Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Charcoal rot was identified in corn this week. Charcoal rot caused by the fungus Macrophomina is a common disease in soybean during hot, dry seasons. Occasionally it is seen in corn causing a stalk rot that in the early stages can look like the common stalk rots that we see here such as Diplodia, Fusarium and Giberella stalk rots. However when the stalk is split the characteristic sign of charcoal rot is the abundant small reproductive structures (sclerotia) inside the rind, especially on the vascular bundles. The inside of the stalk especially the lower 3-4 nodes are gray black giving it the name charcoal rot. Hybrids that have good resistance to other stalk rots often have some resistance to charcoal rot but the hot, dry conditions and early senescing of stalks can lead to infection and symptom development. Harvest in a timely manner to avoid lodging problems.
Charcoal rot on corn. Note the black sclerotia attached to the vascular bundles in the pith. That is the best diagnostic feature for identifying charcoal rot.