Tar Spot in Northeast Iowa

Keep an eye out for this as your doing late season crop scouting, checking corn standability, yield estimates, etc.  I was out doing some spot checks yesterday in Benton, Tama, and Bremer Counties and found this in 3 out of the 5 corn fields I was in.

Our national land grant universities have a helpful map here showing the current geographic distribution of this disease.  Iowa State University has written several articles about this, as have the University of Illinois and the University of Wisconsin among others.

Based on what we’ve seen in the past few days, my guess is that the occurrence of Tar Spot will be far more prevalent than we realize – lots of folks will stop scouting fields once we get into the mid/late grain fill period, and disease identification becomes more and more difficult as crops start to senesce. 

This will be an important discussion to have with your seed dealer over the late fall and winter. Check university trials (like Wisconsin) that publish disease ratings with their trial results. Several fungicides are either labeled or have a FIFRA 2ee recommendation for Tar Spot control (as mentioned here).