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Corn+Soybean Digest

Soybean Rust Will Arrive – Eventually

For U.S. soybean growers, it's not a matter of if soybean rust will hit the states, just a matter of when. And the more educated growers are about the fungus, the better prepared they will be to manage it when that time does arrive.

Soybean rust is an aggressive fungus similar to the rust fungi that cause wheat leaf rust and corn leaf rust. The pathogen originated in China and has since made its way to Africa and South America, leaving yield losses and millions of dollars spent in fungicide treatments in its wake. It's had a home in Hawaii since 1994, but it has yet to be found on the North American continent. Nonetheless, Ohio State University plant pathologists and the Ohio Soybean Council want growers to be on top of the pathogen.

"Estimates from Brazil range from $750 million to $1 billion in additional fungicide costs each year to control soybean rust," said Anne Dorrance, an Ohio State plant pathologist. "In a $4- and $5-bushel marketplace, that would be devastating to our producers. With current $10 soybean prices we could manage it, but it's still a concern. Speculation on potential yield losses in the United States ranges from as high 50% or more. Rust will change the way we produce soybeans – when it gets here."

The American Soybean Association and the Ohio Soybean Council are sponsoring a Regional Soybean Rust Meeting on July 22 at the Der Dutchman Restaurant in Plain City, Ohio, to help soybean producers become better acquainted with soybean rust.

Topics will include an overview of the disease – what it is, why producers should be concerned and what the government and industry is doing to address rust – what Ohio farmers need to know about soybean rust; application methods; fungicide availability and efficacy; and a Brazilian grower's perspective on his personal account of battling soybean rust. The meeting will run from 9:30 a.m. until 2 p.m.

"Our educational process has been in the works since January," said Susie Turner, executive director of the Ohio Soybean Council. "The American Soybean Association started it with a conference in St. Louis, and this summer took the show on the road for a series of seven meetings. We are hopeful soybean producers will put what they learned to work in preparation for soybean rust."

Dorrance encouraged growers to learn more about the pathogen and how it can be controlled and, most importantly, be proactive in scouting their fields.

"The reality is everybody should be scouting their fields. We've always been saying that," she said. "The main thing is that if they see something unusual on their plants, don't ignore it. Take a sample and send it away for analysis,"

To encourage growers to be more vigilant in diagnosing the disease, the Ohio Soybean Council, as part of the check-off program, has agreed to pay for samples to be tested at Ohio State's C. Wayne Ellett Plant and Pest Diagnostic Clinic.

"The Ohio Soybean Council and the soybean check-off want to help producers be preemptive in their approach to soybean rust," Turner said. "Paying close attention to their fields will go a long way in dealing with this disease, and this is just one way the soybean check-off is paying off for producers."

Growers who wish to send plant material to the C. Wayne Ellett Plant and Pest Diagnostic Clinic for testing should adhere to the following guidelines:

  • Place leaf, stem, or pod samples in a self-locking plastic bag and store in cool conditions.
  • Samples that must be kept under ambient conditions should be sealed in a paper bag to prevent mold growth. Once they can be refrigerated the paper bag can be placed in a self-locking plastic bag.
  • It would be helpful if leaves were placed between paper towels or pieces of paper to keep them flat. Care should be taken to ensure the outside of the bag is not contaminated by the sample.
  • Record the collection information on a piece of paper included with the sample. Information should include the date, exact location of the field and sample location within the field, county in which it was collected, host plant and collector's name and phone number.

Send samples to the following address: Soybean Rust-CWEPPDC, 110 Kottman Hall, 2021 Coffey Road, OSU, Columbus, OH 43210.

"We need to take steps to get this fungus diagnosed because it's a select agent, meaning that no one in the United States is supposed to have this," Dorrance said. "It also spreads quickly; it keeps depositing spores on plants before it can even be identified, so we want to treat it as quickly as possible and make the right fungicide recommendation depending on the stage of progress."

When scouting fields, growers should concentrate on areas with low-lying water and in areas with heavy fog. The first signs of the disease are the development of small tiny brown or red brick spots on the top of the leaves. The spots are less than half the size of a leaf hair. On the underside of the leaf, the lesions break open to reveal cream-colored spores. The use of at least a 20X hand lenses is recommended to help spot the lesions and spores.

The process will continue as long as conditions are favorable for fungal development, causing premature defoliation leading to yield losses, fewer seeds per pod, decreased number of filled pods per plant and early maturity.

There are registered fungicides that work well against soybean rust. U.S. Environmental Protection Agency Section 18 Quarantine Exemption requests have been submitted by several states to expand the number of fungicides available. Ohio is one that has submitted a request.

"The catch on the Section 18s is that they do not go into effect until soybean rust is found in the continental U.S.," Dorrance said. "In addition, the products are expensive; Ohio State researchers are currently studying ways to help producers save on application costs."

Ohio State plant pathologists, the Ohio Department of Agriculture, and the U.S. Department of Agriculture Plant Protection and Quarantine have drafted a management plan in the event soybean rust were to cross continental borders. Researchers believe the mode of transmission to be by four specific routes: the Central American land bridge; hurricane winds via the Caribbean; spores on debris in shipments of seed or meal; or an act of bioterrorism. The latter two are the least likely to occur.

For more information on soybean rust, contact Dorrance at (330) 202-3560 or by e-mail at [email protected]; or Ohio State plant pathologist Pat Lipps at (330) 263-3843 or by e-mail at [email protected]. Information also is available in OSU Fact Sheet AC-0048-03, available on Ohioline by logging onto

To learn more about submitting samples to the C. Wayne Ellett Plant and Pest Diagnostic Clinic, contact Nancy Taylor at (614) 292-5006 or by e-mail at [email protected].

Additional information about the Regional Soybean Rust Meeting is available by contacting Susie Turner at the Ohio Soybean Council at (614) 476-3100 or by e-mail at [email protected].

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