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Corn+Soybean Digest

Be vigilant for soybean rust

USDA’s soybean rust announcement has farmers and others in the agricultural sector concerned with good reason, according to Purdue University specialists.

Experience from other areas where soybean rust occurs shows that yield losses can be substantial when the disease isn't controlled.

Shawn Conley, a Purdue Cooperative Extension soybean specialist, says, "Any hint of soybean rust means it's going to be in the growers' best interest to apply a fungicide because of how quickly this disease can move into a field and take it over. It has a very fast life cycle."

Conley says vigilance is the best defensive action farmers can take.

"Walk your soybean fields," he says. "If we look at what's available right now, there's not any genetic resistance for soybean rust in the U.S., so variety selection really isn't the answer. The most beneficial aspect will be scouting and timely application of a fungicide."

Fungicide applications have to be timely because pre-application isn't effective against soybean rust, and experience shows that it takes almost no time for soybean rust to infect an entire field.

Greg Shaner, a professor of botany and plant pathology, says, "It takes a week or so for an infection to produce more spores. Each of these spores can potentially cause a new infection."

If a producer chooses not to apply fungicides when they detect rust, the entire field could be lost, Shaner says.

The big question is whether or not soybean rust will make it to the Midwest by the next growing season. Shaner and others think it's possible.

"Studies of soybean rust in China and Brazil can provide some insight into what we can expect, but our climate and growing conditions are not the same as in those countries," Shaner says. "For instance, China doesn't have the strong jet stream winds that travel our continent. Those winds can transport spores quite readily."

Soybean rust will not overwinter in the Midwest. In the deep South, however, soybean rust can survive the winter on hosts like the kudzu plant, a weed that's prevalent across much of the South. Then, soybean rust spores could be carried by wind currents to the Midwest each spring, Shaner says.

The severity of yield loss from soybean rust depends upon when the disease becomes established. The most damage occurs when plants are infected early in their development.

"I think the first thing that growers need to realize is that we do have soybean rust in the U.S. now, but it's not time to panic," Conley says. "Don't make rash decisions about switching to corn or cornering the market on fungicides based on the limited data that we have in the U.S.

"If we look at South America, there's a lot of bean production down there. They're still able to successfully grow soybeans. We have to manage our production systems to control the disease and just be vigilant,” he says.

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