High residues of endosulfan in burley are prompting researchers to call for a ban.
by Brandy Brinson
Endosulfan, an insecticide commonly used in tobacco production for the treatment of hornworms and other small insects, is being targeted for elimination. Extremely high residues of endosulfan are being detected in tobacco leaf, and that’s not acceptable to tobacco companies. Researchers say endosulfan is not even necessary for controlling pests during tobacco production, and that there are other, safer alternatives.
“I’ve been fighting this issue tooth and nail. Every company has complained about endosulfan residue levels,” says Gary Palmer, associate professor in the University of Kentucky’s College of Agriculture. “In fact, there is no company that has not contacted me about it.”
HIGH RESIDUES. The acceptable standard for endosulfan residues is 1 ppm. However, recent research shows residues as high as 30 ppm in burley.
Paul Denton, professor and burley tobacco Extension specialist at the University of Tennessee in Knoxville, conducted an experiment with burley leaf to measure residues of several different compounds—including endosulfan as well as MH, acephates, and others.
They measured all three stalk positions (cutter, leaf and tip) for two years at two locations—Greeneville, Tennessee, and Springfield, Tennessee. The experiment was conducted with the support of Philip Morris.
They applied commonly used pesticides and growth regulators at the highest legal rate, using maximum application rates, up to the seasonal total allowed by label. They made the last application at the label PHI and sampled the cured leaf for residues.
With endosulfan, Denton and his colleagues found the residues were unacceptably high. “We found residues at all leaf levels in the range of 5 ppm up to 38 ppm. The acceptable level is 1 ppm,” he says.
The mean residues at Greeneville in 2005 were 20.60 ppm at the cutter, 18 ppm at the leaf and 14.17 ppm at the tip. At Springfield the residues averaged 37.96 ppm at the cutter, 29.71 ppm at the leaf and 26.39 ppm at the tip.
It was disturbing to find residues this high. “I was surprised; any time residues are above 1 ppm, questions start to be raised,” says Denton.
The 1 ppm standard is now an international standard for tobacco production. CORESTA, an association promoting international cooperation in scientific research relative to tobacco, has been working to standardize good agricultural practices for tobacco production around the world. As part of those efforts, the Agro-Chemical Advisory Committee issued a list of guidance residue levels (GRL) for many insecticides and pesticides. The committee issued a GRL of 1 ppm for endosulfan. This was published in the CORESTA Guide No. 1 in December 2003.
BIGGER IN BURLEY. While endosulfan residues are a problem in both flue-cured and burley, the problem is much greater in burley because burley growers use more endosulfan than flue-cured growers. Researchers also theorize that residues of endosulfan are reduced somehow during curing.
“Endosulfan is also used for flue-cured, but as I understand, it is not as big an issue because it is neutralized during the curing process,” says Palmer.
Loren Fisher, assistant professor and tobacco Extension specialist in the Department of Crop Science at North Carolina State University (NCSU), says, “Residues for flue-cured are not as big of a concern as in burley. It’s uncommon to find high residues of endosulfan in flue-cured. We just don’t use a lot in flue-cured, and it is not used as widely as in burley.” As to whether the residues are reduced during curing, Fisher says, “that’s one theory, but no one knows for sure.”
WHY ENDOSULFAN? Endosulfan is primarily used for treatment of hornworms and aphids, which are small sucking insects. While it is effective in eliminating these insects, researchers say it isn’t necessary because there are better, safer alternatives.
Endosulfan is available today in a generic form. It was previously marketed solely as Golden Leaf, but now several companies produce it. Some of the brand names on the market today include Thiodan, Helena and Drexel. MANA of North America still produces Golden Leaf.
The biggest problem leading to high endosulfan residues is timing of the application. Many growers aren’t aware of when to properly apply the insecticide and are applying it as late as topping time. “I think [the problem] could be avoided altogether if endosulfan was used well before topping time,” says Palmer.
