Last week, southern corn rust was detected by Dr. Don Hershman on the University of Kentucky Research Station in Caldwell County. Dr. Hershman reported that the incidence in several corn blocks was about one leaf with some pustules for every 30-40 leaves examined. These infected leaves were generally in the mid-canopy. In one block, he found two plants that were severely blighted due to southern corn rust (which is probably where the first windblown spores arrived in the field). Based on the disease levels observed, I am guessing that the fungus blew into the state sometime in the first ten days of July.
As a reminder, southern rust is distinct from common rust, which is also present at low levels in scattered corn fields. Southern rust is a much more aggressive disease under warm, wet conditions than is common rust, especially given rust and common rust can be found in a June 22, 2010 article in this newsletter (http://www.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN1235.pdf). The UK Plant Diagnostic Labs can also be of assistance in documenting cases of southern rust.
Southern rust is not yet prevalent in our corn-production areas. I say this because, on a tour last week through the Purchase Area, I didn’t see any southern rust in the corn fields I visited. Furthermore, several Extension agents in western Kentucky are specifically monitoring for southern rust, and they have not yet found any. However, with the very warm, humid air masses that are predominating lately, conditions are favorable for continued spread.
I am not trying to sound an alarm bell, especially since the disease is not yet prevalent. However, it is a disease worth watching for, particularly for late-planted fields.