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Diplodia Ear Rot of Corn

August 10, 2001
Diplodia ear rot was one of the most severe and noticeable diseases that affected corn in many parts of Illinois in the 2000 growing season. We have received questions concerning whether this ear rot disease will be common again this year. It is still too early in the season to typically see Diplodia ear or stalk rot in most of Illinois. We have, however, received reports of Diplodia ear rot in southern Indiana, and Diplodia stalk rot has been reported from east-central Illinois. Although we don't have a good way to predict whether Diplodia ear rot will be a problem, a review of this disease may help to clarify some of the factors that contribute to its development.

Diplodia ear rot appears to be influenced strongly by certain management and environmental factors. It was a common ear rot disease in the Midwest from the early 1900s to late 1950s but became uncommon in the 1960s as fall plowing became widely used. Diplodia ear rot has been returning to Illinois as minimal tillage has become adopted and as Diplodia stalk rot has become more prevalent. Diplodia ear rot was a significant problem in 2000, apparently in part because there was wet weather at flowering and dry conditions earlier in the spring and summer.

The fungal pathogen that causes Diplodia ear rot is Stenocarpella maydis, also called Diplodia maydis. This fungus not only causes ear rot but can also cause stalk rot and seedling blight of corn. Corn is the only host for this pathogen. S. maydis survives over winter on diseased stalk and ear tissues that have not been buried. In the spring the fungus reproduces on the plant debris and produces spores that are moved by rain and wind to the new crop. The fungal spores land on the plant and commonly infect at the base of the ear if sufficient water is available. Symptoms of Diplodia ear rot frequently begins as tan spots on the base of the husk and ear leaf, which expand over much of the ear; and as the disease progresses, a white mycelial (fungal) growth spreads over and between the kernels.

Diplodia ear rot.

Diplodia ear rot.

Diplodia ear rot.

Although a key to the disease cycle for Diplodia ear rot is movement of the pathogen from infested corn debris on the soil surface to growing plants and vice versa, infection appears to be highly dependent on wet weather for 2 to 3 weeks after flowering. Another factor that contributes to this disease is the amount of Diplodia stalk or ear rot in the previous crop and the quantity of infested debris that remains on the soil surface. Some hybrids are more resistant to Diplodia ear rot than others, which may affect severity of this disease as well as the number of spores that are produced on infested residue.

Options for managing Diplodia ear rot are limited. Fields should be scouted for this disease between now and harvest to help determine if and where it occurs, and to determine if there are differences in resistance among hybrids under your conditions. Resistance to Diplodia should be considered in selection of hybrids, especially in areas where this disease has been a problem. Unfortunately, some high-yielding hybrids are susceptible, and the risks of potential yield loss from Diplodia must be considered relative to potential yield loss from lower-yielding but more resistant hybrids. Another key to management of this disease is rotation out of corn because the fungus seems to survive poorly over time on infested debris. The potential benefits of fungicides to control Diplodia ear rot are still uncertain. Researchers at the University of Illinois at Urbana-Champaign are investigating resistance and fungicides for control of Diplodia ear rot, and in the near future we hope to have more information to help you manage this disease.--Dean Malvick

Author: Dean Malvick

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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