Soybean Rust Discovered in Oklahoma

Kansas farmers need to monitor their fields.

News that soybean rust has been found in several fields in northeast Texas, southwest Arkansas, and most recently south central Oklahoma, means Kansas producers need to be watchful for the disease, says Doug Jardine, Kansas State University Research and Extension state leader in plant pathology.

"This disease has the potential to cause significant soybean yield losses. The recent rust reports from Kansas' southern neighbors could mean that it will arrive sooner than expected in Kansas, so producers need to be vigilant in scouting for it," Jardine says.

Bryan County, Okla., where a sample was collected on July 13 and confirmed on July 20, is about 235 miles south of Coffeyville, Kan., he says. Since then, the disease has also been detected in Choctaw County, Okla.

As of July 30, the disease has never been detected in Kansas.

The latest findings in Texas, Arkansas and Oklahoma surfaced over just a two-week period, Jardine says. All of the incidents so far have been along the Red River.

Kansas State University maintains a network of 20 soybean rust sentinel plots strategically located across soybean producing areas of the state. These plots are scouted by county Extension agents and other university staff and are funded by a combination of U.S. Department of Agriculture funds and soybean check-off dollars.

Producers and consultants in areas of Kansas generally south of U.S. Highway 54 and east of U.S. Highway 81, particularly, should begin actively scouting for soybean rust in fields that have already begun to bloom, Jardine says.

"To scout for soybean rust, you should arbitrarily collect or observe a minimum of 100 leaflets from the lower canopy (older, main-stem terminal leaflets) in each field," he says. "Areas of the field that may be shaded, especially from the morning sun, are good places to look for rust. To observe pustules, a minimum 20X hand lens is needed, but 30X is better. Pustules will be found on the bottom side of the leaflets and have the appearance of small volcanoes within the lesion."

Scouting is currently more difficult in many areas of the state due to the presence of two other similar looking diseases, brown spot and bacterial blight, he explains.

For further information on the disease's symptoms and photos, Jardine encourages growers to view a University of Missouri Web site: extension.missouri.edu/explorepdf/agguides/crops/g04442.pdf.  

Producers or scouts can submit samples of suspect soybean leaves for evaluation through any county or district cooperative Extension service offices, says Jardine, who recommends:

  • Send 10-15 suspect leaves.
  • Place the leaves in a zip-locked plastic bag, and put that bag in another zip-locked bag. Seal both bags securely.
  • Attach a note or write on the outer bag that this is a soybean rust sample.
  • Do not add wet paper towels or other types of moisture to the bag.
  • Try to mail it in the Monday-Wednesday time frame to avoid the possibility of the samples spending the weekend in a hot post office loading area.

"There is no need to apply a fungicide at this time," Jardine says. "Doing so now may lead to having to make a second application later, if and when the rust actually arrives.

Soybean growers and industry people can track the spread of soybean rust on the USDA Legume PIPE Web site at www.sbrusa.net. This site also contains weekly commentaries from Extension specialists in each state on crop growth and development, disease progress and scouting and fungicide application recommendations. Additional information on soybean rust can be found on the Plant Management Network's Soybean Rust Information Center at www.plantmanagementnetwork.org/infocenter/topic/soybeanrust/.  

What is soybean rust?

Soybean rust was first found in the United States Nov. 6, 2004 in Louisiana.

The disease is caused by either of two fungal species – Phakopsora pachyrhizi, also know as the Asian species, and Phakopsora meibomiae, the New World species. The Asian species is the more aggressive of the two, and causes more damage to soybean plants, Jardine says.

The disease is spread by wind-borne spores capable of being transported over long distances.

Asian soybean rust was first observed in Japan in 1902, and was found throughout most Asian countries and in Australia by 1934.

TAGS: USDA Extension
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