Description: Herbaceous perennials are submersed except when branches grow long enough to reach the surface. Stems are thin and reach lengths of 25 feet. Tiny leaves form whorls of 4-8 around the stem. The plant reproduces from stem fragments, axillary buds (turions), and tubers.
Habitat: Hydrilla can grow in a broad range of aquatic conditions, from very shallow, warm water to deep water with extremely low light levels. Waters can be nutrient rich or poor, with salinity up to 7%.
Invasive Traits: Hydrilla grows very quickly (more than an inch per day) and once established, can quickly crowd out native aquatic plants and block light to the water column. Vegetative reproduction via stem fragments or tubers allows hydrilla to spread quickly.
Control: Herbicides approved for use in aquatic systems can temporarily control hydrilla. Chinese Grass Carp have been used for biological control. Mechanical harvesting machines have been used to remove hydrilla from the water but may accelerate vegetative reproduction. Drawing down of lake water levels can expose and kill hydrilla, although tubers can remain viable for 4 or more years under normal levels of dessication.
All photos from Cleveland Metroparks