AgriLife Today highlights salvinia weevil work on Caddo Lake

AgriLife Today, Texas A&M AgriLife's news media outlet, published a story this afternoon highlighting the impacts of the giant salvinia weevil at Caddo Lake this year. In the article titled "AgriLife project weevils damaging invasive giant salvinia at Caddo Lake," they highlight the progress made in the effort to establish weevil populations on the lake and document the impacts they are having on the current giant salvinia population. To read the full story, visit http://today.agrilife.org/2013/11/22/agrilife-project-weevils-damaging-invasive-giant-salvinia-at-caddo-lake/.

Weevil impacts at one of the release sites in November 2013. Open water and salvinia darkening in the background is caused by weevil damage to the plants.

Last Year's Weevil Impacts Bigger than Expected!

Last Friday, Dr. Allen Knutson and Lee Eisenberg made it out to the Back Lake/Bird Roost area of Caddo Lake where weevil releases made in 2012 to confirm the presence of suspected salvinia weevil damage. What they found was extremely encouraging. The salvinia mat at this site was almost completely destroyed with only a few primary and secondary stage plants present over approximately 10 acres or more. 

The density of weevils present at this site confirms that weevils are responsible for this damage. Samples processed from this site averaged 77 adult weevils per kilogram of sample. With about 40 weevils per kilogram of salvinia being the target density to achieve salvinia control, this threshold has been far exceeded.

Since no weevils were released at this site in 2013, these finding prove that the weevils successfully over-wintered at this site on Caddo Lake this past year.In fact, more weevils made it through the winter here than anticipated! Now we can only hope that weevils continue to survive the winters. If so, the weevils' impact can be expected to grow in the coming years!

Go forth and prosper weevils!

2012 weevil release site showing extensive weevil damage and only scattered primary and limited secondary giant salvinia present. Weevils overwintered at this site and have impacted 10 acres or more! (photo by Dr. Allen Knutson, November 1, 2013)

Last Year's Weevil Making Their Presence Known

In the summer of 2012, the primary weevil release site was in the Back Lake area of Caddo Lake. This site was chosen as it is a relatively isolated area of the lake with little boat traffic, it maintained water throughout the 2011 drought and has a dense Cypress break that provided a relatively stable habitat for the weevils. Flow in this area is also relatively calm and typically results in floating vegetation staying in place. One downfall of this release site is the difficulty in getting to this area when lake level drop. Toward the end of 2012 when the water level dropped, it became impossible to enter this site by boat and the team had to wade in to sample weevil populations.

Fast forward one year to 2013. The Back Lake area was abandoned as a release site due to it inaccessibility during low lake levels. That said, this area has been checked out this year to see if the weevils released last year remained in the area and if they were having any impact on giant salvinia.

The short answers to those questions are Yes and Yes! Photos taken at this site show considerable damage to the giant salvinia at this site and a decent amount of open water present as well. We will be going out to this site in the next few weeks to collect samples so the weevil density can be counted and will also survey the surrounding area to see if any other weevil damage can be found.

Weevil damage at the 2012 weevil release site in Back Lake. No weevils were released at this location in 2013.

This find is really encouraging as it shows that the weevils released in earlier years survived the winter in large enough numbers to have a noticeable impact on giant salvinia. While this is only a small success, it is still a success!

Weevils Making an Impact on Caddo

Now that summer is officially over and we move toward the winter months salvinia weevil numbers in the release site have increased to the point where obvious plant damage from the weevils can be seen. Over the course of the spring and summer months, more than 50,000 weevils have been released into an isolated area of Caddo Lake. This may seem like a lot, but when you have about 7,000 or 8,000 acres of salvinia, 50,000 weevils don't cover much ground.

Controlling, or impacting salvinia with weevils is essentially a numbers game. You must have a high enough weevil density, a a sufficient number of weevils per kilogram of salvinia before visible damage is obvious. A weevil density of about 40 adult weevils per kilogram of salvinia is typically that magic level. And the good news is that the weevils we released this year have finally gotten to that point.

According to Lee Eisenberg, the weevil density in July was about 6 weevils per kilogram. By August the density was up to 15 per kilogram and increased to 34 in September. The October sampling hasn't been completed yet, but photo evidence suggests that weevil numbers have now surpassed 40 per kilogram.

The photo below was taken the first week of October and clearly shows a "sick looking" area of salvinia in the release site. Additionally, weevil damage is obvious moving away from the release site as well.

