Aquatic ecosystems are vital resources for all forms of life on earth. They are compose of freshwater and marine habitats and support a wide range of plant and animal species.
As we seek to conserve our vital water resources, we are forced to confront the major threats to Earth’s aquatic systems. Four threats are widely recognized, and they are:
- Human exploitation and development,
- Climate change, and
- Invasive species.
The US government lists invasive aquatic plants as the leading threat to aquatic systems.
The difference between invasive aquatic plants and native aquatic plants
Invasive aquatic plants are non-indigenous or non-native to the habitat which they have invaded. In the new habitat, the invasive aquatic plants lack natural enemies and threaten the habitat and can harm or displace native species.
The invasive aquatic plants become established because they possess the following traits:
- Rapid growth
- High reproductive potential
- Highly efficient dispersal mechanisms
- Ability to alter growth in response to environmental conditions
- Capacity to tolerate a wide range of environmental conditions
- For more information read: Benefits of the Fine Line: Aquatic Organism and Alien Plant Invaders.
Similarities among aquatic plants
Invasive aquatic plants and native aquatic plants share three important growth habits. That is, aquatic plants may grow while totally underwater (submersed), on water surfaces (floating), or partially immersed in water (emergent).
Understanding the growing habit of an invasive aquatic plant is fundamental to adequately controlling the species.
10 Problematic Aquatic Plants to Watch in 2022
Aquatic Soda Apple (Solanum tampicense)
Native to Mexico and the West Indies, the aquatic soda apple was accidentally introduced to the United States in the 1970’s. It is also known as scrambling nightshade or wetland nightshade and is listed as a noxious weed in the United States.
Aquatic soda apple is an emergent plant that invades shorelines and wet soils and thrives in shallow river channels or flood plains.
Aquatic soda apple invades disturbed areas, grows over established native vegetation, and forms dense, tangled monocultures. Consequently, it is difficult to selectively remove from intertwined vegetation.
Aquatic soda apple produces seeds that are dispersed by birds, which increases its potential for spreading and invading other habitats.
There are no biological controls for aquatic soda apples, and mechanical or physical methods are not very effective.
Good chemical control can be achieved with applications of glyphosate, 2,4-D, or triclopyr.
Giant Salvinia (Salvinia molesta)
Native to Brazil, giant salvinia is an aquatic fern that was introduced to the United States by horticulturalists for use in aquariums and garden ponds in the 1990s. It is now classified as one of the world’s worst invasive species and is listed as a federal noxious weed in the United States.
Giant salvinia is a floating aquatic plant that thrives on the surfaces of calm waters. It grows rapidly and reproduces by vegetative fragments. Ultimately, it forms dense infestations that block navigation, cover native plants, and clog irrigation pipes.
Giant salvinia reduces oxygen content in water which can lead to fish kills.
One biological method, a weevil, has been shown to be effective against giant salvinia, whereas mechanical and physical control methods are not.
Chemical control of giant salvinia can be achieved with the application of diquat, fluridone, flumioxazin, glyphosate, or pyroxsulam.
Hydrilla (Hydrilla verticillata)
Hydrilla is native to Southeast Asia and was introduced to the United States as an aquarium plant in the 1950s. It is presently listed as a federal noxious weed in the United States.
Hydrilla become invasive when it was discarded into waterways by aquarium owners. As a submersed aquatic plant species, hydrilla was able to fill the habitat it infested before it was detected.
Hydrilla plants grow rapidly, by as much as 6 – 8 inches per day, in warm climates such as in the southern US states. It can cover entire water bodies within 1 – 2 years after its introduction in a body of water.
Hydrilla can block light and shade out native submersed aquatic plants and deplete oxygen in water that can lead to fish kills. In addition, hydrilla can impede navigation and other recreation activities on open water bodies.
A number of biological, mechanical, and physical control methods have been shown to be moderately effective.
Good chemical control of hydrilla can be achieved with application of endothall, diquat, bispyribac, fluridone, penoxsulam, or topramezone.
Hygrophila (Hygrophila polysperma)
Hygrophila is native to India and Malaysia and was introduced in the United States as an aquarium plant in the 1940s. It is now listed as a federal noxious weed in the United States.
Hygrophila grows as a submerged or emergent plant which thrives in wet soil and water that is up to 15 feet deep. In calm waters, hygrophila can form dense mats which block light for native plants and depletes oxygen in water that results in fish kills.
Hygrophila spreads vegetatively through its roots and stems, allowing the species to disperse itself easily and become established quickly.
Control of hygrophila is expensive and extremely difficult. There are few marginally effective biological, mechanical, and physical methods available.
Good chemical control can be achieved with applications of flumioxazin, diquat, endothall, fluridone, or 2,4-D.
Napier Grass (Pennisetum purpureum)
Napier grass is native to Africa and was introduced in the United States as a forage grass in the early 1990s.
Napier grass is an emergent grass species that grows on shorelines and in wet to dry soils where it forms clumps and can grow to a height of 12 feet.
