Small-flowered jewelweed identification and control
Information about the noxious weed small-flowered jewelweed. Small-flowered jewelweed is also known by its scientific name, Impatiens parviflora.
About this weed
Small-flowered jewelweed is a Class A noxious weed. This means eradication is required throughout Washington including King County.
Small-flowered jewelweed is known as Impatiens parviflora. It is in the balsam family. It is also known as Impatiens nevskii Pobed. Other common names include small balsam and small-flowered touch-me-not.
Why it's a problem
Small-flowered jewelweed can dominate the herb layer of invaded forests. It will form large, monospecific stands, displacing native species. Plants can invade and adapt to a variety of habitats and thrives especially well in moist, disturbed areas where native plants may already be sparse. Plants germinate from seeds earlier than many native plants in the region, giving it a further advantage over these species. Small-flowered jewelweed may have some allelopathic (changing the surrounding soil chemistry) effects. These results have been found in lab studies, but it is unknown how these results relate to natural conditions.
Plant description
Small-flowered jewelweed averages 1-2 feet tall at maturity. Height varies depending on growing conditions. It is an annual – meaning it goes through its entire lifecycle from seed to death in one year. Plant spreads by seeds that burst out of seed pods when touched, like other “touch-me-not” species. It is native to parts of Eurasia.
Flowers are small, pale yellow with red spots inside, tubular with a short, straight spur.
Leaves are toothed on the edges, egg shaped, and come to a point at the end. They grow alternate (leaves which grow staggered, without a pair on the stem).
Plants are hairless and smooth. Stems are succulent (watery) and hollow. They may have swollen nodes near the base and from junctions where they branch out.
Small-flowered jewelweed can grow well under low light conditions. It can also tolerate lower moisture conditions. So far only two populations of small-flowered jewelweed have been found in Washington state, both in King County.
Be aware of look-alike plants
There are several native Impatiens in Washington state: spurless jewelweed (Impatiens ecornuta), western touch-me-not (Impatiens noli-tangere), and varied jewelweed (Impatiens aurella). Plants will need to be identified while in bloom. Care needs to be taken as native Impatiens may grow among small-flowered jewelweed plants.
Check out Burke Herbarium photos of multiple Impatiens species for more photos and information.
Small-flowered jewelweed also looks like two listed noxious weed species in the Impatiens genus, Policeman’s helmet and spotted jewelweed [External link: Washington State Noxious Weed Control Board]. Both Policeman’s helmet and spotted jewel grow significantly taller than small-flowered jewelweed. They also have very different flower size and color. Additionally, small-flowered jewelweed has a much smaller distribution. It is only found in a few locations within King County.
When in doubt, take photos and share them with us or report them on iNaturalist.
What to do if you find it
Property owners are required to control small-flowered jewelweed on lands that they manage. Please notify us if you see small-flowered jewelweed growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. We map all known locations of regulated noxious weeds such as small-flowered jewelweed in order to help us and others locate new infestations in time to control them.
Control methods
We recommend using a combination of methods to control noxious weeds. In areas with few weeds, it is important to act quickly before they become harder to control. Make a long-term plan as it often takes several years to get rid of most weeds. Start in the least infested areas first and then move into more heavily infested areas.
Manual control
Small-flowered jewelweed has a shallow root system and can easily be hand-pulled, especially when growing in damp soils. Make sure to remove the roots, especially in drier soils where plants may break off - hand tools are helpful in these situations. It can be easily pulled but will regrow if the root remains in the soil or if stems are left on the ground.
Plants in the “touch-me-not” family get their name from their ability to eject seeds when pods are mature (flowers may be present) – so be extra careful if pulling flowering plants. Tip: carefully bend flowering plants into garbage bags and cut heads off into bags, then proceed with removal.
Cultural control
Plants may have some seeds that remain viable after the first year, so it is important to track sites and provide more control when necessary. By planting a variety of desirable species, a community will be present to help provide competition. This will help shade weed seedlings, and to provide a food source for pollinators. When possible, carry out control methods when pollinators are not active on plants.
Chemical control
Large populations of small-flowered jewelweed may need chemical control for management. Avoid spraying while pollinators are active. Products containing glyphosate or triclopyr are effective if applied to growing plants.
Stay safe when using herbicide:
- Always read the label before use.
- Wear a long-sleeved shirt, long pants, shoes, and eye protection.
- Follow state and local regulations.
Avoid spraying where there is a chance that herbicide will enter a waterway or wetland unless you are using a state-approved aquatic herbicide and have the required permits and licenses to do so. Use of pesticides in water is regulated in Washington state. See Washington Department of Ecology Aquatic Pesticide Permits for details.
For more information or a site-specific control recommendation in King County, contact the noxious weed program. For information in other counties in Washington state, contact your local weed board or your local cooperative extension office.
Disposal instructions
If the plants do not have seed capsules, they can be crushed and left on site in a dry place to compost. If plants have seed capsules, make sure to bag and put them in the trash.
Also, make sure to clean shoes, clothing, and equipment when leaving infested areas to prevent spreading seed to new locations.
Washington State Noxious Weed Control Board pamphlet on noxious weed disposal