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This giant salvinia was found on Toledo Bend this past summer. (Submitted Photo/Courtesy of John K. Flores)

Recent freezes will impact invasive plants

This past summer, in early August, I spent a day fishing largemouth bass on Black Lake near Natchitoches.
There was one thing interesting about this trip. It was the first time I actually had seen a “drawdown,” on a lake designed to kill giant salvinia – an invasive plant species that chokes lakes and waterways.
It’s strange seeing water so low you actually can see the root system of cypress and tupelo trees. But, drawdowns are not uncommon, and through the years, lakes like Bisteneau, Saline Lake, Lake Martin, False River and others all have seen this method used to control salvinia.
By removing water, the idea is large expanses of the invasive plants will dry out and die. Moreover, it can be treated with chemical herbicides more easily.
The Louisiana Department of Wildlife and Fisheries has an annual budget of $6.9 million that is spent controlling invasive plants. The budget is not limited to just fighting giant salvinia. There are other invasive plants that include cogon grass, hydrilla, Chinese tallo trees and water hyacinth that if not controlled, can wreak havoc on the environment.
Water hyacinth and giant salvinia not only clog bayous and canals, disrupting boat traffic, but also block light to native species plants. This degrades water quality and harms wildlife.
Herbicides control harmful invasive plants by blocking photosynthesis, rupturing plant cell membranes and blocking amino acids during their growth. However, depending on what herbicides, ratio of mixtures and extent of infestation, it can cost $100-$200 per acre to combat undesirable plants.
The problem with herbicides and also pesticides used to control weeds and pests is water pollution. If used improperly, they can contaminate ground and surface water.
There’s also safety to consider. Humans and animals can be exposed to the effects of chemical poisoning where it enters the body through the skin by indirectly swallowing or breathing. Accidental spills and spray-drift are big concerns.
For a number of years, the Louisiana Department of Wildlife and Fisheries has utilized weevils to help control giant salvinia with varying degrees of success. On Lake Bisteneau this past year, the department released 180,855 weevils. The problem with weevils is they are susceptible to severe cold and die off.
It just goes to show sometimes it takes Mother Nature to step in and provide a little assistance to mankind.
For the past couple of weeks, much of Louisiana has seen quite a few days of subfreezing temperatures that have impacted invasive aquatic plants like giant salvinia and water hyacinth.
The first time I saw the effects of severe cold weather on invasive plants was in 1989 when the temperature never got above 32 degrees for three days and had fallen into the low teens overnight. What a mess that was on the St. Mary Parish populace, where schools were closed, roads were iced and pipes busted everywhere.
If there was one consolation, it was the marsh was almost void of water hyacinth the following spring and summer. In fact, it was a couple of years before the evil plants presented a problem again – at least in the region I frequented.
There have been other freezes since. The most recent back in 2010.
In a recent press release from the Louisiana Department of Wildlife and Fisheries titled “Freezing Temps May Provide Temporary Reduction in Giant Salvinia,” LDWF Secretary Jack Montoucetm and state Rep. Gene Reynolds, D-Minden, noted they saw what appeared to be a die back of salvinia on Lake Bistineau. Great news for north Louisiana anglers, as Bistineau is an extremely popular fishery in that part of the state.
Invasive species like water hyacinth and giant salvinia are aggressive and often double in size during the peak of the summer, where temperatures are in the mid-90s. Unfortunately, you can do all the herbicidal spraying you like and put hundreds of thousands of weevils on them but you’re never going to eradicate them.
With another go-round of cold weather this week in the parish, I say bring it on. I might complain a little, but, in my mind, I say, give those invasive plants another dose of freezing temperatures. It’s nature’s way of leveling the playing field. Personally, I can bundle up with a few base layers of clothing.
Another thing I know is the cold weather didn’t come to stay. It came to pass.
EDITOR’S NOTE: Flores is The Daily Review’s Outdoor Writer. If you wish to make a comment or have an anecdote, recipe or story you wish to share, you can contact Flores at 985-395-5586 or or visit his Facebook page, Gowiththeflo Outdoors.


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