AS HURRICANE Dennis churned toward the U.S. in early July, farmers in the Midwest generally had two things in mind: 1) that the violent storm might blow up some much-needed moisture for their drought-stricken crops, and 2) that a repeat of last year's hurricane season might bring Asian soybean rust spores.
As of mid July, infected plants had been found in the Deep South, in sentinel plots and one field of commercially grown soybeans. But Asian soybean rust was notably absent in the Midwest. In early July, soybean disease experts at several field days I'd attended were all but ready to call soybean rust a no-show for 2005, at least in the northern Corn Belt. Most were recommending that growers shift their primary focus to other types of pestilence, such as soybean aphids and spider mites. They also were reassuring chemical dealers and soybean growers that rust-fighting fungicides that weren't used in 2005 could be stored and remain effective for several years.
But on July 8, just as Dennis was pounding Cuba, Purdue University plant pathologist Greg Shaner was one of the first to sound a renewed alert, but not an alarm, about rust in Midwestern fields. “There is the potential for that storm to bring rust spores into this area,” he said.
Shaner pointed out that even though there was some active soybean rust in the South, there still wasn't a lot of rust there when Dennis rolled through. “If spores were picked up by that storm, there's going to be a lot of dilution before those air masses reached us. We wouldn't anticipate a heavy load of spores arriving in Indiana, but there could be some,” he said.
So in terms of a significant rust threat, it probably figures that any rust spore delivery from Dennis will be too little, too late to threaten yields on most Corn Belt soybean fields. According to projections of how rust propagates, we should know by early August whether or not Dennis delivered rust spores that infected significant acreages of Midwestern soybeans.
Experts such as Shaner continue to urge soybean producers to scout their fields for rust. But realistically, squinting through a 20-power hand lens and comparing leaves to pictures of tiny brown rust pustules is easier said than done. Farmers' first line of defense should be the experts who regularly analyze and report on sentinel plots. If rust is confirmed a few counties away from you, chances are good your field may already be infected or soon will be. In such situations, a fungicide treatment that contains both preventive and curative active ingredients provides the best protection.