Napier grass forms tall, dense growths that hinder boat launch and shoreline access. It also hinders flood control by blocking access to canals and impedes water flow.
Napier grass is deep rooted enabling it to tolerate drought, and the species propagates vegetatively via roots, rhizomes, and stem fragments.
There are no known biological control methods for Napier grass, while mechanical and physical methods provide only partial control.
Good chemical control of napier grass can be achieved with applications of glyphosate or imazapyr.
Para Grass (Urochloa mutica)
Para grass is native to Africa and was introduced as a forage grass species in the US in the late 1800s.
As an emergent plant, para grass thrives in wet soils and in shorelines. It grows up to 15 feet tall and forms dense tufts on shorelines. The tufts can break loose from shorelines and form floating islands.
Para grass provides little wildlife value, crowds out native plants, fills ditches and shallow canals, and impedes water movement.
No known biological control methods are available for para grass, while mechanical and physical methods provide limited control.
Good chemical control of para grass can be achieved with applications of glyphosate or imazapyr.
Torpedograss (Panicum repens)
A species that is native to Africa and/or Asia, torpedograss was introduced as a forage crop in the US in the late 1800s.
Torpedograss is an emergent aquatic plant species that thrives in dry land and shallow water no more than six feet deep. It displaces native plants in wet soils, shallow waters, and marshes, and can form thick mats that impede navigation and water movement.
Torpedograss can spread vegetatively via fragments of plant parts, extensive rhizomes, and via seed production.
There are no known biological control methods for torpedograss, while mechanical and physical methods provide only limited control.
Good control of torpedograss can be achieved with applications of glyphosate or imazapyr.
Water hyacinth (Eichhornia crassipes)
A native of South America, water hyacinth was introduced into the US by horticulturalists in the 1880s.
Water hyacinth is a floating aquatic plant species that thrives on water surfaces and grows rapidly, doubling its population in as little as two weeks.
Water hyacinth reproduces vegetatively by producing seeds and can be spread rapidly by wind and water movement.
Water hyacinth forms dense mats which can impede navigation and flood control. It also depletes oxygen in water leading to fish kill.
Whereas there are a few promising biological control options for water hyacinth, mechanical and physical methods provide limited control.
Good chemical control of water hyacinth can be achieved with diquat, 2,4-D, glyphosate, flumioxazin, pyroxsulam, copper, or imazamox.
Water Spinach (Ipomoea aquatica)
A native of China, water spinach was introduced into the United States as a vegetable crop in the mid-1990s. It continues to be spread worldwide by people who plant it as a vegetable crop and is listed as a federal noxious weed in the United States.
Water spinach is an emergent aquatic plant that can thrive on dry land and shorelines where it forms mats and is commonly found in ditches and canals.
Water spinach grows rapidly, forms dense canopies over other emergent plants, and can create floating mats on water surfaces.
There are no known biological control methods for water spinach, whereas mechanical control is discouraged because of the potential for starting new plants from fragments. Physical methods provide only marginal control.
Good chemical control of water spinach can be achieved with applications of glyphosate, imazapyr, or triclopyr.
West Indian Marsh Grass (Hymenachne amplexicaulis)
Native to Central and South America and the West Indies, West Indian marsh grass was introduced in the US in the 1970s.
West Indian marsh grass is an emergent aquatic plant species that thrives in wet soils and shallow water. It forms dense monocultures in marshes and along shorelines and displaces native grasses.
West Indian marsh grass is difficult to control when growing among native grasses because they are susceptible to the same control methods.
There are no known biological control methods for West Indian marsh grass, whereas mechanical control methods are impractical, and physical methods need to be combined with chemical methods for good control.
Good chemical control of West Indian marsh grass can be achieved with applications of glyphosate, imazapyr, or flumioxazin.
How can we control the problematic aquatic plants?
- The invasive aquatic plant species must be correctly identified.
- Upon correct identification, an understanding of the biology and ecology of the invasive aquatic plant will help optimize control efforts.
- For further information, read Understand the Enemy: Pest Biology and Ecology in Aquatics.
- Select the best pesticide product and formulation that will control the invasive aquatic plant species while causing little to no harm to non-targets and the environment.
- Determine what adjuvants are needed to optimize control of the invasive aquatic plant species.
- Read the pesticide label for instructions for using adjuvants, select the adjuvants needed, and prepare the herbicide spray mixture using the guidelines for proper mixing.
- For details read The ABCs of Tank Mixing Pesticides.
- Apply the spray mixture.
- Evaluate the success of invasive aquatic plant control.
- Repeat application of herbicide spray mixture, if necessary, evaluate success, and determine need for further management.
University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS), Center for Aquatic and Invasive Plants. 2021. Most Invasive Aquatic Plants. https://plants.ifas.ufl.edu/manage/ (Verified, December 12, 2021)
- Understanding the Enemy: Pest Biology and Ecology in Aquatics
- Control Invasive Aquatic Plant Species
- What are the Best Practices for Improving Aquatic Management?
- Preventing Algal Blooms from Taking Over Ponds and Lakes
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