Over the past two weeks, severe leaf blighting due to southern rust has occurred throughout central and southern Iowa. The last severe outbreak of southern rust in Iowa was in 1999. This disease was reported in Nebraska and Kansas earlier in the growing season; however, it was only in mid- to late August that Iowa State University started to notice a few lesions in field trials. Temperatures and precipitation in Iowa throughout August were well above normal and thus highly favorable for southern rust.
Southern rust is caused by the fungus Puccinia polysora. Like all rusts, P. polysora spores are windblown to Iowa from the South each season. High humidity and temperatures in the 80-90° range favor the development of the disease. Under these conditions, new infections can occur every seven days, resulting in numerous new rust lesions and extensive leaf blighting.
Two types of rust occur on corn.... Continue reading this article on Integrated Crop Management from Iowa State University