Rust Retrospective

Soybean Rust: What Happens When We Stop Looking?

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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The distinctive yellowing of soybean rust-infected leaves is hard to miss. But plant pathologists worry that after national funding to monitor it disappears next year, farmers could someday be caught off guard by the disease. (DTN file photo)

ROCKVILLE, Md. (DTN) -- University of Kentucky plant pathologist Carl Bradley wasn't hunting for soybean rust when he stumbled across it in Illinois, in a field in Williamson County in early September this year.

The disease was so far from Bradley's mind that it wasn't until he examined the samples back in his laboratory under a microscope -- for another disease, no less -- that he noticed the rust pustules.

The story is a revealing one, right down to Bradley's University of Kentucky affiliation and the fact that he was off the clock, on a weekend family visit.

Nobody in the Midwest is routinely scouting for soybean rust anymore. Next year, even the most rust-prone Southern states will stop receiving funding from the United Soybean Board (USB) to monitor the disease's progress. Gulf Coast states such as Alabama, Georgia, Louisiana and Mississippi may continue to receive some monitoring funds from their state checkoff boards, but even that is not assured in the future, said Auburn University Extension plant pathologist Ed Sikora.

"The important thing about losing this money is it means we'll be taking our eye off the ball," Sikora told DTN. "We won't have people out looking for soybean rust on a regular basis as their primary focus."

Does it matter?

It's true that after 12 years in the U.S., soybean rust has never made it north early enough to do economic damage in the Midwest. However, it has become a disease of prominence in the deep South, where upwards of 5 million soybean acres stretch between Texas and Georgia. With a warming climate and fungicide-resistant strains lurking in South America, soybean rust's threat to U.S. soybeans is not going to disappear, Sikora said.

"Without a major push for monitoring and management of this disease, I do think we'll see problems," he said.


When soybean rust spores first blew into the continental U.S. on the winds of Hurricane Ivan in the fall of 2004, everyone was prepared for the worst.

The disease had proved capable of decimating soybean crops in Africa and South America, Sikora recalled. Reports of up to 80% to 90% yield losses in those regions had American plant pathologists and farmers on high alert.

A 2004 report from the USDA's Economic Research Service gave chilling estimates on potential losses for U.S. soybean farmers: between $640 million and $1.3 billion in the first year of the disease's establishment and annual losses ranging from $240 million to $2 billion after that.

To monitor the disease, USDA provided the funding in 2005 for 320 "Sentinel" soybean plots in 35 states (as well as Puerto Rico) where scientists could track rust's spread. Later, with additional funding from state checkoff boards and other agencies, the network swelled to include nearly 700 monitoring sites across the country.

"We had weekly conference calls during the growing season to discuss what we were seeing with specialists from each state -- there would be 50 people on those calls somedays," Sikora recalled. "It was intense."

The funding source shifted over time, from the Risk Management Agency to the North Central Soybean Research Program and finally to the United Soybean Board.

The disease had a banner year in 2009, when it was reported in 562 counties across 16 states. "But that was the last year we saw real movement into the Midwest," Sikora noted. "By then, it was clear it didn't appear to be a major threat to the Midwest, so funding started drying up."

The United Soybean Board began funding only the most vulnerable states along the Gulf Coast, from Texas to Florida, as well as some mid-Southern states. By 2016, only six states -- Alabama, Florida, Georgia, Mississippi, Louisiana and Texas -- received any funds.

"We were informed we will not receive funding from USB in 2017," Sikora said. "Some states may receive funding from their local state checkoff boards for monitoring, but states that have little soybean acreage, such as Florida and Texas, will be not able to go this route, unfortunately."


Florida and Texas may not boast substantial soybean acres, but they do play a major role in the spread of soybean rust. It's in those states, as well as the southernmost edge of the Gulf Coast, where soybean rust spores hunker down for the winter, usually on kudzu leaves.

That gives the disease a head start on the southern soybean crop. In the deep South, farmers must usually treat for soybean rust (and other diseases) up to twice a year, depending on the weather. So far, common fungicides control the disease very well. But recent reports of soybean rust biotypes with resistance to strobilurin fungicides as well as reduced effectiveness of triazole fungicides in South America have made Sikora uneasy. After all, experts believed the original rust spores that invaded the U.S. on Hurricane Ivan came from Colombia and Brazil.

Because soybean rust is well controlled here, it's easy for farmers to get lax about it -- even with a fairly robust monitoring system still in place, Sikora said.

After two years of drought in 2010 and 2011 kept the disease tamped down in the deep South, some soybean farmers cut their fungicide passes the following year. "We saw anywhere from 10% to 60% yield loss in 2012 in southern Alabama, just because growers took their eye off the ball," Sikora said.

The disease likes wet, humid weather, but its development slows when temperatures creep above 85 degrees. It would actually do well farther north in the Soybean Belt, but high heat, dryness and time constraints have kept it below the Mason-Dixon line most years. Early summer tropical storm systems in the Gulf pose the biggest threat to a northern invasion but those have been quite rare in the past 150 years, Sikora noted.

A warming climate could allow the disease to overwinter farther north on kudzu and volunteer soybeans and get an earlier start, he said. At the same time, increasing dry spells would slow it down.

In short, experts don't know what rust's future looks like in the U.S., but Sikora is fairly confident what will happen as the USB funding for monitoring efforts dries up.

Plant pathologists along the Gulf Coast will have a smaller pool of state checkoff funding from which to pull. It will be harder, if not impossible, to hire scouts to help them travel hundreds of miles around the state, which is required for an adequate monitoring system, he said.

In Florida and Texas, where no soybean checkoff boards exist, no monitoring efforts will be funded at all.

In the past, these states have filled an integral role as an early monitoring system for their northern colleagues, Bradley noted. He relies on reports from these areas to alert him if Kentucky fields should be scouted for the disease. "Without them, we could be blindsided," he said.

Farther north, the state of Illinois doesn't even have an Extension plant pathologist to watch for these Southern alarm bells and to officially monitor for the disease. "Frankly, I don't feel confident that we know what the distribution might be anymore," said Suzanne Bissonnette, assistant dean of Agriculture and Natural Resources at the University of Illinois. "It started early this year and was very prevalent in the South. Given our weather, we would have expected it to come up earlier. We don't suspect any yield impact, but it would be nice to know if there is some."

Sikora also worries that once the plant pathologists familiar with soybean rust start to retire, their replacements may not keep up the shrunken monitoring system now in place.

"People will start to forget about soybean rust as we lose expertise," he said. "And that could be catastrophic to southern growers as time goes by."

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Emily Unglesbee