Draw Up Battle Plans for Soybean Rust…Just in Case

Sentinel plots could prove very valuable as early warning system.

Published on: Mar 1, 2007

Back in the days of the Cuban Missile Crisis and afterwards, during the so-called Cold War with the Soviet Union, much was said about early warning systems that would detect nuclear missiles launched at the U.S. in time to take action and prevent a disaster.

While the severity may not be comparable, the concept of sentinel plots to alert farmers of a possible invasion of soybean rust into their area is very similar. Think of sentinel plots as an early-warning system for soybean growers and custom-applicators who would be called in to mount a swift counter-attack to the advancing fungus.

Sentinel plots boil down to small plots, occupying about 2,500 square feet each, containing two varieties each, and planted early, says Greg Shaner, a Purdue University plant pathologist. He coordinates sentinel plots in Indiana. His counterparts at land-grant universities operate sentinel plots in other major soybean producing states. The result is a network of sentinel plots blanketing the soybean-producing areas of the U.S. The network is so extensive as research systems go that it should be difficult for rust spores to escape detection. The idea, of course, is to discover them very early, before they mount a full-blown infection, so that farmers can make the necessary counter-strikes in terms of fungicide applications.

Shaner managed sentinel plots in more than 25 counties in Indiana last year. that means more than a fourth of Indiana's counties hosted sentinel plots, for the express purpose of detecting soybean rust in a natural way, then sounding an alarm. It could also be likened to early-detection programs for signs of certain types of cancer. The earlier the detection, the more likely that treatment will both be effective and confine the damage to a smaller area.

Whether this will be the year that soybean rust finally becomes enough of a concern to warrant spraying fungicides to prevent and control it remains to be seen. Corey Gerber, head of Purdue's Diagnostic Training Center, helped identify a single rust pustule on a soybean leaf in very-late planted plots at the DTC at the Purdue Agronomy Research Center about five miles west of West Lafayette, in October '06. "We checked 77 leaves and found just a single pustule that turned out to be soybean rust," Gerber says. "But it had spores inside and it was confirmed as Asian soybean rust. It's likely that there may have been pustules on leaves elsewhere in Indiana."

The Lafayette discovery was the most northern discovery in Indiana, and indicates that the fungus can travel that far north. Since it doesn't overwinter in Indiana, spores must blow back into Indiana this summer for it to be a threat in '07.

Last year's single rust pustule wasn't a threat because it developed so late in the season. The plot where it was found was a training plot planted very late on purpose, Gerber says. Soybeans were still green at the time of frost. For the rust fungus to cause a real threat to soybean yield potential, it would have to establish itself much earlier in the growing season.

What was established in '05 and '06 is that it's not necessary to spray for soybean rust unless it's picked up in the nationwide sentinel plot system first, Shaner says. What the discovery of an actual pustule as far north as Lafayette in late '06 demonstrated is that even with the sentinel system, there is no guarantee that there won't be an occasion in the future when spraying is necessary, he adds. The 'future' could be several years down the road, or it could be this summer.

Here's how to stay on top of what Shaner and others find in sentinel plots this summer. You can call the rust Hotline anytime, at (866) 458-RUST (7878). Or visit USDA's rust Web site at: www.sbrusa.net/; or stay on top of what's cooking on soybean rust inside Indiana by visiting the special rust Web site on Purdue's Plant and Pest Diagnostics Lab Web site at: www.ppdl.purdue.edu/ppdl/soybean_rust.html.

Here's hoping that sentinel plots do their job again this year.