Spring Weevil Study Commences

It's documented that correct water temperature is critical for the development of salvinia weevils. As the water temperature increases from 62.6 F to 69.9 F many activities such as feeding, oviposition (egg-laying), and egg-hatch begin. However, spring temperatures (in a water body such as Caddo) at which these activities begin have apparently not been reported. Therefore, a study has begun to determine the temperature and date in which egg-laying occurs on Caddo Lake. It's hoped that the results will help further guide our efforts to control giant salvinia using weevils.

To do this, 30 cages (the same cages from the overwintering study) containing 12 adult weevils with fresh salvinia along with temperature loggers were placed on the lake last week. Each week for the next 10 weeks, three cages will be removed at random and the salvinia within will be extensively searched for adults, newly emerged adults (which will have a red color), and any larvae present (larvae will be found tunneling through the rhizome of the plant). We will be looking for the time and temperature at which "significant numbers' of larvae are present in all the cages.

Also, some recent local publicity regarding Caddo Lake and this project appeared in the Marshall News Messenger on March, 20, 2011.
http://www.marshallnewsmessenger.com/news/article_cca41eb6-52a3-11e0-bf42-001cc4c03286.html

Cold Winter Helped...Salvinia Expected To Recover

We've been fortunate this winter to have had a series of cold spells that knocked back the giant salvinia a great deal. It's expected that much of the dead, brown material that is floating will take several weeks to sink out of sight.
Despite this cold weather, we've found several very thick mats around the lake that show survival of green material under the insulating top layer. It's anticipated that these spots will be major expansion points as summer approaches. The first two pictures show the freeze damaged salvinia with green material showing through. These areas should provide good weevil sites for our early season stockings.


On another note, in late February, we completed the re-filling of our weevil tanks with Caddo Lake water. With the warm, sunny weather we've been experiencing lately, the giant salvinia in these tanks has been greening up nicely. Hopefully, our weevils will flourish and be ready for placement on the lake in the very near future!




















Finally, here is a recent article about the Caddo Lake salvinia project in the Winter 2011 edition of "TX H2O": http://twri.tamu.edu/publications/txh2o/winter-2011/controlling-invasive-weed

Caddo Lake Giant Salvinia Meeting - April 7, 2011

The next meeting of the Inter-Agency Giant Salvinia Control Team will take place April 7, 2011 at 1 PM in Karnack, Texas, at the Karnack Community Center. This meeting is will provide a platform for local, state and federal agencies to highlight what they are doing in the fight against giant salvinia and will hopefully foster further coordination between these groups.

More information on the Inter-Agency Giant Salvinia Control Team can be found at: http://www.salvinia.org/


There will also be a community update meeting for anyone who is interested regarding giant salvinia and other Caddo Lake issues at 6 PM on April 7th, 2011 at the Karnack Community Center.

A meeting agenda will be posted once developed. We look forward to seeing all of you there for the evening update meeting.

 

Giant salvinia mat in Tar Island, November 2010

Weevil Counting Using Berlese Funnels

These strange looking contraptions with lights on top are known as "Berlese Funnels". For our purposes, these funnels are used to estimate the density of weevils (numbers present per amount of giant salvina) located either on the lake or in our weevil rearing tanks.
To use these funnels, a pre-weighed amount of giant salvinia (fresh weight) is placed into the funnel(s) and the 40watt light bulb is turned on for 24 to 48 hours. The weevils, trying to get away from the drying light, fall through a screen and into a mason jar at the bottom of the funnel. By counting these weevils in the jar, we are able to extrapolate how many salvinia weevils are present in an area
of giant salvinia. Although a trip through the Berlese funnel is fatal for the weevils (there is ethyl alcohol at the bottom of the jars for preservation), their sacrifice is not in vain. The weevil numbers obtained from the funnels can tell us when we have sufficient weevil density to put out on the lake.

