If you own a pond in the southeast, you have likely run into problems with duckweed. While the plants do serve several benefits such as bioremediation and biofuel production, nuisance populations can cause negative impacts as well. Although individual plants are among the smallest in the world, duckweed colonies can spell big headaches for landowners, clogging irrigation intakes, impeding navigation, and causing fluctuations to dissolved oxygen that can spell disaster for aquatic life. While these plants don’t usually cause problems in large, public water bodies, they can be a major nuisance to backyard and agricultural ponds as well as water gardens. Control of these minute plants can present many challenges as the small size and staggering reproductive ability of duckweed makes it almost impossible to remove all plants from a system.
Chemical control of duckweed through herbicides has often been a choice of those seeking at least moderate term control. Contact herbicides such as diquat and flumioxazin are successfully used to control duckweeds, especially when thorough applications can be achieved across the entire treatment area. Lemna duckweeds typically coexist with Wolffia species such as watermeal, which present some challenges to control however.
In the past few years, researchers have been looking for alternatives in the chemical control of duckweed when infestations are large and foliar applications become difficult. In 2010, scientists from the Geosystems Research Institute of Mississippi State University began looking at two systemic herbicides, fluridone and penoxsulam, to fit that bill. This work can be found in the Journal of Aquatic Plant Mangement as a published note. Fluridone is a systemic herbicide most famously known to control submersed plants such as hydrilla. Penoxsulam, on the other hand, is most commonly used as a subsurface treatment for Giant Salvinia and Water Hyacinth. Prior to the work of the group from Mississippi State, little to no work had been done assessing these two potential candidates for duckweed control.
Both fluridone and penoxsulam were thoroughly assessed during 2 separate studies, at 3 concentrations, across 4 replicates and a control each. Duckweed from a pond near the University was used for each study. Both studies were completed over a 12 week span, study 1 representing low concentrations and study 2 representing higher concentrations of subsurface applications.
Complete duckweed control was achieved with higher concentrations of fluridone at 25 ppb, 50 ppb, and 75 ppb. Penoxsulam also controlled the majority of duckweed at similar concentrations and up to 60% control even at lower concentrations, however complete control was not achieved. This research concludes that concentrations greater than 25 ppb of fluridone and 25, 50 and 75 ppb penoxsulam can effectively serve as a means for control of duckweed. The group also suggests that penoxsulam be investigated at higher rates to see if complete control might be achieved.
There are several effective products available on the market to control duckweeds. While certainly not the only means of control, fluridone and penoxsulam may provide a means for control of large infestations where water flow and exchange is not an issue. The contact herbicides Diquat and flumioxazin also continue to provide control of duckweed. Please contact your local extension office or land grant University to find out what product might be right for your particular duckweed management situation.
To read the paper in its entirety, click here.
For more information on the biology and control of duckweed, visit the AERF Best Management Practices Handbook Chapter 15.10.
Stay tuned for more from the Aquatic Plant Management Society. If you would like your research featured in the APMS blog, contact Dr. Brett Hartis at firstname.lastname@example.org.The APMS Blog is prepared by Dr. Brett Hartis, NC State University