WSU Extension


Weeds : Smartweeds : Polygonum spp.
(revision date: 4/7/2021)

Family: Polygonaceae
Cycle: Annual/Perennial
Plant Type: Broadleaf

Use Integrated Pest Management (IPM) for successful weed management.

Smartweeds are typically annual weeds with erect or spreading stems up to 3 feet long. The leaves are alternate, attaching to the erect or sprawling stems at enlarged nodes. Many smartweeds have a papery or clear membrane as part of the sheath where the petiole attaches to the stem. The small flowers of smartweeds are typically borne in short spikes or clusters arising in the leaf axils or at the tips of branches. Ladysthumb or spotted smartweed (P. persicaria) is one common species. Although most smartweed species have leaves are uniform in color, ladysthumb has a purplish spot or "thumbprint" at the center of each long, pointed leaf. Other species of interest include water smartweed (P. amphibium), a perennial which reproduces by seeds and from roots and is found in water or wet areas, and smartweed or water pepper (P. hydropiper), an annual species found in pastures, cultivated areas, and waste areas.
Smartweeds can be weeds in cultivated areas, roadsides, waste areas, and other sites, depending on species. They are often found in moist sites including irrigated pastures.

Management Options

Non-Chemical Management
None recommended
Select non-chemical management options as your first choice!

Chemical Management

NOTE: Some ingredients listed here are only available in combination. Read the label carefully on combination products to make sure the product is suitable for your specific situation.

Landscape areas
  • products containing dicamba
Turf areas
  • 2,4-D + MCPP + dicamba
Bare ground areas
  • products containing dicamba
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Caption: Smartweed stem showing sheathing stipules at the nodes
Photo by: J.A. Kropf
Caption: Smartweed
Photo by: T.W. Miller
Caption: Smartweed flowers
Photo by: T.W. Miller
Caption: Smartweed leaves
Photo by: J.A. Kropf