RUSH AN INVASIVE WATER PLANT
by Elizabeth Hugel
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 states 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.
A. Howard Image Collection, Courtesy of Smthsonian Institution
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.
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
- 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.
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.
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.
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.
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
- Inspect your
boat, trailer, and boating equipment (anchors, centerboards, rollers,
axles) and remove any plants and animals that are visible before leaving
- 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
- 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
the Minnesota Sea Grant Program
Appeared in "The
Ile Camera," Friday, October 5, 2007.