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Friday - August 28, 2009

From: Oswego, NY
Region: Northeast
Topic: Invasive Plants
Title: Eliminating smartweed from pasture in Oswego NY
Answered by: Barbara Medford


How do I get rid of smartweed in my pasture?


About 75 species of of plants with "smartweed" in their common names occur in North America. They are mainly identified by their spikes of numerous flowers and encircling leaf sheaths. Both are found in gardens as well as in damp waste places. The seeds of these plants are eaten by songbirds and waterfowl. There are also climbing species of smartweeds. Twenty two members of the Polygonum genus are native to New York, and 12 species with the common name "smartweed" are native to New York. We have selected 3 of these, assuming their management is pretty similar, and will see what we can find out.  In addition (once again, the curse of the common name) there is a dodder, a parasitic plant, that goes by the same common name. Here are the four native plants in our Native Plant Database that we are going to research further; perhaps by following the plant links to the webpage on each plant and by looking at pictures you can determine which one (or more) is causing you the problem. 

Polygonum pensylvanicum (Pennsylvania smartweed) - Polygonaceae (Buckwheat family)

Polygonum erectum (erect knotweed) - Polygonaceae (Buckwheat family) pictures

Polygonum lapathifolium (curlytop knotweed) - Polygonaceae (Buckwheat family)

Cuscuta polygonorum (smartweed dodder) - Cuscutacea (Dodder family) More information on this plant from the Purdue Plant and Pest Diagnostic Laboratory

The first thing we learned is that these are all basically moist soil plants, some are very nearly aquatic plants. One of the suggestons for control was to improve the drainage in the area where they were growing. On the polygonums, since they are mostly annuals, a frequent suggestion was that of clear cutting or pulling while the plants are in early bloom. If you can break the seeding cycle, that will help. However, we also saw research saying the seed of this genus can survive in the soil and remain viable for many years.

Your best resource for help on weedy matters is much closer to home than we are. Contact the Cornell University Cooperative Extension Office for Oswego County. You can bet that if you are having problems with this plant, lots of others in your area are, too, and the people in extension offices are trained to work on that kind of problem.


Polygonum pensylvanicum

Polygonum lapathifolium

Cuscuta polygonorum






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