Since 1994, SePRO Corporation has been an innovative leader in aquatic plant management. After turning the tide against highly-invasive hydrilla (Hydrilla verticillata), SePRO’s flagship product, “Sonar” (fluridone), became the world’s leading brand of aquatic herbicides. David Tarver was a big part of that success. For over 30 years, I have known David and found him to be an excellent source of information on aquatic resource management. That is why, when he asked me to test four of SePRO’s chelated copper products (“K-Tea,” “Nautique,” “Komeen,” and “Captain”) on Pomacea insularum, I was flattered and excited. I promised speedy, conclusive results. How hard could it be? And so, the adventure began.
Bench tests are inexpensive, repeatable, and fairly reliable, though efficacy is always better in a container than in the environment. One simply places the test organisms in identical containers with identical volumes of water, varies the rate of the test chemical, waits 48 or 96 hours, and determines mortality. If, say, a fish rolls over, flairs its opercula, and no longer moves with eyes bulging, it is safe to say that the concentration of test chemical is lethal. Simultaneously, if fish are thriving in the “control” container with no test chemical added and in containers with lower concentrations, the lethal rate can be determined. No problem. Bring on the snails!
Of course, life is full of surprises. Unlike fish and other aquatic organisms, apple snails can present a number of unique challenges to the researcher. First, like fish, Pomacea also have an operculum, but it is not a bony flap protecting the gills; it is a well-sealed “trap door” that chemicals cannot penetrate. Secondly, Pomacea are amphibious, not aquatic. If an apple snail detects a toxic chemical, it can simply crawl out of the test solution. Thirdly, Pomacea are strong enough to push the tops off of containers and crawl away. Finally, a dead apple snail with its operculum closed looks exactly like a live one for many days. As I told David, those are the reasons (excuses?) a simple experiment took me 9 months and 14 trials!
From the first four trials in the fall, it became clear that “Captain” had an edge on the other products that couldn’t be explained by the concentrations of the active ingredient, as metallic copper: Captain (9.1%), Nautique (9.1%), Komeen (8.0%), and K-Tea (8.0%). So, as winter approached, all I had to do was focus on one product, determine the lethal rate, repeat the trial a few times, and report the results. It seemed simple, until I realized that water temperature played a key role in efficacy. At 20o C, all test animals survived, but all died (except control animals) when an identical test was repeated at 28o C. Obviously, the lethal effects of copper to Pomacea are directly related to metabolic rate, but in a greenhouse with only partial control of temperature, precisely repeating bench tests proved impossible.
I did come away with some tentative, experimental results that are worth reporting, however. First, as mentioned above, I suggest using “Captain” to control exotic apple snails. Perhaps, it is the “double chelation” that makes it more lethal by keeping it in solution longer, but it stands above the rest. Secondly, treat when water temperatures are warm (>270 C or 800 F). Of course, that will require more caution regarding non-target damage, i.e. “fish kills.” Third, because Pomacea can completely “clam up” for at least 24 hours, split treatments make sense. Fourth, coordinate physical removal with treatments, if practical. The snails should become vulnerable to hand-picking, as they move to areas shallow enough to extend their snorkels or to even leave the water.
What about the rate? The maximum label for “Captain” is 1.0 ppm (A.I.) or 3 gallons/ac-ft. (see below), but Pomacea insularum were vulnerable at much lower rates. In fact, higher rates may be counter-productive in that snails tended to close their opercula. At 230 C, the snails produced mucus at 0.2 ppm and, at 0.4 ppm, they lay on the sides with opercula open. After 96 hours, 0.4 ppm was lethal at that cooler temperature. At 270 C, 0.2 ppm was lethal after 48 hours. As mentioned earlier, bench test tend to over-estimate toxicity compared to the natural environment. Therefore, if you want to play hard-ball with exotic apple snails, treat with “Captain” at 0.3 to 0.5 ppm A.I. twice, 24 to 48 hours apart.
I am concerned about presenting these tentative results. Someone needs to fund Dr. Linda Nelson at USACOE/WES to conduct more detailed and controlled time/concentration research on chelated copper and exotic apple snails (Hint: SePRO). In any case, “Captain” appears to be your best bet, but carefully read the label. I hope to be able to try this product in the field soon and will report back on the results. My last suggestion is to read my earlier post about copper, entitled “The Copper Question.” It is dangerous to fish, if not used carefully, and is rather non-selective in terms of invertebrates. The environmentally sound way to use copper is seldom. Posted by Jess Van Dyke
P.S. I have no relationship with SePRO, financial or otherwise. My thoughts are my own. You are responsible for the careful use of any pesticide.
Label for “Captain”: http://www.sepro.com/documents/Captain_Label.pdf
SePRO Corporation: www.sepro.com