Flowering rush, Butomus umbellatus, is the only member of the family Butomaceae. The name flowering rush is a misnomer, as it is not a rush.
Flowering rush is native to Eurasia.
It was first found in North America in 1897 along the St. Lawrence River in Quebec and has become widespread in the Great Lakes region.
It was introduced as a water garden ornamental and may also have been brought here in ballast water.
It escaped into natural areas where it has had a serious negative impact on shoreline and shallow water ecosystems and affects recreational activities.
Flowering rush has unknown distribution on PEI, but it is thought to be very limited.
Flowering rush is an aquatic perennial that resembles our native sedge species.
It can be difficult to distinguish from native sedges, unless it is in flower.
It can grow in dense stand both in and out of water.
This species is still sometimes sold in garden centers and is readily available for purchase online.
Here are some key features that may help to positively identify flowering rush:
Can grow to be 1-5 ft tall
Leaf blades are grass-like, can grow to a meter in length and are triangular in cross section
Flowers are showy, pink, 2-3 cm across with 3 petals, and grow in umbrella-shaped clusters at the top of a single flowering stem
Flowers between May and September
Roots are fleshy and rhizomatous
Spreads by seed or bulbets that form on the roots and break off
Roots are buoyant, so part that break off can float and establish downstream
Cold weather in the fall cause leaves to fall down, unlike the native cattail species that remain upright
What it does in the ecosystem
Flowering rush is an ornamental flowering plant sold in nurseries and online as an aquatic garden plant.
This has likely contributed to the rate and distribution of its spread.
Due to its preferred aquatic habitat, bulbils, rhizome fragments, and seeds can be spread long distances by water currents.
Bulbils easily detach from the main plant and germinate quickly allowing new populations to become established.
Wildlife and human activity such as boating and fishing, also contribute to its spread.
Flowering rush grows in dense stands both in and out of the water.
Flowering rush can grow in water up to 3m or deeper.
Even though the plant will not flower when submerged, it continues to spread by rhizomes and bulbils.
Flowering rush reduces biodiversity by crowding out native wetland and shoreline plants.
It creates dense mats which restrict light, dissolved gases, and nutrients that would normally be available to other submerged plants and animals.
Flowering rush is known to alter water temperature and cause shallow water systems to become filled with sediment.
Its dense growth can affect irrigation and drainage system capabilities.
It can restrict boating, swimming, and fishing activities by clogging shorelines and choking equipment.
The best way to manage any invasive species is to prevent its establishment in the first place.
Flowering rush arrived by boat initially and can spread the same way.
Cleaning, draining, and drying all aquatic recreational equipment before moving to a new area is a great first step in managing further spread.
Before selecting a control method, consider the size of the infestation, your available resources, and the amount of effort you are willing to expend.
Often, multiple control methods are used simultaneously.
Consider the local ecosystem and what other organisms or ecological processes may be affected by management.
As flowering rush distribution is thought to be very limited on PEI, we would like to keep it as such.
Report any sightings to the PEIISC as soon as possible.
If working to control flowering rush after seed heads have formed, it is key to avoid further seed dispersal by cutting off and bagging the seed heads carefully.
Carefully place a plastic bag over the seed head.
Cinch the bag around the stem.
Clip the stem below the bag.
This will ensure that the entire seed head has been deposited into the bag, with little chance for accidental dispersal.
If you are heavily invested in management, specialized attachments for excavators exist to remove plants on a larger scale.
Hand-digging of flowering rush plants can be a feasible option for small to medium-sized outbreaks.
This process must be done with care, as flowering rush can grow back from root fragments that are left behind or that break off during management.
Using a sharp shovel, excavate and remove the entire plant from the water to prevent root fragments from being washed away.
Washed-away fragments can sprout and start infestations in new areas.
Cutting the plant regularly below the water level can prevent flowering, and can gradually reduce flowering rush populations over time.
Used alone, this method is unlikely to achieve eradication.
Cutting can be combined with benthic matting where feasible to further suppress flowering rush populations.
Matting will also affect the surrounding ecosystem and prevent all new plant growth. Native plants will be affected just like the flowering rush.
Plants are not the only species affected. Benthic invertebrates, soil-dwelling organisms, and fish will also be impacted. Keep this in mind when implementing matting techniques.
Along with these native aquatic species, the wildlife that relies on them will also be affected by their loss through reduced availability of food and shelter.
Timing of management is crucial.
It is important to consider the spawning time of any fish species found in the affected wetland or watercourse, as fish reproduction can be negatively affected by management.
Waterfowl that nest along the banks of many wetlands and watercourses, so check the area for active nests and delay management until after these nests have been vacated.
Despite the potential negative effects of management, the negative effects of leaving flowering rush unchecked may be greater.
Instead of using one big tarp, it is often best to cut it to the size needed and make smaller patches.
Tarping works because the root system will be deprived of light and the plant’s roots will be continuously baked by the sun.
This is a simple practice on dry land, however, when this plant is being managed in aquatic environments the challenge increases.
Tarps can still be placed in aquatic areas whether they are submerged year-round or even seasonally, however, the tarps will need to be modified to stay in place. Tarps placed at the bottom of a waterbody are known as “benthic barriers”, they are built to be weighted down and built to prevent billowing when gases are released by the decaying plants.
Tarps are available commercially but it is also possible to build your own.
See our guide here for instructions on how to build a benthic mat.
It is unlawful to use herbicides when nearby wetlands and watercourses on PEI, so chemical controls are not a viable option for the management of flowering rush.
In any case, when using chemical controls, all local legislation and manufacturer’s instructions must be followed.
DISPOSAL AND FOLLOW-UP
To prevent spread during the management process, all plant material should be collected, bagged, and prepared for proper disposal.
Bag the plant material in clear plastic bags.
Mark the bags boldly with a permanent marker. Write “INVASIVE PLANT” or “FLOWERING RUSH” on the bags.
If you have a place away from foot and wildlife traffic, you can dry out the material, making it much easier to move.
Leave the bags open and in the sun for a week to dry.
Only do this if you can guarantee that the plant will not be spread from where it is drying
Double bag if the bags are thin to prevent accidental dispersal.
Tie the bags tightly and place them in your usual residential waste collection (THE BLACK BIN)
Never place invasive plants into the compost. This may allow them to become established once they reach the heap.
All equipment used should be cleaned and all plant parts should be removed from your person, tools, and vehicles.
Any proper management plan will include follow-up visits.
These are conducted to assess the effectiveness of control measures and to manage any regrowth that may occur onsite.
If regrowth is seen, you will likely need to repeat your control measures.
Replant the area with appropriate native plants to compete with any new growth and begin to regenerate the area to its natural beauty.
Reach out to the PEIISC for advice on selecting the proper plant for the location.