In 1970, the U.S. corn crop was assaulted by a mysterious “ear rot” malady. As the growing season progressed, entire fields were lost as corn ears rotted from the inside and stalks fell, markets grew jittery and unease among farmers increased.
The problem (eventually identified as “Race T” of the fungus Helminthosporium maydis) rushed first through the South and seemed destined for the Corn Belt. Scientists, who knew little more than that the problem was caused by a fungus, had no answers.
So what stopped the spread of Southern corn leaf blight? Weather and a large dose of luck.
“It should be recognized,” wrote A. L. Hooker, University of Illinois plant pathologist, in 1972, “that dry weather reduced disease spread in the western Corn Belt and delayed northward spread of the disease on the Eastern seaboard. In addition, because of favorable climatic conditions, Northern states had above-normal yields. Without those two features, national disease losses could have been greater than those estimated.”
In the end, 15 percent of the U.S. corn crop was lost to the blight, dropping average yields from 84 to 72 bushels. The epidemic cost farmers over $1 billion. The losses were especially acute in the South, where farmers often lost entire corn operations and some states reported 50 percent of the corn within their borders lost.
Sung Lim references the 1970 corn blight while explaining the importance of Arkansas' newly formed working group. “We can't afford for such a thing to happen again,” says the University of Arkansas plant pathology department head. “We must be better prepared for such possibilities. And we will be.”
As introduced plant diseases become more of an issue, the Arkansas Working Group on Introduced Plant Diseases has brought together plant pathologists in the state — primarily Extension along with several university researchers. Similar efforts are under way in other Southern states.
“We want to focus on some problems that are breaking out around the world and the country that could come in and have an impact on Arkansas,” says Rick Cartwright. “The group helps provide focus.”
While addressing a host of diseases (including Bakanae and sudden oak death), a model for this new system is Asian soybean rust. The disease has been heavily hyped nationwide as a threat to the soybean industry. Over the last few months, the working group has done several things.
“We helped the Arkansas Plant Board prepare and submit a Section 18 exemption to use additional fungicides not currently registered for soybeans,” says Cartwright. “In the event of soybean rust moving into the United States, we want those products available on an emergency basis. That paperwork is with the EPA.
“Several of us have also worked on a draft response plan in the event soybean rust is found here. The plan is very close to completion and will involve regulatory agencies (the Plant Board and APHIS among others) and basically outlines how we'll deal with the discovery of soybean rust inside our borders. The steps are listed — educating growers on the fungicides available, monitoring the disease and a host of other things. We're also in the initial stages of planning a network of people to look at and monitor soybeans in the state. (Extension plant pathologist) Cliff Coker will be coordinating that effort.”
There are unconfirmed reports that Asian soybean rust has moved from Brazil into Venezuela. Of course, there are near constant rumors that it's reached U.S. fields, too. Not so, say all interviewed.
“It's not here — not even close — and these rumors are a pain,” says Coker. “People need to understand that the rumors aren't helping matters. We've been getting calls asking, ‘Should we spray? I've heard about the soybean rust and want to know.’ It's unnecessary to get so worked up.”
The regulatory agencies, politicians, the national media and homeland security employees are all paying attention to the disease. With so many on the lookout, “it doesn't behoove anyone to carry on unsubstantiated rumors,” says Cartwright.
“Hopefully, the working group can temper some of the things folks are so worried about. This is a potentially serious disease, but we deal with a lot of serious diseases and we keep on trucking.”
“Look,” says Coker, “the disease hasn't been found north of the equator yet — that's still a very long way from here. It hasn't even been found in Central America.”
When the rust was found in South America in 1999, some experts believed that by 2003 it would be in the United States. It has yet to make an appearance.
What about claims that Asian soybean rust is only a hurricane away?
In Coker's opinion, that's only a minute possibility. If the disease were in Mexico, that would be a more plausible scenario, “but the spore load that would have to come in from South America would most likely be washed out of the storm before it got here.
“Another factor in our favor is that UV light kills these fungal spores. Three days of exposure — especially in the equator area — means death for spores. I've seen some storm modeling on this and it'll take approximately 11 days to reach our shores from Brazil — that's almost four times the needed time to kill it.
“The more likely way it will arrive here is through Central America. From there it can get here much easier.”
There are other reasons to hold off soybean rust panic. For one, the Brazilian cropping system is much different than those in the United States.
“Brazil goes almost all no-till, crop after crop,” says John Rupe, University of Arkansas plant pathologist. “They also have other disease hosts — like kudzu — that never die out. Here, kudzu dies out in the winter. This appears to be a much more tropically-oriented disease. We're in a temperate zone, which could mean, if it arrives, it won't be as damaging as it is around the equator.”
Even if a storm blows soybean rust spores in, “they'll have to land on a susceptible host, the environment must be right for the disease to proliferate and those conditions need to continue for a while,” says Terry Kirkpatrick, Extension plant pathologist. “Our climate is another barrier for soybean rust to overcome. Really, any spores would have to hit during a three-month window. Spores would need to land in April or May to cause us a problem. All those factors increase the odds in our favor.”
If Asian soybean rust does come in, though, over the short term “we'll be beholden to fungicides,” says Coker. “We have no resistant varieties yet. And if rust does come here, we're hoping it will be a spotty, sporadic problem. We just don't have enough fungicide to spray every soybean acre in the United States twice. The supply just isn't available.”
Reasons for concern
Asian soybean rust, a prolific foliar disease, is very yield-limiting (depending on what growth stage the crop is in when the disease hits, yield can drop between 20 and 80 percent) if it isn't treated quickly, timely and properly. While there are fungicides that can be used, the disease must be identified first.
There are a number of soybean diseases that could easily be confused with Asian soybean rust — many foliar diseases look similar, says Cartwright.
For that reason, no matter what's seen or diagnosed in the field or state labs, “we won't have (Asian soybean rust) until the USDA lab in Beltsville, Md., says we have it. This is being done to avoid the rumors and potential mistakes in diagnosis.”
Working group members have also been told that the secretary of agriculture doesn't want to be informed of a soybean rust discovery through the media. If it shows up, she wants to tell the media herself.
Cartwright doesn't mind: “There are scientific reasons for this. Many of these diseases are difficult to identify because they look so similar. There needs to be a central location to make a confirmation.”
Last summer Arkansas went through an exercise to see how viable the lab setup is. To simulate the problem, one of the state's county Extension offices was sent a photograph of soybean rust. From that point, the photograph was handled as if it were a living plant sample.
“We found that within 24 hours that sample had left the county office, had been shipped and had been confirmed as soybean rust in Beltsville,” says Coker. “We had a confirmation in less than a day — that's fast and should make everyone feel better.”
Training is now being set up for county Extension agents and consultants. As the state plan develops, such training will be crucial.
“Coming together like this is important, but we don't have enough support yet,” says Lim. “Once people understand what we're trying to do — stop a potentially devastating epidemic — they'll understand why we need funding.”
The aforementioned training for county agents and others in the field is planned, says Cartwright. “But there's expense involved, and we need to find additional funding to prepare for this potential problem. It turns out that much of the (soybean rust) education and research dollars have flowed into the Midwest, where the majority of soybean acres are.”
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