MS-Global Agriculture Feedback from Grains Expert：How Southern Rust Impacts U.S. Corn Yields More-20250929

Southern Rust has hurt this year's US corn yield. Southern rust is a disease thatblows into the Midwest on Southern winds, which have historically emerged in mid-August, but appeared in mid-July during the current crop year. The hot and humidconditions that much of the corn-belt has experienced in recent months are ideal forthe disease. Dr. Cordonnier described the disease impact for farmers who useddrones to apply the appropriate chemistry for the disease: strips of the field wherethe drone missed application are dead while areas with effective application aregreen. Dr. Cordonnier caveated that farmers who sprayed proactively for the diseaseare still seeing declines in yield, though not as drastic as those who did not. Withtreatment, yield losses ranged from 10–20 bpa; untreated fields saw up to 50 bpalosses, according to the panelist. The USDA and Dr. Cordonnier have both recentlydecreased their US corn yield projection by 2 bushels per acre. The USDA forecastwas revised to 186.7bps while Dr. Cordonnier projects 182bpa, with a neutral tolower bias.