Weevil damage to giant salvinia at the release site in early October 2013

While this is only a small success, it is still a success that shows the utility of salvinia weevils. It also reiterates the need to have more weevils on Caddo Lake. Additionally, the facts that weevil reproduction is driven by temperature and that the point in the year that population numbers reach the 40 per kilogram threshold is driven by when reproduction begins highlight the need to find weevils that are adapted to colder climates and reproduce at colder temperatures.

Additional Support for Caddo coming from Harrison County Commissioners

In yesterday's Harrison County Commissioner's Court meeting, the court approved an additional $2,000 to "support the Cypress Valley Navigation District's eradication and research efforts regarding the critical invasion of giant salvinia on Caddo Lake" according to an article by Robin Richardson in today's Marshall News Messenger.

Additionally, the Labor Day weekend fundraiser hosted by the Greater Caddo Lake Association netted more than $10,000 that will go toward helping control giant salvinia on the lake.

Harrison County Judge Hugh Taylor said he hopes that these local contributions of additional funding will encourage other entities to help with the control efforts as well.

One thing is for certain; every little bit of additional funding that goes to Caddo Lake will certainly help.

Support for the Fight Against Giant Salvinia Spreading

Just like Giant Salvinia, support for any and all efforts to fight this floating aquatic invasive plant is spreading. In a Saturday article from the Marshall News Messenger, additional funding from the Harrison County Commissioners Court was on the agenda for their Monday, September 8th meeting.

US Congressman Louie Gohmert who represents the area also provided his support for the efforts and need to continue them out at Caddo Lake. Not only did he encourage everyone to visit Caddo Lake and enjoy the lake's unique natural beauty, he also commended the efforts of the Center for Invasive Species Eradication's weevil rearing operation at the Caddo Lake National Wildlife Refuge and the work being done with the salvinia weevil. As the Congressman mentioned, the salvinia weevil does show promise for being able to manage giant salvinia levels in lake at some point in the future, but it will take time and a large number of weevils....both of which are in short supply. 

For now, research at the weevil rearing facility is focused on producing weevils and trying to identify a more cold tolerant strain of weevil that may be more able to withstand the sometime harsh winters that Caddo Lake can experience.

Congressman Gohmert takes a closer look at the salvinia weevil during an August 2012 visit to the weevil rearing facility at the Caddo Lake National Wildlife Refuge

In addition to support from elected officials, local support has greatly increased as well. People are volunteering time and resources to try and get a handle on the giant salvinia issue. Hopefully, weevil production capacity will increase through this increased interest and a step closer to managing giant salvinia can be taken.

Until then, keep up the good fight. And to borrow the "Take Care of Texas, It's the Only One We've Got" tag line from TCEQ and Kevin Fowler; Take Care of Caddo, It's the Only One We've Got"

Support for Weevils Grows...So does Giant Salvinia

This year has turned out to be a bad one for Caddo Lake in terms of giant salvinia coverage. Recent estimates have put the total number of acres covered in the Texas portion of the lake alone somewhere north of 6,000 acres. This level of infestation has drastically reduced use of the lake as boats easily get stuck in the floating mats of giant salvinia that cover the upper ends of the lake.

On a positive note, local support has grown significantly and the use of salvinia weevils is now viewed as the best, long term solution to the problem. In fact, the Greater Caddo Lake Association is hosting a benefit barbeque this Labor Day weekend that will expand the production capacity of weevils around Caddo Lake. An article in Sunday's Marshall News Messenger provides details of the event and further describes the dire situation at Caddo Lake this summer. If you can, please make plans to attend this great event and help support efforts to protect this beautiful lake.

Giant salvinia completely covers Boat Road C on Caddo Lake. Similar coverage of salvinia is present across more than 6,000 acres of Caddo Lake in Texas this summer.

Caddo Lake Giant Salvinia Control Program Updates

It has been a while since the last blog post, but rest assured that the fight against giant salvinia at Caddo Lake has been in high gear. With a relatively mild winter experienced this last year, giant salvinia levels on the lake coming into the spring were already nearing their highest levels in years. One positive of the mild winter was that weevil populations did survive the winter; however, higher water around the first of the year dispersed the remaining weevils widely across the lake.

