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.

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.