THE SOUTHEASTERN U.S. FUSARIUM HEAD BLIGHT EPIDEMIC OF 2003

Authors: Cowger, Christina; SUTTON, ABBEY - USDA-ARS

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2005
Publication Date: 10/26/2005
Citation: Cowger, C., Sutton, A.L. 2005. The southeastern u.s. fusarium head blight epidemic of 2003. Plant Health Progress. doi:10.1094/PHP-2005-1026-01-RS.

Interpretive Summary: Fusarium head blight (FHB) causes serious losses to producers and users of small grains. The disease reduces yields and test weights, and results in contamination of grain with fungal toxins, including DON (deoxynivalenol). Although farmers in other parts of the U.S. lost billions of dollars in the 1990s, FHB was generally not a widespread concern in the southeastern U.S. until the unprecedented epidemic of 2003 in winter wheat. This report provides retrospective documentation of that epidemic, drawing on interviews with 120 researchers, extension agents, growers, and millers. By assigning an estimate of average FHB severity to each of 67 surveyed counties in five states, the researchers found that the epidemic was severe throughout the wheat-growing areas of Maryland, in much of Virginia and the North Carolina Piedmont, and in a handful of counties in northwestern Georgia. Epidemic severity generally decreased from north to south across the region, and from west to east. High moisture and moderate temperatures (59°-86°F) in the week before wheat flowering are known to favor FHB infection, and disease forecasting models currently available in 23 states make use of those pre-flowering conditions. The researchers found that, in the case of the 2003 epidemic, pre-flowering rainfall, humidity, and temperature were not good predictors of ultimate FHB severity for the 67 surveyed southeastern counties. On the other hand, there was a strong correspondence between estimated FHB severity and hours of precipitation in the month after flowering. While the 2003 FHB epidemic did not appear to cause serious economic losses to most growers in Georgia and South Carolina, the authors estimated over $17 million in losses to growers in 40 surveyed counties in North Carolina, Virginia, and Maryland. Mills incurred unexpectedly high costs due to the need to test for DON, increase handling of contaminated loads, and purchase and ship grain from distant sources in order to fulfill contracts. Several million dollars in total losses to mills in the affected region appear to have occurred. With more use of reduced tillage, and corn a major part of the crop rotation, the Southeast may be ripe for other severe FHB epidemics. More attention to forecasting, and a better understanding of how southeastern weather conditions affect disease severity, are needed to help manage this potentially devastating disease.

Technical Abstract: Fusarium head blight (FHB) caused unprecedented losses to southeastern U.S. wheat producers and millers in 2003. The epidemic was documented afterward through interviews with 120 researchers, extension agents, millers, and growers. Sixty-seven counties in five states were individually assigned an FHB severity score of 1 to 4 based on the percentage of growers affected, and 2003 yield data were available for 62 of those counties. The relationships of yield and pre- and post-anthesis weather variables to epidemic severity were evaluated using regression and correlation analyses. Yield as a percentage of the 10-year-average was negatively correlated with estimated epidemic severity (r = -0.588, P < 0.0001). Hours of post-anthesis rainfall were positively correlated with FHB epidemic severity (r = 0.465, 0.590, and 0.619 for 10, 20, and 30 days post-anthesis, respectively; P ' 0.0001). Weather conditions in the seven days prior to anthesis do not appear to have played as significant a role as post-anthesis weather, and were not a good predictor of FHB severity in the Southeast in 2003. The economic impact of the FHB epidemic was estimated using 10-year average production data for each county. With the exception of one multi-county area, Georgia and South Carolina did not experience significant FHB-related economic losses, but estimated pre-milling losses in 40 surveyed counties in Maryland, Virginia, and North Carolina totaled over $17 million. Wheat production in those counties comprised just 71.7%, 45.8%, and 48.0% of the statewide totals, respectively; thus, actual 2003 FHB-related losses to growers in those states were much higher. Additionally, mills in the region suffered losses of several million dollars in 2003 due to increased shipping, testing, and handling costs brought on by FHB.