Aquatic weed scientists consider Hydrilla verticillata the most problematic and invasive aquatic plant in the United States.
This plant, native to Africa, Australia, and parts of Asia, was introduced to Florida in 1960 via the aquarium trade.
Hydrilla forms dense mats that destroy fish and wildlife habitat. Hydrilla has several competitive advantages over other plants. It can grow with less light and is more efficient at taking up nutrients than native aquatic plant species, and it is extremely effective at reproducing. Besides manufacturing seeds, it can sprout new plants from root fragments or stem fragments. Recreational users (boaters, fishermen, swimmers) can easily and unknowingly move fragments from infested waters, spreading this aggressive plant to new ponds, lakes, streams and rivers.
Hydrilla's overall success is linked closely to its ability to produce structures called turions and tubers. Turions are compact buds produced along the leafy stems. They break free from the parent plant and drift to start new plants. They are generally about a quarter inch long, dark green, and appear spiny. Tubers are small, potato-like structures, and consist of white or yellowish overlapping scales formed at the end of roots. Hydrilla plants can produce up to 5,000 tubers in one square meter of soil! Hydrilla produces an abundance of tubers and turions in the fall, and tubers may remain dormant for several years in sediment regardless of ice cover, drying, or herbicides.
Hydrilla closely resembles two other aquatic plants: The non-native Brazilian elodea - Egeria densa (link to photo and info) and the native American waterweed - Elodea canadensis (link to photo and info). Hydrilla is distinguished from these species by the presence of tubers (0.2 to 0.4 inch long, off-white to yellowish, pea-like structures buried in the sediment). Neither Brazilian elodea nor waterweed has tubers. Other characteristics to look for include:
- Leaves in whorls around the stem (generally five leaves per whorl).
- Serrations or small spines along the leaf edges and small spines on the underside midrib.
- The midrib of the leaf is often reddish when fresh.
Currently hydrilla has been confirmed in Wallace Lake in Mill Stream Run Reservation, wetlands in West Creek Reservation, and Sunset Pond and Sanctuary Marsh in North Chagrin Reservation and Blue Heron Marsh at Ohio and Erie Canal Reservation. These represent the only known populations currently in northern Ohio. This means hydrilla is documented in each of the major watersheds in this region with a high risk of spread into Lake Erie. Increased surveillance and future management is critical to preventing future spread of this invasive plant. Cleveland Metroparks has an obligation and responsibility to prevent future spread into Lake Erie.
As with most aquatic vegetation, there are four main methods for eradication.
- Water drawdown (ineffective by itself)
- Physical removal (generally ineffective at reducing tubers)
- Biological control with “grass eating carp” or microbes (effective, but damaging to all aquatic vegetation)
- Chemical treatment (effective, but expensive and very long-term)
Stop the spread!
Clean all vegetation and mud from boats, canoes, motors, trailers, clothing and boots before leaving any location.