As you drive through the countryside this week, one weed that is standing out above the crops is pokeweed. Pokeweed is a herbaceous perennial, which means it dies back to the ground every fall, and sends up new shoots each growing season. Underground, pokeweed has a large, branching taproot, which stores lots of food and water, making it a particularly difficult weed to control.
Pokeweed is a poisonous plant. All parts of the plant contain the toxin, but it is highly concentrated in the roots. Poisoning is rare in animals because they seldom feed on it, but there are documented cases of hogs dying after rooting out the plant and eating the roots. Interestingly, it does not seem to affect birds, which feed on the berries and spread the seeds through the neighborhood.
Pokeweed has some historical significance in our country. Native Americans used the dark purple berries to make a red stain to decorate their clothes and other belongings. The stems and leaves of pokeweed were used as a symbol for the presidential campaign of James Polk, who loaned his name to the plant. Settlers in North America took pokeweed back to Europe, and it has become a weed of concern overseas.
Relatively speaking, pokeweed produces few seeds per plant. The average plant may have 2,500 to 3,000 seeds, much fewer than many of our other weed species. If the plant can be prevented from forming berries, there is a good chance you can keep it under control.
Kelly Patches, a researcher at Penn State, did some interesting research on pokeweed control. She found that a number of systemic post-emergence corn herbicides (glyphosate, 2,4-D, Banvel, Status, Callisto+atrazine, etc.) can provide up to 80 percent control by the end of the season, but none of the products offer complete control. Multiple applications are often needed to ensure the best control.
In soybeans, the results were similar, but there were even fewer options to pick from. Herbicide programs that did not contain glyphosate, however, provided only 39 to 62 percent control.
Kelly’s research showed the importance of timing. Applications made in late June through the rest of summer showed more promise than early spring applications. The late June application coincided with the pokeweed flowering, so it is believed the herbicide is translocated below ground much more effectively during flower and berry formation.
Jeff Burbrink is an Extension educator in agriculture and natural resources. Write to him at 17746 E. C.R. 34, Goshen, IN 46528; call 533-0554; or fax 533-0254.