Alyssa K. Betts, Extension Field Crops Pathologist; akoehler@udel.edu
Earlier this summer we talked some about Tar Spot in corn. We had our first positive confirmation in DE in October of 2023. This week we had our first positive confirmations for 2024 in both New Castle and Kent counties (Figure 1). So far, symptoms have been in smaller areas of the fields and found right before combining so there do not appear to be any yield losses from these later season infections. As a refresher, tar spot is a foliar disease caused by the fungus Phyllachora maydis. The fungus produces small, raised, bumpy black lesions that look like specks of tar, giving it the common name “tar spot” (Figure 2). These structures known as stroma can be on the upper or lower leaf surface and do not wipe off the corn leaf. If you suspect tar spot in your field and need help with identification or other questions contact me with questions, akoehler@udel.edu.
Figure 1. Confirmations of Tar Spot
Figure 2. Symptoms of tar spot on corn leaf. Black specks are the reproductive structures of the fungus.