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.

Interagency Giant Salvinia Control Team Meeting Highlights

On October 16th, 2012 the Interagency Giant Salvinia Control Team convened in Karnack at the community center to discuss recent research findings, speak of control successes and plan for the future. Representative from the Caddo Lake Institute, Cypress Valley Navigation District, Louisiana Department of Wildlife and Fisheries, Louisiana State University Ag Center, Northwestern State University, Texas A&M AgriLife Research and Extension, Texas Parks and Wildlife Department, Texas Water Resources Institute's Center for Invasive Species Eradication, U.S. Army Corps of Engineers, and U.S. Fish and Wildlife Service personnel all spoke of efforts underway to combat giant salvinia biologically and chemically.

Biological control using the salvinia weevil  (Crytobagous salviniae) garnered the bulk of discussion. LSU Ag Center, Texas A&M AgriLife, Texas Parks and Wildlife and the U.S. Army Corps of Engineers are all working to mass produce and research the salvinia weevil and each had progress/success to report as well as planned research to discuss.


Some brief highlights from these groups include:

- effective giant salvinia control is being seen in several location including southern Louisiana and B.A. Steinhagen Lake near Jasper, TX.

- cold tolerance studies revealed significant differences in weevils from Texas, Louisiana, Florida and Australia to tolerate extended freezing

- chemical toxicity trial show that neither chemical nor surfactants commonly used to treat giant salvinia are toxic to the salvinia weevil

- chemical trials reveal effectiveness of chemical/surfactant combinations, but none tested are 100% mortal to giant salvinia


 Ongoing and planned work includes:

- evaluate what factors cause weevils to take flight; assess how well they can fly and what distance they can cover

- work to import weevils from colder climates such as the Argentinian highlands or southern Brazil 

- evaluate combined biological and chemical treatments and evaluate control success

- test impacts of aerial chemical applications in winter through dormant tree canopy


Collectively, the meeting was filled with positives and all parties involved were optimistic about the progress being made. With fair weather and time, the salvinia weevils seem to be well on their way to making a significant dent in giant salvinia infestations. The threat of cold temperatures loom though, and more work to identify strains of the weevil that can tolerate these colder temperatures and begin reproducing earlier in the spring are critical to the successful use of weevils in areas like Caddo Lake that experience periodically cold winters. 

Weevils Numbers Increasing on Caddo

As a part of the efforts to use biological control to suppress giant salvinia at Caddo Lake, monthly surveys are conducted to evaluate weevil populations at the salvinia weevil release site. During the last sampling event conducted on September 20, 2012 by Texas A&M AgriLife Extension Service scientists Dr. Allen Knutson, Dr. Abhishek Mukherjee and Mr. Lee Eisenberg discovered considerable giant salvinia browning. While this is not the drastic reduction in salvinia like what was seen at Lake Steinhagen, this is still proof that the weevils are working.

Lee Eisenberg collects salvinia samples on 9/20/2012 to evaluate salvinia weevil density. The browning of the salvinia here is caused by salvinia weevil damage.

Samples are collected by gathering salvinia in large Ziploc bags. These samples are returned to the lab at the Caddo Lake National Wildlife Refuge where they are weighed and subsequently dried in Berlese funnels. The salvinia is held in a metal funnel and a light/heat source is applied above the salvinia which dries the salvinia and causes the weevils to migrate away from the heat. In this case, the weevils move down and into a Mason jar where they are easily counted.

Berlese funnel used to count salvinia weevils. 

In this and all sampling events, 16 samples are processed each weighing in at 500 grams, or 0.5 kilograms. In total, 178 adult weevils were collected during this event yielding a density of 22 weevils per kilogram of salvinia. This is really good news and shows that weevil numbers are rapidly increasing on the lake. In fact, the weevil population has increased over 500% during the month since the August sampling when only 33 weevils were collected. Another positive finding is that almost 19% of the weevils collected were brown in color indicating that they are very young. These young weevils and other weevils hatched between now and the end of the growing season are those most likely to survive all the way through the winter due to their early stage in life.

So, we are hopeful that the winter will provide hospitable conditions to the weevils and that numbers on the lake will reach levels where effective control is seen. For now, we are pleased with the success that we are seeing and hope it continues.

Steinhagen Success

In a recent news release, the successful application of the salvinia weevil to control giant salvinia on Lake Steinhagen was showcased (http://today.agrilife.org/2012/09/20/weevils-successfully-destroy-acres-of-lake-invading-plants/). In a coordinated effort, the US Army Corps of Engineers (USACE) has been working with the Texas Parks and Wildlife Department (TPWD) Aquatic Habitat Enhancement Program staff from Jasper to use the salvinia weevil to combat giant salvinia on the lake. In late 2010, TPWD began releasing weevils on one area of the lake and through March of 2012 had released about 112,000 weevils. During this time, USACE did not apply chemicals to this area in an effort to see what the weevils were capable of. The pictures clearly describe their capabilities under good conditions.

Giant salvinia coverage on upper end of Lake Steinhagen, April 2012

In April 2012, giant salvinia was estimated to cover about 300 in this area of Lake Steinhagen. By August, the coverage area was conservatively estimated at only 150 acres and had led to open water in the middle of that area. What giant salvinia remains is isolated to the edge of the lake and mats of other vegetation. While the weevils haven't removed all the giant salvinia, they do show the ability to manage giant salvinia when it is present. 

Same area of Lake Steinhagen, August 2012

In an effort to get some more research bang for the buck, Dr. Abhishek Mukherjee of the Center for Invasive Species Eradication team worked with TPWD and USACE personnel to study the weevil population dynamics and document their impacts. Some of their findings describe why and how this successful reduction in giant salvinia came about this year.

