Fungi-controlling chemicals that help soybeans fight off Asian soybean rust infection can hurt wildlife if the products find their way into streams and other bodies of water.
Farmers who spray fungicide on their soybean crops can reduce runoff risks by maintaining a safe distance from waterways, say specialists at Purdue University and the Purdue-based Office of the Indiana State Chemist (OISC).
"A lot of growers and commercial applicators have little or no experience with fungicides," says David Scott, OISC pesticide administrator. "Fungicides, in general, can have an impact on aquatic wildlife and endangered species.
"In that regard, what we're recommending for ground application is that fungicide not be applied within 20 yards of bodies of water, whether it be streams or lakes or ponds. For aerial application the recommendation would be to stay back at least 100 yards from those bodies of water."
The recommendations are based on voluntary setbacks outlined in U.S. Environmental Protection Agency Endangered Species Act bulletins.
Soybean growers in the United States could be using fungicide for the first time this year, should wintered soybean rust spread north from Florida, Georgia and Alabama.
Rust is an airborne pathogen that, if not controlled, can wipe out a soybean crop. For now, fungicide is the only control option available to farmers. Because of the possible rust threat, most fungicides approved for soybean application in the U.S. this year were granted emergency use exemptions by the EPA. The approvals are temporary, pending further EPA review.
The emergency approvals carry a separate product label than the labels attached to fungicide containers, Scott says. Most fungicides are labeled for use on vegetable crops, rice, cotton and other crops not grown in the Midwest.
"A Section 3 is the standard label that farmers and users have grown accustomed to," Scott says. "As we've said for 20-plus years, the label is the law and the user is bound to whatever the use restrictions are for that particular product. But for these emergency registration products, there's a Section 18 label.
"Many times the emergency use products have not been through the full regulatory review process, so some of the safeguards and evaluations have not been done. They may have less than a full label that farmers traditionally are used to seeing. However, farmers will be responsible for complying with both the Section 3 and Section 18 labels."
For instance, Domark 230 ME-brand fungicide has no Section 3 label because the product's active ingredient, tetraconazole, is not registered in the U.S. Domark's Section 18 label states that the product "may be toxic to fish and aquatic invertebrates. Š Drift or runoff from treated areas may be hazardous to aquatic organisms adjacent to treatment areas."
Among the wildlife that could be harmed by fungicide runoff are several endangered mussels found in rivers and tributaries across Indiana.
To minimize risks of contaminating surface water, farmers might want to avoid spraying soybeans planted close to waterways, says Greg Shaner, Purdue Extension plant pathologist.
"If a soybean field happens to abut a pond or a stream, it may mean as a farmer gets near that waterway the sprayer will have to be kept back a certain distance, to prevent these chemicals from getting into the water," Shaner says.
Rust on untreated soybean plants within the setback area could be a source of inoculum for the rest of a field, Shaner says. "However, there will be sources of inoculum in the general area that could serve as inoculum," he says.
Another Purdue specialist says he's confident farmers can protect both their soybean crops and the environment.
"We understand that these fungicides are critical this year to our soybean yields, to make sure that farmers are financially stable and to help in production," says Fred Whitford, director of Purdue Pesticide Programs. "We're just asking farmers to do what they've always done, and that is to be careful when using these products around water and other places, and keep it on site.
"If we do that, we wouldn't expect to have any problems whatsoever."
Additional information on fungicide labeling and application is available on the state chemist's Web site at www.isco.purdue.edu/pesticide/index_pest1.html ; or by logging onto the Purdue Plant & Pest Diagnostic Laboratory Soybean Rust Page, at www.ppdl.purdue.edu/ppdl/soybean_rust.html .