Timely use of fungicides is currently the only tool to manage yield losses from the effects of Asian soybean rust. Other integrated pest management techniques, such as manipulating planting dates, rotating with other crops, and varying row widths, have not been proven to affect the course of the disease. There are also no available soybean varieties with resistance to this disease.
"Because so few soybean producers in the state have ever had to use foliar fungicides to manage diseases, many of them have been inquiring about Section 18 supplemental labels, as well as the toxicity profiles for these fungicides," says Bruce Paulsrud, specialist in pesticide safety education and plant pathology with University of Illinois Extension.
He points out that three families of fungicides have been labeled for managing soybean rust in soybeans as of the end of January 2005 – triazoles, strobilurins, and the nitriles. The triazoles include myclobutanil, which is used in Laredo EC and Laredo EW; propiconazole, which is used in Bumper, PropiMax EC, Stratego, and Tilt; and tebuconazole, which is used in Folicur.
The strobilurins include azoxystrobin, which is found in Quadris; pyraclostrobin, which is found in Headline; and trifloxystrobin, which is found in Stratego. And the nitriles, include chlorothalonil, which is used in Bravo WeatherStick, Echo 720, and Echo 90 DF.
"All of the triazoles and Stratego do not currently have soybean as a crop on their regular labels under Section 3," Paulsrud says. "Each of them, however, was granted a Section 18 supplemental label that allows the product to be used on soybean to protect against soybean rust."
Paulsrud emphasizes that these Section 18 fungicides are not new and untested. All of them already have full registration with the U.S. Environmental Protection Agency (EPA) for use on other food crops.
"If you wish to use a pesticide as directed by a Section 18 supplemental label, you must have a copy of the supplemental label in your possession at the time of use," Paulsrud says. "You can obtain these labels from your pesticide dealer, online label sites, or directly from the pesticide manufacturer. Remember that these labels specifically state where, how, and for how long the product may be used."
He notes that these Section 18 fungicide labels clearly state that a maximum of two total applications using approved Section 18 products collectively are allowed under this soybean rust Section 18.
"The bottom line is that you may not spray any Section 18 product or combination of these products more than twice per acre per season," Paulsrud says. "Like any pesticide, fungicides can be dangerous, so it's important to read and follow the instructions provided on the product container or label."
Paulsrud points out that the danger of any product is evaluated not only by its toxicity but also by the degree of exposure to the product. He suggests looking at the product label and Material Safety Data sheet (MSDS) when evaluating the relative danger of any pesticide.
"The mentioned triazole fungicides are all general use products," he says. "They have signal words ranging from Caution to Danger. Many of them can cause eye injury and most are toxic to fish and aquatic species."
The strobilurins labeled for Asian rust also are all general use products. They have signal words ranging from Caution to Warning. Several of them can cause eye injury, and all of them are toxic to fish and aquatic invertebrates. The chlorothalonils are general use products with signal words ranging from Caution to Danger. They can cause eye injury and are toxic to aquatic invertebrates and wildlife.
"The pesticide label and instructions provide specific and EPA-approved statements to help protect yourself, the environment, and the public," Paulsrud says. "It is important to use caution when interpreting toxicity information from various other sources. Evaluating the usefulness and meaning of human health and environmental studies is often particularly troublesome. We are all too often bombarded by bits of evidence and premature conclusions."
He adds that that well-designed and well-executed health and environmental studies take a good deal of time.
"Accurate conclusions are drawn from the 'weight of the evidence' from all studies rather than individual studies," Paulsrud says. "It is good for those of us non-toxicologists to be watchful but also careful that we don't draw premature and inaccurate conclusions."