He says many growers are using endosulfan at this time unnecessarily. “A lot of farmers are putting in at topping time for good measure,” says Palmer. “One farmer came up to me and said he was just putting it in at topping time because he thought he was supposed to.”
If it’s unnecessary, then why do farmers continue to use endosulfan? The answer is that farmers aren’t aware of the issue with residues. They simply don’t know that it’s creating a problem.
Palmer says he is not sure why endosulfan ever became so widely used in the first place. “I never really recommended it because it’s so dangerous to the farmer.” And, he adds, “It doesn’t even appear to be one of the better chemicals.”
ALTERNATIVES TO ENDOSULFAN. There are plenty of other products that take care of hornworms, including several Bts as well as Denim and Tracer. Palmer says these are listed in UK’s Cooperative Extension Service’s Insecticide Recommendations.
For aphids, Palmer says, “if products such as Admire, Belay and Platinum are used, then farmers don’t need to apply endosulfan at topping time as aphids are inconsequential at this point.”
He says farmers should be using these products prior to transplant or putting them in transplant water. “Farmers have great results with these products and they don’t have a residue problem that I’m aware of.” There are clear, established guidelines for using these products.
There are also other alternatives to endosulfan that can be used around topping time.
However, if a farmer wants to continue using endosulfan, Palmer says he should explore application at different times and check for residue levels. “I’m almost certain we’re getting more than 1 ppm at topping time and even higher levels if the product is applied between topping and harvest.”
He recommends that farmers not ever use endosulfan at topping time. “If you’re going to use endosulfan, use it early.”
The most important thing is for farmers to stay educated. Palmer says, “There are a lot of alternatives now. They don’t need to kill everything that moves.”
LABELING ISSUES. Part of the problem with the lack of awareness has to do with the labeling of endosulfan. “The label says it can be used within five days of harvest of when you cut the tobacco,” says Palmer. “The farmers are not educated on this issue, and the fact that the label says something that contributes to achieving this kind of level doesn’t help.”
Denton says endosulfan should either be eliminated or looked at for re-labeling to indicate a longer pre-harvest interval. The current label allows for application within five to 13 days of harvest. Yet this is what results in residues that are above the acceptable limit. “You could be within the label and have serious residue issues,” he says.
Labeling is maintained by the U.S. Environmental Protection Agency (EPA). Companies retain their labels through a registration process. Unless the EPA or the chemical companies change the label, then it’s up to the tobacco companies to put out their own guidelines.
“I don’t know what we can do when there’s a chemical labeled like that,” says Palmer. He says agricultural dealers could stop carrying endosulfan, but that’s controversial. “I’d like to see the industry call for that product to be dropped for burley production.” He says such a mandate may not be necessary for flue-cured as the residues are not much of an issue.
Denton says he believes the tobacco companies will take action soon. “I feel pretty confident that it’s going to lose its label or buyers will prohibit its use, probably over the next few seasons.” It’s already happening on a global level; Philip Morris International has already said that it will not buy burley that has been treated with endosulfan.
Extension agents are issuing their own warnings and recommendations against using endosulfan. Fisher says Extension entomology specialists at NCSU have pulled the recommendation for using endosulfan for flue-cured. “It can still be used if it is labeled for it, but Extension entomologists do not recommend its use,” he says.
The University of Kentucky has added a warning regarding endosulfan to its listing in the Cooperative Extension Service’s Insecticide Recommendations. “We put a star by the five-day harvest note and say that farmers should not apply within 28 days of harvest, and should not spray in heat of day—when it’s most dangerous to farmers,” says Palmer.
In the meantime, folks like Palmer and Denton are working to educate farmers on the drawbacks and unnecessary use of endosulfan.
“What I’m telling growers is that endosulfan is of great concern. Buyers don’t want them to use it and there are better, safer alternatives,” says Denton.
Palmer says that the tobacco companies ought to take action if they want results more quickly. “I talk to a lot of farmers, but I can’t see them all!”