Russian Knapweed
Acroptilon repens L.
PerennialUp to 3 ft
Grayish clumps with lavender, thistle like flowers and very dark roots.
Lythrum salicaria L.
Purple Loosestrife
Identification
Purple Loosestrife
Lythrum salicaria L.
- Life cycle
- Perennial
- Height
- Up to 8 ft
Purple loosestrife is a perennial that grows to 8 feet and prefers damp soil. Leaves are simple and lance shaped with smooth margins, and they are opposite or whorled. Stems branch and end in flower stalks.
Flowers are rose purple on long, vertical racemes, with 5 to 7 petals and numerous stamens. Roots are large and adapted to aquatic sites. Plants can grow dense enough to impede water flow in canals or ditches.
Control
Controlling purple loosestrife
- Best timing
- Glyphosate works best from July to early September. Triclopyr is effective from pre flower to late flower.
- Mowing and pulling
- Digging works best on plants that are only a few years old.
- Herbicide
- Glyphosate, triclopyr (Garlon) and aminopyralid (Milestone). Near water, use only products labeled for aquatic sites. Do not use Garlon in landscapes or flower beds.
- Biological control
- Two Galerucella leaf beetles have been the most successful, and heavy feeding has greatly reduced some infestations.
Always follow the product label, and check rates in the North Dakota Weed Control Guide from NDSU. Your county weed control officer can tell you what fits your land. Source: NDSU Extension W1411 (December 2025).
Keep Looking
Other weeds on the state list
Saltcedar
Tamarix ramosissima Ledeb.
Shrub or small tree5 to 20 ft
A shrub with scale like leaves and pink to white flowers. Also called tamarisk.
Yellow Toadflax
Linaria vulgaris
Perennial12 to 24 in
Yellow flowers with an orange, bearded throat that look like small snapdragons.
Think You Found It?