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FLOWERING RUSH –AN INVASIVE WATER PLANT
As you cross over the East River Road bridge heading to the Hickory Islands you can see a blanket of vegetation growing in Gibraltar Bay off to the west. Plants cover the north and south side of the bay, divided by the open area created by the Detroit River current that runs under the bridge into the bay. The non-native plant thriving there is Flowering Rush and it has in many ways “invaded” the bay!
The ecosystem in and around Grosse Ile has experienced dramatic changes in recent years as water levels have dropped in the entire Great Lakes region. Under these changing conditions local and indigenous plants and animals struggle to survive. Reduced water levels in the lower Detroit River have allowed several invasive plant species to grab a strong foothold along the shores of Grosse Ile and its outlying islands. Although some residents have worried about the size of the American Lotus bed in Gibraltar Bay, their concern is misguided. The American Lotus- the state’s symbol of clean water is a native and protected plant that provides an excellent habitat for fish in the Great Lakes. Its presence is a good thing! It supports one of the top ecologically productive areas in the lower river. Dr. Bruce Manny, a fisheries expert at the U.S. Geological Survey Great Lakes Science Center, calls Gibraltar Bay “a productive nursery habitat for numerous sport fishes during their first summer of life, including largemouth and smallmouth bass, northern pike and yellow perch”. Manny reports, “Gibraltar Bay is one of the very few reputed nursery areas for lake sturgeon in the Detroit River”.
The American Lotus bed covers a relatively small area of Gibraltar Bay. On the other hand, Butomus umbellatus - the Flowering Rush - covers a large area of the bay and is creating a problem for indigenous plant life. Much like other invasive plants such as Purple Loosestrife and Phragmites, this perennial plant from Europe and Asia was first introduced into the American Midwest as an ornamental plant for water gardens. People who plant Flowering Rush in their water gardens for its ornamental appeal can unwittingly help spread it over great distances if it escapes their gardens and ends up in waterways. Once the plant is in a watershed it spreads by rhizomes and fragmentation. It grows in shallow areas of lakes and bays in very dense stands, ultimately crowding out native aquatic plants such as cattails and bulrush. Once established in a waterway, boaters unwittingly transport and spread it on their equipment. Thus it has especially become a problem for the lower Detroit River since this region is so attractive to sport fishing, with boats traveling from location to location. Muskrats are also responsible for spreading Flowering Rush as they harvest it to build their mounds. The movement of water and ice also transports the Flowering Rush to new areas.
The emergent form of this plant supports a stalk about three feet tall that ends in an umbrella shaped cluster of flowers that are pink to white in color.
The plants only produce flowers in very shallow water or on dry sites. The leaves of emergent plants along the shore may be spirally twisted at their tips. The leaves of submerged plants are limp. While the flowering does produce seeds, studies have shown that very few populations are fertile, and this may explain the relatively slow rate of its expansion by natural propagation over long distances compared to the rapid spread of Purple Loosestrife and Phragmites.
Flowering Rush is particularly sensitive to changes in water levels because it is a pioneer plant, meaning it is one of the first plants to move into an unpopulated area. For this reason, it is fairly easy for it to invade new areas not yet occupied by other plants. The drop in water levels in recent years has exposed new areas for the emergent form of the plant to move into and take hold.
When managing or controlling Flowering Rush there are four key points to remember:
- Native aquatic plants protect lake quality and provide valuable fish and wildlife habitat. Removal of native aquatic plants may require a DNR permit, but a permit is also required to remove Flowering Rush because it is so difficult to distinguish from native plants.
- Flowering Rush is very difficult to identify, especially when not in flower, since it closely resembles many native emergent plants such as the common bulrush.
- Invasive species often move into disturbed areas. Removing native plants may open new areas for Flowering Rush to invade. Protecting native plants is an important way to help keep Flowering Rush out of a shoreline.
- Improper control methods can actually worsen the Flowering Rush problem in an area.
Suggested methods for managing/controlling Flowering Rush include cutting and hand digging. However, cutting it below the surface of the water will not kill the plant; it will only decrease its abundance. Further, multiple cuts may be required throughout the summer as new shoots will grow up from the root system. All cut plant parts must be removed from the water in order to prevent further spreading.
Hand digging is most effective when removing isolated plants that are located downstream from a larger infestation. One must use extreme care to remove all root fragments as any disturbance to the root system will trigger small reproductive structures on the roots to break off and spread further. For this reason, raking or pulling are not recommended.
Herbicides are also not recommended. Any use of herbicide in public water requires a DNR permit. Currently there is no herbicide that is selective for Flowering Rush and care must be taken not to damage valuable wetland plants, such as cattails.
Once Flowering Rush is removed from water it can still grow and spread by sending out new shoots from the root stalk. It is very important that plant pieces are thoroughly dried once they have been removed from the water. Flowering Rush makes excellent compost, but care must be taken not to compost it near a wetland or a shoreline. Finally, large piles of Flowering Rush should be turned over frequently to assure thorough drying.
If you’re a boater, sailor, angler, duck hunter, kayaker or enjoy water sports in general there are things you can do to minimize the spread of invasive plant and animal species. The Minnesota Sea Grant Program provides this checklist:
- Inspect your boat, trailer, and boating equipment (anchors, centerboards, rollers, axles) and remove any plants and animals that are visible before leaving any waterbody.
- Drain water from the motor, livewell, bilge, and transom wells while on land before leaving any waterbody.
- Empty your bait bucket on land before leaving the waterbody. Never release live bait into a waterbody, or release aquatic animals from one waterbody into another.
- Wash and dry your boat, tackle, downriggers, trailer, and other boating equipment to kill harmful species that were not visible at the boat launch. This can be done on your way home or once you have returned home.
- Since some aquatic nuisance species can survive more than two weeks out of the water, it is important to: rinse your boat and equipment that normally get wet with HOT (at least 40°C or 104°F) tap water; or spray your boat and trailer with high-pressure water; or dry your boat and equipment for at least five days, before transporting to another waterbody.
- Learn what these organisms look like (at least those you can see). If you suspect a new infestation of an exotic plant or animal, report it to your natural resource agency.
Submitted by the Grosse Ile Nature & Land Conservancy
Information from the Minnesota Sea Grant Program
Appeared in "The Ile Camera," Friday, October 5, 2007.
