Toledo Bend

[PMantle]

Some places are getting the grass back, I hope they don't start spraying again and wipe it all out.

They never sprayed for hydrilla, and hydrilla is not harmed by the salvinia spraying.

[fishnfireman]

They never sprayed for hydrilla, and hydrilla is not harmed by the salvinia spraying.

so what happened to the hydrilla?

[PMantle]

so what happened to the hydrilla?

High water, currant and turbidity. The chemicals sprayed for salvinia is effective on what y'all are calling haygrass(torpedo grass0, but has zero effect on hydrilla. Here is a quote from a long post made by a person self-described as: Being an avid bass angler myself and former TPWD fisheries management biologist for nearly 20 years in South Texas (I transferred from the Mathis office to the Aquatic Habitat Enhancement office in February 2016), I understand the concern of impacts to non-target vegetation when herbicides are used. Additionally, I understand how important hydrilla can be to a largemouth bass fishery. Choke Canyon Reservoir, one of the lakes I managed while in Mathis, was a phenomenal bass fishery when hydrilla was abundant. I know of eight 15+ lbs fish caught in 2009-2010 and talked to several anglers that had 50+ lbs with their best five. Hydrilla does make great habitat and bass fishing fun.

Glyphosate is not effective in the water column as it is rapidly broken down by clay and organic matter, thus having no impact on hydrilla, coontail, or other beneficial, submersed plant species. However, we suspected and later confirmed through an experiment that glyphosate was killing the torpedo grass. After learning this, we switched from glyphosate to diquat dibromide. In the experiment, we found that diquat would burn the top of the torpedo grass but leave the submersed part of the plant untouched. The torpedo grass would recover and new growth above the surface was observed two weeks after treatment. We did not observe any impacts on other species such as hydrilla, coontail, or other submersed species either. Diquat is a contact herbicide meaning that it only impacts the part of the plant where the herbicide touches. It is not circulated through the plant like a glyphosate. The contractors began using diquat to treat giant salvinia at Toledo Bend in 2017. We use diquat on giant salvinia in many other lakes across the state, including lakes Sam Rayburn and Caddo, and does not affect the non-target vegetation in these reservoirs. This last summer we had the contractors switch herbicides from diquat to penoxsulam to prevent giant salvinia from becoming diquat resistant. We switched the contractors back to diquat later in the fall as water temperature drops and plant metabolism decreases.

The herbicides used to treat giant salvinia on Toledo Bend are mixed in a tank with 100 gallons of water and sprayed over one acre of giant salvinia. For diquat, the mix is 0.5 gallons (0.5% solution) of diquat per acre of salvinia. Diquat can be used to control hydrilla but it must be injected into the water column and applied at a higher rate than what we are using on the giant salvinia. When treating giant salvinia with diquat, the herbicide is sprayed onto the mat. Some diquat will drip from the plant into the water but it is not enough to kill submersed vegetation as it is quickly diluted. Penoxsulam is being applied at 4 fluid ounces per acre and like diquat can be used to control hydrilla and other submersed species. But again, we are using it at a lower rate than needed to kill the submersed species and are applying the herbicide to the mat not the water column. Research has shown that herbicides are rapidly broken down in the environment by UV light (sunlight), microbes, and chemical reactions with dissolved molecules and organic matter in the water column. Typically, the half-life of diquat is less than 48 hours in the water column. While some studies show diquat can remain in the sediments for 160 days, it is not active as an herbicide.

We treat almost 2.5 times as much giant salvinia annually on Caddo Lake (~7,300 acres a year) and beneficial vegetation, including hydrilla is abundant there.

As much as people want it to be true that "they sprayed" the hydrilla, it's not only not true, but chemically non-feasible.

As to why the hydrilla was cut back, but not eradicated,

The best explanation we have for the disappearance of the main lake vegetation as well as the vegetation in the coves and bays is due to nature, primarily muddy water. In the Spring 2016, Toledo Bend experienced a large rainfall event that resulted in much of the main lake being covered with muddy water. For reference, water releases from the dam were near 200,000 cubic feet per second. By 2017 hydrilla and other submersed vegetation species were reduced to many of the coves and bays but spring rains in 2017 made most of these areas muddy. Housen Bay was muddy for several weeks in the Spring 2018. This same pattern has continued through 2019. Muddy water can be detrimental to hydrilla especially in the Spring when it begins to grow. I experienced this several times while I was a fisheries management biologist in South Texas.

Here is the link to the full discussion:
https://texasfishingforum.com/forums...ing-on-rayburn