When you see a new and unfamiliar weed growing in your garden or lawn, what is the first thing you do? First instincts are to pull it out, mow over it, and spray herbicides...only to see it grow back next month/year with a vengeance. Not all species are created equally...and that means some species have characteristics about their life cycle or biology that makes them harder to manage, and ultimately eliminate!
This post will discuss two of the many reasons why homeowners are often frustrated and unsuccessful in managing small scale infestations on their property, rhizomes and seed banks! Rhizomes are a horizontal plant stem that grow underground and are capable of forming new roots and stems. Unless you are able to pull out the entire plant, including all and any fragments, new plants will pop up when mechanical removal strategies are used. Any plant produced from rhizomal propagation is genetically identical to the parent plant. Common examples of invasive species that have rhizomes include Japanese knotweed and Phragmites. The key to dealing with these plants includes targeting treatment options at the rhizomes as the plant will store a lot of its energy here, especially when the growing season is coming to an end. In the case of Japanese knotweed, treatment may include foliar spraying to thin out the infestation, and then injecting herbicide into the base of the plant to kill the roots and rhizomes.
Many invasive plants produce copious amounts of seeds each year. Each Japanese stiltgrass plant can produce 100 to 1000 seeds per plant, and those seeds may remain viable for up to five years. Those seeds are often deposited into the soil nearby, or transferred to other areas via wind, rain and other organisms. Depending on how long the infestation has been a problem, there may be a large and viable seed bank in the area. When trying to manage high seed producing plants, timing is everything! Mechanical pulling can be used for plants that have shallow roots or small infestations, else herbicide. One thing to consider is allowing the plant to grow and then harvest prior to the plant flowering to avoid seed dispersal, and potentially minimizing the amount of plants growing in the area . Trying to mow while the viable seeds are present on the plant could be a recipe for disaster and allow for spread via wind or equipment if it is not decontaminated properly!
Regardless of whether the plant propagates using rhizomes, seeds or both, management efforts will be a multi year effort in order to eliminate the entire plant network and reduce the seed bank. For more information, please visit the below links!
Nitzsche, P. and P. Rector. Japanese Stiltgrass Control in the Home Lawn and Landscape. New Jersey Agricultural Experiment Station.
Michigan Department of Environmental Quality. Phragmites information page.
Shikha Singh is the coordinator for the JLW CISMA. She has a BSc. in Biology from University of Western Ontario, and her master's and PhD at Michigan State University from the Dept. of Fisheries and Wildlife. Her areas of expertise include water quality, water policy, invasive species, education/outreach and public speaking.