, Status, Callisto+ atrazine, etc.) can provide at least 80% control by the end of the season, but none of the herbicides provided complete control indicating the potential for recovery and regrowth the following year. Similar results were seen with soybean herbicides but effective options were fewer. Her soybean 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) only provided 39 to 62% control. Finally, although soil residual herbicides for seedling control were not compared in this work, our research does indicate that residual herbicides will help control seedlings and reduce pokeweed populations over time.

In a separate glyphosate application timing experiment, application in late June through the rest of the summer provided good control of pokeweed, while late spring timings’ were less effective. At least 90% control was achieved when glyphosate was applied at 600 to 800 GDD (48 F base temperature) or later. The late June and beyond applications coincide with pokeweed flowering, so we believe that herbicide translocation to below ground vegetative structures is much greater with these later applications helping to kill perennial plants. This timing research confirmed effective control will be difficult in corn and that planting a shorter statured crop like soybean that allows for later glyphosate application times or crops that are harvested earlier in the summer that present a late summer management window can potentially improve control options for common pokeweed.

Kelly conducted a number of other experiments looking at nozzles, spray volumes, mowing, and seed bank persistence. She plans to distill her results into a Penn State Extension Fact sheet that will be available in the not too distant future. Please feel free to direct your questions about pokeweed to Kelly or myself.

Source : psu.edu

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