Scouting for Disease: Tar Spot

Cool, humid conditions with long periods of leaf wetness – a.k.a., the substance of this early growing season – create the “ideal environment for tar spot,” said Brad Hipsag, Federated ag sales rep out of Ogilvie. And, corn that was planted later is developing later, too, giving tar spot infections time to occur (as compared to “crops planted more timely,” said Hipsag).
 
“Tar spot is a leaf disease that makes black spots on leaves and can cause significant yield loss in corn under the right environments,” said Hipsag. Tar spot symptoms look like specks of black tar on the leaf, starting as brown lesions and leading to black spores that protrude from the leaf. The spots “will feel bumpy and will not rub off,” he said.
 
Though symptoms of tar spot can develop at any growth stage, the signs typically develop most severely in late summer. Your Federated Agronomist can submit a leaf sample for diagnostic testing to confirm the presence of tar spot.