Guys, I sent an email to John and this is his response. They are doing more than we think and there is some good info in this email. He also mentioned that they had a meeting with USACE yesterday and he will try to post up about that. Based on the his info, the future sounds like it will get better from a management standpoint for sure. I will say, my opinion still is that the applicators are over doing it in some cases and causing some of the issues. If that turns out to be the issue atleast it can be identified and then fixed rather than so much going wrong that it's impossible to fix. It's a long email but worth the read, it's very informative.
Howdy Keith,
Thank you for reaching out to discuss the vegetation control issue further. 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.
Hydrilla will always be listed as an invasive species because it is a non-native plant and can create problems in some water bodies, especially the smaller, shallower lakes like such Sheldon Reservoir (60% covered in 2020) and Lake Raven (55% covered in 2017). This is also the reason hydrilla is listed as a prohibited species in Texas. However, just because it’s classified as invasive or prohibited does not mean that TPWD treats hydrilla on all water bodies. On some lakes, such as Sam Rayburn, Toledo Bend, Lake Fork, Choke Canyon, and Lake Amistad, hydrilla has proven to be a critical component in creating phenomenal largemouth bass fisheries and is not treated. Ultimately, the determination as to whether hydrilla is beneficial or problematic is the decision of the fisheries biologists for a given water body. For questions regarding hydrilla and hydrilla management you need to contact the fisheries biologist for the lake in question.
When vegetation is designated problematic by the fisheries biologist, the Aquatic Habitat Enhancement (AHE) team will work with the fisheries biologist(s) on the creation of a vegetation management plan to treat the problem area(s). Minimizing collateral damage is extremely important in the development of all vegetation management plans and the focus is to only treat what needs to be treated. For example, the current hydrilla control plan for Lake Raven is to treat all vegetation, hydrilla included, on the shoreline adjacent to the state park campsites (increase shoreline access) and treat hydrilla in the paddleboat cove (increase paddleboat access in the lake). The other two coves also have hydrilla, but it is less of access issue thus the objective here is to use an herbicide to create a boat lane through the hydrilla mat. Finally, hydrilla on the shoreline opposite of the state park is not treated and left for fish habitat. In 2020, TPWD treated a total of 241 acres of hydrilla across the state. All these treatments focused on boat ramps, designated swimming areas (hydrilla has been blamed for several drowning in the last few years), campsite access, and creating boat lanes through thick hydrilla mats. In the five years I have been the team leader for the AHE, there has never been a management plan to eradicate hydrilla from a public water body.
I went back read my original post and cannot find where I may have led you astray on herbicides are either over applied or the herbicide isn’t target specific. Herbicide use is a highly controversial topic throughout the world. I will agree that herbicides were the primary cause of the reduction of torpedo grass (haygrass) in Lowe’s Creek as well as Indian Mounds and a few other places in 2016-2017. As would be expected, this was very concerning and not what my team, the fisheries management team, or the anglers wanted. We met with the contractors and instructed them to start focusing on only treating mats of giant salvinia rather than spraying all salvinia plants encountered. At the time the giant salvinia was being treated with glyphosate, a systemic herbicide that is circulated throughout the entire plant. 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.
The total amount giant salvinia treated annually on Toledo Bend has decreased substantially since the cold weather in January 2018. Nighttime temperatures fell to the mid to upper teens during that event and decreased giant salvinia in Texas by over 90% at the time. Herbicide treatments have been able to maintain the giant salvinia on Toledo Bend and elsewhere across the state where giant salvinia is not creating access issues. In 2020 we have directed the contractors to treat only from the North Toledo Bend WMA south to Martinez Creek. The purpose for decreasing the treatment area is we wanted to see if beneficial vegetation would return if no treatments were conducted in an area. Additionally, we found giant salvinia weevils south of Martinez, primarily in Housen Bay and Six Mile areas and wanted to see if the weevils could maintain control. As of now the weevils in Housen Bay and Six Mile are keeping the giant salvinia under control. In January we sampled weevils in both areas and found weevil abundance was high enough to maintain control. However, that could change this weekend as the weevils do not tolerate extremely cold temperatures. Unfortunately, the salvinia can tolerate colder temperatures than the weevil.
To protect the beneficial vegetation, we switched herbicides, had the contractors focus on only treating mats of giant salvinia, and recently decreased the treatment area on Toledo Bend. We know that herbicides rapidly bind to clays and organic material (leaves, sticks, etc.) and broken down to the point where they no longer function as an herbicide. The small amount of herbicide entering the water column around the mats of salvinia or water hyacinth will be quickly diluted and not impact vegetation. All these things should have allowed non-target vegetation such as hydrilla and coontail to persist and even expand on Toledo Bend. 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.
