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Tuesday - March 10, 2009

From: Burnaby, BC
Region: Canada
Topic: Invasive Plants
Title: Controlling Pickerel weed (Pontederia cordata) in British Columbia
Answered by: Nan Hampton

QUESTION:

Hello, I am emailing from the west coast of Canada, Vancouver, and I have a plant question regarding a species you have listed on your website. We have recently discovered Pontederia cordata L. Pickerel weed in a natural lake. On searching on-line, the plant is native to parts of the US but as a garden variety. Though it may not be officially invasive here, the garden variety has escaped into a natural area with fish and other wildlife value. As such, we would like to be proactive and control the species before it naturally spreads out of control. From your knowledge, what is the best way to control the species? Once the root system is established, I suppose we have to 'dig up' the roots to eradicate the plant? Any tips you can provide for this, so the work can be done with as little disturbance, would be greatly appreciated. As well, we are hoping to control spread of the plant by cutting off flowers before they seed. Any further suggestions or comments so we can control this plant is greatly appreciated! Kindly, Melinda Yong Environmental Technician

ANSWER:

Pontederia cordata (pickerelweed) is distributed over the eastern half of North America, including Quebec and Ontario. There is also a population in Oregon. The population in Oregon may be of a garden variety, but the ones in the eastern half of North America are wild native populations. Nevertheless, P. cordata is included in the Southern Weed Science Society's Weeds of the United States and Canada list as an invasive and/or noxious weed. I certainly understand your concern to find it in your lake—even though it is native to North America, it is not native to British Columbia. Removing the flowers before seed set is certainly an important measure to use. One recommendation for controlling emersed rooted aquatic weeds (such as P. cordata) given in Aquatic Weed Management: Control Methods by J. L. Shelton and T. R. Murphy from the the Southern Regional Aquaculture Center is to deepen the edges of the pond or lake since these emersed plants generally grow in shallow water (<2 feet). This might or might not be practical depending on the size of your lake, but certainly you are going to have to use some mechanical or chemical means to remove or kill the plants and their roots. According to Aquaplant (Texas Agrilife Extension Service, Dept. of Wildlife and Fisheries Sciences, Texas A&M University) mechanical or chemical control are the only control methods since there is no known biological control for pickerelweed. You can read about various mechanical and physical control methods, as well as chemical controls, from the US Army's Aquatic Plant Information System Online. The mechanical method with least disturbance to the lake is, of course, hand cutting and digging to remove roots and rhizomes. Monitoring and diligence will be required afterwards to keep the plant under control.

Pontederia cordata