In my business, there is a lot of talk about native plants and their use in landscapes, and there is a lot more talk these days about non native plants. These days the conversation very often goes into a discussion about the destructive nature of these invasive aliens.
Hydrilla is one of our largest alien pest problems in the South. Hydrilla Verticillata is a native of the Asian, European, and African continents, and escaped into the Florida waters from the aquarium trade In the 1960's. Since then it has worked it's way throughout the South, and has even been involved in a number of drowning deaths. It clogs waterways making them impassable in some cases, is disruptive to recreational activities in lakes, and causes problems with water systems.
What makes Hydrilla so difficult? 1. It can reproduce vegetatively, so after being disturbed, it may transplant itself. This means that if it is broken into a thousand pieces, 500 new plants may result.
2. It has tubers, which can live in a state of dormancy for 4 years or more.
3. It has large quantities of seed, which can obviously be replanted, although we don't know a lot about seed viability.
4. Areas of the plant, can readily reproduce new adventitious plants in a short time.
5. It has few naturally occurring predators in our country.
6. It has an astonishing growth rate.
Treatment Issues: One of the problems we have when treating aquatic vegetation, is "fish die back". This problem is almost always caused by oxygen depletion, which is the result of dying and rotting vegetation, and not from the chemical itself. This can be prevented by treating no more than one half of the area at a time, and allowing sufficient time between treatments for the complete decay of the plant material.
What to Do If You Find Hydrilla In Your Private Lake: First, don't panic. It is not the end of the world. Early detection is an important first step. Next, make sure it is hydrilla, and not "coons tail" or some other weed. One of the main identifying features of hydrilla for me is the serrated edges, and the spine on the bottom side of the leaf whorl. If you have trouble identifying it, find someone who can. Don't take it to them, have them come to you since it is in the prohibited exotic species list in many areas, and is therefore illegal to transport in those places.
It would be good to report the presence of hydrilla in private ponds and lakes. This information could be helpful to your states authorities in several ways, particularly in tracking the spread of the problem. These days, it is most often spread by sprigs stuck in boat propellers, or in live wells, but can also be spread by the movement of water from an infested pond to another downstream.
You have several treatment options at your disposal. I will list them as: MECHANICAL: The actual physical removal of the plants. The plants have tuber type roots in the soil, and any of these left over can remain viable for several years. Broken stems from the plant can grow new plants at a very high rate, so if you break it into 100 pieces, it is likely that you will have fifty or so new plants. Mechanical harvest is a last resort.
BIOLOGICAL: At present, the only truly viable biological control, is the triploid grass carp. These are voracious eaters of hydrilla, but in a high concentration, they can also do away with a lot of vegetation that the pond or lake may need to stay healthy, thus eliminating food and cover for other fish. They rarely make much progress in the first year, and there is the risk of escape. They are sterile, but can eat a lot of vegetation in any new environment where they might find themselves. If this option is considered, you will need a permit from the TPW inland fisheries division and a barrier to prevent their escape.
CHEMICAL: Most of the chemicals used to control hydrilla, are some of the safest herbicides ever developed. In many cases this is the best overall choice. These chemicals, work rapidly, and degrade quickly. One thing to keep in mind, is that if you use your pond or lake for irrigation, you might want to make plans to avoid irrigating for a few days after treatment. Be sure to read and follow the label directions before making an application with any chemical. In some small bodies of water, the use of dyes for shading may be advantageous.
Other Options: There are other options, such as lowering the water level and then performing mechanical and chemical controls. In most cases this seems impractical. Most vegetation gets its start in shallow water, where sunlight penetrates to the bottom. If your lake level can be raised, that might help. If you can dredge the edge of the pond to increase the depth of the edges, this can help as well.
Most of all, to stem the tide of these alien pests, become informed. Check with your states parks and wildlife departments to find out what is lurking around in your "neck of the woods."