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Rust Is Here; Get Ready To Respond

Editor’s Note: The following special report was compiled by the editors of Corn and Soybean Digest, a sister publication of Delta Farm Press.

Crop News Weekly: A Special Soybean Rust Report compiled from USDA and soybean industry news reports

Table of Contents

1. Rust Is Here; Get Ready To Respond

2. International Sources Say “Plan To Spray”

3. What Will Control Cost And What Fungicides Are Available?

4. On Alert: Symptoms Of Soybean Rust

5. Where Rust Is Expected To Spread

6. Rust’s Impact On The Economy

7. Links To Rust Resources

Rust Is Here; Get Ready To Respond

For months soybean experts have said it’s not a matter of if soybean rust will arrive in the U.S. but when, and that question was answered on Wednesday, November 10, 2004, with USDA’s announcement that Asian soybean rust (Phakopsora pachyrihizi) spores were discovered in soybean plots at a Louisiana State University research farm near Baton Rouge.

It is believed this year’s active hurricane season brought the wind-borne spores into the U.S., officials say. Soybean rust causes early leaf defoliation of plants, resulting in fewer pods and seeds, and yield reductions as high as 80%.

But despite the discovery of this dreaded disease in the U.S., soybean researchers say the timing of it’s arrival is a best-case scenario for two reasons: 1) since most soybeans have already been harvested across the country, the impact of the fungus to the 2004 U.S. soybean crop should be minimal, and 2) with several months before the next growing season, producers have adequate time to prepare to combat the disease next spring.

“Producers should not panic. We do have the tools available to manage this disease,” says David Wright, director of production technologies for the Iowa Soybean Association.

Those tools include early disease detection and aggressive fungicide control programs, which producers are urged to become familiar with this winter. Rust-resistant soybean varieties are not yet available. Most importantly, as this disease becomes more widespread in the U.S., those who have seen soybean rust ravaged fields in other countries stress that producers will need to take immediate action against this fast moving disease. In the words of one crop consultant, “You have hours rather than days to apply fungicides.”

International Sources Say “Plan To Spray”

Soybean growers in Australia, Asia, Africa and South America have been combating soybean rust for years, and from their experience say applying fungicides early will be U.S. producers’ best defense.

Brazilian Eloi Marchett, who manages Carolina Farms, a 63,000 acre operation near Rondonopolis, Mato Grosso, says, “We start spraying for Asian rust at the R4 stage right through R6.” They use four planes to aerially apply the rust-fighting fungicides at a cost of about $22/acre. Despite the expense, Marchett believes it’s simply the cost of growing crops in the soybean mecca of central Brazil, and he reports that those who didn’t spray lost 50-60% of their crop.

In South Africa, where soybean rust was first discovered in 2001, plant pathologist Neal McLaren says spraying has been generally effective for controlling rust as well. He has also researched row widths to see if wider rows dry sooner and reduce the fungus’ ability to spread, but says it didn’t make a difference. “Rotating with corn doesn’t help stop rust’s progress either,” McLaren reports.

Instead, he suggests farmers plant a small plot of a shorter maturity soybean variety as an indicator crop, so if rust hits, they have advance warning, and says, “If you’re in a borderline area, and not sure you’ll be hit by rust, indicator crops are critical. In endemic areas where you know you’ll have problems – spray.”

What Will Control Cost And What Fungicides Are Available?

Soybean rust could cost American soybean growers millions of dollars annually in combined spraying costs and yield losses, according to industry analysts. As an example, since rust was first discovered in South America in 2001, the extra fungicide costs that Brazil’s farmers pay to control it range from $750 million to $1 billion a year.

Most experts gauge fungicide application costs for U.S. farmers at $15-20/acre. However, if soybean rusts infects the crop at the early reproductive stage, two or three applications could be necessary and cause those costs to climb.

Presently there are two active compounds registered for control of soybean rust in the U.S. – azoxystrobin (Quadrisâ) and chlorothalonil (Bravo WeatherStik â and Echo 720â) – found in products made by Syngenta and Sipcam Agro.

Nearly half a dozen additional active ingredients that would be effective against rust have also been requested for labeling approval under Section 18 permits from the Environmental Protection Agency. At least two of these have been approved and others are being considered, reported APHIS senior program official Matt Royer in a November 10, 2004 teleconference.

Approval of these additional compounds should help improve availability of fungicides for rust control and help offer better resistance management, according to South Dakota State University Extension plant pathologist Marty Draper.

Meanwhile, soybean rust research continues throughout the world to learn more about the method, timing, and number of fungicide applications for the most effective, economical control of the disease. Researchers are also working to identify more chemical compounds for controlling rust and are hopeful rust-resistant soybean varieties will be available within five years.

