Organizing Committee


Poster Presentations


Poster Presentations


Analysis of the occurrence and the western pathway of soybean rust in 2007

Presenter: Xun Li

Other authors and affiliations: X. B. Yang. Iowa State University, Plant Pathology, Ames, IA 50010, U.S.A.

Northward movement of soybean rust (Phakopsora pachyrhizi Sydow) this summer was faster than the last 2 years and reached Iowa via western pathway with the first detection in Dallas County on September 25. Subsequent field surveys identified the disease in 14 Iowa counties by late October. Most fields had low disease incidence of 12%. However, in Fremont County of southwestern Iowa, the disease incidence was 1520% with a severity of 25%. Leaf samples from Fremont County showed more clustered pustules, different from the patterns on infected leaves in other counties. Data from Fremont County suggested the occurrence of multiple infection cycles from local inoculum sources since 68 weeks ago. Our forecasts on the dispersal of soybean rust spores indicated possible spore showers in western to central Iowa in middle August, which was consistent with the possible initial infection date in Fremont County. Information from sentinel plots and field surveys in the Great Plain suggested large-scale gradients of disease occurrence in the region. Analysis of spore-dispersal maps over the season together with disease detection data suggests the occurrence of soybean rust in Iowa as a result of long-distance jump(s) of epicenters or bridging sources. The infested fields in southwestern Iowa appeared to be sources for spore dispersal across Iowa, which was favored by the wetter-than-normal weather in August and September.

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