Indiana Disease Update in Corn

Darcy Telenko, Extension Field Crop Pathologist

Tar spot


Tar Spot – We continue to confirm counties with active tar spot. Twelve counties have been confirmed as of July 26, 2023. These counties all had a previous history: Porter, LaPorte, Jasper, Pulaski, Marshall, Kosciusko, Benton, Tippecanoe, Carroll, Tipton, Jennings, and Knox (Figure 1). Gray colored counties on the map are those we have found tar spot in previous years. In most fields tar spot has been found in the lower canopy with low severity.  Please keep a close eye on your fields to make an informed decision to spray fungicides.  Our research has shown that a well-timed fungicide application from tassel to milk (VT to R3) will help reduced disease and protect yield.  Check out the fungicide efficacy resource to help make a decision on product choice ( )

Figure 1. Tar spot map on July 26, 2023.

Southern Corn Rust. We have not had any reports of southern rust in Indiana. The disease is starting to move north in NE Arkansas. Keep scouting and if you suspect it, please send a sample to the Purdue Plant Pest Diagnostic Lab (PPDL).  Southern rust can cause significant yield loss if it builds up to high levels during silking and corn fill. Therefore, it is very important to keep a close eye out for this disease this season to make timely management decisions.

Figure 2. Southern corn rust map for July 26, 2023

We again are requesting if you have any suspect locations to please update us and send a sample for both tar spot and southern corn rust. I am especially interested in those counties we have yet to scout or receive a sample. Even if your county is yellow, I am also interested in learning if you have tar spot or southern rust on your farm and what you might be seeing. Please feel free to contact me ( or the PPDL ( with any major disease issues you may have this season.


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