The funnels were run during the week of February 14, 2011 using samples from the tanks. Despite the very cold weather we've experienced in January and early February of 2011, we still have lots of weevils alive in three out of the four tanks. The one tank that is showing low weevil numbers never got a good population established. We should be able to restock it with weevils from another tank and get a good crop by the time we're ready to release them on the lake. For control of giant salvinia in a system, it's believe that 60 weevils per kilogram of giant salvinia is needed. However, it's believed that weevils should be released for control once they reach 30 per kilogram. One of our tanks is showing over 50 weevils per kilogram of giant salvinia, thus, the sooner we can get these bugs out on the water, the better. The important thing now is to keep these weevils alive and reproducing until it's time to release them on the lake. All in all, the fact that living weevils are present in the tanks shows that the greenhouses have done their job so far.

Big Green Break / Tar Island Salvinia Coverage Video (Fall of 2010)

This video clip was taken November 2010 during an airboat survey (piloted by the TPWD Jasper aquatic vegetation crew) through a thick giant salvinia infestation on Tar Island / Big Green Break on Caddo Lake. This area is a large cypress break located in the middle of the lake positioned on the Texas and Louisiana border. This is a known problem area and is one of the primary giant salvinia nursery areas on the lake. Giant salvinia typically moves downstream into this protected area from other major infestations. It is hoped that this area will become an important weevil release site at some point in the future.

Sorry about the shaky and wobbly footage...airboats are loud, bumpy, and generally difficult to videotape from when using a small, handheld digital camera borrowed from your wife. Notice that at some points, even the powerful airboat struggles to push through the choking giant salvinia mats.

Refilling Weevil / Giant Salvinia Tanks

We are currently in the process (half-way complete) of replacing the well water in our weevil tanks with actual Caddo Lake water. This water replacement is being done with the help of the Karnack VFD and their pump truck; the guys at the Karnack VFD have been extremely helpful in this project and are much appreciated. Lake water is being pumped from the "Starr Ranch" area of the lake on the shore of Goose Prairie.

The reason that we are converting over from well water to lake water is that the well water chemistry was too far from what giant salvinia prefers. The pH and alkalinity of the well water were such that we could not feasibly change the quality of  the water with the typical peat moss and muriatic acid amendments. As you all know, the water in Caddo Lake seems to be more than hospitable for giant salvinia growth, so this is the route we are going to take from here on out.



In addition to a conducive pH and alkalinity, Caddo Lake water also contains higher levels of essential nutrients and minerals as compared to the relatively sterile well water. Nitrogen and iron are critical giant salvinia growth, especially in the weevil tanks, and the lake water will give the salvinia the boost it needs to grow well in the tanks. When the spring growing season arrives, rapidly growing giant salvinia in the tanks will uptake much of the nutrients thus requiring the addition of supplemental fertilizers.

The well water does have the potential to be used in smaller, movable tubs that will be used for a "salvinia nursery" in order to re-stock the weevil tanks once the weevil-infested material is placed out on the lake. Smaller volumes of water are much easier to amend than our 6,000 weevil tanks are.

New Sign!!

A bright and shiny new sign for the Salvinia Weevil Rearing Facility was installed just outside of greenhouses at the Caddo Lake National Wildlife Refuge in Karnack, Texas. The sign is easily visible from the refuge visitor's center and will help to provide information about the weevil and its impacts on giant salvinia. This sign summarizes the project goals along with the biology of the salvinia weevil. If you're in the area, feel free to come to the main office located near the greenhouses and ask for a tour of the facility.

The Salvinia weevil rearing facility has also gotten some local press in the past week. February 2nd of every year is celebrated as World Wetlands Day and during this year's local celebration, an update on the activities going on with the salvinia weevil rearing facility was a part of the discussion. You can read the article from the
Marshall News Messenger regarding World Wetlands Day on Caddo Lake featuring the Caddo Lake Giant Salvinia Project at:
http://www.marshallnewsmessenger.com/news/article_a532fc74-301d-11e0-9872-001cc4c002e0.html

Also, please visit our frequently updated facebook page. From facebook ,you can search "caddo lake" or simply click the link below.

www.facebook.com/home.php#!/pages/Caddo-Lake-Giant-Salvinia-Eradication-Project/162588863767594