Use of geospatially-referenced disease and weather data to improve site-specific forecasts for Stewart's disease of corn in the U.S. Corn Belt

摘要

Stewart's disease of corn, caused by the bacterium Pantoea stewartii (syn. Erwinia stewartii), is important because its presence within seed corn fields can prevent the export of seed corn due to quarantine (phytosanitary) restrictions. Phytosanitary field inspection reports for 1972 through 1998 (500 to over 1300 fields/year), and mean monthly temperatures for Dec, Jan, and Feb preceding each inspection year, were geospatially-referenced by county using ArcView geographic information systems (GIS) software. Warmer winter temperatures during Dec, Jan, and Feb generally allow greater numbers of the insect vector (corn flea beetles, Chaetocnema pulicaria) to survive, thereby increasing the risk of Stewart's disease epidemics due to higher levels of initial inoculum (infested beetles) that will be present during the ensuing growing season. Weather-based models to accurately predict the risk of Stewart's disease in the U.S. Corn Belt, however, have not been developed. Using GIS software, risk maps were created to graphically depict seasonal, regional, and county risks for Stewart's disease. Using this approach, we found that counties with mean monthly temperatures < 24 F (-4.4 C) for at least 2 of the 3 winter months had zero to low risk of Stewart's disease (< 2 percent prevalence), while counties with mean monthly temperatures >= 24 F for at least 2 or 3 winter months had a moderate to high risk, respectively. Using individual monthly mean temperatures for Dec, Jan, and Feb (Iowa State Method), we accurately predicted that 1998 and 1999 would be high risk years for Stewart's disease in Iowa. This study provides the basis to more accurately assess the seasonal and site-specific risks associated with the occurrence of Stewart's disease several months prior to planting. This advance warning will help seed corn producers to make more informed disease management decisions, such as the choice of (low risk) planting sites (which will minimize or eliminate the use of insecticides).