Pennsylvania smartweed
Persicaria spp. (e.g., P. maculosa, P. pensylvanica)
An upright-to-spreading summer annual of wet, compacted, thin turf, recognized by swollen jointed nodes with a papery sheath and pink flower spikes.
Identification
Pennsylvania smartweed (Persicaria pensylvanica, formerly Polygonum pensylvanicum) is an upright-to-spreading summer annual broadleaf with smooth, often reddish, swollen-jointed stems. The hallmark feature is the ocrea, a thin papery membranous sheath that wraps the stem at each swollen node where the leaf attaches, a trait shared with knotweed and other Polygonum relatives. Leaves are alternate, lance-shaped to elliptic, tapering at both ends, and frequently bear a dark purplish blotch or watermark in the center of the blade. It is distinguished from prostrate knotweed by its larger, more erect habit and showier flowers, which form dense, plump, pink to rose-colored cylindrical spikes at the stem tips; the smooth (essentially hairless) flower stalks help separate it from the similar Pennsylvania-vs-pale smartweed group.
Symptoms & Damage
In turf, smartweed grows coarser and taller than the surrounding grass, producing an uneven, weedy canopy with conspicuous pink flower spikes that detract from appearance and uniformity. Its upright clumps shade and crowd thin or struggling turf, and heavy stands in moist low areas can dominate the site, leaving the desirable grass sparse and the surface rough and unsightly.
Biology
Pennsylvania smartweed is a summer annual that completes its life cycle in one growing season and reproduces solely by seed. Seeds germinate in spring as soil temperatures warm, plants grow rapidly through summer, flower and set abundant hard-coated seed, and then die with frost. The durable seed overwinters in the soil and can remain viable for years, so it returns reliably wherever the seedbank is established.
Occurrence & Spread
It favors moist to wet, fertile, and disturbed sites, and is most troublesome in low, poorly drained areas, along pond and ditch margins, in floodplains, and in newly seeded or thin turf. Open, bare, or recently disturbed soil with adequate moisture in late spring and summer gives the warm-season seedlings the room and conditions to establish, so wet spots and recently renovated areas are the usual points of invasion.
Favorable Conditions
Wet, compacted, poorly drained, or recently disturbed soils; thin turf.
Cultural Management
Because smartweed exploits wet, disturbed, open ground, the most durable control is to improve drainage in chronically wet areas and to establish and maintain dense, vigorous turf that shades the soil and prevents seedling establishment. Proper fertility, correct mowing height, and prompt reseeding of bare or renovated areas reduce the open niches it needs; small infestations can be hand-pulled before they set seed, which is important given the long-lived seedbank.
Further Reading
University extension resources — open in a new tab.
Related Reports
No published reports yet for this pest.
Reports will appear here as they are peer-reviewed and published.