On Alert: Symptoms Of Soybean Rust

With the first confirmed case of soybean rust in the U.S., growers across the country are asked to be on alert for signs of the disease. Because the disease is spread through wind-borne spores it is difficult to contain, but early detection during the growing season next spring will be critical to help minimize the impact of the disease.

The primary symptom to watch for is brown-colored spots on the soybean leaf. In the early flowering stages, these microscopic spots are the size of a pinprick and initially appear on the underside of the lower plant leaves. The lesions gradually increase in size and become tan or brown clusters of raised bumps on the leaf, as well as on the stems and pods. Once the lesions appear, the soybean leaves can yellow within a week to 10 days and drop off the plant.

Straightforward as it sounds, USDA-ARS scientist Monte Miles does caution producers that the disease can be difficult to identify as it can be confused with brown spot, bacterial pustule or bacterial blight.

A key difference, however, is that as a bacterial pustule matures it breaks open with a linear crack, whereas the soybean rust pustule opens with a circular pore in the top center of the lesion. Soybean rust lesions will also multiply and form together into small clusters, whereas with bacterial pustule each lesion is a distinct, single spot.

Producers who think they see symptoms of soybean rust in their fields are encouraged to contact their county extension agent or university plant disease diagnostic center immediately.

Where Rust Is Expected To Spread

Although the initial soybean rust discovery has only been confirmed in Louisiana, USDA officials are concerned that the disease could be more widespread. “Based on preliminary models we feel that the entire Gulf Coast region needs to be surveyed. It’s a bit vulnerable,” Ric Dunkle, Deputy Administrator for the Animal Plant Health Inspection Service (APHIS) said in a November 10, 2004 teleconference.

To determine the current extent of the disease, USDA has already dispatched its soybean rust detection assessment team, composed of scientific experts and regulatory officials, to the Louisiana location to scout the remaining portions of the state’s unharvested soybeans and provide recommendations on what further efforts are needed.

Through previous computer modeling and climate data, researchers suspected soybean rust would appear in the U.S.’s southern tier of states first because of its moisture, high humidity and moderate temperatures – which soybean rust thrives in. But no one is certain how the disease will over winter and where it will re-appear next spring.

“The rust spores will likely survive in places like southern Florida and the Gulf Coast where it remains green,” says USDA’s Glen Hartman. Host legume plants such as kudzu, yellow sweet clover, and kidney beans, are known to over-winter the fungus. But research suggests that soybean rust will not over-winter in the cold climates of northern soybean-growing areas.

This means from year to year the impact of rust could vary. “One year spores may blow all the way to North Dakota, other years it may stay in the South,” says Hartman.

“The risk of an outbreak during the next growing season will depend on how early soybean rust emerges in the southern U.S. and how quickly prevailing weather conditions promote the dispersal of soybean rust spores,” says American Soybean Association President Neal Bredehoeft.

USDA reports that it has several active research programs predicting potential dispersal of soybean rust based on climate and wind patterns. These models will be available at the USDA-APHIS website at to assist producers in tracking where soybean rust has been identified. Rust’s Impact On The Economy

The November 10, 2004 announcement of the first case of soybean rust in the United States “will have an impact on prices and production in the year ahead,” says Rick Brock, an economist and editor of The Brock Report.

“Even with large supplies, prices of soybeans will experience some wild swings in the months ahead,” he predicts. Specifically, Brock says this news does nothing to change the fact that there is an excessive supply of old crop soybeans and that the overall price trend will remain down for them. However, he says new crop soybeans will receive support from this news, so expect bear spreading in old/new soybeans.

But, most importantly, Brock says this news could result in producers shifting a significant amount of acres from soybeans to corn this spring. “With many farmers making seed selections now, this news couldn’t have hit at a more significant time. With such an acreage shift, the biggest impact of this news will be a bearish price move in corn,” he says.

USDA’s Chief Economist Keith Collins says he expects the news will have no effect on the U.S. soybean exports. “Our biggest market is China. Brazil, which has had ongoing problems with soybean rust, exports there now. We expect this will have no effect at all on our export markets,” Collins said in a teleconference.

United Soybean Board Chairman Criss Davis, a Wisconsin soybean farmer, is also optimistic. He says, “Like farmers in other rust-infected countries, U.S. soybean farmers will adjust and take the necessary steps to manage the disease, and the U.S. soybean industry will survive.”

Links To Rust Resources

Find more information about soybean rust at these websites:

e-mail: [email protected]

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