June 13, 2006
Scientists on guard for signs of Asian rust
CARBONDALE, Ill. -- Although Asian rust, a destructive fungal disease, did not invade Illinois soybean fields in 2005, the state's agricultural scientists remain on guard with additional early warning "sentinel" plots and a few tricks learned from last season's watch.
In Southern Illinois, sentinel plot planting got under way in early April with early maturing varieties more commonly found in the northern part of the state.
"These flower earlier than those in the farmer's field in this region," said Jason P. Bond, a plant pathologist in Southern Illinois University Carbondale's College of Agricultural Sciences.
"Flowering is a key trigger in the plants showing symptoms of the disease. If we find rust in these sentinel plots, it will give farmers a few weeks to get their fungicides selected and in order."
Many of the plots also have varieties with later planting and maturing rates.
"That way, the plots can serve as sentinels for the entire season," Bond said.
Some plots at sites deemed exceptionally vulnerable will get irrigation so that if the disease does appear, it will have a suitably moist environment, which will help reveal its presence. Bond plans to keep a close eye on those sites, along with a few others featuring either heavy irrigation or low-lying locations.
"And those will probably turn out to be the ones where the disease won't be — it's Murphy's Law," Bond said.
Last year, plant scientists urged farmers to scout their fields intensively. While that has its benefits, scouts likely will not be able to diagnose rust in the field when the disease first enters the state or early in an epidemic. So this year, researchers are taking a slightly different tack.
"One of the things we learned last year was that the majority of the first detections occurred in the lab on leaf samples," Bond said.
"At levels that low, you won't find rust by walking around the field looking for diseased leaves. The best way will be to take leaves out of the plots and look at them under the microscope in the lab. It will be a little more work, but it will take place in an air-conditioned building instead of out in a hot field."
As long as they're out in the sentinel plots plucking off leaves, the researchers will also collect information on other problems.
"For example, we're going to scout for aphids and other insect pests, which we didn't do last year," Bond said.
"We will get a better survey of the state of some of our production constraints, which makes these sentinel plots useful even if rust doesn't show up."
In this part of the state, which likely would get hit first if rust moves up from Alabama and Florida, Bond tried to use University research plots as sentinels wherever he could.
"If rust shows up in our cooperators' sentinel plots, then they may want to immediately destroy it, which would keep us from learning more about the disease and how it spreads," Bond said.
"There's a pile of information there that we don't want to eliminate."
While both Alabama and Florida reported rust in some of their counties earlier this year, weather may keep it from spreading north.
"Fortunately, parts of the southeastern U.S. are in a drought," Bond said. "It's very dry, so that's probably keeping the pathogen at fairly low levels."
Spores from sites along the Texas and Mexico border present a greater threat.
"Because of the prevailing wind patterns, if it's overwintered in Texas or Mexico, it could be there one day and in the Midwest the next," Bond said.
"In that case, the disease would not necessarily have to show up in Southern Illinois. The first sites could be one of our central or northern locations."
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