In February and March 2012, documented weevil densities were in the 20 to 30 weevils per kilogram of giant salvinia range indicating that a sizable population of weevils had survived the winter on Lake Steinhagen. These relatively high numbers of weevils coming out of the winter enabled the population to expand rapidly. By late July, weevil numbers had more than doubled to just over 60 weevils per kilogram of giant salvinia. This number of weevils is widely considered the weevil density needed to suppress giant salvinia growth.

Ultimately, we hope to see similar success with biocontrol at Caddo Lake. The challenge is maintaining adequate weevil populations on the Lake through the winter. With Caddo Lake being more that 100 miles farther north than Lake Steinhagen, this may be difficult. Efforts at Caddo continue to explore ways to enhance the cold tolerance of the salvinia weevils and some live weevils were found late this past winter on Caddo, but their numbers were much lower than those on Lake Steinhagen.

So for now, we will continue releasing weevils on Caddo and hope for another mild winter that will allow their populations to persist and flourish early next spring. 

Congressman Gohmert and Staff Visits Weevil Rearing Facility

On Wednesday, August 15th, Congressman Louie Gohmert from Texas' 1st Congressional District visited the Center for Invasive Species Eradication's Giant Salvinia Weevil Rearing Facility as a part of his visit to the district during Congress' summer recess. The Congressman has been actively engaged and supports efforts to quell the giant salvinia infestation at Caddo and other lakes throughout his district. As a member of the House Committee on Natural Resources, Congressman Gohmert routinely deals with issues that impact our nation's natural resources.

While the Congressman has been on Caddo Lake many times and seen the perils of giant salvinia first hand, many of his Staff have not. This stop on the Congressman's trip gave some of his staff the opportunity to see giant salvinia up close and personal while also getting out on Caddo Lake to enjoy its unique beauty.

The first stop on the tour was the giant salvinia weevil rearing facilities green houses. The Congressman and his staff were briefed on the operations of the green houses and weevil production by Mr. Lee Eisenberg. Also mentioned was the great collaboration that has gone into the establishment and operation of the facility. The Texas Parks and Wildlife Department, the Caddo Lake Institute, U.S. Fish and Wildlife's Caddo Lake National Wildlife Refuge staff and many local volunteers were of great assistance to Texas A&M University personnel in getting the facility constructed and underway. 

Moving indoors to the Caddo Lake National Wildlife Refuge headquarters and the lab we have set up there, Lee continued discussions on how weevils are sampled. An adult weevil and weevil larvae were also available to view under a microscope. Adult weevils are about 2 mm in length, so getting a really good look at them requires magnification.

Following the brief stint in the lab, the visit to the weevil rearing facility wrapped up with a short presentation and video. Dr. Allen Knutson discussed work that he and Dr. Abhishek Mukherjee are conducting to evaluate the cold tolerance of the salvinia weevil. Initial findings indicate that weevils from different geographic locations are adapted to their specific climates making some more cold tolerant than others. The video shown (same video as the previous post) highlighted the current giant salvinia situation on Caddo Lake.

Before the Congressman and his staff departed, we took a short boat tour of Caddo Lake. Joining in on the tour was newly elected Texas House of Representatives Member Elect Chris Paddie. He will be representing House District 9 in the coming session. Given the time available, we weren't able to get the group out to the areas of the lake where giant salvinia is really bad. Regardless, everyone was able to truly enjoy Caddo Lake.

Video of Giant Salvinia and Other Invasives

On July 31, 2012, Mr. Jack Canson of the Caddo Lake Institute and Mr. Robert Speight of the Cypress Valley Navigation District ventured into the Clinton Lake and Bird Roost areas of Caddo Lake and shot some video of the current vegetation situation. The video was shot from a moving boat in the backwaters of Caddo, so it is a little fuzzy sometimes. 

What the video shows is somewhat disturbing in that it shows extensive amounts of giant salvinia along with plenty of other invasive plants. Aside from giant salvinia, alligator weed and American lotus are also problematic this year. In many cases, the alligator weed and lotus are so thick, that it is hard to see the giant salvinia. Anyway, watch the video and then read the rest of the post.

So the video shows some pretty extensive mats of giant salvinia and plenty of other aquatic vegetation. One good thing to note about this video is that salvinia weevils are actively being released into the Bird Roost area of Caddo Lake (where the worst of the giant salvinia was in the video). Two releases have been made this year and at least one more will be made before the growing season ends further increasing weevil numbers. Weevils have shown the ability to persist in this area of the lake through the winter and certainly have plenty of food/habitat here. As a result, weevil populations have the needed ingredients to expand on their own in this location. Additionally, this part of the lake is relatively isolated from the rest of the lake making an ideal weevil nursery.

As more weevils are released, chances of keeping giant salvinia in control increase; however, this is certainly an uphill battle. Continuing to treat giant salvinia with biological and chemical means while educating the public about the perils of giant salvinia are a must.

Please share this video with your friends and family and help show how this plant can take over a waterbody.

Aquatic Vegetation Management Webinar

The Texas AgriLife Extension Service will host a webinar on August 2nd to discuss aquatic vegetation management in private ponds. Dr. Michael Masser, Texas A&M wildlife and fisheries sciences department head and AgriLife Extension specialist will present the information.

To register for the webinar, visit http://naturalresourcewebinars.org or see the news article at http://tinyurl.com/cuzumgh  

One of the most common problems with aquatic vegetation management is proper plant identification. The webinar will discuss plant identification as well as integrated pest management approaches to deal with identified problems. Additionally, 1 CEU for TDA pesticide applicators licenses will be available: 0.5 for laws and regs; 0.5 general.