Cogongrass and hydrilla two invasive plants choking our environment

March 5, 2013

NISAWInvasive Species Awareness: How good is your invader knowledge?

Invasive species are non-native or exotic species that do not naturally occur in an area and cause economic or environmental harm or harm to human health.  These invasive species have become the number one threat to biodiversity on protected lands.  However, invasive species do not know boundaries and as a result public and private lands are affected as well as natural and man-made water bodies and associated watersheds.  Northwest Florida is home to many unique habitats, including upland, wetland, and marine.  These habitats, housing a variety of plants and animals, make this area considered as one of the top six biodiversity hotspots in the country. These invasive species threats can come in the form of both plants and animals, in Florida there are over 500 non-native fish and wildlife species and over 1180 non-native plant species that have been documented.  Exotic species are able to outcompete many natives causing habitats to degrade, animals to leave, and can introduce diseases that can destroy economically important species. This is a worldwide issue that can be addressed on local levels. One of the most effective ways to control invasive species is by prevention, just by becoming invasive aware can help to control some of these issues.

Two of the most destructive species are the cogongrass and hydrilla.

Photo courtesy Chris Evans, Illinois Wildlife Action Plan,
Photo courtesy Chris Evans, Illinois Wildlife Action Plan,


Cogongrass is one of the 10 worst weeds in the world.  This grass is an aggressive grower and forms colonies causing loss of productive forest areas, severe degradation of habitat, and economic issues.  Since its introduction in the 1900s, Cogongrass has spread to most of the counties in Florida.  Reproduction occurs through seed production and the creeping rhizome system.  This plant is prolific once established with the creation of a very dense rhizome system that retains water and releasing of allelopathic chemicals reducing competition from other plants. The main identifying characteristic is the off-center mid rib and its yellow green coloring.
Once this grass invades, it will quickly displace the native species and requires frequent and intensive controls.  Early detection is best since a small infestation is easier and cheaper to treat.  The larger infestations become more time intensive, expensive, and difficult.  There are treatment options for these infestations, make sure that specific instructions are followed and treatment is repeated.  For more information on the biology of this plant and various treatment options visit

Also, by contacting your local UF/IFAS Extension office for assistance and information.
For more information contact the author Brooke Saari, Sea Grant Marine Science Extension Agent, 850-689-5850

Photo courtesy Vic Ramey, UF.
Photo courtesy Vic Ramey, UF.


Hydrilla is a submerged plant that grows in dense mats up to the surface of freshwater habitats, including ponds, lakes, springs, and rivers.  Growing at the rapid rate of an inch a day and up to 25 feet long, hydrilla shades out beneficial native plants and clogs waterways, preventing flood control, boating, shrimping and fishing.  In dense populations, the plant can alter oxygen levels and water chemistry and survive in a wide variety of nutrient conditions, sunlight availability, and temperatures.

Originally found in Asia and introduced to Florida (likely through Tampa and Miami) in the 1950’s as part of the aquarium trade, hydrilla has become a very expensive problem for the state.  Millions are spent annually on chemical and mechanical treatment simply to maintain the plant.  Adding to the problem is the fact that it is still available commercially, even though it has been placed on the US Federal Noxious Weed List.

Methods of control include mechanical harvesters and chopping machines (although fragments of hydrilla left in the water can regrow), introduced insects and fish (particularly the Chinese grass carp), aquatic herbicides, and lake drawdowns. Hydrilla is often transported from one body of water to the other by unknowing boaters moving fragments of the plant left on boats, trailers, or live wells, so learning to identify the plant and cleaning boats before leaving the ramp are helpful in prevention.  Visit the Extension Hydrilla IPM site for more helpful tips at:

For more information contact the author Carrie Stevenson, Coastal Sustainability & Natural Resources Agent, 850-475-5230.