Diplodia ear rot of corn
Diplodia ear rot is caused by the fungus Stenocarpella maydis and S. macrospora and has become a common (and troublesome) disease on corn. These fungi produce mycotoxins in South America and Africa, but no mycotoxins have been associated with Diplodia ear rot in the United States and Canada. This ear rot is recognized as a white mold beginning at the base of the ear that eventually becomes grayish-brown and rots the entire ear. Ear leaves generally die prematurely on infected ears. Often, the entire husk of affected ears will have a bleached appearance. A distinguishing characteristic is the appearance of raised black bumps (pycnidia) on the moldy husk or kernels. Infected ears weigh noticeably less than healthy ears. Occasionally, the white mold will not be prevalent, and kernels will have a brown discoloration. This appearance is called "hidden Diplodia," and you can observe the symptoms only by breaking the ear in half and observing the pycnidia in the cob. White mold on corn ear, indicative of Diplodia ear rot. Image: G. Munkvold
A cross-section of a corn cob with small, black pycnidia produced by the fungus that causes Diplodia ear rot. Image: M. Romero
Diplodia ear rot disease cycle.
The fungus overwinters as mycelium, spores, and pycnidia on corn residue or seed. Spores are spread primarily by splashing rain. Dry weather before silking, immediately followed by wet conditions, favors Diplodia ear rot as does conservation tillage, continuous corn, and hybrid susceptibility. Delayed harvest and wet weather before harvest can allow fungal growth to continue, further reducing grain quality and yield.
Scouting prior to physiological maturity is important to identify areas with mold problems. These areas should be harvested as soon as possible to prevent further mold development. Harvested grain should be cooled, dried, and cleaned immediately after harvest, and stored apart from grain harvested from healthy fields. Insect management reduces the risk of ear rot infection.