I have had numerous discussions regarding Toledo Bend’s once abundant vegetation with the lake’s fisheries biologist. 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. One instance occurred at Coleto Creek Reservoir as water level increased 3.5 feet in one day because of a large rainfall event. This left the reservoir muddy and resulted in a large kill of hydrilla and Eurasian watermilfoil, most of which has not recovered as of present. Sam Rayburn experienced a large, lake-wide water level increase in January 2019 that remained through most of March 2019. Much of the upper end was muddy for several weeks. There was a subsequent rise in June 2019, again creating more muddy conditions in the upper end of the reservoir. By January 2020 there was hardly any submersed aquatic vegetation above the Hwy 147 bridge, however it is slowly coming back. These events on Coleto Creek and Sam Rayburn occurred in only one year and had major impacts on the vegetation in both reservoirs. Looking back at Toledo Bend where the muddy water events occurred for several years in a row, it’s easy to see how these events resulted in mass reduction of aquatic vegetation lake-wide, especially when you consider how delicate hydrilla is when if first begins to grow in the Spring. My office was made aware of lily pads disappearing on Toledo Bend this past summer after being abundant in the Spring. Our herbicide treatment records show the last time TPWD treated Housen Bay and Six Mile was December 2019 and it was November 2019 the last time any contracted herbicide treatments occurred. My team investigated the report and observed moth larvae feeding on American lotus pads in Housen Bay a couple of months in July 2020. The lotus pads above the water or on dry land did not have any marks on them but the pads on the surface of the water had large chew marks that resembled the chew marks of the tomato hornworm. In several places, the larvae had destroyed the American lotus patch. Last fall, several states began reporting moth larvae destroying elephant ear from Louisiana to Florida. This may explain why we have seen decreases in other species Toledo Bend such as the American lotus. Remember native vegetation has natural controls to keep it in check and sometimes these natural controls can go overboard.
As you can see, there are numerous factors that can lead to decreased aquatic vegetation in a reservoir. We have and will always adjust our herbicide-based treatment plan(s) to preserve as much fish habitat. However, sometimes despite our best efforts to preserve aquatic vegetation, nature takes over and we lose the majority of vegetative habitat.
I remember hearing about the dead turtles, but I do not believe herbicides were the cause as TPWD and other agencies treat aquatic vegetation elsewhere in the state and the country and have not seen any issue with turtles. Also, all herbicides must be registered and labeled by the EPA according to the Federal Insecticide, Fungicide and Rodenticide Act (
https://www.epa.gov/laws-regulations/summary-federal-insecticide-fungicide-and-rodenticide-act). Aquatic herbicides must be registered and labeled for use aquatic environments. Since the label must be approved by EPA too, then the label becomes the law for the use of that specific herbicide. Labels provide users with ingredients, safety precautions, human and animal hazards, environmental hazards, physical or chemical hazards, storage and disposal, product information, personal protective equipment requirements, water use restrictions (if any), herbicide application rates, and vegetation species affected. Thus, if there were cautions/warnings regarding use around turtles it would be on the label. The same thing for fish. The regulations are so specific that if a specific vegetation is not on the label, it cannot be used to treat that plant. This website will go into further detail about the aquatic herbicide testing, toxicity, and EPA registration (
https://plants-archive.ifas.ufl.edu...e-testing-toxicity-and-epa-registration/). I have attached the Tribune label as an example. Back to the turtles, it was probably a viral or bacterial infection that killed them.
As I alluded to earlier, herbicides rapidly bind to clays and organic material and are broken down, bacteria, point they no longer function as an herbicide. Glyphosate and diquat can bind to suspended clays and organic materials in less than 30 minutes. According to the label, glyphosate is not effective on submersed aquatic vegetation because of the rapid binding. However, we learned it was extremely effective on torpedo grass at Toledo Bend. Glyphosate is a systemic herbicide meaning it is absorbed by the plant and circulated through the roots, killing the entire plant. This differs from the contact herbicides that only impact the area of the plant the herbicide contacts. Remember in our torpedo grass study on Lake Sam Rayburn we saw contact herbicides affected the part of the torpedo grass that was above the water, but the torpedo grass underwater was still alive and growing. Unfortunately, there is currently not an EPA approved herbicide that only targets giant salvinia or water hyacinth. We have a suite of herbicides available for use that specifically have giant salvinia on the label. Unfortunately, each of them can affect non-target vegetation too. We weigh all the options and consequences before selecting an herbicide to use.
It would be great for all of us to meet and discuss these things over a dinner one night but with Covid restrictions that is not an option. As anglers the best thing to do is talk and work with the fisheries management biologists, create a Friends of Reservoirs group (
https://www.friendsofreservoirs.com/), initiate habitat improvement projects, and ask questions like you did with this email. Most of all please clean, drain, and dry your boat.
Thanks again for reaching out and I hope that I answered your questions completely but if not, please feel free to contact me via email or telephone.