Campbell Vaughn: Privet, kudzu and hydrilla - a trio of invasive plants

Hydrilla (Hydrilla verticillata) was introduced to the U.S. from Asia as an aquarium plant, but is now taking over our waterways. An aggressive grower, is can double its biomass every two weeks in summer conditions. MICHAEL HOLAHAN/FILE

I am a native Augustan and think my home is probably the best city in the best state in the best region of obviously the greatest country in the world. How could I be so lucky?

 

No reason to ponder too much … because I am here and I plan on not going anywhere. But change is inevitable; sometime for the good and sometimes change brings challenges.

Our native landscape is full of wonderful specimens that create ecosystems that work well together. When we disturb these landscapes intentionally or unintentionally, problems tend to arise. Like the introduction of exotic species to native areas that can sometimes wreak havoc.

Exotic plants — meaning anything that is not native to the local area — are causing major issues in our landscape.

An invasive species can be any kind of living organism that will thrive unchecked. Examples include amphibians, plants, insects, fish, fungus, bacteria, or even an organism’s seeds or eggs. They can harm the environment, the economy or even human health. Species that grow and reproduce quickly, and spread aggressively, with potential to cause harm, are given the label of “invasive.” They can directly out-compete natives for things like food, space, and sunlight. They sometimes prey on native species, preventing them from reproducing or even killing their young. Some exotics cause or carry diseases.

Indirectly, invasive species can change the food web by destroying or replacing native food sources with food of little to no value as well as altering ecosystems by decreasing the diversity of native species. Some invasives can change the chemistry of the soil or the intensity of natural wildfires.

What are some examples of exotic invasives in our local plant world?

I am a UGA grad and a Bulldawg to the core. I work for the University of Georgia College of Agricultural and Environmental Sciences. My favorite team plays football ‘Between the Hedges’ in Sanford Stadium on Saturdays in the fall. It pains me that the plant that is used as “the hedge” is one of the most dangerous plants to our environment today.

Ligustrum sinense or Chinese privet is the plant that makes up the famous hedges in Athens. The plant was introduced from Asia as an ornamental for landscape proposes and has escaped. Chinese privet can destroy native habitat because it is fast growing, large, dense and evergreen, which means it provides constant shade. That shade will choke out sunlight needed for other smaller plants to survive. It grows in full sun or shade, which means it can grow deep into the forest as well as in the wide open. It is drought tolerant, but can handle heavy moisture, meaning it does well on a riverbank or in dry highland areas.

Chinese privet is also a prolific seeder. And to add insult to injury, the seed floats. So when a privet seed washes down a drain to a stream it floats until it lands on the bank where it begins to grow. When the banks become full of privet and the seed drop, the water will rise and will move the plant further up the banks as well as downstream.

Control is difficult. Cutting and spraying can be effective. My friends at the Silver Bluff Audubon Center and Sanctuary said they have had good success spraying glyphosate with a surfactant in the winter when all the other plants have lost their leaves. But they admit it is going to be a lifelong battle.

Another invasive we are all very familiar with is kudzu. Kudzu was originally brought to the U.S. as a novelty plant for the 1876 World’s Fair in Philadelphia. It didn’t have a lot of use in agriculture, so it was not actively grown. In 1935, as dust storms damaged the prairies, Congress declared war on soil erosion and enlisted kudzu as a primary weapon. More than 70 million kudzu seedlings were grown in nurseries by the newly created Soil Conservation Service. The SCS offered as much as $8 per acre to anyone willing to plant the vine.

By 1945, more than one million acres of kudzu was planted. And then we learned that this deciduous climbing vine was capable of growing 100 feet. In ideal conditions, it can grow 12 inches a day. The roots can reach depths of 16 feet. Talk about opening a can of worms. Since kudzu was used for erosion, steep banks were often the ideal place to plant this aggressive vine. Constant mowing is an effective control method in flatter areas but is next to impossible on heavy grade inclines.

Cows love kudzu and it is nutritious, but like mowing equipment, bovine don’t do well on steep banks either. Kudzu doesn’t strangle plants like the myth says but actually shades everything it covers to death. Besides mowing and cows, spraying kudzu July thru September with multiple applications in multiple years is about the only other effective way to maintain control.

Introduced to the US from Asia in the 1950s as an aquarium plant, Hydrilla (Hydrilla verticillata) is now taking over our waterways. Hydrilla can grow in lower light conditions than nearly all other aquatic plants allowing it to survive at greater depths. That means hydrilla can grow in water of a few inches to 30 feet.

Hydrilla breaks apart into small pieces and will produce a new plant off a section sometimes less than 1 inch long. These small pieces can survive for up to 7 years in the water or dry land before sprouting. Hydrilla is a very aggressive grower, sometimes doubling their biomass every two weeks in summer conditions. This invasive underwater plant will crowd out native plant species, impedes irrigation systems and can bring some boats to an instant stop. There have also been instances of swimmers getting tangled in hydrilla’s dense mats of vegetation and drowning.

When hydrilla gets too dense, it blocks out sunlight and causes the water underneath to become low in oxygen, which can result in the death of fish and other plants. Another concern is an algae that grow on hydrilla has been linked to a neurological bird disease called Avian Vacuolar Myelinopathy (AVM) that is killing bald eagles as well as some other waterfowl.

According to the U.S. Army Corps of Engineers who oversee Clarks Hill Lake, our very large, local reservoir on the Savannah River, hydrilla now covers 53 percent of the 1,200 miles of shoreline and 7 percent of the total surface of the 71,000-acre lake.

A possible control method for hydrilla includes the introduction of the sterilized triploid grass carp to eat the plants. These carp can eat their body weight in hydrilla daily for their lifespan of about six or seven years. This grass carp method has been very effective in a program to eliminate hydrilla from Lake Murray. The problem with introducing an exotic fish to our waterways is what if the carp prefers eating something besides hydrilla — like our native plants?

Chemical controls can be effective when sprayed according to labels but can be almost an impossible task to cover a lake as large as Clarks Hill.

Be careful with these plants. There might end up exactly where you don’t want them.

Reach Campbell Vaughn, the agriculture and natural resources cooperative extension agent for Richmond County, by e-mailing augusta@uga.edu.

 

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