Extensive giant salvinia coverage during May 2013 along boat road C near Joe Moore Hole

On the biological control front, one weevil release has been made from the Caddo Lake Salvinia Weevil Rearing Facility so far this year and a second release is being planned for the near future. An estimated 34,400 adult weevils were released along with an untold number of larvae and eggs. These weevils were released into backwater areas of the lake where they are least likely to be disturbed.

Weevil research has continued as well and is showing promising results:

- Small frame studies showed that salvinia weevils were able to reduce giant salvinia biomass by 50%

- A "Chill Coma Recovery Test" was conducted to evaluate salvinia weevils resuscitation time following an extended period freezing. Weevils from Australia resuscitated first followed by those from North Texas (Lewisville), South Louisiana (Houma) and from Florida. This suggests that weevils can adapt to localized weather conditions to some extent.

- "Solid Freeze Time Trials" were also conducted to evaluate the weevil's ability to tolerate weather extremes. Weevils were frozen solid for 24, 30 and 36 hours respectively and survival was documented. At 24 hours, survival was good for all weevils; however at 30 hours, Australian weevils survived far better than any weevils from the U.S. At 36 hours of freezing, weevil survival in all samples was greatly reduced.

- Efforts are also underway to collect weevils from higher elevations (cooler areas) in their native ranges in Argentina. Once received, their genetic make up will be evaluated and they will be subjected to "Chill Coma" and "Solid Freeze" tests to determine their ability to tolerate cold weather extremes.

The Problem Spreads

Earlier this week, an article in the Austin American Statesman revealed a growing problem in northeast Texas lakes....giant salvinia. According to Texas Parks and Wildlife Biologist Lynn Wright, lakes with recently reported giant salvinia infestations include Lake O’ The Pines, Gilmer, Murvaul, Wright Patman and Lake Welch.

This recent rash of infestations highlights the need to raise awareness about the dangers of this plant. It's rapid growth rate and lack of natural enemies in Texas give it a competitive advantage in almost any water body. Preventing new infestations is much easier than managing infestations once they arrive and as such TPWD is asking boaters to be extra vigilant about checking and cleaning their boats and trailers both before they launch and after they load.

 

To read the full article in the Statesman, click the link below.

http://www.statesman.com/news/sports/troublesome-plant-continues-to-spread-in-texas-lak/nWHkH/  

How Should Homeowners Deal with Salvinia?

In a recent article in the Marshall News Messenger titled "Before treating salvinia, residents must file paperwork", Tim Bister, Texas Parks and Wildlife Department's district supervisor and fisheries biologist in the Caddo Lake area discussed appropriate steps for homeowners and landowners around Caddo Lake to take if they want to fight giant salvinia on their own.

Caddo Lake is a public water body and as such, is managed by the state.  To deal with nuisance or invasive aquatic vegetation like that commonly present at Caddo Lake, the state requires that a document known as an Aquatic Vegetation Treatment proposal be filled out. What these documents do is outline the type of aquatic vegetation (floating, emergent or submerged), the target aquatic vegetation species name, the estimated amount of aquatic vegetation acreage to be treated, and the proposed treatment type (mechanical, biological or chemical). A map also accompanies these treatment proposals as well and helps TPWD ensure that there aren't any conflicting treatments planned.

While the article provides more specific information about Aquatic Vegetation Treatment proposals, it is always a good idea to contact the TPWD District office to discuss plans. In the Caddo Lake area, TPWD's District Office is located at 3802 East End Blvd. So., Marshall, Texas 75672. You can also contact them by phone at (903) 938-1007.

http://www.marshallnewsmessenger.com/news/before-treating-salvinia-residents-must-file-paperwork/article_50f99050-e992-55b3-bf62-409eab8f50de.html

Cautiously Optimistic About Progress

Through the summer and into the fall salvinia weevils were released by the Center for Invasive Species Eradication team and local volunteers in the upper portions of Caddo Lake where giant salvinia had firmly established itself.  While results were not dramatic, optimism is building that weevils are having an impact on giant salvinia. Lee Eisenberg described this small success in a recent article in the Marshall News Messenger.

http://www.marshallnewsmessenger.com/news/researcher-cautiously-optimistic-weevil-is-eating-salvinia/article_c8d23f7a-87c7-5751-9ae0-b33abd6c4cc3.html

Efforts will continue in the spring with the release of additional weevils into the back water areas of the lake in hopes of weevil populations expanding enough to yield visible results.

Lee Eisenberg wades through damaged salvinia in September 2012. The browning of the salvinia indicates that it is not a healthy plant and is in the process of dying.